If you are making the switch to organic gardening, you may be concerned about losing plants to insect pests. In the short run, this is likely to occur. However, established organic gardens typically lose fewer plants to insect pests than conventional gardens.
This is because most pesticides used to kill insect pests also kill beneficial insects. In many cases, beneficial insects are even more susceptible to pesticides than pests. This is because predators are usually rarer than their prey, and often reproduce more slowly as well. A typical gardener who notices an infestation of aphids might spray, killing 98% of the aphids and 98% of the local ladybugs, too. However, 50 aphids survive, but only five ladybugs. The aphids soon start breeding again but the ladybugs take a little longer. Just as the ladybugs are beginning the long, slow recovery to their previous numbers, the gardener notices that the aphids are all over the place again, and wallops the struggling ladybug population with another dose of poison. And the cycle continues.
In contrast, a typical organic gardener can breathe easy, knowing reinforcements are on their way. If an aphid infestation breaks out, it will quickly be noticed by the resident ladybug population, and without poison artificially reducing their numbers, they’ll breed quickly to take advantage of the boom in food. Soon the aphids will be reduced to manageable numbers again and the ladybug population will also decline as ladybugs starve or fly away in search of better hunting grounds. But a few ladybugs will remain, biding their time and keeping your aphid population under control.
What’s more, organic gardens will contain populations of other beneficial insects, some like ladybugs that feed exclusively or primarily on aphids, others that are generalists that eat whatever they can catch. The more diverse a mix of beneficial insect species in the garden, the less likely it is for any one species of pest to get out of control and wreck real havoc.
During your transition from conventional to organic gardening, you can choose to sit back and wait. If there are harmful insects in your garden, the beneficial insects that prey on them will turn up sooner or later to take care of them now that they are no longer being poisoned. However, you can also take measures to speed the process up (hopefully reducing plant loss during your transition to organic gardening) by choosing plants and designing your garden in a way that will attract beneficial insects.
Types of Beneficial Insect
The four main types of beneficial insect you’ll want to attract to your garden are:
- Predatory Insects
- Parasitic Insects
When choosing plants, the most important thing to remember is that diversity breeds diversity. The best way to maximize insect diversity is to have a lot of different kinds of plants.
Many cultivated flowers are bred mainly to be beautiful to human eyes and have lost their attractiveness to insects. Your best bets for insect gardens are mainly wildflowers and flowering herbs.
Flowering plants are important because they attract pollinators. A healthy population of pollinators can increase the productivity of your garden by 30%. You can make your garden more attractive to pollinators by learning about their preferences. Studies have shown that pollinators such as the honeybee and the many species of native bees are most attracted to gardens that have at least one or two different types of flowers blooming at all times throughout the whole growing season. Bees also like gardens with relatively large plantings that have 10 or more different attractive species planted relatively close together in large swathes or groupings.
Flowering plants attract other types of beneficial insect as well. Following a voracious larval stage, many predatory insects live mainly on nectar and pollen as adults, including many types of lacewings, wasps, and predatory flies such as hoverflies and tachinid flies, so a diverse selection of flowering trees, shrubs, and plants is important to attract them as well. Even insect predators that don’t eat nectar or pollen at any stage in their lifecycles can be attracted by flowering plants. Generalized predators such as praying mantises, which eat both harmful and beneficial insects, are attracted to “insectary” plants, plants that tend to support high levels of insect activity. Most insectary plants are flowering plants.
One of the very best insectary plants is clover. Although in recent decades, clover has been considered a weed, in the past it was routinely included in seed mixes for lawns because of its ability to fix nitrogen in the soils, acting as natural fertilizer for nearby plants. Among the many beneficial insects clover attracts are damsel bugs, big-eyed bugs, ground beetles, bees, and many types of parasitic wasp.
Other great insectary plants include members of the carrot family such as dill, Queen Anne’s Lace, and Angelica, scented geraniums, tansies, asters, butterfly weed (Asclepias tuberosa), marigolds, bergamot, daisies, coneflowers, marguerites, sunflowers, thymes, and sages. Weeds such as dandelion and mustard are also popular, as are some agricultural crops, such as alfalfa.
Creating Habitat for Beneficial Insects
Just as important as choosing the right plants for beneficial insects is providing a place for beneficial insects to call home.
Insects prefer a slightly messy garden to a perfectly manicured one. Many beneficial insects overwinter in leaf litter or rotting wood, so creating a small brush pile in one corner of your yard will give them a hand.
Mulches of wood chips or other organic matter are another way to give many beneficial insects a home, and they also protect soil against early frosts that can kill earthworms before they have time to dig down for the winter. Be careful not to pile mulch too close to tree trunks, as this can harm the tree. Don’t mulch every inch of bare dirt, though – leaving a little open ground will benefit ground-dwelling native bees and wasps. Similarly, the ferocious larvae of the ant lion favor bare sandy soil protected from rain.
Dense plantings are attractive to many insect species because they protect against wind and rain. Hedgerows containing a diverse mix of shrubs, flowers, grasses, and the occasional tree are traditional plantings that can provide a safe haven for beneficial insects. Ground covers and other low growing plants can help maintain proper temperatures and humidity levels for some species of beneficial insects, such as aphid midges and predatory decollate snails.
Other beneficial insects, including predatory ground beetles, like to hide under stones, bricks, or fallen logs, or in compost piles.
A few beneficial insects, most notably damselflies and dragonflies, are semi-aquatic. A small water garden will attract them, and also provide a good source of water for other insects and birds. Many non-aquatic insects rely on dew for water, but others will appreciate large-leafed plants such as leaf lettuces or cupplant (Silphium perfoliatum) that capture dew and rainwater in shallow pools on their leaves.
By designing a garden that is friendly to beneficial insects, you will enjoy the benefits of free pest control, pollination services, high quality compost, and more!