Ornamental grasses offer the garden structure with their beautiful forms. They also provide a neutral backdrop for more colorful plantings and are beautiful in their own right. Some of the easiest garden plants to grow, all they need is a few basic cultural requirements to thrive. Ornamental grasses are a diverse group, so give careful consideration to site and soil conditions for each variety.
Most ornamental grasses are well-suited to growing in temperate climates and can be grown in USDA Zones 3 to 9. Special attention should be paid to growing grasses in colder (Zones 4 and cooler) and hotter (Zones 9 and warmer) climates. Blue grama grass (Bouteloua gracilis) and blue Arizona grass (Festuca arizonica), for example, are well-suited for growing in Zone 3. Autumn moor grass (Sesleria autumnalis) and pampas (Cortaderia spp.) do well in Zone 9.
Most ornamental grasses thrive in well-drained soil. Loamy (mixed) soils with a little humus are ideal. Lighten heavy soils with sand, compost and finely shredded bark. Generally doing well in average or lean soil, there is usually no need to supply nutritional supplement for ornamental grasses at planting beyond compost. A light application of mulch shades roots and conserves water during dry spells.
Some ornamental grasses, bucking the trend, do well in moist conditions. These grasses thrive in low-lying areas, drainage ditches and along ponds and streams. For success with these grasses, amend dry and well-drained sites with compost to improve water retention and irrigate. Plant prairie cord grass (Spartina pectinata), Japanese blood grass (Imperata cylindrical), bronzeschleier tufted hair grass (Deschampaia caespitosa Bronzeschleier) and sweet flag (Acorus calamus) in moist locations.
Most ornamental grasses prefer sites with full or part sun--four hours or more. A few exceptions are Indian rice grass (Achnatherum hymenoides), Andropogon gerardii and carex (Carex spp.), which prefer or tolerate shady conditions. Grow shady ornamental grasses in locations receiving an hour or two of sun in the morning and evening. They can also be grown in containers on covered porches or on shady patios.
Plant grasses so they can grow to their ultimate size without crowding each other. Plants should barely touch each other when fully grown. Proper spacing ensures that the blades and crowns don't rot from damp and keeps insect and fungal problems in check. Ornamental grasses grown as ground covers can be planted more closely together so they achieve full coverage. Plant them one-third closer to each other than grasses planted as specimens.
Sometimes conditions become so perfect that some grasses become invasive. Carefully consider the selection of these plants. Plant them in isolated locations--in closed patio beds or in containers--to keep them in check. Among those grasses often listed as invasive are maidenhair grass (Miscanthus sinensis), common reed grass (Phragmites australis), giant reed grass (Arundo donax) and pampas grass (Cortaderia selloana and C. jubata). Dwarf varieties of pampas are not listed as invasive. Check local agricultural extension offices for invasive plant lists.