Growing Flowers to Attract Beneficial Insects

As a gardener and amateur entomologist, I am fascinated by insects. It's nearly ten years since I first wrote about encouraging beneficial bugs for Mother Earth News, and since then I have added many plants to my garden because they are so attractive to beneficial insects. I know this approach reduces problems with bad bugs. For the last two seasons, I have encountered no insect pest problems that could not be controlled with hand picking.

Over a dozen new plants were recently added to the Garden Planner plant palette, including many chosen because of their value as insectary plants. For example, the dainty little flower known as sweet alyssum attracts hoverflies (also known as syrphid flies) in search of nectar. In turn, hoverfly larvae scour leaf undersides, eating aphids and mites before you ever see them. In similar fashion, phacelia attracts a wide range of beneficial insects including bees, wasps and hoverflies. The nectar produced by cornflowers is extra sweet, which is quickly discovered by little beneficial bugs.

Attracting Beneficial Insects with Flowers

Insect populations change during the growing season, as do the plants that attract them. One of the goals of working with insectary plants is to have new things coming into bloom as others fail, so that beneficials always have a dependable supply of nectar and pollen. Numerous studies from Europe and the US have shown that an abundant food supply helps beneficial insects live longer, healthier lives. Best of all, well-fed beneficial insects have more babies, which means better pest protection for your garden.

The specific insect species present in gardens varies widely with geography, but similar relationships exist between insect predators and the plants that attract them. For example, in a close observation of insectary plantings in Corvallis, Oregon, hoverflies (major aphid predators) began the season on coriander flowers, then moved to sweet alyssum in early summer. By late summer the hoverflies showed a preference for buckwheat flowers. What’s interesting here is that over 2,000 miles away in my garden, I see exactly the same trends. But there’s more. The Oregon study showed that parasitic wasps (major caterpillar predators) were drawn to spring mustard, followed by buckwheat, followed by mint. Again, I see the same trends in my garden. When the mint and catnip bloom in late summer, I can hear the buzz of thousands of little bees and wasps long before I see them.

Companion Planting with Insectary Plants

Good insectary plants range from short-lived annuals (alyssum, buckwheat, coriander, phacelia) to hardy perennials that like to stay put for several seasons (catmint, oregano, mints, monarda and thyme). The Garden Planner will show you the best planting dates for these and other plants that please beneficial insects, but deciding where to grow insectary plants is up to you.

My goal is have beneficial insects active in every part of my garden, so I tend to anchor the outside corners of my garden with weed-resistant perennials that always attract plenty of buzzers – catmint, oregano and mint, for example. Among annuals, herb fennel, dill, and sunflowers make wonderful insectary plants to station around the garden’s perimeter.

To achieve better diversity inside planting beds, I like to plant small clumps or pairs of insectary plants near crop plants, for example pairs of staked cornflowers near tomatoes, and borage twins adjacent to cucumbers. I’ll plant a pinch of buckwheat in any empty spot in summer, and I often use sunflowers to please bees while offering filtered midsummer shade to peppers and bush beans.

Planting insectary plants in pairs or small clumps also sets the stage for good seed production. By far the simplest way to intersperse insectary plants with veggies is to allow selected plants to stay in the garden until they produce mature seeds, and allow many of those seeds to sprout where they fall. I have not sown coriander, herb fennel, or borage in years because they self-sow so successfully. All I must do is pull out the excess plants when they are too numerous or too big.

Just like crop plants, insectary plants provide good fodder for the compost heap as they come and go. Comfrey, buckwheat, and even borage can be grown for composting purposes alone, though it’s best to let insects enjoy most of these plants’ flowering period first. When an insectary plant grows out of bounds, don’t hesitate to clip it back or pull it out. In any competition for growing space, crop plants should always come first.

Gardeners with limited space might consider a different approach – planting a large tub or other movable planter with an assortment of insectary plants. Last summer I saw an old wheelbarrow-turned-planter teeming with borage, buckwheat and alyssum – a movable feast for pollinators and beneficial bugs.

Every garden is different, but if you’re a beginning bug-watcher, here are some good insectary plants that are easy to work with in a vegetable garden. Use the comments below to add your experiences and ideas.

• Insectary Plants for Late Spring Bloom: Overwintered brassicas (mustard, turnip, mizuna), coriander, rocket, radish, phacelia
• Insectary Plants for Early Summer Bloom: Alyssum, rocket, comfrey, dill, fennel and other carrot family crops, buckwheat, monarda, phacelia
• Insectary Plants for Mid Summer Bloom: Alyssum, borage, buckwheat, catmint, comfrey, dill, fennel, monarda, thyme, sunflower
• Insectary Plants for Late Summer Bloom: Borage, buckwheat, catmint, comfrey, mint, oregano, sunflower

By Barbara Pleasant

Bugs, Beneficial Insects and Plant Diseases

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