Which Plants Attract Beneficial Insects to the Vegetable Garden?

A garden that supports a diverse population of beneficial insects has a built-in pest management system. Ladybirds and their larvae eat aphids. Hoverfly larvae consume hundreds of aphids each. Parasitic wasps lay their eggs inside caterpillars and aphids, killing them from within. Ground beetles eat slug eggs and other soil pests. All of these insects need certain plants to thrive — providing those plants is one of the most ecologically sound investments you can make in your garden.

Umbellifers for Parasitic Wasps

The flat-topped, open-structured flowers of the umbellifer family are the most important food source for parasitic wasps. These tiny insects have short mouthparts and can only access nectar from shallow, open flowers — the complicated tubular flowers of many garden plants are inaccessible to them. Dill, fennel (in isolation), coriander left to flower, angelica, sweet cicely, and cow parsley all provide this type of nectary. A block of flowering dill or coriander at the corner of a vegetable bed will support a large population of parasitic wasps that patrol the surrounding plants for caterpillars and aphids to parasitise.

Marigolds and Poached Egg Plant for Hoverflies

Hoverflies are easy to attract. Their adults feed on pollen and nectar, and their larvae eat aphids. French marigolds and poached egg plant (Limnanthes douglasii) are two of the most reliable hoverfly attractors. Limnanthes in particular is excellent — it flowers in early spring when hoverfly populations are beginning to build up, it self-seeds freely, and it forms a neat low ground cover between vegetable rows. Sow it in autumn for spring flowering or in early spring for slightly later flowers. A few plants per square metre of vegetable bed is enough.

Yarrow and Achillea for Mixed Beneficial Insects

Yarrow (Achillea millefolium) flowers attract an exceptional range of beneficial insects including parasitic wasps, predatory beetles, hoverflies, and lacewings. It is perennial, drought-tolerant, and spreads to fill gaps at the edges of beds. The flat flower heads are accessible to many insect species. White-flowered wild yarrow is more attractive to beneficial insects than the coloured garden hybrids. Allow it to naturalise around the edges of the vegetable garden where it will not need management.

Nettle Patches for Ladybirds and Lacewings

A small patch of nettles left to grow in a corner of the garden is one of the most powerful beneficial insect habitats you can maintain. Nettles support the overwintering adults of several ladybird species, provide early-season aphid colonies that ladybird and lacewing larvae feed on before moving to vegetable crops, and host lacewing eggs on their undersides. A patch 0.5 to 1 square metre in a corner away from vegetable beds is sufficient. The nearby vegetable beds benefit significantly from the predator populations that emerge from it.

Allow Some Brassicas to Flower

If you have bolted brassicas — kale, mustard, or rocket that has gone to seed — consider leaving some of the flower spikes rather than removing all of them. Brassica flowers are highly attractive to hoverflies and small solitary bees, and a few flowering plants among your crops significantly increases the beneficial insect population in the immediate area. This is a no-cost companion planting strategy that makes use of plants you might otherwise compost.