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The right bulbs for now; and when beetles invade

Black vine beetles, half-inch-long, flightless pests, have a fondness for rhododendrons.

Black vine beetles, half-inch-long, flightless pests, have a fondness for rhododendrons.

What to do in the garden this week? Here are a few tips.

Don’t cultivate the soil until you can squeeze it in your fist and have it break apart easily when you open your hand. If it remains in a tight mud ball, the soil is too wet to work. Finish cleanup; fertilize shrubs, trees, and emerging bulb foliage; sow peas; apply a pre-emergent crabgrass control when yellow forsythia is in bloom, but don’t combine it with lawn seeds, or it will kill those, too. Corn gluten is the organic alternative for weed control.

Continue reading below

Q. I didn’t get a chance to plant bulbs last fall, but I notice a lot of stores, including supermarkets, are selling bulbs now. Are they to be planted now? Will they actually bloom this spring?

A. Familiar spring blooming bulbs such as tulips and daffodils are planted in the fall. The bulbs you see for sale now are different. They bloom in late summer and fall. They include cannas, dahlias, and gladiolus. They are not cold hardy and should be planted outdoors in late May. If you want to enjoy them next year, you have to dig up these bulbs in October and store them indoors for the winter. Lilies can be planted in either spring or fall. They are summer blooming and winter hardy and for sale now, too. Unfortunately they have a bad pest: the red lily leaf beetle. But if you want to try lily bulbs, plant them as soon as you buy them.

Q. I have two well established foundation rhododendron shrubs on the west side of my house. I noticed last weekend that many of the leaves — on one particularly — have “cuts” on them, it looks like someone took a pair of scissors and cut out pieces. I used Wilt-Pruf in the fall and the leaves look healthy with many, many buds. They are not brown, yellow, or wilted and I can see no sign of insects on the underside of the leaves. I also mulch my gardens. Any thoughts on the cause?

A. Your rhododendrons are probably under attack from black vine beetles. These half-inch-long, flightless insects eat notches in leaf edges at night and hide in leaf litter during the day. Their immature larvae live underground and eat rhody roots. They are resistant to insecticides, which instead kill their main natural predator, the ground beetle, so don’t spray. Instead, prune foliage so it does not touch the ground or bridge to other surfaces and place an unclimbable barrier (plastic coated with Tanglefoot, grease, or Teflon) on the main trunk to prevent adults climbing to feed on foliage. You could also introduce another of their predators, microscopic beneficial nematodes. You can find nematodes at Weston Nurseries in Hopkinton or online at www.biologicco.com. Follow the directions before release, including deeply watering the soil.

Carol Stocker can be reached at Stockergarden@gmail.com. Please include your name and the name of your town with your question.
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