Q I have an ornamental grass about four feet tall that I planted last year. Should it be cut back for winter and if so, how?
A Grasses are attractive in the winter landscape, and you should enjoy them for as long as you can. As long as they are not beaten down and unattractive, leave them until February or March.
Mark your calendar, though, because it is important that you cut them before mid-March. If you wait too late, you will end up trimming this year's emerging leaves along with last year's blades. The result would be a flat top haircut that grows ever higher through the spring.
One safety tip -- don't use pruners to cut back your grasses. A small pruning saw works much better, you'll finish the task sooner, and you won't risk slicing your fingers.
I bought some expensive rose plants last year. They looked healthy and had nice, big roses, but after I planted them new leaves grew that were curly, small and had some white patches on the leaves.
The blooms looked wilted. I watered the plants every day and fertilized every week. I also sprayed a pesticide and they looked a little better but not how they looked in the nursery. How do I salvage these plants?
The leaf and flower ailments are related to a fungal disease named powdery mildew, which can become a serious problem under certain conditions.
Generally, the disease takes hold in roses that are planted in areas of poor air circulation and when the weather is rather cool with high humidity.
Powdery mildew is unusual among fungal diseases. It grows like a tiny crop on the leaf, sending pegs like roots down through the leaf's epidermis to lodge in the leaf cells, where it takes its sustenance. This robs the plant of moisture and makes it more prone to drought stress. The differing levels of water loss results in the curling and distortion that you describe.
Your roses need to be in an area that receives at least six hours of direct sunlight and a site that is breezy. You can still move your roses to another site, if necessary. Don't crowd them with other plants.
Several fungicides of low toxicity are effective against mildew. Horticultural oil, applied in a 1 percent solution, smothers the fungal strands on the outside of the leaves. Products containing neem and its active ingredient, azadirachtin, are also effective. Treat the foliage as soon as the first symptoms are noted in spring and continue until consistently hot weather arrives. If symptoms reappear, don't delay treating the plants.
You must stop watering and feeding your plants so much. Roses do not need to be watered daily unless they are growing in containers in high summer. Water once weekly and thoroughly during dry spells. Use a soaker hose or drip irrigation to keep the foliage dry.
My experience with fertilization is that roses do much better if they have an ample supply of slowly released nutrients, and there is no better way to provide this than incorporating well rotted compost into the planting bed every spring before growth begins. Plants grown with compost tend to have firm stems and seem to be able to bloom through the heat of summer a bit better.
Scott Aker is a horticulturist at the U.S. National Arboretum.
