gardener's Q&A - Brief Article

Flower & Garden Magazine, Sept, 2001

Question: I will have to dig up some dumps of dianthus this fall so the garden can be plowed. I need to know how to care for them.

Ames, IA

Answer: Dianthus, or garden pinks, are by nature rugged characters. They should easily survive transplanting as long as the soil around the root ball is not unduly disturbed as you lift the clumps from the garden. Store the clumps of dianthus in a cool area to discourage soft growth from emerging.

Replant the clumps in lightly limed soil, as soon as possible after the fall plowing is finished so they can settle in for winter. A loose covering of coarse straw will help prevent frost heave during the winter. Rather than growing perennials in a garden that is disturbed annually by plowing, why not reserve an area to develop a permanent perennial bed? In such a location your dianthus would form a gradually increasing mat of color.

Q: Each year toward the end of summer many of my flowers begin to suffer from mildew. Roses, pansies, perennial asters, zinnias and even weeds become mildewed. In the spring, my peas also get mildewed even though we have field peas as a crop nearby and they aren't affected. What can you suggest?

Pullman, WA

A: Warm weather combined with humidity and overhead watering help mildew to spread. All unwanted plants and weeds should be removed, especially if they have, or are likely to have, mildew. Your field peas are apparently a variety with mildew resistance. Try changing your garden pea variety to one that is mildew-resistant.

Good air circulation, elimination of weeds and keeping foliage dry will all help control mildew. If this does not work, use a fungicide. Start in August, or a few weeks before mildew usually appears. Make certain that any product used has been cleared for use on the crop to which applied, and faithfully follow the directions on the package. An alternative to the commercial fungicide would be a mixture of baking soda and water. In one gallon of water mix two tablespoons of household baking soda and apply to all sides of the foliage with a garden sprayer. Apply on a weekly basis throughout the season. Since the mixture is safe, there is no concern for toxicity or residue.

Q: My hollyhocks grow very nicely, then all the bottom leaves die. The leaves get a yellow or orange infection. Is there a spray I can use that will not harm visiting hummingbirds--the reason I plant the hollyhocks?

Malvern, PA

A: This is a good description of hollyhock rust, a disease that can complete its life cycle on one host plant. Sanitation is the first tactic. Remove leaves as soon as pustules appear on the under side. Destroy all foliage and stalks in the autumn. Search around for the ubiquitous weed called cheeses or roundleaf mallow (Malva rotundifolia), and for wild grasses such as Muhlenbergia (nimblewill), Sporobolus (dropseed) and Stipa (porcupine grass), as these, too, carry the same fungus. Chemical warfare comes next. Your garden shop can help you find a suitable product containing a fungicide of your choice. Mix as directed on the package and spray, especially the undersides of the leaves and the lowest leaves, which is where the infection invariably begins. You can safely spray the stems right to the buds until they are almost large enough to open; thereafter, spray only the base of the plants every five to seven days. A year or two of good sanitation and spraying should sufficiently reduce the innoculum so that spraying will seldom be necessary, just the removal of an infected leaf here and there, as soon as noticed. By all means, keep up on the sanitation.

Q: Please tell me what is causing my laurel bushes to brown and die; I have been losing them over the past three years.

Main Line, PA

A: It all depends on what plant you call "laurel"! Mountain laurel is Kalmia latifolia, cherry laurel usually refers to Prunus laurocerasus, and laurel, to a gardener, commonly refers to Laurus nobilis, which is hardy only from USDA Zone 7 southward. Cooks call the latter Portugal laurel or bayleaf. Mountain laurel requires well-drained, acid soil, which never dries completely, the sort of soil in which rhododendrons, and azaleas thrive. Given the wrong fertilizer (non-acidic), a neutral or alkaline soil or droughty conditions, branches yellow and die until the plant is killed. Cherry laurel is not quite so demanding though it, too, fails under droughty conditions. Dieback of the cultivars with large, leathery green leaves usually suggests drought or injury from too much lime.