I have used and recommended coffee grounds as an organic fertilizer for years, but they have another important use. To control slugs, snails and pillbugs, broadcast coffee grounds around plants troubled by the little beasts. To run pests off effectively, use anywhere from 2 – 5 lbs of coffee grounds per 100 square feet.
Slugs in most cases come right up to coffee grounds but wouldn't cross over. Not only is the product organic and works great, but it also replaces one of the worst toxic pesticides on the market, Metaldehyde. Diluted coffee is also an excellent organic fertilizer, especially for orchids, African violets and may have some of the same pest control powers. It's probably worth a try.
Coffee contains N-P-K, trace minerals and the food stuff to stimulate the growth of beneficial microbes. The best part is that coffee grounds are basically free. Just ask your local restaurants or coffee shops to put them in a container provided by you. At the least, save and use your own coffee grounds at home. We do every day.
Coffee tends to develop a green or blue-green fungus that looks like mold. Don’t worry - that’s good. The green fungus is really beneficial (Trichoderma species) while the blue-green one is reported to be moderately beneficial. In any case, moldy coffee is great to use directly in the garden, compost pile and on interior plants.
Here is some research on the subject from USDA – ARS.
COFFEE - Slugs and snails hate caffeine, researchers have discovered. Robert Hollingsworth of the United States Department of Agriculture's Agricultural Research Service in Hilo, Hawaii, and his colleagues discovered this secret while testing caffeine sprays against the coqui frog, an introduced species that infests potted plants. They found that a 1 to 2 percent caffeine solution killed most of the slugs and snails in two days. Concentrations as low as 0.01 percent repelled the pests. A cup of instant coffee contains about 0.05 percent caffeine, and brewed coffee has more.
Coffee grounds can also be used to repel slugs and snails, but a caffeine solution is much more effective. Caffeine is more effective against slugs than metaldehyde products. The United States bans metaldehyde residues in food, but classifies caffeine as safe. It may even qualify as organic, adds Hollingsworth.
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