Strawberry plants reproduce vigorously by sending out horizontal stems called runners (stolons), which root to form new daughter plants. This natural strategy quickly leads to an overcrowded patch, especially in the common matted row system. Thinning is the annual process of removing older, less productive plants and excess new growth to manage the density of the strawberry bed. This maintenance ensures that the remaining, healthier plants have the resources needed to produce a larger, higher-quality fruit harvest the following season.
Why Thinning is Crucial for Strawberry Health
Allowing a strawberry patch to become too dense creates a microclimate that hinders fruit production and plant health. Overcrowding increases competition among plants for resources like sunlight, water, and soil nutrients. This competition results in plants allocating less energy to developing fruit buds, reducing the size and quantity of berries produced.
A dense canopy of leaves also traps moisture and restricts air movement around the crowns and soil surface. Poor air circulation is a primary factor in the proliferation of fungal diseases, such as gray mold (Botrytis cinerea), which thrives in damp conditions. Older strawberry crowns (three or more years old) naturally become woody and less vigorous, consuming valuable nutrients while contributing little to the harvest. Removing these plants redirects energy and nutrition toward the younger, most productive crowns.
Identifying the Right Time and Conditions for Thinning
The ideal time for the major annual thinning, often called renovation, is immediately after the main harvest is complete, typically in mid-to-late summer. For June-bearing varieties, this window generally falls between late July and early August. Completing this work promptly allows the remaining plants ample time to recover, produce new leaves, and set flower buds for the next year’s harvest before fall dormancy.
Visual cues indicate a bed is ready for renovation, such as a densely matted row where individual plants are indistinguishable or the center of the row is heavily congested. An overcrowded bed is also characterized by a significant drop in fruit size after the harvest. While everbearing and day-neutral varieties require continuous runner removal throughout the season, the matted row system of June-bearers demands aggressive post-harvest thinning.
Step-by-Step Guide to Thinning Strawberry Beds
The renovation process begins by preparing the bed.
Preparing the Bed
First, cut the old foliage back to a height of one to two inches above the crowns, using a lawnmower set high or hedge shears. Removing old leaves stimulates new, healthy growth and eliminates lingering disease spores and pest eggs. After cutting the foliage, thoroughly remove any established weeds, as they compete directly for moisture and nutrients.
Managing Row Width
Next, manage the width of the row, especially in matted row systems that spread excessively. Use a hoe or cultivator to narrow the dense rows down to a manageable width of approximately 12 to 18 inches. This step clears the aisles and improves air circulation and sunlight penetration to the crowns.
Thinning Plant Density
The most important step is thinning the plant density within the remaining row width by removing older, woody, and less vigorous crowns. Older crowns are identified by their darker color and hardened appearance compared to the lighter crowns of younger plants. Use a small hand trowel to remove these unproductive plants, retaining the healthiest, most robust crowns.
The goal is to achieve a final spacing of approximately four to eight inches between the remaining strong plants. Clip off any runners that have begun to form to ensure the plant’s energy is directed toward flower bud initiation in the late summer and fall.
Essential Post-Thinning Maintenance
Once thinning is complete, the remaining plants require immediate care to recover from renovation and prepare for the next season.
Watering and Fertilizing
The bed must be watered deeply, ensuring moisture soaks down eight to twelve inches to support the root systems and aid crown recovery. This deep saturation helps the plants quickly establish new root growth for nutrient uptake. Immediately following watering, apply a balanced fertilizer to replenish depleted nutrients and fuel new leaf growth. A complete fertilizer (e.g., 10-10-10 or 12-12-12) should be applied at a rate of one to two pounds per 100 square feet.
Applying Mulch
Finally, spread a fresh layer of organic mulch, such as clean straw or compost, over the newly thinned bed. This mulch helps conserve soil moisture, regulate soil temperature, and effectively suppress new weed growth in the open spaces between the plants.