CAROL STEINFELD The Boston Sunday Globe Magazine
Garden designer Andrea Knowles looks forward to the day when yards aren't full of little flags warning of recent applications of toxic pesticides and herbicides. ``If plants are well nourished and well sited,'' she says, ``they can withstand occasional pests, weeds, diseases, and droughts.''
Knowles, a Billerica resident and founding member of the Ecological Landscaping Association, is one of a growing number of gardeners and landscapers designing outdoor spaces that are chemical-free, healthy places for humans, wildlife, and pets.

She perfected her growing techniques as manager of the formal gardens at Minute Man National Historical Park in Concord, where she could not use any toxic compounds that would harm the nearby Concord River. Most recently, she managed a 30-acre Manchester-by-the-Sea estate that included rose gardens, vegetable and herb gardens, perennial terraces, Japanese iris beds, herbaceous borders, fountains, and ponds full of lotus, papyrus, and waterlilies. "Ecological doesn't mean naturalistic or just woodlands," she says. "It means healthy, not hippie."

The foundation of ecologically sound gardening, she says, is healthy soil, which needs to be built up and fed to produce healthy plants. To accomplish that, Knowles offers these simple, low-cost or no-cost suggestions:

Leave grass clippings on the lawn. The easiest way to provide soil with organic nutrients is to mow grass to a height of 3 inches and leave the clippings where they fall. It is a misconception that this will cause brown spots or suffocate the grass. The clippings will add nutrients to the soil in the form of nitrogen, while providing it with structure and air spaces. ``The soil will be more porous and retain more moisture,'' Knowles says.
Use compost and mulch. Trench compost (decomposed plant matter) into the soil around plants and spread mulch or leaf mold (decaying shredded leaves) around shrub borders and woodland settings. These materials supply nutrients and foster porosity in the soil, helping to store water and create breathing space for beneficial soil bacteria, which in turn convert nutrients into forms that plants can use. They also loosen up soil so that roots have room to grow.

"Compost can be purchased by the bag or truckload, or it can be made at home," says Knowles. "People shouldn't be afraid to compost." Throw all plant trimmings, except woody and pernicious weeds, into a compost pile. Turn it every few weeks to get air to the beneficial bacteria and fungi that transform organics into nutrient-rich and biologically diverse humus in six months to one year. Compost, incorporated into soil, improves water-holding capacity and soil quality and helps fend off plant diseases.

To apply compost to grass, Knowles recommends depositing small piles of the material around the yard and then raking it to a quarter-inch depth. A professional landscaper can also spray compost onto a lawn. Rain will wash it down to the roots of the grass. "Within 10 days," says Knowles, "the grass will green up amazingly."

Use mulch generously.

Knowles prefers leaf mulch to bark mulch. "Bark mulch takes a long time to break down," she says, "and it can act like wooden shingles that prevent water from penetrating into the soil."

Aerate the soil. With a pitchfork, studded golf shoes, or a soil aerator tool, puncture shallow holes in the soil to get air and water to the root zone and loosen compacted soils.

Site plants correctly. Learn about your plants' preferred placement at the nursery or by reading gardening books. Knowing that hostas and delicate flowers don't like the hot sun or that arborvitaes and hemlock won't do well close to a road, where they will be exposed to sand and salt, will save you a lot of trouble shooting.

Don't plant too deeply. To prevent stem rot, take the plant out of the pot, scratch away the soil to the root bulb, and place it in the soil up to where the root and the stem meet.

Plan for low watering requirements. Anticipating dry conditions can save plants, time, and money. Apply mulch, compost, or buckwheat hulls to a depth of at least 2 inches around your plants to hold moisture in the soil. Rather than watering with sprinklers, which can lose water to evaporation, snake drip lines or soaker hoses around plants.

The best time to water is in the morning - between 5 and 9 - before the heat of the day can evaporate moisture.

For further water conservation, place rain barrels, or even plastic garbage bins, under downspouts. Dip a watering can into them as needed or drill and install a spigot low on the barrel.

Or install a rain garden to capture rainwater and allow it to infiltrate the surrounding soil slowly. To create one, dig a 3-foot-deep trench at the foot of a downspout. Fill two-thirds of the trench with 3/4-inch gravel, then top it off with sandy loam or mulch. Plant flowers and shrubs such as redtop, blue joint, switch grass, witch hazel, and red maple, which don't mind wet roots.

Avoid toxic pesticides. Chemical pesticides can kill not only their intended targets but also butterfly larvae, bees, and even birds. "They also kill all beneficial microbial populations in the soil," Knowles says. "Every time you spray, you're destroying a whole ecosystem."

Pesticides should be a last resort, but for especially pernicious pests, Knowles uses nontoxic horticultural oil to combat aphids; neam oil for lily leaf beetles; and insecticidal soap for other insects. These compounds wash away or suffocate pests without poisons. For tough worms like the sandwich moth, she uses bacillus thuringiensis, also known as Bt.

"You have to look at the environment as a whole, then make changes," Knowles says. Often, a plant's poor per form ance is the result of conditions such as improper siting, planting too deeply, too much wind, or not enough water.

"If plants are growing in good soil and in the right place," she says, "they'll thrive and have fewer issues with pests and diseases. That's really the difference between conventional and ecological landscaping. We're just creating healthy environments."

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