Instead of chemicals, habitat plants for pest management

By BONNIE KIRN DONAHUE
Extension Master Gardener
University of Vermont
We spend a lot of time and energy trying to get insects out of our gardens, but what if we thought about trying to bring more in?

Prior to taking the University of Vermont (UVM) Extension Master Gardener course (www.uvm.edu/extension/mastergardener), I got queasy around the insects I saw in my vegetable garden, assuming they were all visiting to torment me and sneak into my salad. After the course, I saw insects in a new way.

The UVM Extension entomologist taught us to ask questions first before thinking that all the insects we see are harmful. It’s a practice that I follow in my garden and you should, too.

If, after careful investigation, you determine that the insects are detrimental to your plants, look first to environmentally sensitive strategies to managing the pests. One good way is with habitat plants.

These are flowering species that produce pollen and nectar, which attract and provide suitable habitats to support “good” bugs. The UVM Entomology Research Laboratory has conducted some valuable research on which flowering plant species can help attract these beneficial insects to your garden. You can read about their findings at go.uvm.edu/landscape-ipm.

Beneficial insects like parasitic wasps (don’t worry; they don’t sting people), lady beetles and a wide variety of predatory insects are natural enemies to common garden pests and can help manage pest populations naturally. For example, the larvae of hoverflies, whose adult form looks similar to bees but are actually flies, feed on unwanted aphids and other soft-bodied insects.

The little red-and-black-spotted ladybug glorified in children’s literature truly deserves all of the fame it has earned. One adult or immature beetle can eat 60 aphids per day, and more than 2,500 over its lifetime.

The challenge that gardeners have is how to attract these beneficial insects to their garden. The UVM researchers have tested different flowering plants, common annuals and perennials (flowers and herbs) to determine which ones are the most attractive to these insects. They evaluated several that flower throughout the season that provide a continuous source of nectar and pollen that these insects need.

Among the annuals, sweet alyssum (Lobularia maritime) was found to be particularly appealing to beneficial insects, but others like zinnias, sunflowers (Helianthus), dill (Anethum graveolens), cosmos, coreopsis, blue cornflowers (Centaurea cyanus), yellow marigolds (Tagetes patula ‘Little Hero Yellow’) and Indian blanket (Gaillardia pulchella) also were effective.

Many commercial growers use these plants to reduce their pest problems without resorting to insecticides. Home gardeners can try these, too, and even experiment with other plant species to see which work the best for their garden. 

You can purchase many common annuals and perennials, including alyssum, zinnias, coreopsis, marigolds and Indian blanket at many local greenhouses or start them from seed indoors to maximize the amount of time they are flowering. Dill, sunflowers, cosmos and blue cornflowers can be sowed directly from seed. 

Plant these habitat plants in your garden beds among your vegetables or in a mixed variety hedge-like row around the garden. They also do well in containers and can be planted just as you would other decorative annual flowers.

To keep beneficial insects happy, it is important that the plants flower continuously and remain healthy through the season. Annuals will need at least six hours of sunlight a day and adequate water. 

Deadhead spent flowers often to encourage more blooms. It is better to have fewer healthy habitat plants than many unhealthy ones, so don’t plant more than you have time to care for.

Since learning about this method of pest control, I have experimented with these plantings and have found that they make my vegetable garden more remarkable than I could have imagined. The dill, zinnias and sunflowers practically pulse with insect activity in addition to being striking accents in my vegetable beds. I have found that it is as satisfying to watch insects enjoy my plants as it is to watch birds and people enjoy them.

 

Bonnie Kirn Donahue is a UVM Extension Master Gardener and landscape designer from central Vermont.