WHEN TO GET ’EM: Fall is the ideal time to get a truckload (or more, depending upon the size of your garden) of woodchips. Spread them on top of soil you want to improve and let them decompose over the winter. The idea is to mimic nature—with no interference from you. If you have nutrient-poor soil, you can put a layer of compost down first, but this is not necessary.
WHAT TO ASK: Call a local arborist or tree-trimming service and ask to have a load delivered free or for a nominal fee. Don’t be shy. These companies don’t want to haul their chipped trimmings miles to a landfill and pay a fee for doing so.
Find out the kinds of trees that were chipped. Some plants contain allelopathic chemicals, which can prevent seeds from germinating or kill young seedlings. According to the website of Dr. Linda Chalker-Scott, Ph.D., a horticulturist at Washington State University, very few woody materials contain them. Black walnut is the most common one. You can find lists of other allelopathic trees on the internet.
BEST BETS: Ask for coarsely chopped chips, because they don’t compact the way sawdust and bark do. They are also less combustible. The fresher the chips the better—they contain more nitrogen.
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Dr. Walker-Scott discounts many myths about woodchips, claiming that they do not acidify soils or cause nitrogen deficiency, except possibly at the interface of the chip layer and soil, and do not attract many pests. She also says that those from diseased plant material do not affect healthy plants or soil.
HOW TO SPREAD ’EM: The beauty of woodchips is that they contain not only wood (carbon) but also leaves (nitrogen), the “browns” and “greens” in compost. When you get a load, spread them over the soil you want to improve, at a minimum of 4 to 6 inches thick. Do not till them in. (Tilling can tie up nitrogen.) Let the thick layer sit there over the winter, insulating the soil and suppressing weed germination, while bacteria, fungi, nematodes and earthworms work their magic, creating nutrient-dense material.
PLANTING TIPS: Come spring, dig down and you should see rich, dark soil with a nice crumbly texture beneath the layer of chips. Don’t plant directly into the layer. Do so in the rich soil just below it. Leave the soil and plants exposed until their roots take hold, then replace the layer of chips up to the plants’ first row of leaves. During the growing season, the layer will protect crops and soil from summer’s heat, conserving moisture, and the plants will utilize the nutrients from the decomposed chips.
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This article was originally published in The NEW PIONEER™ Winter 2016 issue. Subscription is available in print and digital editions here.