At Northey Street City Farm, from around end of March through to September, I plant herbs like dill, fennel, coriander, sweet alyssum, marigold, calendula and cornflower to attract beneficial insects.
I've been propagating lots of sweet alyssum and dill to inter-plant in our market garden. Sweet Alyssum is known to attract hover flies, which is an important beneficial insect that primarily feed on aphids. The larvae of the hover flies are so effective at controlling aphids that study has shown that when hover fly larvae populations are high, they may reduce aphid populations by 70-100%! I’ve also been planting dill alongside brassicas since they've been found to be host plants for hover flies, lacewings, pink spotted ladybird, and parasitoid wasps. Most gardeners are all too familiar with the frustration of having to deal with cabbage white moth caterpillars every year. That's why I plant dill and other herbs to attract parasitoid wasps because they're ferocious predators of the white cabbage moth caterpillars. The wasps lay eggs in the bodies of the caterpillars and the wasp larvae literally eat the caterpillars from the inside! Some predatory insects like these Common Assassin Bugs and White Crab Spider found its way adjacent to our market garden. The assassin bug stealthily preys on caterpillars underneath the foliage of Native Peach (Trema tomentosa) whilst the White Crab Spider lurks in the foliage of Holy Basil, waiting for the next visitor, such as small moths.
It’s important to look at your garden as an ecosystem, and always consider how you can increase forage and habitat for beneficial insects. So, consider reducing or eliminating the use of insecticide or insect deterrents, even if they are organic where possible!
Over the last year, we’ve been busy planting native species in and around our productive spaces, selecting plants that are hosts to native invertebrates, especially butterflies. Some of the plants we’ve been planting include Red Ash (Alphitonia excelsa), Native Mulberry (Piptrus argenteus), Coffee Bush (Breynia oblongifolia), Native Peach (Trema tomentosa), Scrambling lily (Geitonoplesium cymosum), Native Grapevine (Cissus antarctica) and a whole lot more! There are great resources out there on how to attract native butterflies! Helen Schwenke is a local expert on this topic so do check it out. Save Our Waterways Now (SOWN) also has a great resource on locally native plants and in what habitat types to introduce these native plants.
Some native invertebrates (i.e. insects) are host specific so they will only be attracted to locally native plants. Always remember that invertebrates are important food source for other animal so by diversifying host plants, especially locally native plants, we are slowly but surely restoring some of the biodiversity that is currently declining rapidly in our fragmented urban to peri-urban landscapes.
Ko Oishi, Farm Manager