Known for its unique flavor and the juicy refreshment on hot summer days, watermelon is an iconic warm-weather fruit. For home gardeners and farmers alike, watermelon is a regular fixture each year. Though not terribly difficult to tend, watermelons do have needs that might not be readily apparent. Shriveling is a common problem, and quickly diagnosing the causes of shriveling can save a lot of wasted fruit.
Shriveling Causes: The Optimistic Cause
Shriveling can occur in nearly every fruit and vegetable. Causes can be as simple as under-watering and as complicated as plant-specific plagues. But, assuming you've kept your watermelon adequately watered and healthy, you need to consider three factors that might lead to shriveling. Every novice should be aware that, as Farmers' Almanac points out, "drying or shriveling of the stem near the base of the fruit" is one sign that watermelons are ready for harvest. Before troubleshooting potential problems with your fruit, consider whether the shape, size and color of your watermelon are within reasonably expected maturity levels. If so, you might not have a problem at all. You might just have a watermelon that needs to be eaten.
The Oklahoma State University Extension Office notes that watermelons are sometimes susceptible to "blossom-end rot." With blossom-end rot, "the usual order of development is softening, slight shriveling, browning, blackening with extensive shriveling, and sometimes secondary decaying". If you have noticed such signs in your watermelon plant, address these potential causes.
Calcium depletion in the soil or moisture stress are principle causes. PMS Instrument Company describes moisture stress as the relationship between a plant's actual absorption of moisture compared with the demands of its particular environment, including wind, sun, temperature, soil condition and plant strength. You may have faithfully watered your plant, but it is located in an area where it needs still more water.
"Hot, dry winds, nematode damage, excessive fertilizer, low levels of calcium in the soil, pruned roots from late cultivations and other conditions are contributing factors," according to the OSU Extension.
If none of the above causes apply, or if the symptoms don't match, you may have a pollination problem. Watermelons (and most melons in general) require relatively intense pollination in order to thrive. A host of insects provide this service free of charge, but if you have used insecticides, you may have inadvertently repelled the pollinators. Symptoms of a poorly pollinated watermelon include "aborted" melons---those that the plant seemingly gave up on in mid-production---and shriveling. Ray Williams of Beetberry Farms states that, in addition to shriveling and pale white seeds, "A poorly pollinated fruit of any kind will also be deformed and bitter compared to a perfectly pollinated fruit."
If your watermelon problems seem to be of this kind, try employing more natural methods of protecting your watermelons from insects. Though somewhat laborious, introducing honey bees via beekeeping would also ensure proper levels of pollination in your plants.
Minor Adjustments May Yield Big Results
All in all, watermelons are relatively easy to grow and certainly easy to enjoy. Simple adjustments in garden maintenance will eliminate either of the negative causes of shriveling. Properly amending your soil each year to introduce organic matter and nutrients will insure against salinity or mineral depletion, and natural insect management practices will allow bees, butterflies and other pollinators to return in strength. By taking a close look at what is happening in your garden, you should be able to rectify the situation and get back to the fun of harvesting and eating watermelons.