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Published: Thursday, March 10, 2005, SEATTLE POST-INTELLIGENCER
http://seattlepi.nwsource.com/nwgardens/215199_lovejoy10.html

Dry gardens especially need nurturing soil

By Ann Lovejoy
SPECIAL TO THE POST-INTELLIGENCER

The dry garden style we looked at last week is an intriguing design model that combines year-round good looks with greatly reduced maintenance. The central concept is that well prepared and closely planted beds of regionally appropriate plants can set the gardener free. Plant right and you'll do less weeding, less watering, less feeding and a lot more enjoying.

My own dry gardens are very low maintenance, thriving with an average of two hours of attention a week all year round. This means that a little bit of tidying takes place every month, but most of the garden gets only one big tidy session each year.

Usually this takes place in late winter, when the old grass and perennial stems are trimmed back. I never trim back the deciduous grasses or perennials until I see a flush of green at the base, which is generally in late February, or around now. Waiting until late winter reduces the detritus load considerably, which means the work goes much faster.

We also spend part of each fall and winter mulching, alternating layers of mature compost and washed dairy manure. Although I often use a little low-number transplanting fertilizer when putting in new plants, I rarely feed plants after the first year. That's partly why the annual layers of compost and dairy manure are so important, though they also contribute greatly to the tilth and texture of the soil.

Last week, we looked at a few of the plant families that flourish in dry garden settings. In truth, many favorite garden plants are highly drought-tolerant once they are well-established. Walk through old neighborhoods, old parks and neglected lots to see how many plants can carry on just fine without human assistance. This underlines an important lesson: The key to plant happiness in dry gardens is sturdy root growth.

To get optimal root growth, we need to build and nurture great soil. In plant terms, this generally means well-drained yet retentive soil with plenty of humus (organic material). For those gardening on heavy clay or on sandy soils, this charge is equally challenging. In both cases, the secret to success lies in adding adequate amounts of organic material.

In organic gardening, the first principle is to feed the soil and let the soil feed the plants. In dry gardens, this is especially true, for at least two reasons. First, you can damage or kill dry plants with high-number fertilizers, so most commercial fertilizers are to be avoided. Thus, plants must rely mainly on the soil for their nutritive needs.

Secondly, when we feed our soils with mulches of mature, high-quality compost, we solve several dilemmas at once. Mature compost supports colonies of bacteria, fungi and hosts of other microbic biota that bring soils to life. These biota in turn feed the plants by converting compost nutrients into forms plants can readily use.

Compost mulches also repress weed seeds, which need light and air to germinate. Mulching also helps hold moisture in the soil while still allowing good oxygen exchange for plant roots.

For some years now, soil scientists at WSU have been teaching our Master Gardener trainees that tilling is no longer a preferred practice. Instead, we are told to layer on amendments such as compost and let the worms do the mixing for us.

This is very good news, since tilling and turning over soil is hard work. It turns out that it is also destructive work, since it destroys the soil colonies that support healthy plant growth. Thus, layering, which is far less physically challenging than tilling, is the better way to go.

To get started with a dry garden, consider making a new bed or two to try out these new techniques. Over the years, I've found that generously proportioned, mounded beds produce the best plant growth, both initially and over time. My beds are usually heaped about 18 to 24 inches high and a minimum of 6 to 8 feet wide. Some settling will occur, so let the beds stand for a week or so before planting.

If topped with compost, which does not slough in rain, mounded beds do not need to be boxed into place. If you've been frustrated by the rectangularity (and weediness) of raised beds, naturalistically shaped mounded beds will have tremendous appeal.

Whether you have sandy or clay soil, mounding brings immediate benefits. On sandy soil, tilled-in compost seems to vanish almost immediately. On heavy clay, it can make an adobelike substance that really doesn't please plants. On both types of soil, mounded beds built with a base of topsoil and mulched with compost produce excellent growth in nearly all garden plants.

However, good topsoil is pretty hard to find anymore. Most of what is sold as topsoil is a combination of sand, sandy loam, and composted materials of various kinds. Lately, however, we've seen some nasty problems arise because the quality of commercial composts can be very poor. Lawns and all kinds of plants can be burned by an application of raw, unfinished compost.

To be safe, stick with materials that are safe and tested. Cedar Grove offers a very good "Vegetable Garden" soil mix that works for almost any kind of garden plant. Cedar Grove compost is tested for a wide range of pathogens and residual pesticides as well as for maturity.

Next week, we'll look at ways to evaluate compost quality as well as how to improve artificial topsoils or depleted garden soils.

Ann Lovejoy can be reached via mail at: 8959 Battlepoint Drive N.E., Bainbridge Island, WA 98110. Her latest book is "Ann Lovejoy's New Fresh From the Garden Cookbook: Recipes Inspired by Kitchen Gardens" (Sasquatch, 208 pages, $22.95).