by Adrian White
20 December, 2021 by
Lucija Johum

Growing naturally, sustainably, organically – whatever you want to call it – reaps many benefits for the greenhouse grower. There are tons of reasons why this is the case, and it’s not just because it’s better for your plants: it’s also better for soil health and nutrient efficiency, and improves your yields in a cost-effective way. Not to mention, it’s great for the environment, and great for your health (or your customer’s) in the case of growing food.

You can also save money by avoiding monetary investments in chemical fertilizers, pesticides, or herbicides, and manage pest pressure naturally. Plus, chemical-free methods help your soil manage its own pH naturally, which helps prevent a lot of plant diseases. With all this info, are you finally sold on the benefits of going natural or organic?

If your answer is yes, your next question might be: what’s the most cost-effective, steam-lined method of natural growing that helps you replace those needs for chemicals and fertilizers? Natural methods are great, but these methods often require a bit of extra leg-work (such as mulching, composting, and weeding). Enter: compost teas.

Especially in a greenhouse setting, teas are an elegant solution to many obstacles for the natural grower, and may be a relieving option for those transitioning from chemical to organic growing. They’re easy to make, transport, and apply. But the best thing of all: they are the best natural option for your plants, hands down.


For starters, what exactly is compost tea? It is, basically, a liquefied compost, as the name describes – but it is also far more than that. On that note, it’s also important to differentiate tea from other compost-sourced liquid amendments.

To get more specific, the teas most effective for your growing operation – and enough to be competitive with chemical fertilizers – are aerated. That means they were formed with oxygen as part of the process, which in turn helps colonize the amendment with healthy bacteria, fungi, and other microbes. 

This is achieved in the tea-making process not just by suspending compost in water, but stirring it actively (and feeding it as well) to encourage stronger growth of aerobic microbes. These microbes and bacteria (as well as nutrients) are then made available to your plants – and soil – when applied as fertilizer. In effect, this is what makes a true, aerated tea much, much better than other compost-derived amendments: such as manure tea (anaerobic and using animal fecal matter), compost extract (anaerobic tea), or leachate (liquid compost runoff). 

All these preparations do have some very small nutritional and microbial action, but nowhere near a proper aerated tea! It can also be said that aerated liquid amendments contain way more beneficial soil microbes than even regular composts. This, in turn, boosts the ability for nutrients to be made more available to plants (especially nitrogen).

Plus, aerobic bacteria in teas make them pathogenically safe, both for plants and human consumption – whereas anaerobic preparations, like the ones listed above, can contain contaminants, pathogens, and foodborne illnesses.


If you want to use regular compost in your greenhouse operation, by all means, go ahead – there is nothing wrong with amending soils of all kinds with a bit of natural, organic matter. It’s good for them! According to Lownfels and Lewis, authors of Teaming With Microbes however, a brewed tea provides many benefits that the solid type won’t.

The first: making one’s own compost and transporting it is quite a bit of work. Tea brewing, on the other hand, is very lightweight and less labor-intensive (though it does require finesse). Not to mention, application is easy, doable in simple spray or foliar form.

Second: because of the comparative differences in microbial life between the two, nutrients and benefits take a while to become available to plant root systems with regular compost. With an aerated microbial brew, it’s practically instantaneous!


Think of making compost tea like you would making a batch of pickles. It’s certainly not rocket science, but you still need to have a handle on the factors that go into it. With brewing, your important factors will of course be aeration: oxygen and air contact.

For that reason, you would be wise to invest in premanufactured brewing equipment, typically a large container of a certain size combined with an air pump. The compost, along with water, is placed in this container along with a feeder of some sort to get the aerial microbes going (molasses, cane sugar, kelp). With the pump activated, microbial growth and aeration begin!

If you’re more the handy type, making your own brewer is easy: you just need a large bucket, barrel, and air pump. Whether you purchase one commercially or make your own, you can customize your brew setup to any size you like to match your operation. Some are quite big: 20 gallons, in order to cover a number of acres!


Once you’ve made your very own tea – or gotten your hands on it in some way – what can you expect from it? What exactly does it do? And when should you apply it?

More than anything, this fertilizer returns life back into your soils: including the fungi, bacteria, nematodes, and more microbes besides that interact beneficially with the root systems of your plants. The more life in your growing medium, the more it naturally works to provide the nutrients your plants need, and without much interference from the grower. It’s a match made in heaven!

Of course, you’ll get some stray nutrients from the broken-down organic matter of the original compost itself. But tea is, first and foremost, a replenishment of microbes. Not only do these microbes work to provide better nutrition for your plants, they will also work to protect your plant’s root systems, prevent disease, and attract even more beneficial microbes.


Where, when, and how do you apply it? Where do you apply it? How much is too much?

It’s usually easiest to apply it in spray from, whether around the roots of your plants or directly to their leaves as a foliar. Just make sure that you have strained your tea considerably of any matter before putting it in the sprayer. Clogs can happen!

Otherwise, you can apply it from a plastic watering can or simply from a cup to soak soils around your plants, just as you would water them. Especially in a greenhouse with such magnified light, make sure to apply them at times when sunlight cannot harm microbes or evaporate teas. Before 9 AM and after 4 PM are wise timeframes, when the sun is down.

As for how much you should apply: truly, there is no limit. You can toss aside what you’ve learned about fresh compost “burning” your plants here, because tea is different. Feel free to drench your plants (with what they would handle water-wise too, of course) and see the benefits for yourself!

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Lucija Johum 20 December, 2021
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