5 Ways to Garden for Beneficial Insects

In the previous blog post Pollinators, Predators, and Parasitoids, I went over some of the native beneficial insects that can be found in BC and the ways they contribute to pollination, pest control, and the functioning of garden ecosystems. Native insect populations are at a critical all-time low across the planet, and the evidence is pointing the blaming finger at pesticide use, monocultures, and destruction of habitat by our conventional agricultural systems, among other human activities. In this blog entry we’ll cover five ways you can create food and habitat for beneficial insects. No matter the size of your property, whether a huge farm or a balcony container garden, there are ways to support beneficials and boost their populations in your landscape.


1. Beetle Banks

Predatory beetles are important species for controlling caterpillars, slugs, aphids, snails, grasshopper eggs, and other soft-bodied insects. They can be a valuable form of pest control on organic farms. However, as mostly nocturnal hunters that need undisturbed soil and perennial ground cover to shelter over winter and during the day, there’s often not much habitat for them on farms of tilled soil and annual crops. Many farms are now putting in beetle banks – long, mounded permanent beds planted in perennial bunch grasses and native wildflowers intermittently spaced within their growing area. Research is showing that these beds can greatly reduce pest issues on numerous crops and that beetles and spiders residing in these banks will travel throughout a field to provide pest control.

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Above: two examples of beetle banks in agriculture. Below: debris piles and hollow stalks left undisturbed provide habitat for solitary native bee species and other beneficials

2. Hedgerows

Hedgerows are mostly unmanaged areas around the perimetre of a farm or garden consisting of a range of shrubs, small trees and understory plants. They often double as a windbreak and buffer zone, preventing wind damage, erosion, soil loss, pesticide drift, or contamination to crops from nearby roads.

They are also excellent habitat and forage for many beneficial insects, birds, and wildlife. Native species of trees and shrubs such as willow, hawthorn, chokecherry, wild plum, and saskatoon provide some of the earliest blooming flowers which help insects find food at the start of spring. Seeding the understory in insectary flowers adds even more forage and habitat. Hollow logs, woody debris, and undisturbed soil provide spaces for parasitoids and native bees such as mason, leafcutter, and ground-burrowing bees to lay eggs and have protected overwintering habitat. Brush and rock piles provide homes for snakes, spiders, ground wasps, and predatory beetles which are all great at keeping pest populations in check.

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Hedgerows can be a great way to bring diversity to farmland and can include blooming trees, shrubs, and wildflowers

If you don’t have a farm, you can still take the concept of hedgerows and apply it to a small area. Let peripheral areas of your garden be feral and unmanaged. Pile debris and leaves there, let blooming wild shrubs grow tall, scatter wildflower or perennial cover crop seed beneath and avoid disturbing the soil. These areas are great for establishing mycorrhizal fungi which will also benefit your garden. The hedgerows I’m planting at Thimble Hill connect existing forested areas and include hazelnut, willow, lilac, forsythia, yarrow, lupine, and clover. The best part about this kind of “garden” is that, once established, the less you do the better. There’s cause to be proud of your laziness in this zone, as it benefits a whole menagerie of other life forms, which in turn help you grow healthier food.

3. Water

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Constructed pond on my family’s farm on Salt Spring Island, circa 1988. Water storage, swimming hole, and habitat for beneficials. There were dragonflies, frogs, snakes, butterflies, and so much life by that pond

Like all life forms, beneficials and native insects need water. Water sources can be as small as a bird bath or bucket that is filled regularly, to larger features such as ponds and open reservoirs. Respecting and restoring wetlands, streams, and natural waterways nearby goes a long way in helping native beneficial insects. Part of our long term plan at Thimble Hill is to build several ponds for water storage and habitat, but in the meantime we’re collecting rain and irrigation runoff in raingardens and swales, which are abuzz with insect activity on hot summer days.

4. Change Your Gardening Style

When considering the needs of beneficial insects, strive to garden the way nature does. In landscaping and ornamental gardening, cut down on the cultivating, manicuring, exposed soil, and excessive weeding. Never use neonicotinoids or broad-spectrum pesticides, as these kill off the very insects that will help you prevent pest infestations and using them starts a feedback loop that creates dependence on these products. It is actually good to have low levels of pests such as aphids in your garden, as these provide a food source for predator species and ensures that you have the biological controls staying on your site. If you have the approach to annihilate all “bad bugs” you actually make the problem worse by forcing beneficials to move elsewhere.  Save yourself the extra work and let your gardens take on a less-managed, cottage-garden look that is modelled after wildflower meadows and forest edges. Xeriscaping with native flowers and perennials is a great way to create beneficial habitat that takes minimal resources, water, and maintenance.

