Blueberries’ popularity is not only cosmetic, but also because the berries contain higher antioxidant levels than just about every other fruit (primarily due to the blue anthocyanin pigment in the skin). So, there is an increasing demand to have blueberries available year-round.

It is, of course, possible to produce ripe blueberry fruit somewhere in the world on any day of the year. Blueberries will grow out of season in a range of climates, and in Mexico, it is possible to produce them for a considerable part of the year, simply by selecting the appropriate altitude. I saw in a single day fruit ready to harvest and some several weeks from maturity, simply because they were grown at different altitudes.

However, freight costs and damage during transport makes this a demanding activity. And while blueberry fruit probably transport best of all the berry fruit, nevertheless proximity to market is still desirable. A further potential constraint to importation is that of plant quarantine, as many plant viruses can be transmitted by the fresh fruit (I say potential as, although there are frequently stringent quarantine regulations for live plants, these do not appear to be seriously considered at this time for the movement of fruits between different countries).

Theoretically, one can divide blueberries into several different types, (depending on the quantity of chilling units they require), but from a point of view of out-of-season production, the low-chill types are likely to be the most desirable. Other key factors to consider also must be quality, the size of the calyx (at the end of the fruit) and the amount—if any—of damage to the fruit when harvesting.

So, in order to produce large amounts of quality berry fruit locally over a long season, it is essential to use protected cultivation and to incorporate hydroponic systems. A sound knowledge on crop agronomy is a further essential factor.

In my studies at Massey University, I grew a range of different blueberries (with different chilling requirements) in a greenhouse in coir (coco peat) modules, using liner plants and drip fertigation.

In fact, we used 12 different cultivars with distinct chilling requirements. Planting occurred in a greenhouse in mid-December, and the plants were 23.62-in. tall by the end of the summer—thanks to the magic of growing in protected cultivation using coir modules and adequate water and nutrition.

Monthly from March 1st, plants were placed in a cool store at 44.6°F for two, four and six weeks so that they experienced varying degrees of chilling, and also different day lengths up to the start of chilling. A set of plants was also retained in the greenhouse without any chilling treatments.

No difference in flowering was noted between any of the treatments, although the early varieties flowered first. All the plants produced flowers, which were pollinated by bumble bees. However, the harvest was poor due to the cunning of the local birds, who would sit on the automatic ventilators until they opened in the morning, when they would then have breakfast!

The following year we had some problems because the water pH at Massey is over 7.0, and we experienced some iron deficiency problems; nevertheless, there was little doubt that blueberries could be successfully grown out of season (possibly even to produce fruit year-round) and that it might be possible to obtain two crops per year by using early-maturing types.

Clearly if there is a serious interest in the availability of fresh blueberries year-round, and quarantine measures preclude importation, then a small research program should be able to determine the way ahead. The key points appear to be the use of containers filled with a well-drained growing medium, an efficient watering and nutrition program, and (of course) the appropriate selection of varieties.