Liquid Fertilizers and Aerated Compost Tea

By Steve Solomon
7 July, 2016 (last modified 31 July, 2016)

 Liquid Fertilizer

Certainly for centuries, maybe for thousands of years, gardeners have made liquid fertilizer by immersing manure or leafy vegetation in water for days or weeks, then fertilizing with the soak water, usually diluted considerably. These days we also fertilize with worm bed drippings. There are organic concentrates like fish and kelp extracts that conveniently make a similar fertilizer. Any of these can be poured over plants in sufficient quantity that it coats the leaves and wets the surface inches of the root zone (drench), or better, put more deeply into the root zone (fertigation). Farmers and market gardeners mix soluble fertilizers into sprinkler and drip irrigation. Gardeners can fertigate quite conveniently with a bucket.

Home-made liquid fertilizers or the usual organic concentrates like fish and kelp make a positive difference, especially when they are added to already fertile soil in relatively good balance. I urge every gardener to try fertigating a few plants and see what it does.

Here’s how-to fertigate on the cheap:

water--fertigation-2Drill one 6 mm (¼ inch) hole in the side of a plastic bucket just a squidge above the bottom. I prefer using big white 20 litre (5 gallon) ones because around mid-summer the larger plants in my garden can use that much at one go. But even household pails of 2.5 gallons (10 litres) will serve in a pinch. Set that bucket on the soil next to a large plant or what will soon be one, like a tomato, cucumber, zucchini, etc. Position the drain hole so it is close to the plant’s stem. Tilt the bucket slightly away from the hole and pour in the amount of fish/kelp concentrate or manure/compost extract to make a full strength solution in the amount of water going into the bucket. Then with hose and nozzle, fill the bucket as fast as possible. (You could also premix the fertilizer in one bucket (without a hole in it) and then pour the solution into the fertigation bucket.) It’ll take a few minutes for the bucket to empty because the drain hole was intentionally made small, so that the outflow can sink in without spreading out. (If your soil is slow to accept moisture, then drill a 3/16th inch (4 mm)-diameter drain hole. If your soil is sand, water tends to go straight down without spreading out much. In this case, better results might happen by drilling two holes , 180 degrees apart.)

When the bucket is lifted you should see a small wet spot no larger than a tea cup saucer. The moisture has gone deep and spread out below the surface. The amount of water to provide at each fertigation should be enough to saturate the entire soil volume that the plant’s root zone has occupied plus what it probably will come to occupy in the next two weeks. That judgement is always a guestimate. With an already large plant, say a half-grown tomato vine that is starting to ripen fruit, 10 litres/2½ gallons is about right. Assisted by that fertigation, in a few weeks the plant should be double the size. The next fertigation could use at least twice the previous amount.

The performance of fertilizer concentrates varies greatly and there are a great many of them to choose. The least effective are the two traditional organic garden standbys—liquid kelp and fish. Both are useful but are far from the best possible alternative. Liquid fish that is genuinely organic as I was instructed by Rodale to define the word organic when I was a newbie gardener in the 1970s, is made with fish and water and maybe a non-synthetic preservative. Nothing else. Definitely not anything synthetic! Rodale so strongly implanted the organic mantra in gardeners’ minds that it still is having an effect–synthetic is bad; natural is good! Fish fertilizer containing nothing but fish and water is mostly a nitrogen source that lacks enough phosphorus to properly balance the N and is very short potassium. Kelp extract provides a useful amount of potassium but is very short nitrogen and also provides little phosphorus. You might hope that half fish and half kelp together provides N from one and K from the other but unfortunately, neither one provides nearly enough phosphorus or effective levels of what soil analysts call “trace elements”—boron, copper, zinc, manganese, maybe molybdenum too is needed in large enough quantity to be considered a trace element and not a “micronutrient” as some soil scientists have it. A lab analysis of fish or kelp would show that these materials do contain measurable concentrations trace elements, and that kelp does contain a wide range of micronutrients probably at useful levels (selenium, cobalt, etc.), but when the actual amounts of trace elements in solution are evaluated it becomes obvious there is far too little of any of them to accomplish what trace element supplementation is capable of achieving. So if someone asserts that a fish or kelp product supplies anything except NPK, keep in mind that quantities of trace elements involved are insignificant.

Regarding phosphorus: if you should encounter a liquid “organic” fish extract providing more than one percent phosphate, then you should know that the source of most of the P was food-grade phosphoric acid, a synthetic substance that was manufactured in a chemical factory. In my opinion, phosphoric acid makes excellent fertilizer when it has been diluted slightly below the concentration normal used to give fizzy cola drinks a subtle sour taste under all that sugar. Until recently, organic certification rabbis banned the use of phosphoric acid on religious grounds, but they did allow the use of chlorine to preserve fish extracts—you go figure. They now reckon phosphoric acid is kosher when it is used to as a “preservative” to prevent fish extracts from spoiling. I find that justification amusing because the quantity used to stabilize the extract is the exact amount needed for balanced fertilization.

