Decoys in the Garden

Decoys are usually associated with duck hunters. However another type of decoy is also in use in the garden – and it’s an invaluable tool in the battle to control pest insects. Read on to find out how you can use decoys in your own garden.

Have you ever had the experience of finding one plant in your garden simply covered in aphids (or some other pest insect), while all the plants around it are virtually pest-free? If so, you’ve witnessed the power of the decoy (sometimes called a trap-plant) in action. A decoy plant is a sacrificial plant which encourages insects away from other desirable plants in your garden. In some cases, it does this by being more attractive to pest insects than the plants around it. But (and this is very often the case in the edible bed) it can also act as an attractant to insects by being at a more mature stage in its life cycle than the plants around it.

Insects are particularly attracted to plants in the reproductive stage of their development –the period when the plant is forming buds, flowers, fruit, and seeds. These parts of the plant are energy-rich and full of nutrients such as sugars, oils, and proteins – the very food sources insects crave, especially during their breeding period. Insects are aware of plants in the reproductive stage, alerted to them through visual clues (bright flowers with a dazzling array of patterns on their petals), fragrance (fruit is particularly fragrant as it ripens or rots), or sex pheromones (chemicals that attract insects in search of mates). If you can provide insects with a plant at a reproductive stage, they will (at least to manageable levels) skip the younger plants around them as they head for the object of their desire.

To provide insects with decoy plants, you will need to plan well ahead. As an example, let’s assume broccoli is the vegetable you want to keep as pest-free as possible. Get out your diary, and note down the week and month in which you intend to plant your broccoli seedlings in the garden. It takes around 100-120 days (from seedling stage) for a broccoli to produce the pale yellow flowers so attractive to pest insects. This means you will want to plant your decoy seedling about 100-120 days before you plant the broccoli seedlings producing your actual harvest. If you live in a cooler part of the country, this means your decoy will need to be planted in late autumn, and it may not survive through the winter – in which case, we have other tricks up our sleeve…

If growing a decoy plant through the winter is just too difficult in your climate, you have two options: plant your decoy broccoli plant in a pot in the greenhouse where it can grow through the coldest months. As it’s about to mature and produce flowers in spring, move it out into your garden. If this feels like too much work, try this: broccoli belongs to the brassica family, and many brassica (especially those in the ‘Asian greens’ family), mature much more quickly than their broccoli cousin and are just as attractive to pest insects. Mustard and mibuna, for example, produce flowers in just 1.5-3 months from the time they are sown as seed. If your winter climate is harsh, sow fast-maturing brassica as soon as the ground is warm enough so they are in reproductive stage before you plant the broccoli seedlings you hope to harvest from.

A decoy plant is best sited around 2.5-3.5 meters from your harvest crop and it will need to be cared for (at least until it flowers) as well as you would any other plant in your edible bed. Once it has done its job and is smothered in insects, it’s time to dispose of it. To do this, cover the plant in a large bag (a plastic rubbish bag works well), tie the end of the bag around the base of the plant, then cut the plant off at its base below this point. Remove the plant, with the insects trapped inside the bag, and dispose of it (don’t be tempted to put it in your compost).

Growing and ‘harvesting’ decoy plants really does work. It will not keep your garden pest free, but it has a very good chance of keeping pest insects to a pleasingly manageable level.

Enjoy experimenting with decoy plants in both your edible and ornamental beds, and don’t forget to keep us posted on the results!