A slice of cool, crisp watermelon is a delicious summer treat. Growing your own watermelons ensures they are organic and have the best flavor. Watermelons thrive in well-drained, sandy soils rich in organic material. Feeding your watermelons the correct type and amount of fertilizer helps them grow large and juicy. Without the proper soil and fertilization, your watermelons will not grow right.
Soil pH Level
Watermelons require soil with a pH level of 6.0 to 6.5. Most gardening supply stores sell pH testing kits that allow you to insert a probe into the ground and receive an instant pH reading. Adding dolomitic limestone increases the pH level of soil. Once the pH level of the soil is correct, add magnesium sulfate to improve the fertility of the soil. Soil pH testing and treatment should be done six months prior to planting.
Before planting your watermelons, work 4 inches of composted organic material into the soil. Cow manure, peanut hulls or cotton gin waste give soil the necessary nutrients for growing watermelons. The soil also needs 10-10-10 or 16-16-8 all-purpose fertilizer. Apply 4 to 6 cups for every 100 feet of row.
Feed watermelons a 20-10-20 fertilizer weekly until the vines start to bloom. Carefully follow the instructions on the fertilizer's packaging for correct amounts. Switch to a 20-20-20 fertilizer when the vines start blooming and continue using it through out the growing season.
Watermelons need 1 lb. of ammonium nitrate per 100 feet or 2 lbs. of calcium nitrate per 100 feet of row. Feed your watermelons nitrogen before the vines start to run and again after fruit has started to develop. Do not give watermelons too much nitrogen. Doing so will decrease the amount of fruit produced. Avoid getting nitrogen on the leaves because it will cause them to burn.