If there's one thing we want to avoid in our garden, it's pests. Here are some natural methods to prevent pests from becoming a problem (for organic treatments to manage present pest see Pests: Organic Management).
Provide Diversity
Why do large monoculture farms use so many pesticides? Because, their huge fields of a single crops in long, straight lines are like big neon signs to insects that like to feed on them, saying, "24-Hour All-You-Can-Eat Buffet!" A diverse garden with lots of different kinds of plants creates a more natural environment that lets nature work with you instead of against you. Even in a residential garden, you will have more pest problems if you grow nothing but twenty varieties of tomatoes than if you grow twenty different species of plants. A synergistic garden includes a diversity of vegetables, herbs, and flowers, attracting beneficial insects that keep pests in check. A really simple way to do this is to separate similar crops (even by just a few feet), grow a few herbs or flowers in between your vegetable crops, and let some of your herbs produce flowers.
Attract Beneficial Insects
Along with a diversified garden, you can also lure beneficial insects to your garden by planting specific plants that provide them with food sources and/or reproduction habitats. Planting a variety of these, especially so you have some of them blooming throughout the season, is ideal. Some of these plants include:
Ornamentals:
- Alyssum
- Bee balm
- Cosmos
- Feverfew
- Marigolds
- Zinnias
Herbs:
- Cilantro
- Dill
- Fennel
- Lavender
- Lemon balm
- Parsley
- Thyme
- Buckwheat (cover crop)
Some beneficial insects include: bees (pollinators), lady bugs (larvae and adults eat aphids), green lacewings (eat spider mites), ground beetles (eat pest larvae, slugs, snails), soldier beetles (eat aphids, cucumber beetles, grasshopper eggs), spiders (eat a variety of insects), praying mantises (eat many pests including beetles and grasshoppers), and trichogramma wasps (their larvae feed on cabbage worms, corn earworms, and tomato hornworms).
Sow Trap Crops
A trap crop is a planting made around or near another crop to draw pests away from the desired crop. It won't be eaten by you; it will be sacrificed as an offering to the pests, and pulled up before it completes its lifecycle. This method is more experimental, as not all experts agree on its effectiveness, and some worry that trap crops will actually draw more pests to the garden; but it is a method worth experimenting with in your garden. For example, radishes are a pretty big draw to flea beetles in spring, so planting them near other brassicas may keep the beetles busy enough to ignore the other plants. Other examples are planting dill near tomatoes to draw hornworms away, and planting nasturtiums near lettuce to draw aphids away. Planting 10-20% trap crop near the crop you are trying to protect is a common method.
Grow Healthy Plants with Better Defense Systems
Have you ever heard that predators in the wild look first for the weakest animal in the herd? It's also true in the plant world. A healthy plant that is getting its needs met (nutritious bio-diverse soil, adequate water, plentiful sunlight, and good air circulation) is less attractive to predators and can divert more of its resources from survival to defense. Healthy vegetable plants produce more antioxidants, substances that are nutritious for us, but are deterrents to predators. When you grow plants in ideal conditions, you give them the resources they need to defend themselves.
Use Floating Row Covers
A floating row cover is a light, gauzy type of material (available at your local garden center) that helps protect plants from flying pests like aphids, flea beetles, and birds. It allows enough sunlight through for plants to grow, protects plants from frost in spring or fall, and provides a little shade for frost-tolerant crops, like lettuce, in summer. For plants requiring pollination to produce fruit (i.e. squash, pumpkins), row cover must be removed in the morning for a few hours to allow access for bees and other pollinating insects.
Time Your Plantings
If you have had repeated failures with a certain crop because of pests, it may be a good idea to switch your growing season where possible. For example, if flea beetles are skeletonizing your brassicas (broccoli, cabbage, cauliflower, kale, mustard, radish) every spring, you may be amazed by how much better they grow if you sow in late summer for a fall crop instead. In fall, pests are often winding down, becoming much less populous and active, and will be less likely to cause problems. Frost-tolerant crops are also more likely to achieve a large size without bolting when the weather is consistently cooler, usually in the fall. Obviously, switching planting seasons isn't a luxury available in short-season areas, but you could consider growing successive crops throughout the summer. If squash bugs decimate your first planting of pumpkins in spring, they may not attack the second crop sown a month later. Then, with a little frost protection in fall, you still may get a great crop!
Vigilance
There are lots of great choices when it comes to natural ways to deal with pest problems. There is, however, nothing better than prevention. Keeping an eye on the health of plants and cycling of insects in your garden will give you an accurate assessment of what is necessary to maintain a healthy, beautiful, and productive garden. Well-tended gardens are less apt to suffer devastating infestations. Walking through your garden a few times a week, inspecting plants closely, will help you recognize, treat, and prevent problems before they get out of control.