Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Strawberry growers should finish orders for September plasticulture strawberry plantings soon. It takes plug growers four weeks minimum to grow plants from tips. Below are recommended varieties for our region. See the Strawberry section of the Mid-Atlantic Vegetable Production Recommendations for additional information.
Short Day Early
AC Wendy, Galletta, Ruby June (trial), Sweet Charlie
Short Day Midseason
Benicia (coastal VA, shipping only), Camarosa (shipping only), Camino Real (VA and DE), Chandler, Flavorfest, Rutgers Scarlet (trial)
Short Day Late
AC Valley Sunset
Day-Neutral
Albion, San Andreas, Seascape, Sweet Ann (VA, high tunnel)
Each variety has susceptibilities and resistance to different diseases, and none are completely resistant to any disease. Be aware that AC Wendy and Flavorfest are especially susceptible to angular leaf spot, a bacterial disease. Galletta and Flavorfest are fairly resistant to Anthracnose Fruit Rot, while Camarosa, Chandler, and Ruby June are especially susceptible. Sweet Charlie and Flavorfest are very susceptible to Phytophthora diseases. Day-neutral varieties are susceptible to Anthracnose Fruit Rot and Powdery Mildew.
Early to Mid-September is the optimum period for planting strawberries in the plasticulture system on Delmarva. Most strawberry varieties should be planted by the third week in September for best spring yields.
Strawberry establishment in the plastic bed takes 3-4 weeks. During establishment, the goal is to have plants root as quickly as possible in the soil and start to send out new growth. This requires attention at planting. Most Delmarva growers are using plugs. Plant so that the plug is at the level of the soil or is just covered with a small amount (1/8”) of soil but avoid getting soil into the crown of the plant. Deep planting will result in reduced stands and weak plants due to rotting in the crown area. Shallow planting (where part of the plug is out of the ground) will result in plugs desiccating and reduced stands. Soil should be firm around the plug and water provided at planting. It is advantageous to overhead irrigate several times, even if you are also drip irrigating, to reduce plant shock. Also, in sandy soils it is hard to wet beds completely with the drip system and plants can easily become drought stressed.
Rooting also requires adequate bed soil temperature. Raise high beds, the higher the better to allow for good drainage. Lay plastic making sure there is a firm crowned bed. The goal is to have the plastic tight against the soil to allow for good heat transfer. Loose plastic will have poor heat transfer and can reduce fall growth. Beds with depressions that allow water to accumulate can lead to disease problems in strawberries.
The goal coming out of the establishment period is to have 3 or more fully green leaves on the plant. After establishment, plants will send out new growth and develop branch crowns during October and November. The goal by late fall is to have 2-3 branch crowns form from the mother plant. Crown growth occurs when temperatures are above 50°F. Flower buds are also initiated during this time. Often, growers receive plugs or plants later than September 20. For later plantings, low tunnels offer an opportunity to maintain temperatures above 50°F for a longer period achieving this goal. Early row covers may also be used to achieve this goal – research has shown that early row covers may not increase crown number but can increase flower bud initiation in the fall. While planting too late can reduce spring yields, planting too early risks too many crowns being developed, especially in Chandler, leading to smaller, unmarketable berries. That is why we don’t plant in late August on Delmarva
Plant size in the fall is also critical for high yields the following spring. Plants should be about 8 inches in diameter going into winter. Sugars produced in leaves are translocated into the crowns of the plant where they are converted into starch for winter storage. This starch is then used in the spring at greenup. Inadequate starch storage will also lead to lower yields in the spring. Plants should also go into winter with enough leaves to help insulate the crown.