Backyard Aquaponics
A place to discuss aquaponics

Organic Compost Tea vs. Leachate

Some bin manufacturers suggest that the liquid that drains out of a worm bin is compost tea. Bin instructions sometimes encourage worm bin users to pour water into their bins to get more "worm tea", as it's called. Unfortunately, this is leachate, not tea. It's a common misunderstanding. This leachate contains only a very small percentage of the nutrients and microorganisms of tea, as well as a significant amount of undecomposed organic matter, that will quickly cause the liquid to turn anaerobic. Be careful, and only give this liquid to your plants if it is still aerobic (your nose will tell you), and don't pour water through worm bins. Use only finished stable vermicompost and follow specific tea-making instructions.

If you want to try out tea, without investing in a brewer, you may be able to find tea at a local nursery or commercial compost producer. If you cannot find fresh-made tea, you may have to buy a tea brewer.

Some of the confusion regarding whether or not to use leachate results from the current popularity of so called "compost teas" and "castings teas". To ensure we are all on the same page, "teas" are defined as a steepage generated by placing finished, stable compost and/or worm castings in water; some folks agitate the water, some don't; some folks aerate the water, some don't; some add nutrient solutions to amplify the biology, some don't. Regardless, "teas" all use as the substrate from which the initial biological community, nutrient and other chemistry are extracted, finished, stable material.

Leachate, on the other hand, is liquid that drains from an actively decomposing mass of organic matter, thus it is liquid that is in contact with undecomposed material in the system. It is this factor, coupled with the cause for liquid to be draining in sufficient quantity that it can be collected, that creates concern.

Composting and vermicomposting are processes understood to destroy or significantly reduce pathogenic organisms, typically rendering their numbers suficiently low to pose little threat to human health. Because leachate drains through material that has not been thoroughly processed, however, pathogens like e-coli and salmonella associated with household organic waste and even yard debris can potentially be picked up in the leachate and contaminate the surfaces of fruits and veggies to which it is applied. It's important to understand that the concern is not that plants might take these pathogens up through their systems, but is a concern over surface contamination of garden produce. Those who chose to use leachate on edible plants are encouraged to wait several weeks after application before harvesting to ensure pathogens have died off before produce is eaten.

Water is generated by the composting and vermicomposting processes as well as being released from OM as it is broken down. In most healthy worm bins and compost piles the released moisture is absorbed by the the surrounding OM, thus little water drains freely from the system. A healthy worm bin, for instance, generally produces little more than a few ml of liquid per week. A system from which liquid is draining freely is typically a system that is saturated, thus, it can hold no more water. This is of concern because the water saturating that system is displacing oxygen, setting up conditions favorable to anaerobic microorganisms. Even if there are no significant odors, very wet compost piles and worm bins tend to have significant levels of anaerobic activity. The by-products of anaerobic decomposition, phenols, terpenes and alcohols, are water soluble and are toxic to plant roots, thus leachates often contain significant concentrations of these phytotoxins though there is no outward evidence of such. These leachates applied to plants often cause damage and can even kill sensitive plant species or plants treated with leachate with significant levels of phytoxins. To be sure, many people use leachate with excellent effect, but for every leachate advocate whose garden sees tremendous benefit I can introduce you to someone who killed or weakened their garden with leachate use. It's a risky thing using leachate. Many people will dilute the leachate (the general recommendation is 10 parts clean water to one part leachate) which often, if not usually, does remediate problems, but dilution also tends to dilute the benefits, rendering the stuff little more benefical than plain water.

So, bottom line; leachate is generally discouraged for garden use, particularly on food crops.

A healthy worm bin, for instance, generally produces little more than a few ml of liquid per week. A system from which liquid is draining freely is typically a system that is saturated, thus, it can hold no more water. This is of concern because the water saturating that system is displacing oxygen, setting up conditions favorable to anaerobic microorganisms. Even if there are no significant odors, very wet compost piles and worm bins tend to have significant levels of anaerobic activity. The by-products of anaerobic decomposition, phenols, terpenes and alcohols, are water soluble and are toxic to plant roots, thus leachates often contain significant concentrations of these phytotoxins though there is no outward evidence of such.

I'm going to open a can of worms here (lol) but worm farm leachate IS NOT worm tea.

in one of the links i posted at the start is goes into great depth on why.

i just had this arguement with mum tonight. FAR to many websites say thatworm tea is the run off (leachate).

The leachate contains partially decomposed plant matter, alcohols, terpenes and often anaerobic bacteria. It is nutritionaly very poor compared to true worm tea and needs to be diluted atleast 10:1 becasue the above mentioned products are actually phyto-toxins that will damage the plant.

worm tea is the water in which worm castings have been steeped in.

Much of my original post was about the further step of airating and adding some brown sugar or molasas (with no sulphite) for 48 hrs to grow the popuilation of beneficial organisms.

yep worm casting look like fertile black dirt, and can take quite a while to be complete depending on the amount of worms. there should be no visibile remenants of the original organic matter.

Also, leachates can be high in pathogens which would be destroyed by the gut process of the worm in the finnished castings.

rant over

i will agree with you that aerobic microbs might remediate leachate, particularly if seeded with some finnished aerobic castings, but then will they also process any alcohols terpenes and others that are the metabolic byproduct of the original anerobic bacteria?

We have been using 1 teaspoon of molasses to a gallon of water as an insecticide against cabbage white butterflies and their caterpillars.It seems to deter the butterflies from landing on the brassicas and laying eggs AND it does not seem to have any effect on the fish in the tank.