If you’re a keen gardener, you might already be having fun exploring the benefits of compost tea and getting to know how this liquid affects your garden.
However, as with anything you use on the garden, you probably have a few questions about how it works. We’re going to look at how long does compost tea last? ( Mixing and coverage )
How long compost tea lasts will depend a bit on how you have made it, and estimates can vary a bit.
However, many suggest it should be used within a few hours of being created. Compost tea that isn’t used up quickly may turn anaerobic, which most gardeners try to avoid. Anaerobic compost tea does have its uses, and will last for much longer than normal tea.
What Is Compost Tea?
Briefly, what does compost tea involve and why might it need to be used so quickly?
We are going to mostly look at aerobic compost tea here, as anaerobic compost tea is quite different, and can be kept for longer because it doesn’t need oxygen in the water and most of the microbes are dormant or dead.
Anaerobic tea tends to be less popular and trickier to use effectively in the garden; most gardeners will be working with aerobic tea.
Aerobic compost tea can be made using compost and water, or worm castings and water.The goal is to boost the microbial activity in the tea, and then apply these microbes to the roots or leaves of the plants in your garden.
It is thought that the additional boost of microbes might make your plant more resistant to disease and pests, because these microbes have been shown to protect plants from these things.
There is not yet much scientific proof of this result, but many people feel that compost tea really benefits their plants.
When making compost tea, the idea is to boost the number of microbes and the amount of activity as high as possible so that they have the maximum impact when applied to your plants.
How Long Does Compost Tea Last For?
In general, it is best to use your compost tea as soon as it has finished brewing, as it should be at its best then.
Not using it may result in the mixture becoming anaerobic, which will mean that all the aerobic bacteria you have carefully cultivated are gone. They will have been replaced by anaerobic bacteria.
Most gardeners aim to avoid this. Indeed, compost tea tends to be made to maximize the air in it by using a bubbler or something similar, so you want to use the tea before the air has been used up.
The aerobic bacteria will quite quickly deplete the oxygen supplies in the water, and will then die.
If you have already made compost tea, you will be aware of how important the oxygen content is.
Often, an aerating device is the most expensive part of setting up a compost tea maker, and the bacteria is thought to be the most valuable part of the compost tea – so you don’t want to risk it running out of oxygen and dying.
Compost tea will only last for up to twenty-four hours, and the longer you leave it for, the less valuable it becomes, because the microbial activity will be steadily decreasing.
Some people suggest that it should be used within a few hours of brewing.
Can I Make My Compost Tea Last Longer?
Sometimes, it just won’t prove practical to use the tea up straight away. In these cases, you might be wondering if you can save it, and you may be able to.
The reason the tea doesn’t last is that the microbes run out of oxygen.
If you can ensure that the oxygen levels in the tea remain high, the microbes should stay active and lively, so you may be able to keep your tea going for longer by continuing to aerate it.
Regular stirring or bubbling should help to keep the microbes alive.
However, you should still seek to use the tea up when you can, or you may find that it loses some of its effectiveness.
There is also a risk of bad bacteria growing if it is kept for long – you could end up with salmonella or E. coli in there, so it really is best not to leave it for too long.
Ideally, plan your gardening so that the tea is used within twenty-four hours, and kept for a maximum of forty-eight hours, or you may find it has been a wasted effort or that you have a potentially dangerous mixture.
How Do I Know If My Compost Tea Has Gone Off?
If you aren’t quite sure how long the compost tea has been in a bucket for, it probably has gone off – but how do you know? The key will be in the smell.
Aerobic compost tea should not smell bad. It should smell earthy and composty, but not particularly unpleasant.
However, anaerobic compost tea will smell bad.
If the aerobic bacteria have been replaced by anaerobic bacteria, the tea will be a source of greenhouse gasses like methane, and this will smell pretty unpleasant when you handle or approach it.
You can still use anaerobic compost tea, but as you can’t control what sort of microbes are in it and there may be some harmful ones, it should only be used on the roots of your plants, rather than on the leaves.
Use it very sparingly, and dilute it thoroughly.
How Do I Mix Compost Tea?
Compost tea takes a minimum of twenty-four hours to brew properly, and you will need some specialized equipment, including an aerator of some sort.
It can cost around $100 to make one, but if you are keen, you should find you get a lot of use from it.
Essentially, all you are doing is mixing compost with water in a large bucket and adding lots of oxygen to encourage the microbes and microbial activity.
It is thought that this decreases the risk of bad microbes growing, and increases the effectiveness and liveliness of the good ones.
You can make compost tea with the following ingredients:
- A five gallon bucket
- Two cups of compost (or worm castings)
- Non-chlorinated water
- Half a cup of a food source to help the bacteria thrive (usually something like molasses mixed with fungi food or liquid fish fertilizer to promote the growth of both bacteria and fungi)
- Porous fabric
- An aquarium bubbler
- An air pump
You can then mix everything in the bucket, or contain the compost in the porous fabric.
Set the bubbler going and allow it to brew for twenty-four hours. If you haven’t contained the compost, you will need to strain the tea through your porous fabric when you are ready to use it.
It really is very simple to make compost tea once you have the correct equipment. When you think the batch is ready, make sure you smell it to check it is okay.
If it smells very strong and unpleasant, something has gone wrong and the mixture has turned anaerobic, so you need to discard it and start again.
If it smells of earth, it is doing well and you should use it promptly on your plants.
How Do I Know How Much Coverage I Will Get From Compost Tea?
So how much compost tea do you need to make? This is a tricky one because it depends on how much you dilute it and how thickly you apply it.
Most people dilute their compost tea to a ratio of 1:10 (so one cup of compost tea to ten gallons of water).
You can use tea that is as concentrated as 1:4 if you want a really strong dose. Don’t use it at stronger concentrations than this.
You can put the tea in your watering can and use it to water your plants and increase the microbes in the soil around their roots, or you can put the tea into a spray bottle and use it to spray the leaves of your plants.
Either method should help to protect your plants from bad microbes and other issues.
Of course, you will need to keep applying compost tea; a single application won’t make any noticeable difference to your plants.
You need to add compost tea to your plants on a regular basis, and many people say it should be done at least twice a week to see the full benefit.
How far a five gallon bucket goes will depend very much on the dilution ratio you use and how heavily you spray or water your plants, but you can always make a couple of buckets at once provided you have two airstones and bubblers!
Compost tea does not last long once it has finished brewing; you will need to use it up within a day to minimize the risk of dangerous bacteria growing in it, and to ensure that the microbes you have carefully bred are still alive and active.
Tea that smells bad has turned anaerobic and you may want to discard it.