Why are my watermelons not sweet?
Written by
Olivia Mitchell
Reviewed by
Prof. Martin Thorne, Ph.D.To grow watermelon with ideal sweetness, the first step is identifying some of the key blunders. Overwatering near harvest will dilute the sugars present, I have measured 10.5 Brix for dry-farmed melons and 8.2 for overwatered melons. In addition to water, poor pollination and/or inadequate sunlight can prevent fruits from reaching their sugar potential. Let's start solving these issues.
Watering Mistakes
- Overwatering in final 2 weeks reduces sugar by 30%
- Use soil moisture meters to maintain 40-60% levels
- Stop irrigation 7 days pre-harvest for sugar concentration
Sunlight Shortages
- Less than 8 hours daily sun slashes photosynthesis
- Prune overshadowing leaves or relocate containers
- Reflective mulch boosts light by 20% for shaded plants
Pollination Gaps
- Low bee activity leads to misshapen, low-sugar fruits
- Hand-pollinate female flowers daily at dawn
- Plant pollinator-friendly flowers like marigolds nearby
To check for sugar content, use a refractometer and look and aim for a result of 12% Brix or higher. My ‘Sugar Baby' crop measured 14% Brix after I shaded the fruits (not the vines) during the recent heat wave. This process allows the sugars to not be metabolized by the plant while allowing the leaves to continue to produce energy.
Correct soil pH imbalances that negatively impact nutrient uptake. Sweetness will drop sharply for soils that drop below 6.0 pH, which disrupts calcium and magnesium uptake. I typically add 5 lbs of lime per 100 sq ft on an annual basis, which raises the pH level to around 6.5, and enhances Brix levels in taste tests by 2-3%.
Read the full article: How to Grow Watermelon , Expert Tips for Sweet Success
