What Is an Herbaceous Perennial?
A perennial plant will live for more than two growing seasons; a true herbaceous perennial will completely die back in the winter, while its roots remain persistent, with clumps of stems or buds at or below ground level. Every spring they send out new shoots from the ground. Some perennials can be short-lived and may last only three years, while others may last for decades.
The care and maintenance of your perennial garden need not be complicated or daunting. Much of good gardening is a combination of some basic horticultural principles with common sense and a good eye. The following is a list of some of these basic principles.
Site
Carefully study the existing site. Know the site conditions--light, temperature, soil, slope, drainage, and air circulation.
Soil
This is the single most important factor in growing healthy plants. Most perennials grow best in soil that is well drained with good fertility and a pH of 6.0 to 7.0. Adding organic matter to soil improves the fertility, texture, and water-holding capacity. Apply a two to three inch layer of mulch to conserve water, reduce the need to weed, and keep soil temperature cool. Applying a winter mulch of evergreen boughs when the ground is frozen prevents plants from being pushed out of the ground by alternate freezing and thawing. Winter mulch is used only on newly-planted or divided perennials and tender plants. This mulch most be removed gradually in the spring.
Plants
Knowing the needs of each plant in the garden is essential. Does it need sun or shade? Should the soil be dry or moist? Know the size of the plant when it reaches maturity so the plant can be properly placed. A garden that is too densely planted is difficult to maintain. Plants whose mature height is 3' or above should be planted 2' to 3' feet apart, and plants 2' to 3' tall should be spaced 1.5' to 2' apart. Below 2' tall, spacing should be 1'.
Most perennials benefit from lifting and dividing every three to four years. However, some perennials resent being disturbed and are better off being propagated by cuttings or seed. When dividing plants, rejuvenating the soil by incorporating organic matter such as leaf mold or compost is important.
Watering
Soak the plants immediately after planting and check regularly to prevent drying out. The rule of thumb is to add one inch of water per week for established plants. Less frequent but deep watering encourages perennials to root deeply. Perennials that are said to tolerate drought are drought tolerant only after they have become established. The addition of mulch will help to reduce the need for frequent watering.
Fertilization
Most perennials do not need much fertilizer. Many overfertilized perennials will produce excessive soft growth and produce very few flowers. A soil test will help to determine the amount of fertilizer needed. Fertilizers with a formulation of 10-10-10 or 5-10-5 are sufficient, unless a soil test indicates otherwise.
Staking
Some plants need staking to prevent flopping over in the garden. Plants with heavy flower heads or long thin stems tend to blow over or are beaten down by heavy rains. Staking should be done early in the spring to allow the plants to grow through and around the stakes, usually hiding the stake by midseason.
Seasonal Care of Perennial Beds
March
- Cut back tall grasses
- Prune roses
- Test soil
April
- Gradually remove winter protection
- Weed, mulch, and edge
- Thin and divide plants
- Plant bare root plants
- Prepare stakes and cages
May
- Weed
- Finish mulching not completed in April
- Water newly-planted plants
- Fertilize as per soil test when establishing new beds or planting new plants
- Pinch plants back
- Stake
- Thin plants
June
- Weed and water as necessary
- Scout for pests
- Pinch and deadhead
- Cut back
- Stake
July
- Weed and water as necessar
- Fertilize heavy feeders such as ever-blooming daylilies and mums
- Deadhead (stop pinching mums in mid-July)
August
- Weed and water as necessary
- Deadhead
September
- Edge beds
- Water as necessary
- Move and divide plants
- Cutback
October/November
- Weed and water as necessary
- Mulch
- Winterize the garden after the ground is frozen (late November or December depending on your area)
Prepared by Shirley Wagner, Master Gardener Coordinator, Penn State Extension, Lancaster County and Connie Schmotzer, Consumer Horticulture, Penn State Extension, York County
