Compost has been used in gardens forever. Compost tea is sort of a new fad. I’ve been using them both for a while and noticed several important distinctions.
Good compost is arguably more beneficial to gardens than compost tea, but both are useful in specific circumstances. Compost is much better at building up lasting fertility, conditioning the soil, and, increasing water-holding capacity. Compost tea offers a mild burst of water-soluble plant nutrients.
There’s a lot more than that. I’ve gone through several tons of compost and barrels of compost tea. Here’s what I’ve learned.
Compost is More Fertile than Compost Tea
Compost tea contains only a small percentage of the nutrients from compost. Many of the nutrients in compost take time and biological action to become available to plants and are simply not extracted when making compost tea. Still, it provides a functional boost in plant nutrients.
Compost has a wide range of nutrient levels. It usually has an NPK of approximately 0.5-0.5-0.5 or 1-1-1. Those levels are what in market gardening, I call equilibrium. Meaning, that’s where the soil itself should be at. With the 0.5 or 1 percent primary nutrients, it’s not considered a fertilizer, but a soil enricher.
Compost tea usually contains half or less of the nutrients from the compost itself. The weaker the compost, the less water-soluble nutrients can be extracted from it in compost tea. Most store-bought compost is 0.5 percent strength. That’s half a percent nitrogen, phosphorus, and potassium.
High-quality compost can be up to 3 percent, which makes it a weak fertilizer. But, it’s hard to find much over 1 percent. That’s the minimum I try to get. Anything lower waters down my soil.
A compost tea is usually quite weak, but it does contain one of the best parts of compost, Humic acid. That’s a water-soluble, black chemical that contains a lot of locked-up nutrients of all kinds.
Humic acid is a long chain molecule built on carbon (hence its black color) that holds a rich amount of plant minerals in a molecular bond. Plants can’t break it down, but fungi and bacteria can. Humic acid is the best way to increase beneficial mycorrhizal fungi, building healthy soil and strong plants.
You can buy humic acid, it’s expensive. You could also extract it from compost with a compost tea and apply it during the growing season. Plus, it still contains the free nitrogen and other minerals that haven’t been taken up into the carbon bonds within the compost. I hope I didn’t get too science nerd there.
Neither are Thought of as a Fertilizer
Neither compost nor compost tea are considered fertilizer due to their regularly low strengths. Compost is a soil amendment and soil conditioner, and compost tea is what I would call a soil enricher. Not quite a fertilizer, but still helpful. You could call both a mineral supplement or a biology boost.
I generally consider anything with an NPK number of 3 or more to be at least a weak fertilizer. At that point, it’s possible and at least somewhat feasible to use it to provide most or all of the nutrients required for many types of crops.
Compost tea is just a weak extraction of all the available water-soluble minerals in compost. many of those minerals are in a form, like humic acid, that provides food for soil microbiology, generally precursing an increase in soil life which in turn, improves soil quality, texture, and fertility.
Compost Tea Absorbs Immediately into the Soil
The best reason to make compost tea is that it absorbs into the soil and the available nutrients are immediately ready to be taken up into a plant’s roots. I have used compost and manure teas in my perennial herb beds when it suddenly became apparent that there was a mineral deficiency.
Dumping a load of compost in a tight growing bed of chamomile didn’t sound good to me. That would have dirtied and damaged the flowers I was about to harvest. Instead, I mixed 20 gallons of compost tea and applied it with a watering can.
Compost Tea can be Applied Anytime
Applying compost can damage a growing crop. For example, attempting to spread compost in my bed of butterhead lettuce would end up with heads full of filth and damaged leaves, no matter how cautious I was being. Compost tea can help in that instance.
That’s by far the biggest reason to mix a compost tea in my experience, and one of the only instances I would feel compelled to do it now. It can be applied as a foliar spray and I’ve tried that. I don’t exactly recommend that, but it can work if it’s quite strong.
Compost Fixes Poor Soil
The biggest reason to use compost is that it’s simpler and because compost fixes poor soil and improves any and all soil types. Compost makes soil fluffy and allows water to soak in and air to penetrate deeper. The carbon matter, the black part of compost, attracts and soaks up water and plant nutrients.
Compost feeds all the beneficial organisms in the soil, lessens fertilizer leaching, and allows the soil to build up a natural, long-lasting fertile state. Fortunately, if you are making compost tea, you still have the compost to use later. It will be less fertile, but still very beneficial.
Is Compost Tea Actually Better than Compost?
I’ve asked myself “is compost tea really any different from just tossing compost in the garden and watering it”? The answer is not really, but it can be in specific circumstances. There are few benefits of making compost tea vs simply using compost.
Lately, the idea of making compost tea as a microbiology boost to your soil has become a popular experiment. There’s been some impressive findings and reports. Unfortunately, I see little if any difference in function between healthy compost and healthy compost tea.
If you want to brew the compost tea long enough to get to be a biology powerhouse, it needs to be aerated. Otherwise, it will turn anaerobic, take on a foul odor, and become a breeding ground for bad bacteria. Running an aerator in a tank of compost and water for two weeks can be unfeasible.
Honestly, Good compost has plenty of microbiology in it. If you did create a super biology-boosting tea what happens to the microbes when you apply it? Is there enough organic matter in the soil to feed them? if so, there are probably already enough microbes in the soil.
I’m all for experimenting and discovering new methods, but I am also very practical and down-to-earth. In order to be sustainable, we need to keep our energy and resources in things that matter, show good return, and that build up the soil.
I consider compost tea only a way to extract water-soluble nutrients from compost. When I do make it, I don’t let it soak for more than a day or two, and I’ll agitate it with a shovel or how to mix it well. I like to fill a bucket about 1/3 up with compost and top it off with water, then let it soak and warm up for a day.