How Do You Make Compost Tea?

  • By: composthq
  • Date: April 3, 2022
  • Time to read: 9 min.

Have you ever heard of compost tea? If you haven’t, you’re in for a great treat. If you have, you’ll know what amazing properties it is said to bestow on your plants.

Some claims may be a touch exaggerated, but compost tea is certainly something that can give your plants a boost and help them grow.

Let’s look into compost tea and how it works in more detail. We’re going to explore what it is, how to make it, and whether it really does all the incredible things that the internet claims.

What Is Compost Tea?

Compost tea is a nutritional liquid that you add to your plants to give them a boost in fertilizer.

It’s become very popular in recent years, and many gardeners swear that it makes their vegetables bigger and tastier, and their plants stronger and lusher.

It’s also said to help fight diseases and kill unwanted bacteria.

Compost tea looks a bit like actual tea, but its name is a little misleading because it doesn’t involve boiling water or teabags – it’s about brewing compost in water for a period of time,

Almost like you would brew beer, to concentrate bacteria, fungi, and other goodness into the resulting liquid.

It can be used on your plants at any time of year, and while it is thought to make a big difference to their health and growth, it’s a very mild fertilizer, so it shouldn’t upset even sensitive blooms.

Compost tea is said to be valuable to plants because it concentrates the microorganisms and beneficial bacteria that help them to survive.

Although few studies have been done on compost tea thus far, it’s claimed that it strengthens the soil life and can kill off disease in some situations, saving plants that are sickly.

More specifically, compost tea is thought to increase the presence of predatory nematodes, which help to defend the plants from hostile organisms, and mycorrhizal fungi, which do the same.

Different Types Of Compost Tea

There are two different means of making compost tea, so if you’re interested in doing so, try one or both of these methods at home.

Neither is particularly more complicated, and which one offers better results seems to be up for debate – so let’s explore both.

Aerobic Fermentation

You have probably come across the terms aerobic and anaerobic during your early composting forays – and you may even have experienced an anaerobic compost heap. It’s not pleasant, but easy to fix.

In case you haven’t met the term yet, it means that oxygen is present or that the process depends upon oxygen being present.

This method does involve slightly more work and equipment, and is sometimes called aerated compost tea.

The advantage of this method over the other is that it does not smell nearly as bad.

It is also thought by some to be safer, as many anaerobic bacteria are harmful, and it can be hard to get the “right” bacteria in your anaerobic tea.

Anaerobic Fermentation

The other kind of compost tea is made anaerobically. That means you’ll be putting a well-fitting lid on your bucket to keep the air out.

Anaerobic tea does still need some oxygen, however, and you have to be a little careful when making it, as many of the organisms that are harmful to plants prefer anaerobic conditions.

Anaerobic fermentation is less work than the aerobic kind, however, and needs less equipment.

The payoff is that you will have to deal with a really bad smell every time you handle the stuff, and you will need to handle it from time to time (even before you’re ready to use it on your plants).

How Do You Make Anaerobic Compost Tea?

Making anaerobic compost tea is straightforward. You will need:

  • A five gallon bucket with a well-fitting lid
  • Two or three cups of compost, well aged (take it from the bottom of your compost pile)
  • Non-chlorinated water. You can either gather some rainwater, or you can let tap water sit in the open for a couple of days, until the chlorine has evaporated off.
  • A porous fabric
  • A stick for stirring

You can just put your compost in the bucket and pour water on the top, but how do you later separate liquid and solid? You don’t want your compost tea full of lumps.

You can strain it, as you would strain a cup of tea, or you can put the “tea leaves” (i.e. compost) in a “tea strainer” (i.e. porous fabric) and save yourself some work later.

An old stocking or piece of burlap is best.

  • Add some compost to a stocking, tie a string around the end (so you can pull it out easily), and put it in the bucket.
  • Fill the bucket with non-chlorinated water.
  • Let it sit for around 3-4 days, stirring once per day if possible. Stir very gently; you only want to add a little bit of oxygen.
  • Strain the liquid off the solids (or remove your sock if you have used a sock). The solids can go back on your compost pile.
  • Use the tea promptly. You should test a small amount on a plant and see how it responds before you start using it in quantities on a regular basis – some plants may not get on with the compost tea.

For more sensitive plants, seedlings, or young plants, dilute the compost tea with water, at a ratio of 10:1.

For established plants, you may want to dilute it a little, or use it in its concentrated form – just check with small quantities first to ensure your plants don’t object to it.

While nothing should theoretically be harmed by compost tea, it is worth remembering that few scientific studies have been done on it, and you might occasionally end up with harmful bacteria and microorganisms in your tea, as well as the beneficial ones.

Use it sparingly and don’t get over-excited.

