My wife and I go on an almost daily watermelon-eating binge during July and August, but I don’t even bother trying to grow watermelons in our own garden. We leave that crop to growers in warmer, inland areas. Watermelons can be spectacular performers, often yielding 40,000 pounds of fruit per acre, but they really do need more heat than we get here on the coast of Italy.
Growing watermelons can be complicated, too, not only because there are three basic types: normal, hybrid and seedless triploid. Each type needs a different culture.
When planting watermelon seeds, the first, most important factor in growing watermelons is that the soil should be healthy and warm. In fact, many growers don’t direct seed, and prefer to plant well-established seedlings into the fields. This is especially true of growers trying to produce early crops.
The next important factor in watermelon culture is accumulated heat. Once pollinated, if it gets sufficient heat, a watermelon will mature within four months. Watermelons grown inside polytunnels, or a hoop house, can mature even more quickly. The best and sweetest melons grow very quickly and produce a lot of sugar at the moment of maturity. Slower maturing melons produce less sugar.
Another important consideration is the fact that watermelon vines appreciate sufficient water, but overwatering can be a problem if the vines are not grown on fast draining sandy soils.
Probably the single most common modern cultural practice in watermelon culture is the use of black plastic to cover the raised beds on which the melon plants are planted. The black plastic heats up the soil, and this is quite beneficial. Watermelon fruits produced on black plastic will usually produce earlier and more quickly, with sweeter fruits.
Here in Italy, a lot of growers now grow watermelons in polytunnels. The tunnels significantly improve the speed of growth and sweetness of the fruits, as well as protecting the fruits from physical damage.
The biggest problem in watermelon culture is probably pollination. Some growers are lucky and they grow where there are abundant wild pollinators, others regularly rent beehives for the pollination period. It requires perhaps seven or eight pollinator insect visits to fully pollinate a female watermelon flower. Unfortunately, though, watermelon flowers aren’t very tasty to bees, so they will often select other feeding sources and ignore the watermelon flowers. Growers who use polytunnels are almost obligated to hand-pollinate, just because attracting enough bees inside the tunnels is a difficult task.
It’s almost a joke how many different potential pests and diseases can be problems for watermelon vines. Just about everything can create problems. In general, the better the soil drainage and the drier the environment, the better the possibility that a vigorously growing watermelon crop won’t be seriously affected by a pest problem.
Timing the harvesting of a crop of watermelons can be assisted greatly by testing the sugar levels in some sample melons with the use of a hand refractometer. Melons harvested at an immature stage may develop a much redder color after harvest, but the sugar level will never rise after harvest.