Q. My rhubarb has some type of bug. It’s planted at the edge of my garden. It’s not as hearty as it was in the past, and now it has brown spots.
– Phyllis Clark
A. Crown rot can cause brown, sunken, water-soaked spots on the base of the leaf stalks. Leaves yellow, and stalks collapse and die. The disease thrives in waterlogged, heavy soils and attacks the crown and base of the stems. In the insect world, rhubarb curculio can cause black spots on the stalks. And the small stems can be caused by a number of things, including lack of fertilization, overcrowding, crown rot and poor drainage.
Every 8 to 10 years, lift your plants and cut away any weak shoots and roots in the late fall or early spring. Consider improving the drainage of the area. Add 3-4 pounds of 12-12-12 per 100 square feet of bed area and, ideally, 2-3 inches of well-rotted manure. Till this in, then replant only vigorous sections of the plant. Set the crowns in rows in shallow furrows so the crowns will be only 2 inches below the surface. Place the crowns 3 feet apart in the rows and each row of plants 5-6 feet apart. Fertilize after harvesting with one-third pound of ammonium nitrate per 100 square feet of bed space.
Q. How do you propagate clematis? When is the best time to move older plants? Are they deep-rooted, and, if so, how far do you dig? What fertilizer do you use?
– Lois Holcomb, Hudson, Ind.
A. Clematis is best propagated by cuttings, which root in about five weeks. Young wood taken in late spring to late summer is most commonly used. Treating the cuttings with a rooting hormone, and misting the cuttings will aid the rooting process. The clematis you buy at a nursery are usually grafted onto a stronger rootstock, so your best bet is to grow purchased plants. However, you can get decent results from growing your own cuttings.
Transplant your clematis in the early spring or just after flowering. Dig down about 12 inches and try to maintain soil contact with the roots.
An annual application of 5-10-10 sprinkled around the base along with a layer of well-rotted manure as a mulch will keep clematis happy and healthy. They prefer to have their vines in the sun and their roots in cool soil.
Q. I have a wisteria vine that is growing on a water tower that is about 70-80 feet tall. We figure the wisteria has been growing on there for 35 years or more. It bloomed several years ago but not much since then. What should I do?
– Melanie, Scottsburg, Ind.
A. Wisteria need lean soil, infrequent watering and full sun. Too much fertilizer, shade or water will keep them vegetative, preventing them from flowering. Most gardeners can prune their vines just after flowering, but that would be tricky and probably illegal if it’s growing on a water tower! You may not be able to control the fertilization of surrounding turf or the amount of water the plant receives either. However, other home gardeners can take note of the culture required to successfully coax wisteria into blossoming. In your case, the immensity of the vine limits your options. I suggest you enjoy the foliage&emdash;it’s better than looking at a water tower!
Quince Question Revisited
In a recent column, I wrote that ornamental quince (Chaenomeles japonica) can be used to make jellies and preserves. Indeed it can, but the fruiting quince (Cydonia oblonga) is preferable for its large size and sweeter flavor. It has white or pink flowers and a bright, yellow fruit that may be as large as a very big Bartlett pear. If you choose to make preserves from ornamental quince, you’ll need to have more sugar on hand!