Stirring your anaerobic tea gently and occasionally may marginally reduce the chance of the wrong bacteria multiplying, but you should still be careful.

How Do You Make Aerobic Compost Tea?

Aerobic compost tea is a little more involved, but still fairly simple and inexpensive, and can be a fun project to do with kids. It also doesn’t smell as bad as anaerobic compost tea!

You will need:

  • A five gallon bucket
  • Two or three cups of well aged compost
  • Non-chlorinated water
  • A tablespoon of sugar per gallon of water (many people like to use molasses and other sugars, but white sugar will work if you don’t have access to them)
  • A porous fabric
  • An air pump
  • An aquarium bubbler

Again, if you want to, you can put your compost and sugar in something like a sock, or you can strain the compost tea through the porous fabric when you are ready to use it.

  1. Mix your compost with some sugar, using about five tablespoons if you have a five gallon bucket.
  2. Add the compost and sugar to your bucket or your sock (remember the string if using a sock).
  3. Set up the air pump and aquarium bubbler, and then fill the bucket with water and switch them on so they are aerating the compost.
  4. Let it run for a couple of days, checking on it regularly. It should start to produce a sweet, soil-y smell, and you’ll see foam collecting on the surface.
  5. After two or three days, it should be ready to use. You don’t want to keep this system running for too long, because your bacteria will run out of food and will die off or go dormant.
  6. Strain your compost tea, and then you’re ready to start using it on the garden! Remember to dilute it for sensitive plants and seedlings, and start by just adding a little to see what effect it has.

What Else Can You Do With Compost Tea?

As well as pouring it on a plant’s roots and adding microorganisms to the soil that way, you can spray the diluted tea to serve as a foliar spray on the plant’s leaves.

If you haven’t heard of foliar sprays, they are a way of applying nutrients directly to a plant’s leaves, where it absorbs them more readily and quickly.

This is a “quick fix” for nutrient deficient plants, although it’s worth noting that it’s not a substitute for good soil health and plant care.

It is thought to give plants that are sick or have an infestation a boost, though you should still look to address the causes.

Do not spray your compost tea onto the leaves in its concentrated form. You should always dilute it 10:1 with water before putting it on a plant’s leaves.

It should look like weak tea. You’ll need to spray a plant several times before you start seeing results. Spraying a couple of times a week should work well.

It’s not a good idea to use compost tea on the leaves of plants you are going to eat, as you may accidentally ingest microbes and bacteria that are harmful to people.

If you have done so, consider discarding the plants or giving the leaves a very thorough wash before consumption. You don’t want to make yourself sick!

Does Compost Tea Really Work?

Of course, with any “new” thing (it’s been around a while, but is becoming a more popular practice), there will be skeptics who challenge the claims, and people who exaggerate the benefits.

So, is it as good as people say?

One of the problems with compost tea is that almost all the evidence is anecdotal at best. Lots and lots of people seem to have had success with it, but can they prove it?

Some people have done rudimentary tests at home, trying to measure the impact of compost tea by getting two identical plants in identical conditions, and only giving the tea to one.

Most say that they can see a visible difference, and the plant getting the tea is healthier and bushier.

However, these tests are not conducted in a laboratory setting, and haven’t really – despite the best efforts of the testers – got much scientific backing. There aren’t control groups, and there may be many factors unaccounted for.

It is also very difficult to measure compost tea even in a lab setting, because every person makes it in slightly different ways, and every batch will be different.

There are so many variables, such as the age of the compost, what was used to make the compost, what goes in the bucket, how often it’s stirred, etc.

This makes it almost impossible for anyone to measure whether compost tea is harmful or helpful.

It may be that some batches are really good for your plants, while others introduce bacteria you would rather not have added.

There are studies that have shown positive results, and it’s certainly true that adding compost tea does add nutrients to the soil – just as adding compost would.

It seems unlikely that we’ll find out any time soon whether all the claims of compost-tea-advocates are correct (some probably aren’t).

But if you have fun making the tea and you feel your garden benefits, you at least aren’t likely to be doing any harm to the plants.

Just don’t use compost tea on leaves you plan to eat.

Conclusion

Compost tea can be very interesting to make, and if you have a microscope, you should be able to use it to view some of the bacteria and microorganisms that are swimming around in your tea.

This is great fun, both for adults and for children, so it’s definitely worth doing the experiment for that reason.

You can also rest assured that your garden will see some benefits from the tea, even if they are comparable with simply adding the compost (rather than fermenting it).

If you want to, you could try some “at home” science experiments yourself, and see how you feel about the efficacy of your compost tea brew.

Whether compost tea will remain an exciting and important aspect of gardening or fade away as time passes remains to be seen, but we encourage everyone to try new things in their garden, and to engage with and understand their plants’ needs as much as possible.

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