Companion Planting: Sweet Alyssum with Broccoli

I’ve always liked sweet alyssum flowers. We planted them back in our San Francisco community garden plot before we moved out of the city to start farming, and they made a lovely delicate ground cover that attracted the most beautiful little crab spiders. The spiders are experts at camouflage, and can turn different colors depending on the color of flower they are on. The ones on the white alyssum would be white, but those on yellow flowers would be a bright yellow instead. They were welcome predators in the garden plot.

For the past couple years we’ve been planting sweet alyssum in the rows with our broccoli, kale, and lettuce plantings to attract beneficial insects that can keep the aphids in check. Predatory wasps, lacewings, and ladybugs love the sweet alyssum, and so do syrphid flies. The syrphid fly larvae are voracious predators of aphids and other pests. The adults have a striped back and look a bit like yellow jackets—they feed on nectar and pollen. (At right is a picture of a syrphid fly on one of our pear blossoms.) The alyssum next to the broccoli provides a perfect habitat for the syrphids—the alyssum provides flowers for the adults, and the broccoli provides aphids for the larvae.

Aphids are one our biggest pest problems. They absolutely love broccoli and the other brassicas, but lately red aphids have taken out some of our lettuce plantings too, and sometimes it seems that there is a different colored aphid for just about everything we grow. The aphid problem waxes and wanes with the time of year, the weather, and even what is planted at the farm next door.

We count on our insectary hedgerows on the farm perimeters to provide habitat for many beneficial insects. But planting the alyssum directly in the rows with the broccoli or lettuce makes sure that the predators are right there where we need them. Several years ago, a graduate student from UCSC conducted a study on our farm and others with hedgerows to see how far the beneficial insects penetrated into the farm field from the hedgerow. The results showed that the insects were most certainly visiting the crops, but the number of beneficials found decreased the farther away from the hedgerow she tested. Our hedgerows provide stable ongoing habitat for our beneficial predator population. But the alyssum is a targeted crop-specific approach that brings the syrphid flies and other predatory insects right to where we need them when we need them.