Why Watermelons Are Not Sweet and How to Grow and Fix Them for Higher Sweetness

Many people wonder why some watermelons taste sweet and juicy while others are not sweet. Eating a sweet one puts you in a good mood, while eating an unsweet one makes you feel you wasted your money. So why are watermelons not sweet? How can you grow them to improve sweetness? How do you choose a sweet watermelon? What do you do with a watermelon that is not sweet?

1. Why are watermelons not sweet?

Reason 1: Different varieties. Because watermelon varieties differ, their sugar content differs, and by comparison one variety will seem less sweet than another.

Reason 2: Insufficient light. The sweetness of a watermelon is mainly determined by how much sucrose, fructose, glucose and other sugars it contains. The formation of these sugars depends on photosynthesis, so if photosynthesis is weak, the watermelon will not be sweet.

Reason 3: Improper application of nitrogen fertilizer. Nitrogen fertilizer is extremely important for the growth and development of watermelons. If too much nitrogen fertilizer is applied or it is applied too late, and there is a lack of carbon during the transformation process, the watermelon's absorption and use of nitrogen fertilizer will be affected, its sugar content will be low, and the watermelon will not be sweet.

Reason 4: Nutrient deficiency. If the soil does not provide sufficient nutrients, it will affect the synthesis, transformation and transport of sugars within the watermelon. With insufficient sugar, the watermelon will not be sweet.

Reason 5: Small day-night temperature difference. Everyone knows that the famous watermelon-growing places are Xinjiang, Lanzhou in Gansu, Dezhou in Shandong, Dongtai in Jiangsu and other places, and these places all share one characteristic: a large day-night temperature difference. If the day-night temperature difference is small, it is not conducive to sugar accumulation, the watermelon's sugar content will be low, and it will not be sweet.

Reason 6: Improper water control. Many watermelon-producing areas have the saying “drought melons are sweet.” If heavy rain occurs or the plants are watered before harvest, the watermelon will not be sweet.

Reason 7: Not ripe. Many melon growers pick watermelons that are not fully ripe in order to bring them to market earlier. A watermelon that is not fully ripe is naturally not sweet.

2. How do you grow watermelons to improve sweetness?

Method 1 for growing watermelons with higher sweetness: Choose good varieties. Grow watermelons that are sweet and that customers like.

Method 2 for growing watermelons with higher sweetness: Increase the intensity of photosynthesis. Strong photosynthesis during the day can increase sugar transformation, accumulate more sugar and improve watermelon sweetness. This can be achieved by increasing light intensity and extending light duration, which applies to watermelons grown in greenhouses. To increase light intensity, you can use low-temperature-resistant, anti-aging drip-free greenhouse film and frequently remove dust from the film to enhance light transmission; to extend light duration, you can use artificial supplemental lighting.

Method 3 for growing watermelons with higher sweetness: Increase carbon dioxide content. During the peak growth period, watermelons need carbon dioxide to help transform sugars. You can increase carbon dioxide content by piling fresh horse manure in the greenhouse, or by burning propane and coke in the greenhouse, or releasing dry ice.

Method 4 for growing watermelons with higher sweetness: Apply nitrogen fertilizer reasonably. Applying too much nitrogen fertilizer will affect watermelon quality, and applying nitrogen fertilizer too late will affect the transformation of sugars in the watermelon.

Method 5 for growing watermelons with higher sweetness: Increase the day-night temperature difference. High daytime temperatures and low nighttime temperatures are conducive to sugar accumulation. For watermelons grown in greenhouses, the temperature inside the greenhouse can be controlled manually, and ventilation can be increased at night.

Method 6 for growing watermelons with higher sweetness: Harvest appropriately. Do not water for 7 days before harvest; if growing in the open field and it rains, you can postpone the harvest time. Although postponing harvest will lower the selling price, watermelons of good quality will still fetch a higher price.

3. How do you choose a sweet watermelon?

To pick a sweet watermelon, check whether the circle on the bottom of the watermelon is smaller, whether the color of the rind is green, whether the stripes on the rind are neat, whether the stem end is curled into a circle, and whether the watermelon makes a hollow “thump-thump” sound when tapped.

4. What do you do with a watermelon that is not sweet?

You can scoop out the flesh and put it in a bowl, add an appropriate amount of white granulated sugar and mix it before eating; you can also put the watermelon in the refrigerator and eat it after it is chilled; or you can make honey-drizzled watermelon, make a fruit salad, juice it into watermelon juice and add a little sugar, or boil it into watermelon syrup.