Strawberries are primarily grown in the matted row system in Indiana, in which bare-root strawberry plants are set in the spring, fruit is first harvested in the second year and plantings are renovated each year for a few seasons. Growers in Southern Indiana have expressed interest in growing strawberries in the annual plasticultural system. With this annual system, plants are set in the fall and harvested in the spring of the following year. Plantings are not normally carried over a second year. Although the annual plasticultural system is very popular in the southern states, its usage is limited in Indiana mainly because our short fall weather conditions pose a challenge for strawberry plants to develop enough branch crowns, which allows them to achieve the optimal yield in the following spring.
In the past two years, we have been testing the annual strawberry production system with additional protection from high tunnels and low tunnels at the Southwest Purdue Ag Center in Vincennes, IN. Although we are far from coming to a conclusion about the production system in Southern Indiana, I would like to share with you some of the facts we have learned in this journey.
Plant materials
The most commonly used strawberry plant materials are bare-root strawberry plants and strawberry plugs. Strawberry plugs are more expensive than bare-root plants. However, plugs survive better, grow faster, and establish earlier. They are suitable for mechanical transplanting with a water-wheel. This is particularly beneficial for large-scale planting. Easy transplanting is also an advantage for less experienced growers.
Strawberry plugs are normally not available until the end of August. Sometimes, it is a dilemma whether to plant them in late summer. It is true that any of the warm days in the end summer and fall are very good for plant growth. But on the other hand, extremely high temperatures (above 95 °F) can cause plant leaf burn (Figure 1) and eventually kill the plants. This could particularly be a problem in high tunnels.
Figure 1. A severe case of plant leaf burn under high temperatures.
To attain the same plant growth in the fall, bare-root strawberry plants should be planted 1-2 months earlier than the plugs. It is important to note that bare-root plants do not have an actively growing root system, in addition, they are planted in the middle of summer. Continuous overhead watering in the first week following transplanting is essential to ensure plant survival.
Day-neutral and June bearers
Most strawberries grown in Indiana are June bearing, or short-day plants. Interest exist among growers in day-neutral strawberries for extended season production. However, in the experimental trials we have done in Southern Indiana, we did not see a dramatic benefit in terms of season extension with day-neutral strawberries. Day-neutral cultivars could produce some fruit in the fall, but the yield is normally too low to justify the labor cost. It is also true that day-neutral strawberries can be continuously harvested in the summer, but the temperature is usually too high to allow the plants to produce high quality berries. Using shade cloth may help to solve the issue. This is an idea that we would like to test in our future trials. So far, growing a combination of varieties with the different flowering habit, and the use of season extension tools, such as high and low tunnels, row covers, etc. is recommended to extend the harvest period.
Winter cold and Spring frost protection
In general, we recommend use floating row covers for the annual strawberry production system (Figure 2). Although row covers are much more expensive than straw mulch, benefits gained from using row covers can normally justify the cost. First, row covers can be easily removed and recovered. If strawberries were grown inside high tunnels, the plants would benefit from additional growth in late winter if row covers were removed in sunny days and covered back at night. In the open field, it is not recommended to remove row covers in the winter, but temporarily removing and recovering the plants is needed to protect blooms from late frost in the spring. Secondly, compared with straw mulch, strawberry plants covered with row covers normally develop faster in the spring which leads to early yields.
Figure 2. Strawberry plants were covered with straw mulch and row covers in the winter
It should be noted that straw mulch is more effective at retaining heat compared with row covers when temperature is extremely low in the winter. A detailed comparison of winter temperatures under straw mulch and row covers can be found in this article https://vegcropshotline.org/article/strawberry-winter-protection-straw-mulch-vs-row-covers/