Dear Miss Floribunda,
I am thinking of bringing my house plants back inside after their summer vacation outside. In the past I didn’t worry about insect pests. I used plant food sticks containing a systemic insecticide and never had any trouble. Then I had a baby, now a toddler. I am very careful about not having anything poisonous around. I gave away my dieffenbachia and philodendron. Last year I just used regular fertilizer and no chemicals on my remaining plants but they were a sad sight by spring. My Norfolk Island pine had webbing on it and most of the needles had fallen off; gooey, cottony little things clung to my dying jade plant; the leaves on my well-watered hibiscus, ficus and orange trees had turned yellow and dropped off; and the ficus and orange trees had brown warts on their stems. There were teensy gnats flying about. The plants recovered after going outside, but I’m afraid they will not do well again inside. What do you suggest?
Not Optimistic on Nicholson Street
Dear Not Optimistic,
You are right to assume that your indoor plant troubles will recur if you do nothing. I shared your letter with my friend, Posy Potter, who keeps a flourishing indoor garden all winter. She advised you to wash your plants well, especially in the leaf nodes, and repot them in new sterile potting soil before you bring them inside.
You should first soak their pots and saucers in a solution of water and 10 percent bleach for a minimum of 15 minutes before the plants in their new soil go back into them. As a preventative, Posy sprays some of the repotted plants with mouthwash having a high alcohol content, some with hot pepper wax, and some with both before bringing them back inside.
It depends on the susceptibility of the plant, she says. Aphids, mealy bugs, and spider mites hate alcohol. Scale and whiteflies are “burnt up” by hot pepper, she says, and the wax spray suffocates larvae as does horticultural oil.
Posy informed me that your jade plant had mealy bugs, and that you should spray it with the alcohol mouthwash from week to week. Your ficus and orange trees are susceptible to scale — those “brown warts” — and the hot pepper wax spray ought to prevent that. If it does reoccur, weekly spraying should control it. If you are afraid your toddler will accidentally taste the hot pepper and suffer an unpleasant learning experience, then spray the plant with a nontoxic horticultural oil.
Posy diagnosed the malady of the Norfolk Island pine as an infestation of spider mites. She suggests you spray it with alcohol weekly. If the mites recur nonetheless, you could also introduce a predatory mite known as phytoseiulus persimilis, which will devour its rival and yet not harm the plants. Posy uses this method because she has a veritable mini-forest of bonsai susceptible to spider-mite infestation, but she hopes the alcohol will suffice for your one tree.
Your hibiscus tree probably has whiteflies, which are those “teensy gnats.” Posy hangs little yellow cards near her hibiscus and smears them with petroleum jelly. The mealy bugs are attracted to the color yellow, and then of course are trapped in the jelly. (If this seems as ghastly to you as it does to me, then horticultural oil sprayed directly on the tree is a good alternative.) Another possible culprit is the fungus gnat, which will attack the roots of your plants. In that case, you might drench the soil of the plant with neem oil or BT, bacillus thuringiensis israelensis.
Posy emphasizes that the best all-around way to keep your plants pest-free is to make sure you don’t overfeed or overwater them. Succulent new growth and soggy soil will encourage insects and disease. However, humidity around the plants should be high. What you need, Posy declares, is “dry soil and moist air.” It would be worth your while to spray your plants with water frequently or have a humidifier nearby.
To discuss these and other topics, as well as to participate in a potted plant exchange, please come to the next meeting of the Hyattsville Horticultural Society at 10 a.m. on Saturday, October 15, at the home of Joe Buriel, 3909 Longfellow Street.