Liquid kelp buying guide

Kelp has long been used for food, for fertilizer and in more recent times, for the extraction of alginates—valuable chemicals with a wide range of uses. Kelp also contains natural growth regulators and vitamin-like substances that help plants resist stress and diseases. Kelp extracts that retain these hormones (not all do) make container grown seedlings develop roots at several times the usual rate. When I am raising seedlings, in addition to a complete fertilizer concentrate I add 2 ml of top quality kelp extract to every litre of water. Kelp provides the full range of micronutrients because it grows in sea water. I include kelpmeal in my usual garden fertilizer. But if the price of kelpmeal seems beyond your budget, try foliar feeding liquid kelp every few weeks.

Some liquid kelp fertilizers are industrial by-products from alginate extraction. Unfortunately, the phytamins and growth regulators got extracted along with the alginates; by-product liquid kelp still has value, it contains the minerals, but liquid kelp works much better when it hasn’t been denatured. Don’t expect recyclers of alginate-extraction waste to tell you that’s what they are doing. Tasmania, where I live, has kelp beds off its west coast and several manufactures of proper kelp extract. All their brews produce excellent results. I can tell you with fair certainty that Maxicrop, a soluble dry powder widely sold in North America, is almost certainly a residue of algenate extraction. My assumption being correct, Maxicrop would be the least desirable type. I am not in a position to evaluate the many brands available in North America. But you’ve been warned.

Foliar feeding and more effective fertigation

Leaf surfaces assimilate plant nutrients that are dissolved in water. They do this especially well when their breathing pores (stomata) open because moisture stress is low—early morning or shortly before sunset. Think of foliar applications like providing vitamins—minute quantities of essential somethings the plant could use if it but had them. To carry that analogy another step, think of NPK like carbohydrates, proteins and fats that make up the greatest portion of essential human nutrition; consider the trace elements like vitamins. It would be possible, but difficult, to provide the large amounts of NPK a plant requires only through foliars. I tried that once as an experiment; to keep the plants growing fast I had to spray every other day. But a very small dose of a trace element like zinc applied to leaves has as much (or more) result than ten times more of that same element put into the soil.

On a garden scale, foliar feeding is done with a pump sprayer. I have a 600 square metre vegie patch(6,000 sq. ft); I can cover every plant the garden that can use a foliar feed with one load in a 14 litre backpack pump sprayer (3.5+ gallons). Plant nutrient elements that have been dissolved in water are sprayed on the top surfaces of leaves. When drops first start falling from leaf tips, the sprayer moves on. The effectiveness of foliars can be increased by adding spreader/sticker to the water, allowing the droplets to spread out into a thinner film that adhere instead of forming larger drops that quickly run off the leaf. For home garden purposes ordinary dishwashing liquid works well enough, just two or three drops per litre or quart added along with the concentrate before the spray tank is filled with water. If any soapy bubbles form whilst filling the spray tank, then too much detergent was used.

The underlying principle of using foliars

When environmental conditions allow the plant to grow rapidly, it almost certainly could use more nutrients than soil can possibly provide. It doesn’t matter how fertile the soil has been made, the plants almost certainly could use more nutrients than comes through their root systems. When environmental conditions are such that the plant can’t be growing fast, then it doesn’t need extra nourishment.

While food crops are already making rapid vegetative growth they benefit greatly from weekly foliar feeding. When plants have switched their focus from only building structure (vegetative growth stage) and now beginning to ripen fruit, they can be fed every two weeks. In this category go climbing beans, all the cucurbits and solanums. Potatoes are in vegetative growth mode until flowering ceases. If it’s a type of plant that ripens everything at once, like apples or sweet corn, the last feed should be a generous month before harvest. Maybe six to eight weeks before harvesting late-maturing applies. Slow-growing cool-season crops could use a foliar feed early in autumn and again a month later if they still have significant growing potential in front of them. I can imagine foliar feeding in southern and central California during the winter. I can’t imagine foliar feeding in the Willamette Valley from late autumn until spring regrowth begins.

A plant that should be growing but isn’t could be foliar fed one time with something very complete. If that didn’t make a difference appear within days, you might try drenching the plant. But if that didn’t help, don’t feed it again because lack of nutrients wasn’t the problem.

