Strawberries benefit from strategic coverings that protect them from temperature extremes, moisture loss, and external threats like pests and disease. The type of covering depends on the season and the specific challenge being addressed. During cold months, the primary goal is to insulate the perennial heart of the plant to ensure survival and maximize future yield. When plants are actively growing, the focus shifts to managing the soil environment and excluding pests that damage developing fruit. Selecting the correct material and applying it at the right time is paramount to maintaining a healthy and productive patch.
Insulating Crowns for Winter Dormancy
Protecting the strawberry crown during winter is necessary for ensuring a strong harvest the following year. Crowns are the short stems where buds and leaves emerge, and they can be damaged if temperatures drop below approximately 15°F without covering. Covering also helps prevent soil heaving, where alternating freezing and thawing pushes shallow-rooted crowns out of the ground.
The proper time to apply insulation is after the plants have fully entered dormancy, typically after the first two or three hard frosts, and when the top inch of soil has frozen. Mulching too early can trap warmth, causing the plants to lose cold hardiness prematurely. Once the leaves have taken on a grayish, dormant appearance, apply a loose layer of insulating material.
Clean wheat straw is often the superior material for winter protection because its hollow structure traps air, providing effective insulation without packing down. Other materials like pine needles or specialized winter blankets can also be used. Avoid materials that mat when wet, such as tree leaves or sawdust, as these can smother the plants and promote rot. Apply the straw loosely to a depth of four to six inches over the rows, as this layer will compress significantly. Rake the covering back in early spring when new growth begins to emerge.
Ground Covers for Growing Season Management
Once the danger of hard frost has passed and insulation is removed, ground coverings focus on moisture retention, weed control, and keeping the fruit clean. The use of straw as a growing season mulch is historically common. Straw pulled from the winter covering can be placed between the plants, or a fresh two-inch layer can be applied.
Organic mulches like straw or wood shavings help moderate soil temperature and significantly reduce water lost to evaporation. By creating a physical barrier between the developing berries and the soil, they prevent contamination and reduce the chances of soil-borne diseases splashing onto the plant. For intensive cultivation, growers often opt for plastic sheeting, such as black or red plastic mulch, or specialized landscape fabric.
Plastic sheeting provides maximum weed suppression and is highly effective at warming the soil in the spring, accelerating plant growth and fruit development. Black plastic absorbs solar radiation, while red plastic reflects specific light wavelengths that can enhance yields. These impermeable barriers retain soil moisture but prevent rain from reaching the roots, requiring the use of drip irrigation underneath.
Above-Ground Barriers Against Pests and Sun
Coverings suspended above the plants address external threats to the foliage and ripening fruit. The most common external threat is damage from birds, which are highly attracted to the sweet, bright red berries. Bird netting, typically an inexpensive plastic mesh, is highly effective when draped over the patch. Support the netting using hoops or frames to keep the material off the tender fruit, preventing accidental damage and allowing access for harvesting.
For smaller pests, such as the tarnished plant bug or various small beetles, a finer material like a floating row cover is necessary. These covers are lightweight fabric sheets that exclude insects while allowing light and water to pass through. If the covers are applied during the flowering period, they must be temporarily removed to allow for insect pollination.
In regions that experience intense summer heat, especially when temperatures consistently exceed 85°F, shade cloth can be suspended over the patch to prevent sun scorch. Excessive heat can slow photosynthesis and reduce fruit size, making shade necessary for continued production. A shade density of 30% to 40% is preferred, as it reduces heat stress without limiting the light needed for proper fruit development. Installing shade cloth over a frame helps ensure adequate airflow and prevents the material from resting directly on the plants.