We know we can improve soil by tilling several inches of finished compost into the top 8 – 10″ of garden soil before planting, or a similar amount onto bare ground prepared for laying sod. But what about areas with established vegetation? How can we apply compost to existing lawns, ornamental beds, trees and shrubbery without uprooting them?
One way is to simply put a top-dressing on the soil by laying 1″ of compost on top of the soil for shrubbery or trees, ¼” for lawns. The living organisms in the soil will come to the surface to feed on the organic matter and pull it back into the soil with them. As water falls from rain or sprinklers, nutrients will leach into the soil. This is one effective application method for established vegetation.
However, if you want to get nutrients and living microorganisms down into the soil as fast as possible, consider brewing a batch of compost tea. Use the tea to water the plants. In liquid form, compost nutrients and microorganisms can reach the root zone very quickly.
How to Create Compost Tea
Fill half of a 5-gallon bucket with compost, then fill with water up to the rim. Let it sit for a day or overnight, stirring occasionally to add air. When you are ready to use, you may pour the mixture through cheesecloth to strain if you desire but it is not really necessary.
If you want to distribute your compost tea to a separate area from where you will use the remaining solid compost, straining is a good idea. Otherwise, it’s just an extra step.
Some people put the compost in a burlap sack rather than leaving it loose in the bucket, which makes it easier to separate the compost from the “tea.” However, if you are going to use it to water plants, it won’t hurt if solids are included. The compost leftovers from the process should be used as a top-dressing anyway.
Caution Against Going Anaerobic
Remember to stir frequently, and don’t let your tea sit so long that it begins to smell foul. A foul odor indicates that the tea has become anaerobic. This is the natural result of leaving organic matter in stagnant water over time, so don’t beat yourself up for “doing it wrong”! Just remember next time to stir more often and don’t let the tea sit so long before using it.
If your tea does begin to smell badly, try adding air by stirring and adding more water. If the odor can’t be resolved, you can always pour it back into your compost pile and it will right itself very soon.
How to Use Compost Tea
Use the compost tea (essentially “dirty water”) to water your lawn or garden. The water will seep into the soil to bring more of compost’s benefits down to the root zone.
Some sources suggest using compost tea as a foliar spray which reportedly controls various pests and disease. If you want to use compost tea as a foliar spray, you should use a pump to keep the tea aerated the entire time it is being brewed. I’ve written instructions for a simple pump you can make at home, or there are several commercial tea brewers on the market that provide aeration.
Using compost tea to water plants is much easier than using it as a foliar spray. Use as a foliar spray requires better straining, and also involves more care with regard to the strength and composition of the tea.
What’s In It? (Remember the “Garbage in, Garbage out” Principle)
When food manufacturers package their goods, they often list the ingredients and nutrients on the label. They can do this because they have total control over the exact inputs to their product.
Home composting and even some large composting operations do not have that level of control over what goes into their compost pile. Be wary of anyone telling you that a specific brewer will yield a compost tea with specific nutrient content.
The level of specific nutrients and microorganisms in your tea will be determined by what was in the compost that was used to make the tea. Unless someone has the nutrient analysis of the compost used, they cannot tell you what will be in the tea with any certainty.
There are many scientific tests which show that compost tea used as foliar spray is effective against a specific pest or disease. If you want to use compost tea to battle a specific pest, you will need to research what ingredients went into making the compost that was used to make the tea that was tested in the study.
These studies are quite fascinating reading, but are impractical for the average homeowner who has limited variety of compost inputs to choose from. If, however, you have access to a variety of input materials, you may want to investigate the scientific research and conduct some compost tea experiments of your own.
Mary Tynes, Master Composter, www.mastercomposter.com
Image (top left): 22-Gallon Earth Tea Brewer
Image (middle right): 5-Gallon Compost Tea Brewing Kit