Advanced orchardists have made a science out of foliar feeding. They frequently do leaf analyses during the growing season to determine exactly when to economically apply the specific nutrient(s) needed for each crop. Gardeners do nearly as well by foliar feeding a complete balanced fertilizer on a regular schedule. I know organic gardeners who spray kelp and sometimes fish on their fruit trees. And I know it helps visibly! These folks might have an illuminating experience from trying something complete, with the appropriate balance.

I have come to think that no matter how fertile, or how balanced the soil is, no matter how vibrant the soil ecology, it is not possible for a plant to uptake from the soil all the nutrients it could use. Plants enjoying balanced fertile soil will resist most diseases and insects, they will be nutritious. Foliar feeding an already healthy plant will create improvements you can experience almost the next day—the overall growth rate will noticeably increase; the head of broccoli forming immediately after a foliar feed will taste considerably sweeter because it is also much more nutrient-dense.

Practical stuff and side-tracks

Because I haven’t lived in North America for 20 years I have lost touch with the products available there. So I moused around Peaceful Valley Farm Supply’s website considering the numerous organic liquid fertilizer concentrates on offer. Some of them were reasonably well balanced in terms of NPK but none of them even listed trace elements as being in the brew. That doesn’t mean they are devoid of traces. It probably means that the amount present is below a legal minimum concentration required to put the item on the label (and below the concentration that would make a strong difference if the plant was deficient in that element.)

BFA certified organic concentrates for growing cannabis do an excellent job growing vegetables, probably that’s because the retail price of recreational cannabis is powerfully connected to its potency and other subtle qualities. Here’s another way to put that—cannabis prohibition provided the motivation for applying enormous creativity and intelligence to producing the best dope possible to achieve. I find this situation full of irony. Imagine had all that intelligence and creative drive been focused elsewhere. Imagine what it might be like if cannabis had never been regulated any more than celery or grass seed. Maybe some of the finest young minds in America would have turned their attentions to inventing something other than improved cannabis vaporizers. We’re maybe about to see in some American states or whole countries like Uruguay, what does happen to people when cannabis is commonly used—if that result isn’t obscured by impending social chaos. Here’s my prediction on what’s coming cannabis-wise for Colorado, Washington and Oregon (etc.). Assuming that the USA continues more or less as before—50 years from now somewhat fewer people will use cannabis for recreational purposes than at present and a great many will use it for relief and healing. Cannabis-derived medicines will be specific, effective, and pretty much free of “side effects” unless, the stone itself acts as a relief from stress/anxiety, or is unavoidable (as with Rick Simpson’s cancer cure, which depends upon ingesting large quantities of psychoactive THC for its result).

Back to using BFA-certified cannabis-raising concentrates for growing better organic vegetables. Hydro shops offer a bewildering assortment of plant nutrients, most of them chemically based for hydroponics. Most chemical-based hydroponics fertilizers don’t work well in soil culture; many are two-part preps that aren’t convenient to mix. The labelling on many products is bewildering to someone who doesn’t grow cannabis (and even bewilders some who do). However, there is one Dutch company, Canna, whose high quality products are sold in almost every hydroponics shop. Canna produces a BFA-certified organic product line in addition to a great many chemical products intended for hydroponics or soil cultivation.

Canna fertilizers are unnecessarily spendy for growing food crops. I mention them because Canna is readily available. I urge readers that strongly adhere to the organic gardening belief system to try both fertigation and foliar feeding with Canna Bio-. There are two formulations—Terra and Flores. Terra is formulated to support vegetative growth; Flores works better when the plant starts forming fruit or seeds. Either works well enough at any time or stage of growth; if I had to choose only one for the garden I’d try Terra. Foliar feed at the dilution the bottle recommends for soil application. You’ll be impressed, especially if you’ve been using fish/kelp, but you will soon be looking for a less-costly alternative. You should also know that I have spoken to shy cannabis growers trying not to be noticed whilst shopping in my local garden centre’s hydroponics isle, and have been told that Canna’s Bio-line is good but their non-organic products perform markedly better.

