After their outdoor vacation and summer in the sun, houseplants will be thriving and ready to green up the interior of a home during the cooler months. But one gardening expert, Gail Pabst, marketing communications officer for the US National Garden Bureau warns that the last thing you want to do is bring a whole load of damaging and destructive pests along for the ride.
She said: “Hitchhiking pests such as aphids, spider mites, mealybugs and scale can rapidly become a severe problem in a warm indoor environment without insect predators, as the population has the ability to go through several life cycles indoors. It is vital to clean them before bringing them inside your home.”
Gail recommended instigating an at-home IPM (integrated pest management) system. If this sounds complicated, don’t worry. Put simply, all it means for home gardeners is giving plants a thorough hosing using horticultural soap and water, followed by a treatment of horticultural oil.
Horticultural soap is usually made of potassium fatty acids that kills pests on contact. Horticultural oil can often be petroleum-based, or derived from fish and plants.
There are also insecticidal soaps and oils which may contain chemicals. Always check the label carefully, especially for those who favour natural gardening methods.
Whilst soap and water work well on soft-bodied insects, oil targets hard-bodied pests, such as beetles and scale, by smothering them.
Marissa Schuh, extension educator, integrated pest management at the University of Minnesota said: “We still don’t understand exactly how soap kills (or doesn’t kill) an insect.
“The working theory is that the soap washes off a protective coating on the insect’s body, causing it to dry out. Because of this potential cause and effect, only certain insects are susceptible; small, soft-bodied insects are those most likely to be controlled.
When cleaning houseplants, Gail’s advice is to start with the soap and water, trying to remove as many insects as possible using your fingers and rinsing with a garden hose afterwards.
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Then spray with a horticultural oil, using your hands to make sure it coats all parts of the plant, including the front and back of the leaves.
Many gardeners claim that neem oil, often found in skincare products to treat acne and eczema rashes, makes a fantastic natural insecticide for garden plants.
The neem tree (Azadirachta indica) is part of the mahogany family and is native to tropical areas of India and Africa. All parts of the neem tree contain an oily substance, which helps the tree defend itself against attack from insects and grazing animals.
It’s a natural pesticide and fungicide, but unlike many pesticides it’s not toxic to humans or pets.
The oil is most concentrated in the seeds and has been used in India for centuries by gardeners and farmers watering plants with a neem oil solution to control plant insects and diseases.
Neem oil will take two or three days to kill bugs and will remain effective on plants for up to a week before it needs to be reapplied. For moderate pest infestations, apply a neem oil mix once a week for three to four weeks.
In between neem oil sprays, gardeners can water their plants as normal – just don’t water right after spraying as this could dilute or even wash away the neem.
There is a slight risk to overusing this oil on houseplants. If used too liberally, it can burn the leaves, causing them to brown and wither. For most plants, this would require drowning them in the stuff, but some are more susceptible.
If leaves start to go black, brown or yellow, stop using the neem oil immediately and instead spray with a water and dish soap solution. This isn’t as effective as neem oil, but will help to stop the risk of a bug infestation.
If the plant has a severe infestation, gardeners may need to repeat this process several times until they can no longer see insects roaming their plant.
Gail said: “Giving a plant a bath with horticultural soap and a hose before bringing it back inside is fantastically freeing, as you don’t need to worry about indoor surfaces and can spray with abandon.”
However, she warned that gardeners should always remove any leaves that are yellowed or heavily infested with insects, rather than trying to treat them.