By Marie Hofer
HGTV Ideas magazine
In a perfect world, fall is the perfect time to take steps to improve your soil. Why? There's time to correct soil imbalances, time to let amendments work their magic, time to prepare for the freezing and thawing that will loosen well-worked clay soils. And there's plenty of free organic matter at hand.
But chances are you'll be doing a lot of amending this spring. Whether you're planting perennials and trees, opening up a new landscape bed or expanding the vegetable garden, your garden will benefit from your toils in the soil. Here's some advice from the experts.
Test your soil
Depending on what type of soil you have, adjusting its pH usually takes months. Next to its structure (size and arrangement of particles), no other factor of your soil so affects the availability of nutrients and the vigor of your plants. You can lob on the fertilizer, but none of its ingredients will be available to your plants unless the pH is correct.
Add organic matter
Organic matter improves tilth (fluffiness) and opens the pores of the soil, allowing easier penetration of roots, air and water. It also sustains millions of microbes--beneficial bacteria, protozoa, nematodes and fungi--that help contribute to a healthy ecosystem. In sandy soils, it encourages the retention of water and nutrients. In clay soils, it decreases the hard lumpiness, makes it easier to work and improves drainage.
Can you add too much? Yes, especially if it's the wrong kind. High-carbon material such as bark and sawdust can create nitrogen deficiencies; add either a nitrogen fertilizer or manure to speed decomposition and restore a healthy nitrogen balance.
Even adding finished compost temporarily sets off another imbalance, says Roland Meyer, extension soils specialist with University of California at Davis. "You're presenting a whole new food basket for the organisms. They have the first crack at the nutrients, so if you plant, the plant is shortchanged. That's going to happen to a certain extent no matter what organic material you use, even really green grass clippings that have high nitrogen." The lag time can last anywhere from a few weeks to a few months-another good reason for adding organic material in the fall, not in the spring.
Add wood ash in moderation, unless your soil is extremely acid. A valuable source of nutrients, wood ash--particularly that of hardwoods like oak--is a potent source of lime and will drive up the pH of your soil. If your soil is neutral or alkaline, don't use wood ash at all. Also, don't apply ash when seeding; it's too salty for seedlings.
Holes: To amend or not to amend
For decades, the advice of the day was to add liberal quantities of bagged topsoil, bark chips and other goodies to the holes in which shrubs and trees were being planted. Then university research in the '80s found that roots could actually go into a kind of shock when they first left the cozy surroundings of the amended hole and encountered the real thing.
"Our philosophy is to get the plant established in the native soil in which it 's going to spend the rest of its life," says Gary Alan, host of The Designer's Landscape. "If you're adding amendments, you're just creating a pot in the ground, and you're not encouraging the roots to branch out as far as they can."
But there are times when you might want to bend--for example, when sandy soil needs organic matter in order to give young plants or trees a good start, says Alan.
Don't work wet soil
Refrain from working your soil when it's wet--no matter how wonderful your tiller or other tool is. Manipulating wet soil causes compacting--especially in clay soils but even in sandy loams--forcing layers to collapse together where they harden into iron fists.
To determine whether your clay soil is dry enough for tilling, squeeze a handful of soil into a ball; if the ball crumbles easily, it's ready to till.
To avoid compaction of the subsoil beneath the six inches or so that are being cultivated, consider reducing the number of passes you make with your tiller--or even not tilling at all after the garden's initial preparation.
Leave some organic matter on the surface
New research by the USDA's Agricultural Research Service in Saint Paul, Minnesota, suggests that leaving plant matter on the surface helps encourage earthworms to dig vertical tunnels to reach their food source. The vertical tunnels--unlike the usual horizontal patterning--help channel water into the ground.
In his backyard, Randy Southard, soils professor at the University of California at Davis, practices no-till: cutting cornstalks and leaving all garden refuse on the surface. "It's hot and dry here, and organic matter decomposition rates are fairly high. One of the things I've noticed is that if I mix the stuff in and get the microbes working on it, there's less organic matter on the surface and much less water filters into the ground."
No matter whether you're reducing soil water loss or you're simply lazy, you'll rest easy knowing that the organic matter will some day give your soil the color and texture of homemade chocolate cake.
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