How to Flush out Garden Pests in Winter

15 December 2016, written by Benedict Vanheems

Winter – and I mean a decent, cold winter with multiple frosts – can be actually be a boon to the gardener. The trick is to tame the cold and turn it to your advantage. One way to do this is to use it to flush out lurking insect pests. Expose them to the frosts, as well as a legion of hungry birds, and they’ll have no chance! The combination of piercing cold and probing beaks will put a big dent in pest numbers, giving your plot a head start come spring.

Expose Grubs to Frost

One of the very simplest ways to quash overwintering bugs is to work out where they’re hiding and bring them to the surface. The best way to do this at ground level, particularly around fruit trees and bushes, is to rake up and remove fallen leaves, before turning over the top few inches (5-10cm or so) of soil. Even simply tickling the soil surface with a border fork to ruffle up the leaf litter can bring hibernating grubs to the surface. In their state of torpor, they won’t be going anywhere and the icy grasp of frosty nights can be left to do its work.

Where thick mulches cloak the ground around winter crops, start by peeling the mulch back. Rake it away during the coldest weeks of the year to allow the frost to penetrate the ground and cleanse the soil. Of course, you will probably want to keep some crops (for example parsnips and carrots) covered to facilitate lifting them out of the ground during iron-cold weather.

There’s a balance to be found here – between slowly feeding the soil over the quieter months, and giving it a frosty ‘deep clean’ in time for the new growing season. A good compromise is to expose soil for three or four weeks over the coldest time of the year before covering it back over with mulch.

The Role of Birds in Pest Control

Tickling, turning and uncovering the soil also yields a veritable feast for insectivorous birds. In the deep of winter, when the ground is hard and there’s little wild food, a bonanza of newly exposed fleshy grubs and bugs will help our feathered friends through a very hard time.

Additional feeding of birds will help keep them on side. Far from detracting their attentions from natural pest control, a well-stocked bird feeding station will draw in more wild visitors, making your garden a local hub. More birds in your garden mean more eyes and more beaks, which can only be a good thing for pest-weary gardeners!

Bird foraging in grass below fruit trees

Fruit cages are invaluable at protecting fruit bushes and small fruit trees from birds during the growing season. Winter is a good time to temporarily remove the netting to allow birds free access to the invertebrate snack bar. If you have chickens you can also allow them access. Their inquisitive beaks will turn over the soil surface to ruthlessly flush out and devour the lurking pests beneath.

One word of caution is required when removing netting from fruit cages. Sometimes birds such as bullfinches and tits will feed on young fruit buds, causing severe damage that necessitates pruning in order to encourage replacement shoots. So clearly a degree of monitoring is required, with netting replaced as soon as any damage is suspected.

Flush Out Pests With a Winter Wash

Winter washes are another weapon in the gardener’s fight against insect pests. A winter wash is a fish or plant oil-based solution that’s sprayed all over the exposed branches of fruit trees and bushes. The object? To kill overwintering pests, either on contact or through smothering and suffocation. Winter washes are effective against many types of mite and sap-sucking aphids. By controlling these insects the incidence of viruses is also greatly reduced – a double win!

Spraying an apple tree with a winter wash

Winter washes are sprayed on, often using a pump-up pressure sprayer, so you’ll need to wait for a completely calm day before applying it (you don’t want clouds of it to simply blow away). Try to get the best coverage you can, spraying the wash into every nook and cranny. Smaller trees and shrubs are the easiest to cover, for obvious reasons. Larger trees can be tricky, but concentrating on those areas you are able to reach will still make inroads on pest numbers.

Clear Away Weeds

Weeds are another hideout for overwintering pests. It’s good practice to remove weeds from your winter vegetable plot and from around fruit trees so that frost and prying beaks can get in and do their work.

Don’t be too thorough, though. Many seedlings of biennial flowering plants such as calendula should be left to provide essential flowers to entice next season’s beneficial bugs – the predators that will keep common pests in check once warmer weather returns. The same goes for ladybird and lacewing-friendly plants such as nettles. Concentrate on removing seedlings you know to be annual weeds, as well as maintaining your assault on pernicious perennial weeds such as couch grass (twitch), bindweed and ground elder.

Removing habitats for overwintering pests, while at the same time actively going after them is a great way to wipe the slate clean for the new growing season. As you go about your pest purge, please remember to let us know what you find. You can report any bugs you see – including beneficial ones – at the Big Bug Hunt website. In doing so you will be part of a major citizen science project that we’re coordinating. Its aim is to eventually develop an early warning system against pests, so a small investment of time on your part could yield a massive impact on how we all deal with garden pests.