Once established, ornamental grasses tend to be relatively carefree. In general, they require little in the way of fertilizer and water inputs. However, as is true of all plants, some tender loving care is needed to keep them healthy and attractive.
If not done before planting, it is beneficial to mulch around ornamental grasses. This will keep the soil cool, retain moisture, and help with weed control.
Ornamental grasses, in general, should be irrigated less often and to a greater depth than other parts of the landscape. Some fescues and other drought tolerant grasses may need much less water overall. During July and August, a weekly irrigation with about 2 in. of water should be adequate in most soils. In sandy soils, less water should be applied on a more frequent basis. The amount of water applied should be cut back during the cooler spring months, the late fall, and during those infrequent periods of rain.
Most ornamental grasses need very little in the way of fertilizer. They may benefit from a spring application of a fertilizer high in nitrogen at the equivalent of 1-3 lbs nitrogen per 1,000 sq. ft. On the other hand, some years, no fertilizer of any kind may be needed. Determination of requirement is based on growth response. If the previous year, plants were slow growing, small, with yellow color, add some fertilizer.
The only consistent need for ornamental grasses is removal of dead leaves and flower spikes at the end of the season. For many species, those that break, shatter, or fall over in the winter, this should be done in late fall. For grasses that remain attractive through the winter, this can be done in early spring. Cut grasses back to a height of 4-5 inches before new growth appears.
There are no options to completely replace hand weeding in ornamental grasses. Mulching with organic matter or weed barriers will help by blocking germination and growth of weed seed. Perennial weeds that creep into beds create the most difficult problems. If hand cultivation provides inadequate control, it may be necessary to hand apply a herbicide, such as a glyphosate product, by hand with a sponge or other wicking material.
Most adapted ornamental grasses can withstand winters without winter protection. However, a layer of mulch over the crown may allow the plants to be more vigorous in the spring. Proper winter mulching consists of application of 3-4 inches of compost, leaves, wood chips, or other organic matter. The mulch should be removed from around the crowns in early spring to help prevent premature growth of shoots that may be damaged by frost.
For more information on the general care of ornamental grasses, see the following two web sites:
Disease and Insect Control
Ornamental grasses have very few consistent pest problems. However, there are a few organisms that can infest grasses and make them less attractive. Some of these are listed below. For detailed information on control of these insects and diseases, as well as information on other pests, see the Insect and Disease Pests section of this site.
Mealybugs: Are sucking insects, one species of which can become a problem on the Miscanthus grasses. Mealybugs are easily recognized by the presence of a cotton-like white substance they deposit for protection. In cases of serious infestation, the plants will be stunted and go dormant earlier than healthy plants.
Control of mealybugs can be had by spraying the plants with a direct stream of water, using and insecticidal soap, or using a registered insecticide.
Slugs and Snails: Prefer damp soil and humid conditions. Slugs and snails often hide during the day and feed at night. Symptoms include chewed leafs and glistening slime trails on plant surfaces. Although slugs and snails will not do significant damage to most ornamental grasses, the thick foliage may provide a haven from which they will emerge and damage surrounding plants.
Control snails and slugs with baits.
Leaf Rusts: Are caused by several related fungal pathogens that penetrate and kill leaf tissue. Symptoms are usually typified by a yellow, orange, or brownish discoloration of the upper leaf surface on older leaves. The leaves eventually decline and die. These diseases are usually worse following a wet spring.
Removal of all dead plant material at the end of the growing season helps prevent many leaf spot diseases in subsequent years. In-season control usually requires use of a registered fungicide. Maintaining overall plant health is important in controlling fungal leaf diseases. Ensuring proper aeration among plants will reduce humidity and slow the progress of rusts.