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Master Gardenersm Column for the Week of April 13, 2009
Judy Koehly
Brunswick County Extension Master Gardenersm Volunteer
Planting a Garden Insectary
As you plan your vegetable garden you will choose what vegetables you wish to grow and you should also choose which plants will attract beneficial insects. A garden insectary is a small garden plot of flowering plants designed to attract and harbor beneficial insects. These "good insects" prey on many common garden insect pests and offer the gardener a safer, natural alternative to pesticides.
The garden insectary is a form of "companion planting," based on the positive attributes plants can share in deterring pests, acquiring nutrients, or attracting natural predators. By becoming more diverse with your plantings, you're providing habitat, shelter, and alternative food sources (such as pollen and nectar), something many predators need as part of their diet.
For example you can control aphids with an aphid predator like aphidius, and you can encourage aphidius to set up shop by planting sunflowers or lupin. The idea of inviting the pests in to munch on plants in your insectary may seem alarming, until you understand that you are doing so to encourage host-specific pests. The pests remain on the desired plant in your insectary yet provide an ideal breeding ground for the associated predators and parasites.
Your insectary plot does not have to be large, just big enough to hold six to seven varieties of plants that attract insects. Once the garden has matured, you can watch your personal security force of beneficial insects do the work for you.
If you intersperse vegetable beds with rows or islands of insectary annuals you will add decorative elements to your vegetable beds while luring beneficial insects toward prey. If you allow some of your salad and cabbage crops to bloom the Brassica flowers (cabbage, broccoli, Brussels sprouts, bok choy) are also appreciated by beneficials. If you include plants of different heights in your insectary you will give ground beetles required cover that is provided by low-growing plants such as thyme, rosemary, or mint. Lacewings lay their eggs in shady, protected areas, so providing such places near crop plants is a good idea. Tiny flowers produced in large quantity are much more valuable than a single, large bloom. Members of the Umbelliferae family are excellent insectary plants: fennel, angelica, coriander, dill, and wild carrot all produce the tiny flowers required by parasitoid wasps. Composite flowers (daisy and chamomile) and mints (spearmint, peppermint, or catnip) will attract predatory wasps, hover flies, and robber flies.
Herbs work especially well as companion plants. They multitask by attracting beneficial insects and repelling pest insects and their fragrance and foliage make them good companions in both the vegetable garden and the ornamental border.
A garden insectary should be thought of as a long-term permanent component of your garden. Results are not instant and conclusive; rather, the benefits to your garden are cumulative. As your plantings mature and resident populations of beneficial insects are established, the need for chemical pesticides and other aggressive insect control techniques will diminish. Your garden will become a more natural and balanced environment for the healthy production of vegetables and flowers.
Another thing you can do to make your garden attractive to insects is to provide water and shelter. Using a thick layer of mulch (2 to 3 inches) will attract ground beetles, spiders (they are good for your garden!) and toads. All are considered beneficial to your garden; they all devour many insects. The side benefit of mulch is that it cuts down on weeds and conserves water in the soil.
If you have room plant a patch of native wildflowers in or near your garden; this will attract native beneficials that will use them for shelter and food. And plant as many native plants as you can since they are adapted to the area and in general will grow better than some exotic plants.
Butterflies and moths are considered beneficial, in addition to being beautiful. They don't actually eat when they are in this adult stage, but they do sip nectar and in the process help to pollinate flowers. Moths are most often active at night and this is why so many white or pale flowers bloom at night and have a scent that is attractive to moths. Think of moonflowers or four o'clocks that actually do start to bloom in the late afternoon. There are hawk moths that fly at night and are attracted to nicotiana, moonflowers, cleome, and petunias. Do you ever notice the scent of a petunia at dusk on a hot summer evening? So does the moth.
Dr. Russ Mizelle, an entomologist with the University of Florida, feels that crape myrtles (Lagerstromia indica) are probably the most important woody landscape plant in the southeastern United States for augmenting and sustaining many beneficial insects. There is an aphid which only attacks crape myrtles, so you don’t have to worry about them spreading to any other plants. Marigolds are another easy–to-have in the garden plant that repels many of the bad bugs!
It is obvious that you shouldn't use chemicals if you want to attract beneficial insects. The chemical can't tell the difference between good and bad bugs-you are most likely to kill all the insects. Even if you follow the directions carefully, there will be at least some good insects that will be killed. When insects do return to your garden, you may have destroyed the balance between good and bad and the bad insects will take over. If you feel that you have too many aphids and you don't see any ladybug larvae, you can always shoot a hard stream of water on the aphids and knock them to the ground. They will not be able to climb back up to the tender tip of a stem. Or try an insecticidal soap on appropriate plants and insects. To get rid of caterpillars, pick them off and try to control their numbers by attracting birds to your garden. Slugs and snails can be discouraged with crushed eggshells, cut hair, sharp grit and oatmeal sprinkled on the soil.
And most important of all, spend time in your garden every day to monitor the insect life and the health of your plants. No one can get rid of every bad insect so learn to live with an insect population that is kept in check by the good guys.
To see a chart of companion plants go to http://www.canadiancountrywoman.com/garden/companionplants.php, or http://attra.ncat.org/attra-pub/complant.html, or http://en.wikipedia.org/wiki/List_of_companion_plants
“Nature is always hinting at us”………………Robert Frost