Extension News

Pruning Lilacs and Removing Mulch from Strawberries

Note to media editors: This is the ISU Extension Garden Column for the week beginning Friday, March 13.

3/9/2009

By James Romer
Extension horticulturist
Iowa State University

With warmer temperatures, it’s time to begin outdoor garden chores. March is an excellent time to prune large, old lilacs.

Pruning Lilacs

The common lilac (Syringa vulgaris) is a large shrub that may reach heights of 15 to 20 feet. As lilacs mature, the shaded lower portions of the shrubs usually lose their leaves, resulting in leggy, poorly shaped specimens. Large and old lilacs can be renewed or rejuvenated by two different pruning methods.

One way to renew a large, overgrown lilac is to cut the entire plant back to within six to eight inches of the ground in late winter (March or early April). This severe pruning will induce a large number of shoots to develop during the growing season. In late winter of the following year, select and retain several strong, healthy shoots to form the shrub framework and remove all the others at ground level. Head (cut) back the retained shoots to just above a bud to encourage branching.

A second way to prune old lilacs is to cut back the overgrown shrubs over a three-year period. Begin the procedure by removing one-third of the large, old stems at ground level in late winter. The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new growth. Retain several well-spaced, vigorous stems and remove all the others. Finally, remove all of the remaining old wood in late winter of the third year. Additional thinning of the new shoots also should be done. Since lilac wood needs to be three or more years of age before it blooms, this pruning method should allow you to enjoy flowers every spring.

When properly pruned, a large, old lilac can be transformed into a vigorous attractive shrub within a few years. Once rejuvenated, pruning should be a regular part of the lilac maintenance program. The shrub can be kept healthy and vigorous by removing a few of the oldest branches every two or three years.

Removing Mulch from Strawberries

While March is an excellent time to prune many deciduous shrubs, some garden chores should wait until later in spring. To reduce the chance of frost or freeze damage, home gardeners should leave winter mulch on strawberries for as long as possible. Removal of the mulch in March or early April may encourage the plants to bloom before the danger of frost has past. Temperatures of 32 F or lower may severely damage or destroy open flowers. Since the first flowers produce the largest berries, a late spring frost or freeze can drastically reduce yields. Leaving the mulch on through March and early April will delay or slow growth and reduce the risk of frost or freeze damage.

To determine when to remove the mulch, periodically examine the strawberry plants in early April. Remove the mulch from the strawberry planting when about 25 percent of the plants are producing new growth. New growth will be white or yellow in color. (If possible, the winter mulch on strawberries should remain until mid-April in central Iowa.)

When removing the mulch, rake the straw to the aisles between rows. If there is a threat of a frost later in the season during bloom, the mulch can be lightly raked back over the strawberry plants.

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Contacts :

James Romer, Horticulture, (515) 294-2336, jromer@iastate.edu 

Del Marks, Extension Communications and External Relations, (515) 294-9807, delmarks@iastate.edu