Watermelon problems

I am in a new area, with acidic soil. Since there is so much water, I decided to put plants that do not like wet feet on the mound around the tornado shelter.

One of those items was the watermelons, since they are technically a desert plant. I apologize that there are no pictures (I can't get my cell phone to transfer anything to my computer, or to the cloud) but I planted six watermelons of two different varieties. Three of those watermelons now have white cotyledons and the true leaves are starting to bleach out. It rained a few days ago so there should be plenty of water. They get morning and afternoon sun. The mound is directly under a female red cedar (juniper) but I can't find anything about this particular symptom under problems with acid soil. The water amount isn't so high that I think it might be drowning them.

Any ideas about what might be happening? The other three watermelons appear to be healthy enough, as do the peppers planted on the far side of the same mound and the blueberries planted downhill.

If these die I will seed more of another variety in the same locations.

Are you living in a swamp or has there been a flood?

Sorry it took me so long to respond. No, no floods or swamp. The watermelons are planted in this area because it's higher and the soil has a little less clay. At this point I'm thinking there might be something wrong with the soil, because everything else planted in here is struggling as well. The weird thing is that they're all showing different symptoms.

The elderberry just died within days of being planted. The sweet potatoes are showing leaf necrosis, almost like sunscald which makes no sense at all since they're only in full sun in the afternoon. The blueberries have growing tip dieback. The watermelons cotyledons turned white, and have now fallen off, but the true leaves are coming out twisted and deformed like sulfur toxicity. The other three watermelons still look perfectly normal.

One died, one is recovering, and the third is healthy enough that I can't remember which one it is. I THINK it's the one that's now three or four times the size of any of the others and starting to vine, but I'm not sure. In either case, it recovered completely.

I think I may have figured out what was wrong. These have been grown over generations in highly alkaline/sand dry soil. I planted them into highly acidic soil. If they'd had fully developed roots I think they might have been fine because they could reach for the water they needed. Seedling watermelons have pretty weak roots.

I think what happened was that they have not developed the ability to absorb nutrients in an acid/clay soil as they have in alkaline/sandy soil. Sulfur is one of those that is absorbed most easily in an alkaline soil, which explains the bleaching.

It should be interesting to see how this develops over the next few years as I work on drought tolerance in a new environment. I am not going to water these watermelons, ever.