New Mexico Master Gardeners
 

Perennials

by Ellen Reed, Lifetime Master Gardener

Perennial plants live more than two years and usually bloom and produce seed in the second year.  Most are herbaceous (i.e. not woody) and die to the ground once a year, usually in winter.  Some may rebloom if they are dead headed or cut back after blooming.  Dead heading may be done as you walk around the garden. Some, such as peonies will live and increase the clump size for many years.  Mark the place of ones which die to below the ground, such as balloon flower, to prevent digging them up accidentally when they are dormant. Cut back dead stalks after frost.  Remove fallen leaves that pile too thickly over crowns or they may rot.  Winter protection may be provided with cut evergreen branches to keep the soil cool and prevent it from drying out in the winter.  Water once or twice a month in winter on a warm day depending on rain or snow fall. 

Perennials may be considered good investments as they usually live many years, but they are not 'no work.'  Many need to be divided every 3-5 years. The more vigorous outside parts of clumps are replanted in soil renewed by compost and slow acting fertilizer.  Discard the woody centers.  Butterfly weed, bleeding heart, gas plant, balloon flower and others with deep taproots are better not divided.  Division of spring bloomers is usually done in the fall and summer and of fall bloomers in the spring.

Perennial plants vary from low ground covers to plants 6 or 8 feet tall and thrive in a variety of situations.  By experimenting with different sites, many plants can be accommodated.  Culture is easier when plants which prefer the same sun/shade and wet/dry conditions are grouped together.  They are often planted in beds along lot lines or used in free standing islands to be viewed from all sides.  Often it is more pleasing if the edges of these beds are slightly curving.  Their outlines may be established by laying out a garden hose until the desired shape is attained.  Usually taller plants are placed toward the back of beds or center of islands.  Occasionally, taller, lacy varieties may be used toward the front for contrast.  The siting (N, S, E, W) will influence what will thrive as will the background, i.e. against wall, under house eaves, on a berm or near tree roots.  The edge of shady areas may be used for plants which need half sun.  Filtered shade at noon may extend bloom time by preventing flowers from sun burning.  Early spring bloomers may get enough light to flower before deciduous trees leaf out.  Some bulbs whose foliage is above ground in winter may photosynthesize enough during that season to allow them to flower in relatively shady spots. Tree roots, especially of mulberry, Norway maple, elm, and Arizona cypress greedily use water and fertilizer.  The heavy shade and root competition from low growing junipers and blue spruce is a very challenging environment and few plants thrive there.

Perennials generally have only a 2 to 4 week period of bloom so it is important to consider their appearance after the flowers fade.  Many have attractive leaves or disappear completely when through blooming.  Some will rebloom if faded flowers are removed and the plants are lightly fertilized.  Choose plants with complementary or contrasting foliage which is attractive throughout the seasons.  Some seed stalks remain interesting and may be a source of food for birds in winter.

Because these plants are expected to perform for many years, the bed should be enriched with compost and slow acting phosphate fertilizer at planting time.  A nitrogenous fertilizer may be scratched in around the clumps as they emerge in spring. The bed may be foliar fed with a soluble fertilizer at biweekly intervals during the summer.  Mulching with compost or other organic material helps the soil to retain moisture and renews it’s organic content.  Eventually the plants may cover enough of the soil to furnish their own root shade.

Bulbs, annuals and shrubs may be mixed in perennial beds, but it is best to plant bulbs toward the back of beds so maturing foliage is disguised by new growth.  Since it may be necessary to divide crowded bulb clumps, it is easier to plant them in drifts between drifts of perennials so that digging one causes less disturbance to the other. Because most perennials are deeply rooted the soil surface may be allowed to dry between deep waterings.  Tall plants and ones in more shade may need staking.  Various wire and fencing methods are available.  These are best placed before the plant flops, this allows for new growth to hide the support.

  In planning a perennial garden consider what blooms together.  Observe neighbors gardens and keep records.  Think about what is important to the gardener, i.e. plant form, flower color or form, flowers for cutting, fragrance, views from windows, and the season the garden will be viewed.  If you are away all summer plant a spring, fall and winter garden.

Choose plants which are not invasive either by roots or seedlings and which will not need great efforts to control their height or spread.  A few are thugs and should be avoided. Spanish bluebells or Lady bells (adenophora), Bishop’s weed, snow on the mountain, Aegopodium, lily of the valley or perennial Vinca may all be invasive as are some campanula (blue Bells). Some self sow vigorously and must be dead headed after bloom. Euphorbias and columbine are notorious for sending seed far and wide.

Plants that do not live up to expectations should be removed.  Unsatisfactory plants take as much water and fertilizer as ones that please. Dealing with disease or insect problems takes more trouble than avoiding pest prone plants.  As you enjoy the garden, keep an eye out for pests so as to stop an infestation before it gets out of hand. Pull weeds when they are small and before they go to seed. Weeds such as purslane, spurge and annual blue grass that have gone to seed should not be put in the compost pile unless it is a very hot active pile.

Sources of perennial plants are seeds, mail order nurseries, local nurseries, plant sales and friends.  Always be alert for hitchhiking pests and weeds.