Marigolds in the Vegetable Bed: What They Really Do
They're said to repel aphids and ease the load on the soil – but what's true about marigolds? A sober look before you clear them away this October.
Hardly a vegetable bed goes without a few orange blooms, and most gardeners have heard that they keep every pest away. Part of that is true, part of it is garden folklore. Now in October, shortly before the first frost, is the best time to sort it out.
Two plants, two different jobs
French marigold (Tagetes patula) and pot marigold (Calendula officinalis) often get lumped together. They are only distantly related and do different things. French marigolds smell sharp and spicy, pot marigold resinous and mild.
Myth: the scent drives off aphids
That the smell of French marigolds reliably keeps aphids or cabbage whites away is hardly backed up by trials. Aphids sometimes sit right next to them anyway. Don’t count on a single flower to protect your bed.
What the evidence supports: nematodes
There is good evidence for certain root nematodes, for example on potatoes or tomatoes: the roots of Tagetes patula and Tagetes erecta release compounds that reduce these roundworms in the soil. The effect only shows when the marigolds grow across the affected spot for a whole season. A single pot at the bed’s edge won’t do it.
Pot marigold as a magnet for beneficials
Pot marigolds bloom right into frost and offer nectar to hoverflies and other insects. Hoverfly larvae eat aphids, which helps indirectly. They also self-seed readily and keep the soil shaded.
What you can do now in October
Let the flowers stand as long as they are still blooming. Pot marigolds tolerate light frost, while French marigolds are not frost-hardy and die at the first frost. Collect dry, ripe seed heads of both on a dry day, ideally before the first frost, and store them in a paper bag somewhere cool and dry. Seeds from F1 varieties won’t come true. Healthy plant remains can be cut and left as mulch, the roots stay in the soil. Diseased parts, for example with mildew, don’t belong on the bed.
Plan them in for next year
Write down where the flowers stood and whether anything improved there. If you want to know for sure, compare two seasons. In the Rootivo plant encyclopedia you’ll find site, sowing time and good neighbors for both species.