Factors That Can Make or Break Greenhouse Strawberry Production

Strawberry (Fragaria × ananassa) has traditionally been a field crop in the U.S., but it is extensively produced in greenhouses in Asia and Europe for autumn, winter, and early spring production. Interest in off-season greenhouse strawberry production has been growing in North America, which is good for those of us who want local, better tasting strawberries outside of local peak season production.

Greenhouse strawberry has a distinct set of criteria for good growth and yield. Although all environmental and nutritional criteria critically impact plant response, this article will focus on those things that especially differ from most other greenhouse food crops.

Advertisement

Genetics Rule

Genetics play the biggest role in how strawberry plants will respond to their environment. Various varieties of strawberries can respond very differently in the same greenhouse production system, and the same variety of strawberry can respond quite differently in different greenhouse production systems and geographic locations It is important to trial multiple varieties in your system to find which will work best for yield and fruit quality. One genetic factor is a photoperiodic response, with short-day (SD) varieties (a.k.a., June bearing) requiring less than 13 hours of photoperiod to initiate flowers, and long-day (LD) varieties (a.k.a., everbearing or day neutral) that respond positively to longer photoperiod. Short-day plants tend to produce fruit consistently, with weekly yields being similar. Long-day varieties tend to have cyclical production, with flushes of flowers and fruit followed by minimal flowering and fruiting. Having both SD and LD can help assure fruit will always be available, if the photoperiodic responses are accounted for.

Reviving older genetics may be possible with greenhouse production. For example, older, high-flavor varieties, abandoned for disease or other issues that may not be relevant to greenhouse production, could be reintroduced.

Top Articles
New Survey on Sustainability in U.S. Floriculture Industry

Propagation for Greenhouse Still in its Infancy

Planting into greenhouse production systems for off-season production can occur as soon as late August. Although there is some movement toward accommodating greenhouse strawberry growers with timely transplants, planting material currently available is largely produced and timed for field production. One of these, dormant bare root (frigo) runners, is available in the spring, but usually no later than the end of May. These plants can be potted up and grown in high-density benchtop arrangements over summer, with some maintenance, to plant in the production system in late summer. An advantage of this approach is larger, more developed plants at planting time.

Another of these planting materials, the plug plants used for field plasticulture production, is available usually in September and is smaller than ideal, requiring a longer period of vegetative development that will push initial yields to later in the season. But they can be used and are, in fact, the size that works with substrate slabs designed for strawberry.

Tray plants are a type of planting material developed in Belgium and Holland but not yet widely available in North America. They are a transplant produced with multiple floral buds that will develop into multiple flower trusses early in the production season, resulting in good, early yields. Tray plants of the European standard variety ‘Elsanta’ can be stored long term and are therefore available when the grower needs them. Greater demand for transplants suited and scheduled for greenhouse production systems will increase their availability. However, not all cultivars can work well as tray plants, which is an area we need to investigate more to establish a better supply chain of planting materials suitable for greenhouse production.

Focus On the Root Zone

Nearly all commercial strawberry production is by hydroponic substrate culture using an organic substrate in a slab or container irrigated with nutrient solution by drip irrigation. Strawberry has a very high root oxygen demand and requires a substrate with good moisture- holding capacity that is also well aerated, with more oxygen availability than substrates used for other greenhouse crops.

There are several different commercially available strawberry-specific, coco coir-based substrates that have these required characteristics. In general, for substrates with greater water-holding capacity, larger volume (e.g., 100 ml) but less frequent irrigations are needed to displace the nutrient and oxygen-depleted solution in the substrate. Lower water holding capacity substrates require lower volume (e.g., 50 ml) but more frequent irrigations to replace the diminished solution in the substrate while maintaining consistent substrate moisture. Desired drainage percentage for strawberry (20% to 30%) is lower than for high-wire crops (30% to 40%). Typically, too high of a drainage percentage in strawberry means too wet of a substrate.

Hydroponic nutrient recipes for strawberry have much lower concentrations of essential nutrients than for high-wire crops like tomato and cucumber, as the plant does not produce large amounts of foliar growth or fruit mass. Consider how much new foliage a tomato plant produces in a week, compared to strawberry. When you look at strawberry hydroponic nutrient recipes you will notice that the NH4+ to NO3- ratio is about 1 to 10. This is necessary to prevent the plants from being too vegetative from too high a percentage of NH4+.

Lighting the Crop

As with most greenhouse crops produced in temperate regions, strawberry will need some supplemental lighting during the winter months, typically November through February. A commonly cited value for minimum light at the canopy level needed to produce a reasonable yield for many greenhouse crops is 12 moles m-2 d-1, but if 14-15 moles m-2 d-1 can be provided crop responses of yield and fruit quality will be much improved.

Somewhat unique to greenhouse vegetable production, strawberry is a low-profile row crop, and targeted lighting can be used to illuminate the crop canopy without wasting photons on lighting the aisle floor. Use of targeted lighting can make the use of supplemental lighting considerably more efficient than evenly distributed lighting. Specific red-blue ratios optimized for strawberry are little studied, and so white LEDs are a good choice, especially when considering fruit is harvested based on color, and white LEDs do not distort the appearance of the fruit color.

For most growers new to strawberry, the most prudent way to move into this crop is to start small scale, trial many different varieties and a couple of substrates, and just learn how the crop grows. With the gained expertise, and your refined variety list in hand, the second season will be much more rewarding.


Are You Cool Enough?

The ideal 24-hour average temperature for strawberry is 64°F. However, nighttime temperatures are preferably 54°F to 55°F, with higher than 57.2°F resulting in higher acidity due to too high fruit respiration. With few exceptions, this limits greenhouse fruit production to an October to May season.

While this disappoints many people who want to grow in their greenhouse year round, the period between May and October has the lowest price points of the entire year, and not competing against that is not necessarily a bad thing.

8