Before harvesting fruits, look for signs that they are ripe. Check the tendrils where the melons connect to the plant. The tendrils near a ripe melon will be dry and brown while tendrils near an unripe melon will still be green. Also, check the rind of the melon. The rind should be very hard and the part that was resting on the ground should have a creamy coloring.
Light
Like all melons, the black diamond watermelon requires lots of sunshine. At least 6 to 8 hours every day are needed to keep these plants growing strong.
Soil
Black diamond watermelons enjoy soil rich in organic material. They prefer neutral to slightly acidic, warm, moist, well-draining soil mediums. A layer of organic mulch such as straw underneath the vines and fruits will help retain soil moisture.
Water
Watermelons may be some of the juiciest fruits around, so it is no surprise that they need consistent water. Keep the soil moist, but not soggy. Regular watering will keep these plants thriving. Water the vines where they are rooted into the soil and try to avoid getting the leaves wet which can lead to fungal problems. Once the melons grow to about the size of a tennis ball, only water when the soil begins to dry out. Around two weeks before the fruit is ripe, stop watering to increase the sugar content in the fruits.
Temperature and Humidity
These melons prefer hot temperatures and do not handle cold well. They prefer moist conditions, though very high humidity can cause fungal problems.
Fertilizer
Black diamond watermelons love rich soil and do well in organic material. Amending the soil with plenty of compost before planting will ensure these melons receive the nutrients they need. Fertilizer can be applied when flowers appear to help encourage healthy fruit production. It is best to use nitrogen-based fertilizer in the early stages of growing, then switch to phosphorus and potassium-based fertilizers when the plant produces flowers.
How to Grow Black Diamond Watermelon From Seed
These juicy melons take some time to mature, so it is best to start seeds indoors about one month before the last frost. Here’s how: For areas with long, hot growing seasons, these melons can be planted directly into the garden. Follow these steps:
Common Pests & Diseases
When growing black diamond watermelons, be vigilant for the most common pests which include melon aphids, cucumber beetles, squash bugs, and squash vine borers. Fungal diseases, such as powdery mildew, alternaria leaf spot, stem blight, and downy mildew, can also attack this plant. It is best to avoid planting melons in an area where plants of the cucurbit or squash family were grown the previous year.
