Stress can make rhubarb bolt

Garden Q&A

November 10, 1996

My three large rhubarb plants (6 years old) were a real disappointment this past spring and summer. The plants sent up seed-stalks in May, and then all I got were a few thin stalks to eat. What am I doing wrong?

Sounds as if your plants are overcrowded. Rhubarb will bolt (produce a seed-stalk) when they are stressed in any way. Plants should be divided every four years. Cut them back to the crown (the base of the plant) and then split the crown into four pieces (very large plants could be divided into six to 10 pieces).

Replant one piece and give the others away, or replant them 2 1/2 to 3 feet apart. Fertilize in early spring and again when you have finished harvesting.

Gardeners considering planting rhubarb should know it is only marginally hardy and productive in most areas of the state. It doesn't do well when temperatures are the 90s. Before planting, enrich your bed with organic matter. Maintain an organic mulch of straw or shredded leaves around the plants. Valentine is a recommended variety; it has red stalks that are bolt-resistant.

Now that the leaves have fallen from my ornamental plum trees, I'm seeing some abnormal black growths on the branches. What are they, and what should I do?

What you are seeing is either the result of black knot disease or the egg masses of the Eastern tent caterpillar. Black knot is caused by a fungus and is frequently seen on cherry and plum trees. Twigs and branches covered with the "knots" eventually die. Pruning out the affected branches is the most effective remedy.

Eastern tent caterpillars spin large webs in trees in early spring. The webs are home base for the white-striped caterpillars as they feed on the trees. The larvae form egg masses that are black and shiny and resemble plastic foam. Prune off the branches where you see these masses.

My two Chinese chestnut trees finally started producing nuts this year. I picked up a half bushel of nuts, but after I brought them into the house I noticed small holes drilled into the nuts. These holes were surrounded by a fine dust. What's going on?

Your chestnuts were visited by the chestnut weevil. The adults are small, dark beetles with long snouts. The female inserts her eggs through the spiny husks (outer covering) of the chestnut and into the developing nut meats (quite a feat). The larvae hatch, feed inside the nut and then crawl out in their pupa stage when the husks open and release their nuts in October.

To reduce weevil damage next fall, pick up all nuts off the ground. This will keep the weevils from wintering under your trees and getting into the soil. To halt these pests even sooner, spread a white sheet on the ground under your tree in August. Shake or tap the tree branches. This will cause the adult weevils to drop down onto the sheet for easy disposal. You can also try wrapping your tree trunks in July with corrugated cardboard coated with petroleum jelly. This will help you trap weevils during their daily migration up and down your trees.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions or if you have questions of your own, call the center's hot line at (800) 342-2507.


Apply well-rotted manure to garden beds and till it under if possible. Bare soil that is prone to erosion should be covered with leaves or straw.

Don't fertilize any trees or shrubs until they are completely dormant (late this month in most cases). Early fertilization will lead to a spurt of new, soft growth that may be killed over the winter.

Pub Date: 11/10/96

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