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Doing what comes naturally

June 03, 2004|Emily Green

The problem with pesticides is not just the health risk we face from exposure to chemicals, but that they mask the way plants actually grow. If you use them in your garden, you will have to keep using them, because the natural systems, good soil, smart conditions and predators of pests will have been driven out.

Since taking over the Arboretum of Los Angeles County in 2001, superintendent Timothy Phillips has slashed chemical use by 80% and replaced it with more natural horticultural practice. Homeowners with less than 127 acres to manage needn't use chemicals at all, he thinks.

One exception: He'll allow that sometimes the only weapon against a runaway plant, say bamboo, is Roundup, the most benign of the weedkillers. Here are tips from him and his garden's botanical information consultant, Frank McDonough, about nonchemical garden practice:

Plant choice: Buy robust plants. Hostas attract snails; certain types of roses are predisposed to mildew. To make appropriate choices, never go to a nursery without a copy of the best local plant books: "Sunset Western Garden Book" and the "Southern California Horticultural Society's Selected Plants for Southern California Gardens." Avoid runaway plants. If a hackberry tree keeps coming back from a root or bamboo takes over, you may need to treat it with a weedkiller containing glyphosate, such as Roundup. Don't just saturate it. Get advice from the Arboretum or UC extension specialist on how to remove it safely and with the least amount of chemical. This may involve cutting it down, treating the stump, cutting again. Beware of using glyphosate formulations near water: Many kill tadpoles and other amphibians.

Plant diversely: To prevent buildup of whitefly and spider mites on vulnerable specimens, avoid monoculturing, where the landscape is dominated by one kind of plant. Roses and hibiscuses are best grown in or near mixed beds where grasses, salvias, lavender and wildflowers create reserves for beneficial insects and birds. If buildup starts, spray affected foliage with a hose repeatedly every day for a week.

Create zones: Mixing water-loving plants, such as impatiens, with woody, drought-tolerant specimens, such as rosemary, is a recipe for root rot. No fungicide will cure it. Group plants that need similar treatment for healthiest results.

Improve soil and check pH: Soil condition dictates the availability of nutrients. For annuals and kitchen gardens, plant nitrogen-fixing cover crops such as clover and peas in the winter.

Water shrubs and trees with soakers or irrigation lines. Do not water beds with sprinklers, but keep water around root balls, so as not to promote weeds and pockets of water where mosquitoes can breed.

Avoid insecticides: Even the mildest ones do not differentiate between beneficial bugs and pests. Without the beneficial bugs, the pests will have no predators, and often an infestation only worsens as they become resistant to the insecticide.

Mulch: A 3-inch mulch base will prevent weeds, preserve moisture and break down into a soil conditioner. Most trees should not require fertilizer. Keep mulch from contact with trunks to avoid crown rot.

Avoid chemical fertilizers: These encourage weak, watery foliage that attract sucking insects, whereas slower, stouter growth is better equipped to resist predation. Instead, use manure and fish or meat and bone meal. Dilute the meal so dogs and critters don't dig it up.

Aerate plants: Fungus and mildew can usually be cured by strategic pruning to aerate dampness. Check if the plant is getting enough sunlight. Try spraying with water before morning sun hits it. If the problem persists, remove the plant.

Snails: Keep a clean garden. Avoid plants that attract them such as hostas. Eat or clear old sorrel and leafy refuges. Plant lilies and irises away from susceptible plants such as Meyer lemons. Finally, learn to live with them until a predator arrives. No poison will strip a garden of snails more efficiently than lizards or possums.

Restrict pruning to the autumn and winter to promote nesting gleaners such as bushtits from February through June.

Lawns act as verges between houses and storm drains, so avoid chemical fertilizers, pesticides and weedkillers that will wash into the ocean. Try leaving mown grass to dry and break down on the lawn, so it acts as a soil conditioner, or use clippings to start your own compost pile for fallen leaves and kitchen cuttings. Put all weeds through composting, or in green bins for city composting, to kill seeds and avoid pathogen build up.

Help: For information on gardening workshops, or advice from Frank McDonough, botanical information consultant of the L.A. County Arboretum & Botanic Garden, call (626) 821-3236, go to www.arboretum.org or e-mail frank.mcdonough @arboretum.org.

Pesticide profiles: To look up active ingredients in pesticides, go to a site run by a collection of land-grant universities, including UC Davis: http://extox net.orst.edu/index.html.

For health questions, call the Department of Health and Human Services and Centers for Disease Control at (888) 422-8737 or go to www.atsdr.cdc.gov.

To dispose of pesticides safely, contact Pat McKnight at (213) 473-8277 or (800) 988-6942 for sites and opening times of Los Angeles disposal sites or local pickup programs.

-- Emily Green

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