The sweet taste of out-of-season strawberries
Planting dates could be varied early results of Palmerston North trials are showing.
The normal method of growing strawberries in New Zealand is to obtain runners in May from one of the specialist strawberry runner producers, and to plant them in the field into a raised bed covered with a black polythene mulch.
The result is that ripe fruit, depending on the district, will become available from October through to Christmas for short day varieties, with the possibility of a second crop in the autumn. The day-neutral varieties will actually crop continuously throughout the summer.
In recent years the production of strawberries in greenhouses, usually high plastic clad tunnels, hydroponics, and table-top growing systems, has significantly changed the way in which strawberries are grown. It’s significantly increased yield and quality and also extended the harvest period, by weather proofing, to some extent, the production system.
This development has not, however, considered whether the planting date of the young runners should, or could, be modified, and what effect such changes might have on yield and harvest time.
Over the past few years my former colleague Damian Duggan-Jones and I have undertaken a preliminary study to examine the effect of planting date on the productivity of greenhouse strawberries. The results clearly demonstrate that even in Palmerston North, which could never claim to have good winter light conditions for greenhouse crops, that ripe strawberries can be produced at any time of the year. More details of this study will be presented in a future article.
My interest in out-of-season strawberry production began in my early teens, when I attempted, unsuccessfully, to
Locally grown, freshly harvested fruit should certainly expect a premium over tired imported produce
grow pots of strawberries on the kitchen window of my parents’ home in England. This was stimulated by a book on commercial berry fruit production by Charles Oldham, articles which my grandfather had saved from garden magazines on producing out of season fruit in greenhouses in the walled gardens of stately homes and I am sure the impact of the outstanding exhibit of pots of strawberries at the world renowned Chelsea Flower Show by Waterperry Horticultural School near Oxford which regularly was awarded a Gold Medal-the shows top award.
Sixty years later I supervised a student’s hydroponics greenhouse study of strawberry production, and this re-ignited my interest in the crop. This resulted in my visiting Belgium, where year-round strawberry production is a well established industry, and undertaking a series of greenhouse experiments looking at such aspects as varieties, plant density, growing medium and more recently planting date.
The first question to answer is there any demand for out of season strawberries?
Certainly the demand (currently?) is not as high as in the summer, but importers still find it worth-while to bring in product from Australia and United States even though it has to be treated against fruit fly, and is several days old from harvest before it reaches the supermarket shelf. Locally grown, freshly harvested fruit should certainly expect a premium over tired imported produce
The yields which we achieved are probably much lower than might be achieved, because all plants received exactly the same watering and fertiliser regimes irrespective of planting date or variety - although of course less frequently in the winter. This meant that the less vigorous varieties tended to be overwatered, as did the newer plantings.
Another possible increase in productivity during the winter would certainly be achieved by using supplementary lighting, both to increase the length of day for photosynthesis, and possibly provide additional light during the day on dull days. High Pressure Sodium (HPS) lights would be one option, but eventually (inevitably) LED’s will take up this important role.
One of the big attractions of New Zealand’s horticulture to me is that it is a very dynamic industry, very willing to look at new innovation.
▴ Greenhouse strawberries in Belgium in May.