Yard and Garden: Strawberries

AMES, Iowa — Fresh strawberries, a favorite of almost everyone, are relatively easy to grow and hardy throughout Iowa. Strawberry plants require full sun, well-drained soils and good management to produce abundant, sweet fruit. Horticulturists with Iowa State Univesity Extension and Outreach provide care and management information for the home gardener. To have additional questions answered, contact Hortline at hortline@iastate.edu or 515-294-3108.

When should strawberries be harvested?

Harvest strawberries when the fruit are uniformly red (fully ripe). Pick the berries with the caps and stems attached to retain firmness and quality. Pinch off the stem about one-fourth inch above the cap.  

Strawberries should be picked about every other day in warm weather, every three to four days in cool weather. The harvest period for some June-bearing cultivars may last three to four weeks. Strawberries can be stored in the refrigerator for up to five to seven days. Optimum storage conditions are a temperature of 32 degrees Fahrenheit and a relative humidity of 90 to 95 percent.

Some of the strawberries in my garden are covered with a gray, velvety growth. What is it and how can it be controlled?

The gray, velvety growth on the berries is probably gray mold. It is also known as Botrytis fruit rot. Gray mold is favored by poor air circulation and a high humidity in the strawberry planting. The most commonly infected berries are those touching the soil or other infected berries.  

Cultural practices can reduce losses due to gray mold.

  • Do not fertilize June-bearing strawberries in spring. The application of a nitrogen-containing fertilizer in spring promotes lush, vegetative growth. Dense foliage slows the drying of the strawberry planting, resulting in a more favorable environment for gray mold.
  • Control weeds in the strawberry bed. Weeds reduce air circulation and slow the drying of the strawberry plants.  
  • Mulch the planting with straw to keep the berries off the ground. Berries resting on a damp or wet soil are more susceptible to gray mold.  
  • During dry weather, irrigate in the morning when using a sprinkler. Plants dry quickly when irrigated in the morning.  
  • “Clean-pick” the strawberry planting. Harvest frequently. Pick berries as soon as they are ripe.
  • Handle berries carefully during harvest to avoid bruising the fruit. Immediately refrigerate the unwashed berries. Berries that exhibit symptoms of gray mold should be picked and removed from the bed.  

Fungicides are used by commercial strawberry growers to control gray mold. However, cultural practices are the best way to control Botrytis fruit rot in home gardens. 

There are small, black, yellow-spotted beetles feeding on my strawberries. What should I do? 

The small, black beetles are likely sap beetles. They also are known as picnic beetles or picnic bugs. Sap beetles commonly feed on overripe or damaged fruits and vegetables in the garden.  

Sanitation is the best management strategy for sap beetles in home gardens. Keep the strawberry patch as clean as possible through timely picking and removal of damaged, diseased and overripe fruit.  

Insecticide sprays are available for sap beetles, but they are difficult to use because they are applied to a crop that is ready for harvest or while harvest is underway. If you do spray, use an insecticide with a short harvest-waiting interval and follow label directions carefully. 

Why do my strawberries have a slightly bitter taste? 

The flavor of most fruits and vegetables is influenced by weather conditions. In regards to strawberries, warm sunny weather produces the most flavorful fruit. When the weather is extremely hot, the berries may have a slightly bitter taste. Strawberry plants produce smaller quantities of sugars when the weather is cool and cloudy. As a result, berries are not as sweet when the weather is cool and rainy in May and June.  

Leather rot, caused by a fungal disease, can be a problem in wet weather. Infected fruit have a leathery texture and bitter taste.

How long can I expect my June-bearing strawberry planting to be productive? 

June-bearing strawberry plantings that are well-maintained and renovated annually should remain productive for four or five years. Poorly managed beds may be productive for only two or three years. It’s time to plant a new strawberry bed when berry size and numbers decline.