In gardens where watermelons are plagued with blossom end rot year after year, a soil test is in order — often the pH is out of range, making calcium unavailable to plants. When pH is outside of a range of 6. 0 to 7. 0, lime can be applied to correct soil that\’s too acidic and sulfur added to alkaline soil.
Exactly how much is needed will depend on several factors, including how far out of range your garden is and the composition of the soil. About 1/4 pound of elemental sulfur per square yard can drop garden pH from 7. 5 to 6. 5; 1/2 to 2/3 pound of lime is often enough to raise the pH of a square yard from 5. 5 to 6. 5.
PH-modifying amendments should be mixed into the garden in the fall to allow them time to work before planting season.
Although you can\’t control the weather, you can control cultural conditions within your garden.
To prevent belly rot in the future, amend heavy soils with compost, peat moss or manure to improve drainage. In some cases, you might have to build raised beds. Black plastic laid over the soil provides a clean growing environment that keeps soil diseases at bay.
Snip holes in the black plastic to plant the watermelon. You can also place a board or 4 inches of weed-free straw mulch under the maturing fruit. Crops should be rotated so watermelon doesn\’t grow in the same garden spot from year to year.