Compost Tea is gaining popularity not only as fertilizer for the soil, but as a spray to invigorate the plant's defenses against pests and disease. You can make compost tea from finished good-quality compost. Or you can make the tea using worm castings. I like to use worm castings. (I'm mostly composting chicken bedding, which I would not want to spray onto the plants.)
Many people make teas from compost or manure by just soaking, without aeration. If you elect to do that, be aware that it will be very smelly if you leave it very long, because the anaerobic bacteria (those that can live without oxygen) cause wet organic matter to rot and stink. The bubbler puts oxygen into the brew, and the aerobic, oxygen-loving bacteria have a pleasant, slightly beery smell. Aeration will also put more nutrients into the brew.
WORM CASTING (OR COMPOST) TEA
To make this tea, you need an aquarium bubbler, which consists of an electric compressor pump, some tubing, and an air stone. Alternatively, you can agitate the brew to keep it oxygenated. You would need to stir it vigorously 2 to 4 times a day. Smaller batches may be shaken vigorously in a jar. A compromise between buying an aquarium bubbler and using just hand stirring would be to use an electric mixer a couple of times a day.
Combine in a five-gallon bucket:
Mix everything together and stir well. Turn on the bubbler, with the airstone down on the bottom of the bucket. Let it bubble for 36 hours. In cold weather (below 60) it will take twice as long. In very hot weather (above 80), one day will suffice.
It's then ready for use. If you do not use it right away, keep bubbling it. Do not keep more than 5 days. Use it to water your plants, either straight or diluted half and half with water. Use it diluted half and half as a foliar spray.
Korean Natural Farming is a style of organic gardening that uses microbial cultures to make the garden healthy and strong. KNF teaches ways to grow your own fertilizers, pest controls, and plant supplements using the free microorganisms native to your area. All of the preparations are simple, cheap, and need no equipment. Here are the two easiest to make. We use them all season, from greenhouse to harvest. We also use LAB to keep our chicken coop sweet-smelling and fresh.
The easiest KNF brew to make is the Lactic Acid Bacteria (LAB), which is basically what is in yogurt and sauerkraut. It is also a good one to know because is supplies different kinds of microorganisms than compost tea does. They make a great pair, either to use on different days or to mix immediately before using.
The University of Hawaii has done a lot of research on Natural Farming ferments. Here's a link to their pdf on Lactic Acid Bacteria brew.
Fermented plant juice (FPJ) is a growth enhancer. It uses fresh, actively growing plants form your own area and concentrates them. So you get the nutrients and hormones that produce strong plants in your conditions. We usually use weeds for this, as they are so vigorous and well-adapted.
Again, the University of Hawaii has a pdf with the recipe and uses.