Scale on spider plants, sparse arborvitaes

DEAR JESSICA: I have many plants that I take in for the winter after dousing them in sudsy water. After several weeks on the porch, the spider plants become infested with bugs. When I read your response to another reader advising antibacterial soap for a similar problem, I tried it but had no luck. Also, it was very costly for the amount needed for all my plants.

I am now cleaning everything off that is underneath my plants. Everything is sticky, what a mess. Please advise me on some household magic that would work. We are seniors and the plants give us a feeling of being outside all winter. -- Marilyn Rudden, North Bay Shore

DEAR MARILYN: Spider plants are generally easy-to-grow, low-maintenance houseplants that aren't particularly susceptible to pests, but the presence of a sticky substance likely indicates a scale infestation. Scale are tiny brown, green, tan or black parasitic insects that attach themselves to plant parts and can either be so tiny they aren't noticed or mistaken for unusual growths on stems and leaves. Like aphids, they insert their piercing, sucking mouthparts into soft plant parts and suck the life out of them.

As with all living creatures, what goes in must come out: That sticky substance that's making a mess of your house is called honeydew, and it's scale excrement. Soon, the honeydew will turn black as sooty mold grows on it. Oftentimes, people notice an ant infestation on their plants and believe the ants are killing their plants. But the ants are just there for the honeydew.

Look closely at stems and leaves, especially under leaves, to locate the concentration of scale. Usually, if they're on only a few leaves, removing and discarding the affected leaves solves the problem. But I'm under the impression your problem is widespread. If that's the case, and you identify scale on most plant parts, there are two remedies that will be effective.

Insecticidal soap or neem oil usually is the first line of defense. Weekly applications according to package directions should kill the insects. You mentioned you applied soap and soapy water, so my assumption is that you purchased insecticidal soap. You don't say how often it was applied, but if you just applied it once, I recommend instituting a spraying regimen with weekly applications until the problem is resolved.

DEAR JESSICA: Can you please tell me the right fertilizer to use on my 40 arborvitaes? They are 15-20 feet tall, and haven't been doing well for the past couple of years. They are getting sparse, and I was told I should cut about 2 feet off the top to give them more strength. -- Joseph Ferraro, Dix Hills

DEAR JOSEPH: It's normal for evergreens, including arborvitaes, to shed their inner needles over the winter. This is the case if you find that branch tips are healthy but inner stems are bare. There are other possibilities as well, however, so you'll need to investigate a few things.

Arborvitaes can become sparse if they're planted in too much shade. Oftentimes, trees that thrived in the past suddenly become sparse because neighboring trees have grown over the years and begin to shade them out. If that is not the case, insects could be to blame. If foliage has little cone-like appendages, bagworms could be present. Mite infestation could lead to leaf loss, too, and can be identified by the discoloration of needles.

The arborvitae leafminer is a caterpillar that develops into a small tan moth that lays its eggs between leaf scales. Its larvae overwinter in plant tissue and then tunnel into the foliage for feeding, repeating the cycle, resulting in brown leaf tips, which is first noticed in late winter or early spring. If that's what you're seeing, the good news is that affected trees can make a really nice comeback with the help of a systemic insecticide containing either acephate or spinosad as long as at least 20 percent of its foliage has survived the attack.

Arborvitaes also can be susceptible to several different fungal diseases, so it's important to space them sufficiently to allow for air circulation through and around each tree and to avoid wetting the foliage with sprinklers. Direct water at the roots instead.

Branch pruning is a good idea for trees that have become crowded or unruly, but cutting off their tops would be a mistake. The main trunk, or leader, will remain flat permanently, as no new growth will occur from that point afterward. The practice is ill-advised except in cases when the top has become broken or damaged.

Arborvitae aren't heavy feeders. Applying a slow-release fertilizer, such as Holly-tone, once a year should suffice.