There are several factors that can contribute to garden watermelons not being as sweet as desires. Here are some common reasons:
- Harvesting too early, here is link on how to tell when watermelon is ready to be harvested
- Nutrient Deficiency, soil lacking in essential nutrients, particular potassium can impact the sweetness. Conduct a soil test amending the soil with appropriate fertilizer and organic matter.
- Inconsistent Watering, especially during fruit development can stress the watermelon plants and lead to bland tasting fruit. Watermelons require regular moisture throughout the growing season, especially during the hot dry summer
- Overcrowding, planting watermelon vines too close together can result in overcrowding.
- Pest or Disease, can affect the overall health of the plants, including sweetness.
- Environmental conditions such as temperature fluctuations, excess humidity or poor weather during flowers and fruit set can impact watermelon sweetness
Here is an article on how to grow watermelon