In vegetable production, there are many ways to alter your growing habits to encourage beneficials. Adopting a no or low-till approach to soil management, at least in part of your production, creates habitat for beneficials and encourages a range of ground-nesting species. Use mulches, chop-and-drop cover crops and build soil by adding organic matter to the surface. Avoid plastic mulches that prevent beetles and bees from accessing the soil. Let plants that you usually cut down before they go to flower – like rhubarb stalks, bolting brassicas, alliums, mints, and herbs in the carrot (Umbelliferae) family – continue to bloom, as many parasitoids in particular love these small clustered flowers. In the fall, don’t ‘clean up’ too much. Hollow stalks from sunflowers and corn might have mason bee cocoons inside, leaves and mulch on the soil create protected habitat for beetles and ground bees, and debris piles provide shelter from predators. While mulches are great at protecting the majority of your soil, leave small sections of earth exposed so that ground-nesting bees can burrow. Rather than removing orchard prunings in winter, chop them small and use them as mulch around your tree’s dripline, as this small-diametre wood is ideal food for beneficial fungi and creates habitat for helpful insects right where you want it – below the trees that will need pest control and pollination.  If gardening for biodiversity gets priority over manicured landscapes, our food sources and ecosystems will feel the benefits.

5. Pollinator Gardens & Insectary Flowers

Pollinators and beneficials need flowers. There are many ways to integrate them into your landscape. Some gardeners include low-growing flowers and cover crops, such as alyssum, clover, buckwheat, or phacelia, as a ground cover below taller crops. Others plant clusters of flowers at the end of rows or as intermittent rows among vegetables. If you have limited space, even a few hanging baskets or pots of flowers in an urban setting can help beneficials get rest and forage on their travels between wilder spaces and larger habitats. In an orchard setting, flowers can make a great understory, planted below berry and tree crops. These flowers provide full-season forage so that beneficial insect populations are high before they are most needed, such as when fruit crops need pollination during mid-spring blooming, or when control is needed on caterpillars, pest larvae and aphids in summer.

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My mother and her partner grow an inspiring amount of food on their urban lot. They’ve used the marginal space on the outside of their fence to grow an enormous flower garden that blooms from snow melt to snow fall.

In planning a garden for pollinators, aim to have a diversity of flowers of different colours and shapes blooming throughout the growing season, particularly in early spring as insects are just emerging. Including wild and native flowers ensures that you have the best food source for native pollinators. Some overly-cultivated varieties of flowers are actually sterile and have no benefit to pollinators, as they have been selected only for their aesthetics and not as a pollen or nectar source.

Some pollinators are generalists, such as honey and bumble bees, collecting nectar and pollen from a diversity of flowers. Others are specialists and only collect from flowers with a particular shape or from blossoms with a particular colour. Colour actually plays a big role in helping pollinators locate flowers, as many can only see certain colours in the spectrum. There are Squash Bees that feed only on curcurbit flowers, and Sunflower Bees that stick to the sunflower family. Short-tongued bees like open flowers like aster and daisy; long-tongued bees go for complex and deep flowers such as penstemon, lobelia, and lupine. Certain pollinators have specialized anatomy, such as the proboscis in butterflies or the narrow beak of a hummingbird, that allows them to collect nectar from longer flowers that other insects can’t physically enter. Monarch butterfly populations depend on milkweed, as they lay their eggs and their caterpillars feed exclusively on the flowers, which makes milkweed a key species to include in any insectary planting. There’s some pretty fascinating research out there on the ways flowers advertise through scent and colour to attract the right pollinators.

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Clockwise: Swallowtail on Echinacea purpurea, Green Sweat Bee on Calendula, our kids splashing in the rain garden with Bee Balm and Anise Hyssop in foreground, and Crimson Clover cover crop – one of our favourite orchard understory plants.

The world of flowers for pollinators is huge and I could study and observe for years and still be learning. But, the take home message here is that flowering plants are vital to a healthy garden ecosystem. Sustainable agriculture needs to provide food for us, as well as for a wide range of other organisms. Our long term food supply and the functioning of our ecosystems depend on this. Look around your landscape and see where more habitat and food for beneficials could fit in. Consider adding beetle banks, hedgerows, water sources, and pollinator gardens to your own farms and gardens if you haven’t already. It’s not too late to order wildflower and blooming cover crop seed, or stop by local Seedy Saturdays/Sundays to see what you can find. And I’ll be here if you want any insectary flower starts this spring. Below are some of the beneficial flowers that I’m planning to have available for sale this year through Thimble Hill Nursery:

 

Lupine Forsythia Flowering Purple Sage Alyssums Hawthorn Saskatoon Chives and other alliums Tulsi (aka Holy Basil) Columbine, red and garden cultivars Dalia Sweet peas Cleome - spider flower Milkweed, swamp and butte

A list of great resources and reading on this topic can be found at the bottom of the previous post, Pollinators, Predators, and Parasitoids.

Thanks for reading!

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