It's Been Nice, But...

The unseasonably warm weather the past few days has drawn many home gardeners outdoors. While late March is an excellent time to clean up the yard and garden, prune trees, and purchase seeds and other supplies, it is too early to remove the mulch from strawberries and apply a preemergence herbicide for crabgrass control.

Application of Preemergence Herbicides

A key to successful control of crabgrass in lawns is the correct timing of the preemergence herbicide application. Crabgrass begins to germinate when soil temperatures reach 60 F and continues to germinate over several weeks from spring into summer. If the material is applied too early, crabgrass seeds that germinate late in the season will not be controlled. Normally, preemergence herbicides should be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa, and late April to early May in northern areas of the state. If the warm spring weather continues, gardeners should apply the preemergence herbicide early in the normal time period for their area. If cold weather returns and stays for a few weeks, apply the herbicide late in the recommended time period. Gardeners still uncertain as to when to apply the preemergence herbicide can look to nature for helpful signs. Preemergence herbicides should be applied when the forsythia blossoms start dropping or when redbud trees reach full bloom. Crabgrass germination begins after these events.

Mulch Removal from Strawberries

To reduce the chances of frost or freeze damage, gardeners should leave the winter mulch on strawberries for a few more weeks. Removal of the mulch in March or early April may encourage the plants to bloom before the danger of frost is 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 in late March and early April will delay or slow strawberry growth and reduce the risk of frost or freeze damage.

To determine when to remove the mulch, periodically examine the strawberry plants in the spring. Remove the mulch from the strawberry planting when about 25% 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.) Rake the mulch to the center 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 plants.

The warm weather the last few days in Iowa have been very enjoyable. The warm weather, however, should not tempt gardeners to apply a preemergence herbicide to their lawn or remove the winter mulch on strawberries in March.

This article originally appeared in the March 24, 1995 issue, p. 30.

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