French connection

French connection One way to keep pests at bay is to grow French marigolds – but check they pass the smell test

- Bob Flowerdew

A TRADITIONAL and commonly known companion planting suggestion is to have French marigolds in your greenhouse to prevent whitefly, a pest of so many greenhouse plants. These were once hard to eradicate, although now they are controlled by introducing the commercially available biological control Encarsia formosa. However, these wee wasp predators are not inexpensive and have to be re-introduced every year.

Thus, it’s always wise to closely inspect every new plant, not just for whitefly but also for other common culprits such as scale, red spider mite and aphids. You can even knock the plant out to see if vine weevil grubs are eating the roots. Ideally, it’s good to make a ‘quarantine cold frame’, somewhere plants can safely sit awhile so that hidden infestations or infections can show up before they have been introduced into your greenhouse.