Answer: I know how frustrating it is to plant and replant watermelon, only to have it die. Although you live in the desert of California and the daytime temperatures may be warm, it's possible that the nighttime temperatures are still too cold for your plants. Watermelon thrives when daytime temperatures are 80 and above and nighttime temperatures are 70 and above. It's a little early in the season for even the California desert to offer warm nighttime temperatures. In this case, you'll want to look for watermelon varieties that can tolerate cooler nighttime temperatures.
In general, watermelons grow best in full sunshine, in rich, well draining soils. Amend the growing bed with some organic matter (such as compost) to make it rich and friable. After planting water deeply, then water again only when the top of the soil dries out. I think if you plant again in June that you'll have better success with your watermelon plants.
Best wishes with your garden!
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