How to - Pests & Diseases

How to avoid and eliminate indoor plant pests

Learn to spot the signs of a houseplant in distress

Aphids and earwigs and ants? Oh my! While you might not notice what lives on your plants outside, once you bring them in for the winter, common garden pests like aphids, ants, mealy bugs, slugs, spider mites, white fly, scales and pillbugs are hard to ignore.

Don’t blame the cooler weather. The plant itself or its soil is the pest’s final destination, not your heated living room. However, once inside, the warm climate and lack of predators mean these unwanted guests can multiply rapidly and infest other plants.

Keep the great outdoors outdoors
When frost threatens, hauling your plants indoors can bring in more nature than you intended.  "Careless cleaning and careless examination is the biggest cause," says Mary Ann Gilhuly, of the Kitchener Master Gardeners. To ensure your plants make it through the winter unscathed, remember:

  • Looks count: Wilted, yellowing foliage, holes in the leaves or spots of mould aren’t just unsightly--these are signs your plant is weak. Strong, healthy plants withstand insect infestations better than frail ones, so unless the plant in question is rare and expensive, abandon it. You can buy a healthier, prettier specimen next season.
  • Go slowly: Your dry, dim house can be a shock to plants accustomed to sunshine and breezes. Before temperatures dip, move designated plants to a shady area for a week to acclimatize them to lower light levels.
  • Flush out the bugs: Before you move your plants indoors, immerse the pots in lukewarm water. This will force insects that lurk in the dirt to surface. Then rinse the leaves from all angles with a gentle spray to dislodge any hangers on. Examine the plant for insects, paying close attention to the underside of the leaves.

Have bugs, will panic
Sometimes, despite our best efforts, pests sneak inside. While most infestations are easy to control with early detection and a quick response, not all plants can be saved.

  • Know when to hold ‘em: As soon as you find insects, rinse the leaves with a jet of warm water, then wash them with a mild, soapy water. If you find webs, cocoons or egg sacs, remove them with a cotton swab dipped in isopropyl alcohol.
  • Know when to fold ‘em:  Pillbugs are harmless. Slugs can be plucked off. But scale and mealy bugs are persistent and develop pesticide-resistant coats. "If your plant is cheap and you're not attached to it, it's easier to toss it," Gilhuly says.

An ounce of pest prevention
Selecting the healthiest plants and controlling infestations are a good start. To maintain their pest-free status:

  • Initiate lock down:  If possible, keep all new plants away from other houseplants for a couple of weeks. This applies to plants from your garden, a florist and friends bearing potted hostess gifts. Don't worry if you don’t have enough window space for quarantined plants. "A plant will live in low light conditions for a couple of weeks," Gilhuly says.
  • Neglect your plants: Allow plants to dry out a bit between watering and cut back on fertilizer. Dry soil discourages moisture-loving insects, like springtails and fungus gnats, while scale and mealy bugs will starve without nitrogen-rich soil.
  • Keep watch: While a monthly shower for your indoor plants discourages insects, look for pests every time you water.

Charmian Christie is an avid gardener and home cook. When she's not digging in the dirt, she's charting her culinary adventures on her blog, Christie's Corner.

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