Monday, July 6, 2009

The Benefits of "Spider Mulch"

I stopped by the local Goodwill thrift store today and came home with a copy of The Experts Book of Garden Hints: Over 1,500 Organic Tips and Techniques from 250 of America's Best Gardeners. The book is copyrighted 1993, so it's a bit dated, but it seems to have some very useful information in it and, after all, only cost me $2.

I was thumbing through the book, looking for information about how to eradicate Japanese beetles (nothing new on that front), when I stumbled across the subheading "Use 'Spider Mulch'" under "Bringing In the Good Bugs."

Apparently, by using grass clippings as mulch in my garden, I am using what one of "America's Best Gardeners" calls "spider mulch," apparently because it attracts spiders (I have seen lots of evidence of them in the garden where I have mulched--[shiver]), and those spiders are beneficial critters that eat the bad bugs. Here's the entry about "spider mulch":

Mulching your crops with hay or dried grass when you plant in the spring will attract spiders--a formidable natural "pesticide" that can drastically reduce insect damage in vegetable gardens, says Susan Riechert, Ph.D., a professor of zoology at the University of Tennesee at Knoxville. Dr. Riechert conducted a two-year study comparing the insect damage in hay-mulched and bare-ground vegetable plots. She found 60 to 80 percent less damage--and natural spider populations 10 to 30 times higher--in the hay-mulched gardens. Then when Dr. Riechert regularly removed the arachnids from the mulched plots, insect damage immediately climbed to levels comparable to those in the bare-ground gardens.

Spiders need high humidity, moderate temperature, and some type of structure to hide in. Peak spider migration occurs in April and May, when most gardens are still fairly bare. A garden mulched early in the growing season will provide a better habitat and end up with more resident spiders, Dr. Riechert explains.

Any bulky mulch that keeps the ground moist and cool offers an attractive habitat. Hay mulch, shredded newspaper, and leaf litter are examples.

Dr. Riechert adds, "You can't use any chemicals, or you'll wipe out the spiders along with the pests. But that shouldn't be a problem. In my opinion, backyard gardeners can virtually eliminate the need for chemicals by using spiders."

On reflection, I realize that the only bugs I have noticed in my garden are the spiders that crawl out of the mulch when I move it or add to it. I'm using both shredded newspaper and grass clippings, so I'm sure I've encouraged many spiders to move in. I don't use any chemicals on my garden since I don't want chemicals anywhere near my food, so the spiders have a safe haven for food foraging. Let's hope that they find Mexican bean beetles and squash bugs tasty--those are the two pests that my past gardens have had the most trouble with!


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