Despite the great importance of strong plant material in the increasingly complex cultivation of strawberries, the storage methods did not change much in the last decades. Is it sufficient or do plants require a different conditioning? Time for a new step in improving the storage method.
Relevance for practice
Strawberry cultivation, and thus also the cultivation of strawberry plants and the storage of this planting material, are an important part of the horticultural sector. The consumption of strawberries has been increasing for years. The chain has developed into a closed production chain with almost year-round production. This places high demands on cultivation techniques, but certainly also on the quality of the plant material and its storage.
The correct plant stage at harvest time is important for a successful strawberry production. The sugar content of the plant and the number of cold hours appear to be important for the production quality. The required cold hours (< 7 °C) depend on the variety. The threshold of 600 hours is often set as the minimum level for good hardening. But this moment is reached later and later. In 2020, in the Netherlands, this threshold was reached only at the beginning of December. Given the sugar content of the plant, it is better to harvest the plants in November, but the cold hours are insufficient. It seems to be a mismatch between when the strawberry plants have had enough cold hours and the sugar content in the root required for storage. And we did not talk about the labour availability yet.
Optimal cold hours
The optimum number of cold hours depends on the variety and is often higher than the stated 600 hours. If we compare 4 varieties, Magnum needs the fewest cold hours with an average of 700 hours. Opera follows with an average of 900 to 1000 hours, while Elsanta requires 1000-1600 hours and Sonata 1600 hours.
Correct cold hours is important for production and production quality. Too short of cold hours can lead to poor pollen quality and misshapen fruits, while too many cold hours strengthen a plant that is too vegetative, reducing the total number of fruits.
Finding a method for storing planting material with fewer cold hours seems to be a logical step in improving production and quality of fruit cultivation.
In view of the importance of high-quality plant material, the attention for the storage of plant material has been limited in recent years. The practical results with plant storage seem to be sufficient. Nevertheless, developments in the sector towards high-quality production systems, partly in other cultivation periods, require renewed attention, especially for the storage method. The goal: less plant loss, better outgrowth with higher fruit production/quality.
More rest during storage
During storage, the aim is to bring the plant material to complete rest. This is mainly done by applying the right temperature. For other products, the activity of the product is further calmed with CA (Controlled Atmosphere). In strawberry plants, CA storage has been limited to research. It was already shown in 2000 that CA storage of waiting bed plants adds a lot to Elsanta in terms of production volume and production quality. The physiological background is simple. By further inhibiting the plant activity during storage, more energy remains for plant growth.
Questions from practice
Discussions in the sector with various plant breeders, strawberry growers and custodians point to the importance of improvements and insight. The questions are diverse.
The harvesting and packing period of plant material starts earlier and earlier; the climate is changing and as a result less product meets the right stage at harvest time. Given this situation, what adjustments does this require in the retention method? Which condition gives the best (production) quality for which plant characteristic and storage period or cultivation. Isn't a higher impact temperature better for "little cold hours of product"? And what does this mean for the retention period?
More and more planting material is kept longer for autumn and winter cultivation. Are the advantages of CA storage with waiting bed plants an indication of the advantages with longer storage of tray plants? In the meantime, great steps have been made towards interactive storage with CA storage for various products. What possibilities does this give for plant material?
Cooling rate, lower limit in product temperature and temperature range are frequently discussed. But how does this relate to the plant type, but also to usefulness and necessity? With today's experience, the effects of storage temperatures for medium-term storage seem limited within a normal range, but how is this for the longest plant storage? After all, the differences in conditioning between plants at various positions within a cell are often large. Both by the position on the pallet and the position of the pallet within the cell. This is not all different the cooling rate but also the further temperature range. Are these experiences useful for proper conditioning and is this true for each storage period?
The industry has a certain amount of competition, but it also cooperates in many ways, even internationally. In cultivation, planting material propagation, storage, but also advice and research, partners have indicated that they are open to more attention for the storage of planting material. Within the Dutch research structure, the above questions are researched using government funding together with the private sector for practically usable research work.
From the experiences with improvement processes of various product groups with storage technology, sufficient possibilities appear to be available for improving the result. Until then, the core of storage will remain focused on well-considered cooling and temperature realization. This is where settings, stacks, but also barrels and packaging come together. Experiences show that many improvements are possible through focused attention on product temperature distribution within spaces.