The moment a gardener stops clinging to the organic belief system a whole world of possibility opens up. If you’re not familiar with chemical concentrates, the cheapest and most convenient way to experience what foliar feeding can accomplish during the vegetative growth stage is with Miracle Gro. This stuff is sold in almost every garden centre in small quantities at a modest price. I suggest buying only the smallest package (1/2 pound) for a trial. There are several Miracle-Gro variants sold in Australia and it wouldn’t matter much which one was used for foliar trial. Let me say for starters that I do not like Miracle Gro, I have experimented with it but do not routinely use it. I only suggest Miracle Gro because it is a cheap and convenient way to make a test. The reason Miracle Gro works well is because all the Miracle Gro variants are heavy in trace elements, and it is the foliar fed traces that bring much of the result that foliar feeding creates. When concentrates are used for fertigation, not foliar feeding, their NPK ratio affects how plants respond more strongly when they are used as foliars. Especially this is so when fertigation is the source of nutrition when producing seedlings in greenhouses. That is why Scott, the globalist international maker of Miracle Gro, also gobbled up a professional line called “Peters.” I think Scott long ago bought and then disappeared Rapid-Gro, which some Oregon gardeners considered noticeably superior to Miracle Gro when both products were available. Scott recently acquired a small Australian company that make garden centre products like Miracle Gro but better. That brand has reappeared in my local garden centre. The containers are far more attractive but the contents have been redesigned in a degraded direction. Peters fertilizers come in many NPK variations but all are quite similar when it comes to trace elements. When I check the net for what forms of Miracle-Gro are sold retail in the USA I only find one, “Miracle Gro All Purpose Plant Food.” The label calls for mixing it at 1 tablespoon to the gallon. Try spraying it at that dilution once a week on the leaves of a wide range of vegetables during a time of year they should be growing fast. See what happens. Miracle-Gro is balanced to produce vegetative growth. it does not do so well once flowering/fruiting/seed forming begins.

I find many very negative comments about Miracle-Gro on the net from organic circles. Whatever you might currently opine about putting chemical fertilizers into the soil, consider this: when plant nutrients are foliar fed, very small quantities are sprayed on leaves, and little ends up on the soil. The applied chemicals have no direct effect on the soil biota. Actually, trace element foliar nutrition creates a very positive effect in the soil by pushing the plants towards a higher state of health and photosynthetic efficiency. A person who is totally certain that natural is good and synthetic is evil, has closed their mind to many possibilities. The truth is, better nourished vegetables exude more sugars and other microbe foods out of their roots, thus bringing about a far higher population of beneficial soil microbes in their rhizosphere. These microbes proceed to liberate soil nutrients and increase all the other benefits that come from a healthier and more abundant soil ecology. If you want to know more about this, I suggest reading John Kempf’s blog at

Let’s briefly analyze what Miracle Gro provides. Here’s the data on the label:

N  24%    P  8%    K  16%
Boron  0.02%     Copper   0.07%   Iron  0.15%     Manganese  0.05%   Zinc   0.06%   Molybdenum  0.0005%.

DOES NOT CONTAIN: sulfur, magnesium, calcium, nickel, cobalt, selenium . . . .

First, consider the NPK. I think the ideal ratio of N:P:K for most food crops in vegetative growth mode is in the range of 1:1:1 to 1:2:1. Vegetables usually become more nutrient-dense when P exceeds N and K. But potassium is cheap, it is cheapest in the undesirable chloride form whilst phosphorus is expensive, so it is not surprising that in non-specialist preparations there isn’t abundant phosphorus. Miracle Gro is 24:8:16 or if that ratio is reduced, 3:1:2—short phosphorus, barely enough potassium and too much nitrogen. The specific  chemicals Scott uses to supply NPK are not what I’d choose, probably because less costly ones will work reasonably well and in Scott’s world, price is everything. And in Scott’s world, probably as it is in the picture packet seed business, “the gardener is not a critical trade.” But take my word for it, what Miracle Gro provides in the way of trace elements is quite adequate to make a big difference. And that’s why I assert that Miracle Gro will usually outperform fish and kelp as a foliar—if the soil is already in balance and is already providing adequate NPK, calcium, magnesium and sulfur, which garden soils usually do.

When a product like Miracle Gro is used as a soil drench or for fertigation, the NPK ratio and the sources of that NPK do matter a lot. That’s the main reason that Scott, the maker of Miracle-Gro, also makes its “Peters” line. These are professional fertilizers mostly for the glasshouse and nursery trade. Different NPK ratios, and which particular chemicals are used to obtain those ratios, have profound effects on how plants grow. The glasshouse trade knows this quite well. Peters fertilizers provide NPKs over a wide range. But all these variants are similarly rich in trace elements, just like Miracle Gro. I repeat! I recommend Miracle Gro only for a cheap quick convenient foliar feeding trial, and only during the vegetative growth stage. I do not recommend its use as a drench, for fertigation, and especially not as the main source of soil fertility. Miracle-Gro doesn’t do so well either raising vegetables seedlings for transplanting in light-weight wood-waste based growing medium that usually is devoid of calcium, magnesium and sulfur. There are far better products, and far cheaper ones than Canna Bio-.

