Watering frequency varies with sun and wind exposure, temperature, soil type and individual plant water needs. Drooping leaves or stems and blossom drop often are signs that irrigation needs to be increased. New plantings in full sun often need water every two days the first few weeks or so after planting, depending on weather conditions. Progress to longer intervals between watering (four to six days) to encourage roots to expand into surrounding soil. Mulched plants will not dry out as quickly. Adjust watering frequency accordingly.
The water needs of a perennial garden are different from turf so water them separately. However, automatic irrigation systems can still be utilized in perennial gardens. See 7.239, Operating and Maintaining a Home Irrigation System, for more information.
Maintenance during the growing season consists of periodic weeding, removal of spent blossoms (deadheading), staking if necessary and pest control. Depending on species, early spring or fall maintenance consists of trimming and removing old leaves and stems. Ornamental grasses are generally trimmed in early spring. After three to five growing seasons, some perennials may need to be divided to prevent overcrowding. Overcrowded perennials often bloom poorly or not at all.
Division of perennials may be necessary when the side shoots or runners become crowded by other plants. Aggressive varieties such as shasta daisy, Oriental poppy and aster often need division every three years. Others can go longer before division is necessary.
Spring and early-summer blooming perennials, such as peonies and poppies, are usually divided in the fall or when foliage dies (mid-September through mid-October). Plants that flower in mid- to late summer and fall, such as chrysanthemums and asters, should be divided in the spring before growth begins. Iris and daylilies usually are divided immediately after flowering.
Use a spade, shovel or fork to dig around and under the entire plant and lift it out of the soil. Remove most of the soil from the roots by hand or by washing with a hose. Use pruning shears or a sharp knife to cut apart the healthiest part of the plant, often on the outside. Most clumps can be divided into four or five smaller clumps, after dead and discolored parts are removed. Replant divisions as soon as possible after improving the soil. Protect with mulch (2- to 3-inch depth) in late summer and fall. Water as necessary.
Mulching is one way to reduce weed growth and conserve water. For more information on the attributes of organic and inorganic mulches, see fact sheet 7.214, Mulches for Home Grounds.
Watering during the winter is very important, depending on weather conditions. Colorado winters characteristically have dry air and low soil moisture. These conditions, along with little or no snow cover from October through February, can damage plants, especially new plantings. Water only when temperatures are above freezing, during the early part of the day. Some perennials prefer well drained dryer soil in winter to survive. See fact sheet 7.211, Fall and Winter Watering for more information.
To print the complete fact sheet on Perennial Gardening as written by D. Waltman, J.E. Klett and R.A. Cox (12/09) click on the link http://www.ext.colostate.edu/pubs/garden/07402.pdf