Strawberries are one of the most popular fruit crops produced in Missouri. The typical field production season for this high-value crop is mid- to late May through June for matted row (open field) berries. High tunnels may give growers the opportunity to produce early-season or late season strawberries in Missouri. High tunnels are unheated, plastic-covered, solar greenhouses. Ventilation is passive through roll-up side walls or curtains and roof vents. Crops are grown in native, mineral soil under the high tunnel. The high tunnel protects the growing crop from environmental extremes such as wind, hail, rainfall, insects and diseases which allows for significantly earlier and higher marketable yields. Since high tunnels have low startup and operating costs, a single crop often provides enough revenue to pay for the cost of the structure.
In 2006, I initiated a high tunnel strawberry evaluation using ‘Chandler’ variety. ‘Chandler’ is a productive, plasticulture strawberry variety which performs well even as a field variety in southern Missouri (Zone 5B and 6). ‘Chandler’ is relatively susceptible to anthracnose, a fungal disease often triggered by rainfall.
Using plug plants obtained from Jersey Asparagus Farms, Inc. (see appendix), the strawberries were planted in mid-September 2005 in each of four high tunnels (20 ft wide x 12 ft high x 36 ft long) in Columbia, MO. Each high tunnel had a single layer of 6-mil plastic. Rooted, plug plants are more expensive than using dormant runner tips, but good quality plants with strong root systems are quick to get established. Dormant runner tips can be purchased from many northern nurseries and rooted in 50-cell trays. Tips should be rooted in late August since it will take approximately 4 weeks to develop a root system. To accelerate root growth, the runners stubs can be dipped in a rooting powder (e.g., Rootone®) (Figure 2). Try to root runner tips as soon as they arrive.
Each runner tip can be rooted using standard potting mix and 50-cell planting trays. If there is variability in size of the runner tips, the larger tips can be rooted in a 38-cell tray. After planting in trays, the plantlets can be placed in a greenhouse under a mist bed. Some growers have had success rooting strawberry runner tips by placing the trays on a wagon in indirect sun and watering twice daily.
A. Fertilizer and Soil Fertility
A soil analysis should be performed prior to planting strawberries with in a high tunnel. The optimal pH range for strawberries is 5.8-6.5. Preplant, granular fertilizer (10N-10P-10K) can be broadcast over each raised bed prior to laying plastic mulch. Approximately 30-40 lbs (per acre equivalent) of nitrogen is sufficient for strawberries which is 0.7-0.9 lbs of actual nitrogen/1000
ft 2 of bed area. Generally speaking, a granular fertilizer (such as 13-13-13) broadcast over the beds before planting is best, but if you choose to not apply fertilizer this way, you can apply a soluble fertilizer (such as 20N-20P-20K) through the drip irrigation system. It’s very important not to apply too much preplant nitrogen to strawberries (especially ‘Chandler’). Also, if a lot of manure or compost has been applied to the soil within the high tunnel, no preplant nitrogen will be needed. Excessive nitrogen will result in an abundance of branch crowns. When a strawberry plant has too many branch crowns, the average fruit size is significantly reduced.
When the strawberries emerge from dormancy the following spring and resume growth, additional nitrogen (approximately 5 lbs/acre/week equivalent of actual nitrogen or 1.8 ounces of actual nitrogen/1000 ft 2/week) can be applied via the drip system. At first flowering, a tissue test should be performed by taking a few leaf samples from each high tunnel, drying them, and sending them to a diagnostic lab for analysis. Always choose a recently mature leaf from a single variety. Generally 20 leaves per high tunnel per variety will be sufficient. Consult your local extension agent for details about sufficiency ranges for tissue tests. Strawberries are especially sensitive to salt in the soil. Have the soil tested for soluble salts. Soil salinity can be a problem if a lot of high salt fertilizers or animal manures are used over time. Normally rainfall would leach these salts out of the root zone, but since the high tunnel excludes rainfall, salts will accumulate. Salts within the soil make it harder for the plants to extract water from the soil (Upson, 2006)
In the high tunnel, strawberries can be rotated with such crops as tomatoes or peppers. It is true that both tomatoes and strawberries can share certain soilborne diseases (Verticilllium wilt). However, as long as you don’t have a disease outbreak, rotation is flex ible within the high tunnel.
B. Spacing and Planting
Each plant was planted 12 inches apart within the row with rows spaced 12-15 inches apart. Each row was offset from the other so as to produce a staggered planting arrangement (Figure 3). All planting within the high tunnel was done by hand. After planting, apply a starter solution (for example, 9N-45P-15K fertilizer) to encourage root growth. One of the keys to success with high tunnel strawberries is obtaining an optim al plant population. A four-row bed with each plant spaced 12-15 inches apart is an optional planting arrangement for high tunnels (Figure 2). In a commercial high tunnel (2500-3000 ft2), approximately 1200-2000 strawberry plants can be planted using the twin to four row planting arrangement.
C. Drip Irrigation
When there are 2 or more rows per bed within a high tunnel, 2-3 drip lines are essential for uniform watering. This is particularly true with coarse or sandy soils. Each drip line can be placed between each row on the bed. Choose drip lines with a 4-6 inchdripper spacing, and bury the drip line about 1-2 inches in the bed with thedrippers (emitters) facing upward. Burying the 3 drip tape protects it from rodents and prevents movement of the drip line in hot or cold temperatures. If Queen Gil® drip tape is used,it must be buried to properly distribute water. In early fall after transplanting, irrigate approximately 3-4 hours per week. When the weather gets cool, and the plants are transpiring less, irrigation frequency can be scaled back. No irrigation will be necessary during the winter months when the strawberries are dormant. Irrigation can be scheduled using either anirrometer (tensiometer) or the “feel” method. If anirrometer is used, the reading should be in the 20-30 cb range at the 12” depth. For details onusing the “feel’ method, consult the Midwest Vegetable Production Guide (Table 8). It is essential not to over water strawberries since they
do not thrive in waterlogged soils.
Do not plant the strawberries too deep. I usually plant about midway up the crown, making sure not to bury the crown (Figure 4). Strawberries should be planted within a high tunnel from mid-September until mid-October in Central Missouri. Planting too late will result in less branch crowns per plant, poor winter hardiness, and the plant may produce an abundance of runners the following spring.
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Strawberries in High Tunnels in Missouri