Watermelon Plants Keep Dying After Transplant

Plant Age

• The older a watermelon or other cucurbit plant is, the less likely it is to survive transplant. These crops produce wide, spreading roots that are easily injured during transplant. Sow watermelon seeds no earlier than two to three weeks before you expect to plant them in the garden. Transplant young watermelon plants when the second true leaf begins to emerge. The true leaves grow above the watermelon's pair of rounded seed leaves.

Starting Seed

• To minimize the potential for transplant shock, sow watermelon seeds in peat pots or other containers that break down in the soil. Plant one to three seeds per container, and thin seedlings out so just one or two plants remain per pot. Plant the watermelon seeds in a well-drained, soil-less germinating medium, keep the medium constantly moist but not wet and maintain a temperature around 80 to 85 degrees Fahrenheit to encourage germination and avoid disease problems.

Hardening Off

• Before transplanting the seedlings into the garden, provide them with a transition period, or hardening off, so they do not experience shock related to temperature fluctuations or the amount of sunlight in their new location. Begin by placing the watermelons in a protected spot out of direct sunlight and drying winds for a few hours, then gradually increase their time spent outdoors each day and the amount of light the plants receive until you can leave the plants in a location with conditions that reflect those in the planting site for the entire day and night.

Transplanting and Post-Transplanting Care

• When transplanting watermelon plants, work about 1 cup of high-phosphorus starter fertilizer with a formula such as 10-52-17 into each mound. Break or cut off the lip of the peat pot if it is far above the surface of the germinating medium. Plant the watermelon transplant at the same depth at which it was previously growing, and make sure that none of the peat is exposed to air or it will act as a wick. Water transplants well and regularly to encourage root growth. Transplants benefit from regular, though not excessive moisture, around their roots, so water the plants as needed so the soil around the roots never dries out completely. The amount of water required and how frequently to apply water varies depending on soil texture and weather. As a general rule, actively growing watermelons benefit from 1 to 2 inches of water weekly through rainfall and supplemental irrigation.

  If the transplant experiences four or five days of continuously cloudy or rainy weather when soil temperatures drop below 55 to 60 degrees Fahrenheit, the young watermelons' roots will not absorb water. When the sun does eventually appear, the rate of transpiration from the watermelon leaves is greater than the rate at which roots can take up water, resulting in relatively fast wilting and death. Timing transplant well with the forecast in mind, spreading an organic material mulch in a layer 2 inches thick around the transplant to regulate soil temperature and shading the young transplants from hot, direct sun with a temporary, makeshift shelter following cool, cloudy weather can help prevent this problem.