Q Last fall my husband thought it would be a good idea to hill up our rose bushes with sawdust mulch instead of soil. His reasoning was that sawdust is a wonderful insulator, and perhaps the roses would survive better with sawdust protection. We were away at the time we would normally take the mulch off. When we finally started to remove the sawdust, we noticed the canes sticking above the sawdust had started to leaf out, but the new foliage had begun to wilt. Upon uncovering the stems, we found canes had turned brown underneath.
Ann Arbor, Mich.
Sawdust is not recommended for hilling around roses because of the formation of a type of alcohol that is harmful to plant tissues.
Landscapers have discovered that trees mulched heavily with shredded bark so that it reaches several inches up the trunk can cause fatal injury to the cambium layer. It is now recommended that bark chips or shredded bark be pulled away from the trunk to leave it exposed to air.
In the case of your roses, soil is probably the best winter insulator, but never use the soil from the rose bed. This practice may expose roots. Move soil from another location.
Q Awhile back you told of a plant that acts as a mole repellant. I wrote the name on a slip of paper, but my messy desk has consumed the note. We appreciate the helpful columns in the Monitor.
Q Some time ago you listed Thompson and Morgan Company as a source for mole plant or caper spurge. I wrote to this company but received no reply. Can you suggest another source, please?
Grand Rapids, Mich.
One of the repellant plants is Crown Imperial or Ritillaria imperialis. It is a three to four foot bulbous plant with a cluster of flowers resembling a crown. Red or yellow varieties can be purchased from most bulb companies selling spring flowering bulbs.
The other plant, caper spurge, is usually listed in catalogs under Euphorbia lathyrus. It is the same family as poinsettia and has a milky sap. Plants grow about three feet tall and readily self sow.
We would be happy to hear comments about the effectiveness of these plants. A catalog that lists caper spurge is: J.L. Hudson, PO Box 1058, Redwood City, CA 94064. You might try Thompson and Morgan again. Perhaps they did not receive your request. Their address is: PO Box 1308, Jackson, NJ 08527.
Q For the past two summers, I have had a problem with my bush beans. I have planted both the green and yellow types; and as soon as they are growing well, they break off right at ground level. I can see no insects or worms on the soil.
Thank you for any help to prevent the same problem this year.
Your problem is probably due to surface cutworms, which do their dirty work at night, cutting off stems at ground level. Climbing cutworms are similar, but they attack plants after crawling up stems. All are the smooth, fat larvae of night-flying moths, repulsive gray or brown, striped or spotted.
In the North there is usually only one brood. In your area they would overwinter as partly-grown caterpillars, resting just under soil surface, or in debris and clumps of vegetation.
Mechanical barriers or collars are sometimes sold in garden stores. But more often gardeners make their own from tubes inside paper towels or toilet tissue. We cover ours with foil to make them more durable. They work well if they are slit and put around the plant stem, closing the seam as tightly as possible. Also, they should be set down into the ground one to two inches.
There are poison baits in garden stores, but a nontoxic bait can be made by mixing some cornmeal with a few drops of molasses, then adding some Bacillus thuringiensis. This is nontoxic to humans, pets, and wildlife. The bacillus comes in trade names BT, Dipel, Thuricide, and Attack.
Another repellent some find effective is a layer of wood ashes, a few inches wide, around the base of each plant.
Q I have noticed pictures of beautiful yellow flowered plants listed in several catalogs lately. The name of the plant is Euphorbia polychroma. Quite awhile ago you mentioned a Euphorbia plant that is supposed to repel moles. Is this the plant you referred to?
Sioux Falls, S.D.
Euphorbia polychroma (also called E. epithymoides) is not mole plant. A common name is cushion spurge. The common name of mole plant (E. Lathyrus) is caper spurge. E.polychroma is being acclaimed as one of the ten best perennials to grow in a perennial garden.
Wayside Gardens of Hodges, S.C., extol its virtues as: ``... long-lived reliability, ease of cultivation, neat impressive form, and outstanding color.'' We have observed the planting that borders one side of the peony gardens at Cornell Plantations in Ithaca, N.Y., in spring, summer, and fall.
We agree that it is a spectacular plant as it changes in spring from sulphur yellow tiny blooms and bracts atop purple green foliage, to bright green with yellow bracts in summer. It is equally impressive with its red fall coloration.
Q I have become terribly discouraged about raising cabbage or broccoli in the garden. The cabbage worms riddle them before we can harvest a mature head. I have become skeptical of using toxic pesticides, and my wife suggested we write to you asking for your suggestions.
Fortunately there is a biological control called Bacillus thuringiensis. It is readily available in garden stores. It acts on the digestive systems of larvae of moths and butterflies as these worms feed on treated leaves. You may find it under trade names such as BT, Dipel, Thuricide, and others. The name of the bacterium will be on the label. It works only on specific pests. Researchers are discovering and producing more and more such pesticides.