How to make your own compost tea and worm farm

Last updated on March 15th, 2023 at 02:31 pm

How to Brew Compost Tea for Growing Vegetables

Different compost teas have different properties, and the recipe you choose will depend on how you want to use it. Home grown vegetable crops will benefit from fertilization with a compost tea that is high in bacterial activity and rich in nitrogen.  A mixture of vermicastings – created by worms (see below) – liquid kelp or seaweed and cane sugar creates a fabulous bacteria rich brew.  Compost teas complement traditional compost and mulches.  So how does this translate into a recipe?

• 1 ounce of liquid kelp/seaweed powder
• 2 ounces of cane, or white sugar
• 1.5 pounds of vermicastings
• A cup of garden soil

Seaweed powder is more quickly broken down than fresh seaweed, which has a tough rubbery consistency.  You can add raw seaweed to your compost pile, and it is rich in potassium and trace elements, but for a liquid brew it’s quicker to use liquid kelp or powder.

However, if you have a couple of months before you want to use it, you can steep fresh seaweed in a bucket of water, after rinsing well to get rid of salt.  Stir the mix every two to three days.  When you can no longer smell ammonia, you can use the liquid.  You can soak the seaweed twice to make a brew, then put the spent seaweed on your compost pile.  Seaweed adds hormones, enzymes and vitamins to the soil. [Note from Kisten: I remember reading Jackie French saying she used the need to collect some more seaweed as a good excuse for a trip to the coast a couple of times a year.]

So – to get back to the tea!  Mix the ingredients in a five gallon plastic bucket, top up with rainwater and introduce air with an aquarium kit, which includes tubing and a pump.  Some organic gardeners prefer to introduce air by stirring the tea every day.  The pump just increases oxygen faster than if you do it by hand.  Anaerobic tea will smell bad, and is not as good for the garden.  Aerobic ‘microherd’ bacteria populations break down bad pathogens in the soil, and though anaerobic compost tea is simpler to make, and also beneficial for the soil, by introducing air you make a more effective fertilizer.

The tea takes about two or three days to brew, and you should use it straight away, either on foliage or in the soil, preferably in the spring. When the mix smells yeasty or earthy, and may have foam on top, it should be ready.  If it doesn’t seem right, leave it for up to a week.  Even in unaerated compost tea there will be some aerobic activity for several days.

When it is warm outside, the tea will brew more quickly, and so the colour, the smell and whether it is foamy on top will vary depending on the weather.

How to Make Your Own Worm Farm

Vermicastings, or worm castings are the end-product after worms have broken down organic matter, like your left over vegetable scraps.  Also known as worm compost, (oh OK, you can call it poo, too) it can be bought readymade, or produced in your garden or yard.  You can buy a custom made worm farm, or improvise one using plastic containers.  About three containers, with tapering sides in order to stack them, would be ideal. Make sure the top one has a well fitting lid.

Earthworms will do the job, though red worms or wrigglers are much better, if you can get them, as they rise upwards to feed, and leave the poo beneath them.

Drill holes of about a quarter of an inch (6mm) across the base of the top two containers, or bins, spaced about two inches (48 mm) apart.  This allows for the compost worms to wriggle upwards, as well as for ventilation and drainage.  Do the same about four inches (96mm) from the tops of the bins in a continuous ring, for ventilation.  The lower, or sump bin will collect the leachate, or worm tea. A hole drilled just above the base can be used to drain out the liquid – either fitted with a tap, or by tipping up the container.  If you fit a tap, be sure it is well sealed with lock nuts and washers.  Place the base bin on bricks, to raise it up and allow for you to drain off the worm tea.

To provide ventilation and to stop the bins getting stuck together, place wooden blocks or sealed food jars of about 6 inches (150 mms) in height between the two upper bins.  Also place smaller blocks of about 4 inches (100mms) in the lower bin.  Then place dark waterproof cloth over the small gaps between the bins to stop bugs from crawling in, or rain from getting in.  Place the farm in a shady spot, or in a shed or garage to avoid frost.

Now you can introduce the worms to the top bin, after putting in shredded newspaper, some compost, a handful of damp soil and organic vegetable scraps, or bits of bread and pasta.  Keep the lid on top to discourage animals and pests from foraging in your farm!  Every now and then sprinkle some water on the top bin to prevent the farm from drying out.

Once there is a fair quantity of compost in the second bin, swap it over with the top one and repeat the process.  The worms will wriggle back up again towards the food, via the blocks or food jars.  About three weeks or so later, you’ll have enough compost to swap them around again.  The worm tea is a rich source of nutrients for your garden, and the vermiculture can be used in the compost tea recipe above.

Eileen O’Sullivan is an English freelance writer, who once lived in beautiful Sydney (sigh!), where her first son was born. She passionately enjoys contributing to global health – and grow-your-own is a perfect start to sustainable living.