How to keep critters at bay in your greenhouse
If you’re a newcomer to greenhouse gardening, you may not be aware of the many pests which can invade edibles and ornamentals under glass.
Common pests include vine weevil, grubs, whitefly, thrips, aphids, fungus gnats, slugs, mealybugs and spider mites, warns BBC Gardeners’ World presenter Mark Lane.
“All these pests can be dealt with in several ways, just like you would in the garden, with the exception that you are working in an enclosed environment,” says Mark, gardening expert for stairlift and home lift company Stannah (stannah.co.uk).
“Opening doors, windows and vents will help with air circulation and aid against diseases and pathogens to some extent, but when it comes to the critters in your greenhouse you need to take immediate action.”
Here are Mark’s tips for a pest-free greenhouse.
KEEP IT CLEAN
Emptying it and washing down every surface (including tools, pots and trays) with warm water and a little detergent or an insecticidal soap, at least once a year, will allow you to start with a pest-free environment.
Throughout the year, remove all plants and debris and maintain a weed-free greenhouse.
CHECK PLANTS REGULARLY
You can see if there are any slugs hiding in the soil or under the pot, and whether there are mealybugs or other pests. Once you have plants in your greenhouse check regularly for any signs of infestations.
USE SHOP-BOUGHT COMPOST
Use shop-bought composts for potted plants as this will have been sterilised which means no pests. Soil from the garden will contain several pests as well as beneficial insects.
SET TRAPS
Hang fly papers or sticky insect yellow
sheets, as well as wasp traps. Sticky white traps help detect fungus gnat. Vents and windows essential for altering air flow and humidity will allow pests in. Fly netting on doors will provide good ventilation but stop unwanted guests.
For thrips and whitefly there is a simple trick of wrapping sticky tape around your hand, with the sticky side facing outside, and then gently rubbing your hand over the infected plants. You can then dispose of this properly.
Slugs and caterpillars are best picked off by hand and removed or
destroyed – I add mine to the bird feeders as tasty treats.
COOL OFF
If your greenhouse is hot and dry, spider mites can be a problem. Wet the floor with water, which will evaporate throughout the day cooling the temperature and adding moisture to the air.
Try to eliminate pools of standing water, however, as algae and moss can grow which are sources for fungus gnat and shore fly.
Another simple trick is to take potted plants outdoors during the warmer days of summer to help reduce the number of spider mites.
Pests also hate the cold, so during the winter leave the doors and windows open for a couple of days (if no frost or freezing weather is forecast), as this will help kill off pests, eggs and larvae.
TRY BIOLOGICAL CONTROLS
Over the last few years, we have seen several biological pest controls come to the market. This is a natural way of removing the pests. A specific pest control for each pest will feed on it, and, once all the food is used, will die.
I would urge all gardeners not to use pesticides, especially in an environment like a greenhouse.
TACKLE PROBLEMS EARLY
With any pest, early detection is key. You can then diagnose the problem and act accordingly.
Sticky tapes and paper are brilliant for managing infestations, but to clear and reduce large numbers of pests you may need to revert to mass trapping products.
Monitor your trapping products, keep plant material away from them and replace when required.