The Best PH for Watermelons

Watermelons and pH

• Watermelons will tolerate a pH range from 5.0 to 6.8 according to Ohio State University but grow best in a pH range of 6.0 to 6.8. This range is typical for many traditional garden vegetables and allow a variety to be planted in the same small space. Other squashes, lettuce, onions, carrots and radishes also do best in this range.

Mixed Garden

• Corn, pumpkins and tomatoes do well in a wider pH range, from 5.5 to 7.5 according to the University of Nebraska–Lincoln. Beans, cucumbers and peppers do better in a more narrow 5.5 to 7.0 range, while eggplants need a more acid, 5.5 to only 6.5 range. Planting all these vegetables with watermelons will allow them to do well if the pH is somewhere between 6.0 and 6.5, which they will all tolerate.

Testing for pH

• Measuring the soil pH for watermelons with an inexpensive commercial test kit is easy. While each test kit is slightly different they all require a soil sample from just below the surface of the garden soil. The sample should be before you put any fertilizer in the soil. The soil sample is mixed with water and a strip of provided testing paper is put into the water. The color the paper turns to is compared to the provided color chart and the pH measure is estimated from the comparison.

Soil Amendments

• Changing the pH balance to provide an optimum soil for the watermelons requires mixing what is traditionally called soil amendments into the ground. If the soil is less than 6.0 lime is the standard soil amendment to change it from very acid to less acid. Lime works quickly and the amount you use depends upon how much you need to raise the pH and how big the space is. Sulfur works to lower a pH so if your reading is over 7.0, this is what you would mix into the soil to change from alkaline to acidic. Sulfur works slower than lime so it takes more time to prepare the soil for planting.