Perennials come back year after year if left undisturbed. Most do not bloom the first year but develop roots and foliage to support flowers the next year and after. The illustration below shows planting depths, while the following Perennial Charts offer tips on optimum spacing.Setting Perennials
Set irises and yuccas with roots barely covered with soil (#1). Plant peonies, lilies of the valley and hostas with buds 1-2 inches below the surface of the soil (#2). Set plants with a distinct crown with the crown even with the soil surface (#3). Plant those without a distinct crown, that look like a chunk of root, 1 inch deep. If you can't tell which end is up, lay the root on its side (#4). Some plants with distinct crowns should be planted with the crown 1 inch below the soil (#5).PERENNIAL CHARTS
Listed bloom times for each item give a general idea of when plants will flower. Some varieties bloom for several months, but most bloom for 2-3 weeks, so it's best to select a mix of plants that bloom at different times for continuous color.
Perennials require little care after planting. Mulching helps keep weeds down and retain moisture and should be used heavily to prevent frost damage in fall-planted perennials. Remove faded and dying flowers often to prolong the plant's flowering period. Most perennials need to be divided every 3-5 years to rejuvenate the plant as it spreads. Ground covers are a special breed of low-growing plant often used on banks and slopes where it's difficult to mow. Water regularly in summer and remove any large weeds between plants.
Crown Vetch - Plant crowns 2-3 feet apart, roots pointing straight down and tops above the soil. If tops are indistinguishable, plant crowns on side and cover with 1-2 inches of soil. Water well until established and mulch to reduce weeds. Plants don't make much progress until the second season, when they form a solid mat of ferny growth.
Iris - Plant in early fall or spring in a sunny, well-drained spot, working soil to a depth of 12 inches. Most irises prefer moist ground, with rhizomes set just below the soil surface. An exception is the bearded iris, which likes it dry; 1/3 to 1/2 of its rhizomes should be left above ground. Divide and replant from July to October when plants are dormant. Remove all but 4 inches of leaves and cut rhizomes to 4-6 inches in length, discarding the older portion. Water well after replanting.
Mum - Plant in full sun and almost any soil, adding lime if ground is acid. Water during dry spells and feed weekly after midsummer. To keep bushy, pinch tops off each strong shoot when plants are 7 inches tall. For larger blooms, remove all but 2 buds per plant. When end bud is bigger, remove the other one. Dig, divide and reset plants every 3 years.