I searched the net to find for something a lot better for North Americans. And I discovered Dyna-Gro “Liquid Grow 7-9-5.” Its NPK ratio is properly balanced. It has high levels of traces and better, it provides useful levels of calcium, magnesium, sulfur, cobalt and nickel—all of these are missing from Miracle Gro. Best, Dyna-Gro is packaged in sizes from 8 ounce bottles to 55 gallon barrels. Dyna Gro is conveniently distributed by and many others in North America. The product displays the National Home Gardening Club Seal. It received a 98% approval rate from the members. Dyna-Gro makes variants on this recipe that better support fruiting crops in specific growth stages, much like cannabis fertilizers are for “veg” or “bloom.” The price is far lower than an equivalent product from a hydro shop and should work as well or better. Dyna-Gro is distributed in Australia by Bio Leaf Plant Nutrients, 11 Gillett Place, Botany Downs, Auckland, New Zealand, I’d like to see Australian garden centres stocking it or something like it. Members of the Soil and Health Forum (Yahoo) have been experimenting with Dyna-Gro this summer. The reports so far are entirely positive and enthusiastic.

In Australia there is a readily available superior alternative to Miracle-Gro—500 ml bottles of Maxicrop Seaweed Plant Food Concentrate. It is found on the shelf of virtually every garden centre. It is not “organic.” It is chemical fertilizers in a base of kelp extract. The NPK roughly is 4-1-3 with trace element concentrations somewhat exceeding Miracle Gro.

My food garden occupies more than half of a quarter acre building block so it makes strong economic sense for me buy enough foliar concentrate to last a few years. By being willing to invest a few hundred dollars I also get the finest food-growing foliar made in the world in my opinion, but then, I haven’t had the opportunity to try Dyna-Gro products (which are compounded in a very similar manner). I use Nutri-Tech Solutions (Qld), 10-10-10 Vegi Tech. This concentrate costs me about $11 per litre of concentrate when purchased by the 20 litre container, which is the minimum size offered. Our local garden club was not daunted—we bought 20 litres and everyone went home with a 1 litre milk jug of it. Each litre of concentrate makes about 140 litres of foliar spray. Currently, a local farm supply sells 20 litres for around AUD $210. Nutri-Tech recommends dilutions between 3 ml/litre up to 10 ml/litre. I think 10/litre is a bit too strong. For foliar use I mix it at 7 ml/litre. Full information is available at


Aerated Compost Tea

Well made fully finished compost contains a very high concentration of beneficial microbes—bacteria, fungi, protozoa, etc. Plants grow much better when their root zone is densely populated by these kinds of microbes. One way to accomplish that is to spread and work in a large quantity of excellently made compost, say in excess of 10 tons per acre per year. Maybe 20 tons. Unfortunately, industrial compost you can buy is far from ideal. Making excellent vegetable garden compost requires using very little woody material as feedstocks, but the main ingredient of industrial compost is woody waste. Excellent compost must include clay and living soil (together about five percent by starting volume). These are materials that industrial composters couldn’t possibly obtain or manage.

Compost of the quality I’d term “excellent” is something I can not purchase at any price in Tasmania. However, when I visited the USA earlier this year I discovered compost makers supplying the legal cannabis trade in Washington State, and they do make an excellent product. But . . . and this is a big but, I would not pay their price for vegetable gardening purposes.

If I were to set out to manufacture enough excellent compost to sustain my entire vegie plot at the peak of soil health, then I’d have to process every bit of kitchen and food garden waste plus all the non woody waste from my wife’s ornamentals occupying an eighth-acre, include a generous cubic metre of sawdust or planer shavings that has first been well scratched for months as it gets mixed with chook poo. And to that I’d have to add three to four tons of grain straw—and considering the (light) weight of the rather loosely packed straw bales I’ve purchased in the last few years, I reckon it would take more than 50 of those bales to weigh one ton. The cost of straw seems highly daunting. Not to mention the amount of effort involved.

So I supplement what I produce with industrial compost. This seems practical, affordable and sensible. My own compost adequately covers about one-third of my beds. So once a year I spread industrial compost over the remainder. The beds receiving industrial compost grow plants excellently, but I am seeing improved crop performance on those beds from spraying aerated compost tea.

I apologize in advance for the brevity and incomplete nature of my discussion of aerated compost tea. It is short because I am writing this with only one year’s experience. But I feel compelled to tell my readers about ACT because using it has improved my own garden’s performance so much.

Aerated compost tea is not at all like soaked compost tea. As I mentioned earlier, gardeners have long made potent liquid fertilizer by soaking manure/ compost/green leafy material in water and then pouring the resulting extract (diluted) over plants. Aerated compost tea is something else entirely. It is the result of a brewing procedure that rapidly increase a complex ecology of beneficial microbes by jillions of times their starting number, all in 24 hours. The industrial device that does this is termed a “bioreactor.” An effective home garden bioreactor can be made from two white plastic buckets and a few bits of gear from a pet shop.

