Production cycle

Fig. Typical off-season strawberry production cycle using greenhouses

When to end the production

Strawberry production cycle is almost always limited by temperature conditions achievable in the production system. When temperature is too warm, strawberry plants do not produce high quality fruit (size and taste/flavor) or in some cases stop producing fruit. Nighttime temperature has a stronger impact on fruit quality than daytime temperature. As controlling greenhouse nighttime temperature is more predictable than greenhouse daytime temperature, we almost solely use nighttime temperature as a guide to determine the ending time of production. For example, we used to end the production cycle in Tucson, Arizona, by end of April, but extend the ending time to the end of May in Columbus, Ohio because the nighttime temperature in May is not desirable in Arizona but acceptable in Ohio.  Beyond that, night temperature becomes too warm (above 16 C or 60 F), which makes fruit size smaller and fruit more acidic.

A year-round production is possible as long as the microclimate in the greenhouse or indoor farm is favorable for high quality fruit production. In North America, some Canadian greenhouse growers and indoor (vertical) farmers use a one-year production cycle. We need to obtain more information to judge if the strawberry productivity can be sustained for longer than one year of production.


When to start the production

The starting time of production also considers temperature. For example, fruit quality in October in Arizona was more acidic, being distinctly inferior from the quality of fruit produced in late November and beyond.  Another important factor affecting the decision regarding production cycle is the photoperiodic type of cultivars selected. June-bearing (short-day) cultivars will not have harvestable fruit until late December unless plants were artificially conditioned to have flower initials induced at the time of transplanting. Ever-bearing and “day-neutral” types can start producing fruits without conditioning. Lastly not least, market price is also an important factor for determining target starting time of production. As part of off-season production, the holiday seasons (November and December) are essential market targets and it is desirable to time large production peaks to align with these seasons.


Transplant flower initials determines the early productivity

Approximate duration of time for flower initials (< 1 mm size) to develop harvestable fruit is 8-10 weeks, depending on the growing environment and cultivar.  Therefore, if the planting materials are tray-plants having flower initials already developed in meristems, transplanting directly to the production system should be scheduled 8-10 weeks prior to the target first harvest of fruit.  If you are planting materials with limited vegetative growth (such as bare-rooted plants or rooted runner tips) directly in the production system, you will need to add at least 4-5 weeks to develop vegetative growth (a minimum of five or more fully developed new leaves and 1-cm crown diameter) before letting flowers set fruit without removing them.

The amounts of flower initials developed on planting materials determine the early production of strawberry. Tray-plants, a type of transplant commonly available in Europe, have a minimum of 6-7 viable flower initials (apical and axillary meristems) that can result in early fruit production. Frigo-storage technology in Europe allows tray-plants to be available almost year-round and growers can use such plants to produce fruit from short-day cultivars throughout long-day summer months. Transplant technology is a crucial factor determining production cycles and early productivity. Our preliminary experiment showed that rooted runner tip productivity was far below that of tray-plants during the initial two months of fruit production. This is because rooted runner tips had only one crown with one flower initial on the apical meristem, while tray-plants had two crowns with flower initials on apical as well as axillary meristems.

Fig. Comparison small rooted plugs vs. large tray plants as planting materials for off-season production (Kroggel and Kubota, 2017; unpublished data).