Whenever I begin a new project I put my gardening cards squarely on the potting table: I do not advocate using chemical pesticides under any circumstances in the domestic garden. They are the large, dangerous gorilla sitting on the pristine, chemically drenched, worm-free lawn. There is a paradox in our odd relationship to how we garden. We have a tendency to obsess about pests and even the use of raw manures in our compost heaps, yet we do not consider the considerable damage that toxic pesticides do to the food we grow, plant life, soil, water, insects, mammals, birds and the unseen eco system that is the average urban garden.
Why do we feel the need to be at war with our garden and its pests? Can we not live with the occasional imperfect plant or food crop, safe in the knowledge that is truly toxin free? We do have choices that are clean and safe, and will result in a domestic garden with strong, healthy plants. By letting the natural order prevail in our gardens, they will produce plants that can fend for themselves. A multi faceted approach is best.
Soil
Successful gardening begins with good soil. Healthy soil results in healthy, vigorous, pest resistant plants. We are notoriously lax in the care of our soil here in Southern California. We expect it to produce 365 days a year, expose it to intense heat and winds, we sometimes allow our gardeners to blow the soil away each week with polluting gasoline driven blowers. Yet we wonder why our plants struggle! Get the soil balanced, well composted, not over watered and mulched to assist in plant root development, good drainage and development of microbial life as well as a healthy worm population. This alone can result in preventing many pests from invading your patch. Pests would rather attack weaker plants.
To aid in the development of your soil, grow a cover crop of vetch, buckwheat, clover or Austrian field peas. These plantings serve many purposes. They act as a rotational crop which can rid the soil of in ground pests that attack specific crops. They attract beneficial insects. When dug into the soil they prove a rich diet of organic matter and nitrogen (especially the leguminous crops), and they enrich the soil with a healthy dose of microbial activity.
Companion planting
The next line of defense is companion planting. This approach is very effective in attracting an array of beneficial insects that prey upon plant pests by eating them or using them parasitically to reproduce. There are a host of lovely plants that attract the good bugs. Members of the Umbelliferae family (Fennell, Carrots Dill, Cilantro, Parsley and Queen Anne’s’ lace) with small flowers are favored by wasps, lacewings, dragonflies, ladybugs, praying mantis, hoverflies and spiders, all good bugs. Unfortunately, these insects are routinely killed by broad spectrum insecticides, which ruin the natural balance in the garden. The marigold is reputed to act as a great sensory foil for pests. The strong odor it emanates confuses certain pests, keeping nearby crops free of infestation.
Hedgerows
Grow a hedgerow. A large or small hedgerow can be a fine way to attract birds and wildlife that readily eat many harmful pests. Use California natives such as Berberis, California Wild grape, salvias, California wild roses, boysenberries or raspberries. You can allow the hedgerow to grow wild, space permitting, or keep it manageable in a smaller garden by growing it on a trellis and pruning twice a year. It will provide a safe, home to birds, lizards, butterflies and many beneficial insects, adding a rich and unusual aesthetic feature to your garden. Do not forget to have a bird bath and feeder nearby.
Organic Pesticides
Finally there are organic solutions. I have left this until last because while I do not choose to use these either they are a much better alternative to synthetic products. Just because a product is non-synthetic and labeled organic does not mean it is 100% safe or non-toxic. Some of the choices are as follows.
Pyrethins
Derived from Chrysanthemum, this is a quick acting low toxic spray that kills all insects on contact. Use only when you have a major pest attack.
BT (Bacillus thuringiensis)
Many strains of these bacteria are used in powder form to kill insects in the immature larval stage. It is very effective against Cabbage White larvae that attack brassicas.
Rotenone
A powder made from the roots of a tropical legume. Very powerful when dusted onto plants, but it is a broad spectrum and will kill honeybees. Use sparingly and only when really needed.
Neem Oil
This is made from the seeds of the Neem tree. Applied directly on the plant it impedes growth in immature pests. It is a broad spectrum insecticide so only use when a heavy infestation is present.
Diatomaceous earth
Finely ground fossilized remains of diatoms, which were a hard shelled algae. It is very effective in killing slugs and snails. Remember to not over-water around plants that are attacked by slugs and snails. They do not like dry soil.
Copper
A strip of copper can also be effective in stopping slugs and snails by delivering an electrical shock on contact.
Insecticidal Soaps
These are by far the safest pesticides, and kill on contact. Some plants can be sensitive to soaps. Avoid using them in high temperatures and in direct sunlight.
There is no need to use chemical pesticides in your garden. I would also suggest using organic methods sparingly and only in cases of really bad infestation. Your healthy garden ecosystem will be its own best defense.
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