Benefits of ACT

When aerated compost tea is sprayed at low rates, like 100 litres per acre, it inoculates the soil with a beneficial microbial population. ACT used this way helps fodder crops, orchards and cultivated farm crops grow better. Proponents of ACT assert that it may allow the use of less compost over a given area. Maybe that is so; I couldn’t comment from my own experience at this point. ACT sprayed on plants heavily inoculates leaves and stems with beneficial microbes. My plants look much healthier the morning after being given ACT because they use part of their energy budget to resist disease. High concentrations of beneficial microbes on external surfaces unburdens the plant’s immune system. Then the plants grow faster and become healthier.

One more potential benefit: ACT that is made with a feedstock very rich in plant nutrients  acts like a foliar feed. But it will create a markedly greater growth response than had that feedstock been simply sprayed as a foliar feed without first brewing microbes in it.

How to make and use ACT

It is easy to quickly multiply compost microbes. All you need is a small quantity of excellent compost to use as a starter-inoculant, two- 15 to 20 litre plastic buckets (one as the brewer, the second upside down next to the brewer makes a secure platform to put the airpump very close to the action), a four-outlet fishtank air pump and some air stones. To make strong brews where nights are cool, a fishtank immersion heater that is a size larger than what would keep tropical fish comfortable inside the house in a five gallon tank helps maintain the brewer at 20° C.

This is the procedure in short: Microbe food is dissolved in water, a starter culture of beneficial microbes is added, a strong air pump is engaged to vigorously and constantly oxygenate the brewing medium and soon, there are jillions of microbes.

Starter culture

It is essential to start the brew with high quality compost that arrived at being properly “finished” not too many months previously, has remained moist since then and has not been packaged in an airtight plastic bag. I opine that the best starter is humified compost such as I make mostly from vegetable crop waste and about which my current in-print books instruct. If the starter compost dried out and/or sat around for more than a few months after being finished, then the surviving ecology will be less complex. I have made ACT from the cow-horn cow-manure compost that is used by my Biodynamic friends to stir BD-500. This makes excellent ACT starter. I have suggested to my BD friends that ACT is BD-500 taken to the next level. I can assure you that an attractive airtight plastic bag of industrial compost conveniently purchased from the garden centre won’t have many living microbes in it.

The crumbly worm castings at the bottom of a worm composting container makes excellent ACT starter. And in my opinion, every urban/suburban gardening household should use worm composting to dispose of kitchen waste.

Farmers who regularly brew microbes purchase starter cultures in dry powder form, much like bakers buy yeast. These provide diverse ecologies of highly beneficial microbes; sometimes ACT is started with specific microbes that suppress specific diseases. According to Tad Hussey, “most of the ‘instant’ or ‘starter’ compost tea products you find in stores don’t produce much biological activity when you put them to test under a microscope.”

A reliable volume of compost to inoculate a brew is 2.5% of the volume of water (for up to around a 1,000 litre brewer). Thus 20 litres x 2.5% = roughly 2 cups.


The brew must be done in water that is free of chlorine because chlorinated water will initially kill a great many microbes. Municipal water can be freed of chlorine by running air bubblers in the brewing solution for an hour or two before introducing the inoculant.

Fill a brewing bucket no more than three-quarters full of nutrient solution because foam sometimes develops on top.

Microbe food

Brewed microbes can control pests and diseases. Interventions with specific microbes at key points in the crop’s growth cycle often are as effective as chemicals without suppressing the entire ecology. And cost much less than chemicals. Advanced growers may incorporate a specific trace element into a microbial brew because providing that nutrient at that moment makes a huge difference.

Culturing specific microbe species can involve bespoke nutrient solutions. Internet publications and videos suggest using many different materials and recipes when brewing ACT. Some of these recipes provide enough nutrients to breed up a very high concentration of microbes if there is enough oxygen present. The higher the concentration of microbes goes, the higher their demand for oxygen becomes. Market gardeners and orchardists who brew microbes invest in quite noisy (not suitable to suburbia) high capacity air blowers that can fully oxygenate very rich brewing media in 1,000 litre shuttle tanks.

But for the (especially urban/suburban) home gardener, making more litres of ACT at one go than your airpump can thoroughly oxygenate is an invitation to failure. Making a nutrient-rich brewing medium also increases the need for oxygenation. The home gardener’s requirement is to brew a diverse ecology of beneficial aerobic microorganisms at an effective concentration, not necessarily the peak possible concentration. If what is produced is only half as potent as what might be possible to achieve—what of it! It’ll still work magic. And 10-15 litres of brew is enough to cover almost anyone’s home garden.

