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Ask the Gardener: Should you spray for gypsy moth caterpillars?

Ask the Expert Gardening
Some native birds, such as cuckoos, downy woodpeckers, gray catbirds, and common grackles, will eat gypsy moth caterpillars but, unfortunately, not in large enough quantities to have an effect during an outbreak, according to Mass Audubon.
Some native birds, such as cuckoos, downy woodpeckers, gray catbirds, and common grackles, will eat gypsy moth caterpillars but, unfortunately, not in large enough quantities to have an effect during an outbreak, according to Mass Audubon. John Tlumacki/Globe Staff/file 2016

What to do this week: Gardening can be wonderful for your physical and mental health, but wear a hat, long sleeves, gloves, and sunscreen. If you live in deer country, spray your socks with an insecticidal product such as Sawyer’s permethrin for clothing and pull them up over your (long) pant legs. Avoid knee-high grass, which can harbor ticks. Keep weeding before invasives like garlic mustard go to seed. Sprinkle bulb fertilizer around bulbs while you can still find them. Snap off spent flowers of large bulbs such as daffodils, but don’t bother with small (so-called minor) bulbs such as crocus, which may self-seed if left unbothered. Harvest radishes, the top half of mesclun mixes, asparagus, and rhubarb. Sow cilantro, sunflowers, beets, carrots, lettuce, and beans. Start shopping for annuals, herbs, and container plantings.

Q. I think gypsy moth caterpillars are chewing up my trees. Should I have them sprayed, or will the birds eat them?

S.S., Dover

A. To spray or not to spray is always a thorny question. I prefer to let the birds eat my insects. Compared with hiring someone to spray, this is the easy, healthy way — and it’s free. But to paraphrase Shakespeare again, here’s the rub: Most birds don’t like to eat gypsy moth caterpillars; maybe they’re too hairy. I was going to have my apple orchard sprayed with spinosad, a natural substance that kills both gypsy moth and winter moth caterpillars if applied during the merry month of May, but then my orchard started blooming, so I just canceled my order. While relatively eco-friendly, spinosad is very toxic to bees in the short run, and my neighbor keeps two hives.

How will my trees do without spraying? They will probably be OK, thanks to biological controls scientists have introduced. Gypsy moths are the sole target of an introduced fungus called Entomophaga maimaiga. It thrives in wet weather, so if we have a rainy spring, most of the gypsy moths may die a natural death. Fingers crossed. Similarly, winter moths are on the wane, thanks to its natural enemy, the parasitic fly Cyzenis albicans, which was released here in 2011. Bravo to the UMass Department of Entomology and the state Department of Conservation and Recreation! If my trees do take a hit, I will give them extra water throughout the year to help them put out new leaves.

Q. Can I plant a magnolia tree in a pot?

C.M., Charlestown

A. Yes, if the pot is big enough and the tree is small enough. Grow a tree with a 1-inch-diameter trunk in a pot 2-feet wide. As the tree grows, you will need at least a foot of pot width for each inch width of tree trunk.

There are many small or dwarf magnolias. Try a star magnolia for screening and fragrant flowers. But when the tree outgrows its pot, you may need to give it to someone with the space to plant it in the ground.

When buying containers, I always look for self-watering pots, which contain small reservoirs at the bottom that cut down on my watering chores. I also make sure there are plenty of holes at the bottom so the water can drain out. When planting containers, I place several inches of rocks in the bottom first so it won’t blow over, then I fill in around the root ball with lightweight soil-less potting soil so the roots are barely covered and there is at least an inch of air left at the top for watering.

Events

The Garden Club of America flower show “Alchemy: The Magic of Nature’’ is a regional horticultural, photography, and conservation exhibit with floral designs. It is free to the public on Tuesday, May 22, from 2 to 5 p.m. and Wednesday, May 23, from 9 a.m. to 2 p.m. in the Boston/Dedham Hilton (25 Allied Drive, Dedham).

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