Protect Your Greenhouse Crops the Environmentally Friendly Way
Photo: Nina Ewald
Originally written by Nanna Stærmose
Edited by Louise Curly
Protecting crops from pests is an essential part of growing, but as more of us are reluctant to use chemicals to manage infestations, here are The Greenhouse Forum’s suggestions for natural ways to protect plants in a greenhouse.
First of all, regularly inspect your plants, particularly the undersides of leaves, for signs of problems. If you can spot an issue early on it’s much easier to keep it under control.
Spray away aphids and white fly with a jet of water from a hosepipe, or alternatively squish them with your fingers.
Natural insecticides known as fatty acid sprays are derived from plants or other natural substances. Use on a cool day, on a morning or evening. You may need to repeat after 7 days. It’s worth bearing in mind that by spraying you can also kill the larvae of beneficial insects such as ladybirds, and don’t use these natural insecticides if you’ve released biological controls (see below).
Sticky traps are attractive to pests like white fly – they’ll fly to them and then get stuck. They’re not necessarily a control in themselves but are a useful tool and a good way to monitor the problem.
Biological controls harness certain creatures to control pests. For instance, the parasitic wasp Encarsia formosa will lay its eggs inside the larvae of whitefly, killing them, and nematodes (microscopic worms) can be watered onto pots to control slugs. Biological controls can be bought online or from garden centres.
Companion plants such as French marigolds, poached egg plants and calendula should be planted in containers or beds by the entrance to the greenhouse to attract insects such as lace wings, ladybirds and hoverflies. As well as looking pretty these beneficial insects and their larvae will eat aphids and white fly.
Nina Ewald is a horticultural journalist, author and speaker.
Om Nanna Stærmose
Nanna is the Danish writer of many of the articles in the Greenhouse Forum.
Nanna visits happy greenhouse owners and tells their stories about basic cultivation, but also those stories that are more oblique.