Tim Wilson and Tad Hussey (whose websites will soon be referenced) are crop advisors in the Cascadia Bioregion. Both have done the real hard yakka when it comes to researching this topic. Both of them assert that the safest dependable way to brew home garden microbes is with nothing but unsulfured black strap molasses (BSM). I urge you to follow their lead, at least until you have experienced several successes with it. Make sure it is unsulfured because sulfured molasses has strong anti-microbial properties.

Please brew microbes in unsulfured black strap molasses dissolved into the brew water at 0.5% (5 ml/litre). Add nothing else!

I am fully aware that the recommendation above disagrees with Dr. Elaine Ingham and her followership. You will find many Elaine Ingham videos on youtube. I think these should be seen by all who are interested in ACT. I do not agree with Elaine Ingham’s assertion that ACT makes remineralization unnecessary.

Dr. Elaine urges us to brew beneficial microbes in a solution of organic fertilizers that all by itself, could function as a potent foliar spray, drench or fertigation solution. During the brewing process microbes convert those plant nutrients into microbial biomass and amino-acid chelates that fertilize far more effectively than simple elements in solution. These compost microbes also transform soil, much as though compost had been dug in. Because there is so much microbe food available during an Elaine Ingham brew, a very high level of oxygenation must be maintained or else the brew goes anaerobic. If that should happen, even briefly, not only does the process fail, but what results might damage plants and gardens. To keep control, an expensive microscope is needed and checks are made every few hours during a brew cycle.

The people who persist at brewing will work out how to accomplish this. Keep in mind the brew from a thousand litres shuttle tank will only treat five- or maybe seven acres, so these folks have a strong motivation to make that brew as concentrated as possible so it can be dispersed as thinly as possible. As a gardener with only a quarter acre or so to manage I do not have a reason to be that efficient. Maybe I’m becoming more a Tasmanian because our State Motto should be “near enough is good enough.” The method this book proposes will not make as potent a brew as Dr. Ingham tantalizes us with, but the approach is nearly fool proof. And judging by what a molasses-only brew does in my garden, it’s potent enough.

Air supply

Tim Wilson advises using an air pump that supplies 1.4- to 2 litres of air per minute for each litre of brew. That’s enough air to fully oxygenate a plant-nutrient-rich growing medium being held at a temperature high enough to make the microbes reproduce at near maximum speed. A four-outlet home aquarium air pump (all four outlets combined) usually puts out 10 litres per minute. Practically speaking, this is enough to oxygenate 15 litres of brewing solution if the nutrient is molasses, the concentration of molasses is moderate, and the temperature stays below 22°C.

Ten litres per minute is barely enough to oxygenate a bucketful. It is essential to have an air stone of some sort on every one of those four outlets. It is helpful to keep the air lines as short as possible because the supply tubes from aquarium shop pumps are very small diameter and strongly resist air flow. For this reason I set my pump on the bottom of a similar-sized upside down bucket placed one inch away from the brewing bucket.

To brew larger quantities of ACT at one go requires a much larger air pump. The really large ones used to oxygenate 1,000 litre shuttle tanks and above are not found in pet supply shops. They are high pressure “blowers,” not “pumps,” so they’re really noisy and they won’t be cheap. I simply can’t imagine being able to run one of these with houses on quarter acre blocks on two sides of my place, and a 60 unit retirement village on another. One day soon I’ll write about those oldies across our back fence. They can see into our ornamental garden when they stroll (and sometimes shuffle with a frame) by; we speak with a few of them and one couple belongs to our garden club. I am 73, Annie is 76. The differences between our physical condition and that of most of the oldies across the fence is remarkable. And the reasons for that are well worth discussing.

You may wish to learn more about ACT and in that case I suggest starting with Tim Wilson’s web page ( and Tad Hussey’s website ( and especially one of Tad’s KIS Organics forum posts about ACT  (we’ve had trouble with this link, so just in case it doesn’t work, here’s the actual link to Tad’s article: (

Temperature and oxygen demand

Most of the microbes developing in an ACT brew are bacteria and fungi. The fungi can rapidly form thready hyphae. In a brew that encourages them, hyphae can become so numerous and grow so long/large that a silk stocking leg can be filled with hyphae captured while draining a few litres of just-finished ACT out of a 1,000 litre shuttle tank. I experienced that. Bacteria can divide every 20 minutes but a stocking won’t capture them.

The amount of time required for each microbial doubling and the corresponding quantity of oxygen consumed by the brew are both determined by temperature. Roughly speaking, oxygen demand doubles for every 10° C increase whilst at the same time the capacity of water to dissolve oxygen decreases considerably with increased temperature. Allowing for the limited oxygenation provided by a four-outlet fishtank airpump, I think a bucket brewer should be run in a temperature range of 18° to 22° C for 24 hours after it has been inoculated. A few degrees warmer would be okay in the beginning of the brew but probably not okay towards the end when there will be so many microbes that increasing the temperature will increase demand for oxygen above the level the equipment can maintain it. A 50 watt fish tank heater should be able to maintain 15 litres of brewing solution at 20°C in ambient conditions above 15°C in an unheated out building. If the ambient temperature drops too low then the brew bucket can be wrapped with insulation, like an old blanket or thick towel. Or a larger heater used.

The microbes in a finished brew are consuming oxygen at a high rate, so the brew must be distributed within an hour of turning off the air bubbler. Much sooner than one hour would be better; immediately would be best. As soon as I turn off the airpump I empty my brewer into a sprayer and immediately distribute the entire brew.

A brew should not be allowed to go on past the point all the food has been consumed because from this point the microbes must eat each other and consequently, the ecology gets ever more simplified. Without a microscope it is not possible to observe the peaks and valleys of the microbial ecology so it is simplest just to distribute the entire brew at 24 hours.

A good brew finishes with a pleasant earthy-plus-molasses aroma. I have been advised that if it smells unpleasantly sour or “ugly” at the end, don’t use it; it might damage plants. If you follow directions I don’t think there’s much risk of a bad result. All the brews I made last summer/autumn smelled nice. There should be no need to invest in a microscope as long as the brewing medium is only molasses at 5 ml/litre, the brew is bubbled strongly, the temperature is held between 15° C and 22° C and the brew time is 24 hours, plus or minus one or two hours.

Mesh bag or free suspension

When starting the brew it is okay to toss the compost into the water and let it float. I like to vigorously stir the inoculant with a stick for a few minutes when first putting it into the brewer. I think this helps knock microorganisms off bits of compost and into the nutrient solution. Generally, the brew forms a higher density of microorganisms by dumping starter culture materials into aerated nutrient solution pre-warmed to brewing temperature. Using ACT with bits of compost floating in it works for drenching soil, but I spray it onto leaves. For a small quantity such as gets brewed in a bucket, the best option is to pour the finished brew through a large-sized fine-meshed strainer before putting it into the spray tank. Removing particles from ACT by the 1,000 litres isn’t so easy. People who brew on a large scale put the starter inoculant into a woven sack, like a big sock that dangles in the brew tank like a teabag. The bag must have a very strong air bubbler inside of it, strong enough to constantly shake up the material or else the microbes (especially fungi) may not be knocked loose to enter the brewing solution and/or the mass of compost in the bag will settle into an airless mass at the bottom of the bag, not good at all.

Cleaning the brewer

Brewed microbes deposit a thick slime on all the surfaces in the brewer. This slime is easy to scrub off whilst it is still moist. But these surfaces can be very difficult to get clean after the slime dries. This slime could inoculate the next brew with undesirable microbes. So the brewing gear must be scrubbed clean immediately after the brew has been sprayed.

Take special care to brush the airstones severely.

Large volume brewers do not use airstones. These folks manufacture a plastic pipe bubbler with hundreds of tiny holes drilled or punched into it. This may be easier to clean of slime. On Tim Wilson’s website you’ll find plans to build small airlift brewers aerate like a coffee percolator. This design makes much more efficient use of the low output from a fishtank airpump.

Frequency and method of use

You can use ACT (made only with molasses) as often as you wish. I would find it interesting to use a 1,000 litre shuttle tank brewer, make a new batch almost every day and make undiluted ACT the only source of irrigation for an entire country garden. What a garden that would be!

In my opinion the most efficient way to use ACT is to spray leaves with it as though they were being lightly foliar fed (maybe half the quantity it takes to see moisture dripping off leaf tips). I see no need to specifically address the soil. I suggest spraying the entire vegie garden this way once/month.

The best time of day/weather to spray ACT is just before dark, or on overcast drizzly days. Moisture that is already on the leaves at the time of spraying gives the microbes time to find a niche and get established. Microbes washed off the leaves inoculate the soil.

Some growers add foliar fertilizers and/or more molasses and/or humic acid to finished ACT just before applying it. Tim Wilson discovered from before and after microscopic analysis that adding fish hydrolysate at 5 ml/litre killed or put to sleep almost half of the microorganisms he had just brewed. Now he foliar feeds separately. And this is what I recommend doing.

Tags: Compost tea, fertilizers, foliar feeding

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