You don't say where you are, but melons like heat. Several months of it. Squash do fine without heat. Melons want full sun as well. Squash are more tolerant of partial sun.

Do you prune your watermelons? I tried growing watermelons before and failed even in zone 7 just had tiny melons, been doing a lot of research and it seems to get the best quality is to prune them. I am trying that this season.

What are you pruning? It is ok to limit the number of melons per plant. That is a form of pruning. Pruning basic leaves ...not so good as the health and vigor of the plant could be lessened.. Melons need great vine, root and leaf health to finish up, nice fruits. Better get it right soon as disease can set in on melons by year 3.

I'm from Tunisia (Zone 10b) temperature in summer can reach 113F (45c), I don't prune the watermelons vines. I plant seeds in early March and I harvest in late june/early july, It looks like my watermelons vines stop growing and start yellowing from late May (just after flowering) and struggle to grow fruits, the vines stop at 7 feets length maximum and the plant start it's decline for some reason although my pumpkins keep growing and fruiting fine.

Sounds like you've got the heat! The fertilization schedule for melons is early application of nitrogen, switching to primarily potassium and phosphorus after flowering to aid fruit production. You may have a deficiency in those. FWIW, I've heard that watermelons in particular also need magnesium. Magnesium deficiency is marked by leaf veins remaining green, while the rest of the leaf starts to turn yellow. A soil test looking at such minerals may be in order.

but the fertilization for squash is nearly identical.

What variety of watermelon are you growing? Do you know others who grow watermelon in your area who have been successful? Where did you get your seeds? Bacterial fruit blotch is a disease that comes from contaminated seed.

The diseases might be a problem. Look for verticulum wilt as the one of them. Your soil never freezes, and this make very good environment for verticulum. As for me, I cannot grow melons, they wilt from what I think is bacterial wilt, the squashes and watermelons however do just fine.

@Ohiofem @glib @daninthedirt

*I planted Ali Baba watermelon variety and some other variety but the result is the same

* yes there is people who grow watermelon successfully in my area,

* soil is almost sandy,

* seed are bought each year

I think the problem is in the soil, a disease or a deficiency that pumpkin and squash can handle or resist but not watermelon. I'm not sure which one and I don't know if cantaloupes will do better or maybe I should graft watermelon/cantaloupe onto pumpkin rootstock.

Perhaps you just don't have the right genetics for watermelons to survive in your area. I think what you should look into is into developing your own custom landrace watermelon like what Joseph Lofthouse has done for his climate. I garden in Northern Colorado and i failed for 5 years of trying watermelon. After collaborating with Joseph and doing mass watermelon grex breeding i now have my own watermelon landrace that thrives here where very few single watermelon varieties do. I'm pretty much the only person who grows watermelon successfully here.

My first guess is that it's too hot. That's just because it sounds like heat is the most extreme characteristic of your location.

Are you growing the same variety as the people who are succeeding? Are those people growing in full sun, or do their melons maybe get some shade? Do you have a shady part of your garden, or can you create shade? (Maybe, for example, growing the melons under fairly closely spaced corn?)

If I had an infinite amount of space, and I were in your position, I would:

- Grow several watermelon varieties.

- And several other melon varieties.

- Each variety in full sun and in some shade.

- And observe what works.

If it is the heat, I find myself wondering if the heat is a problem through the whole growth period, or if it might just be causing a problem with pollination. I wonder if providing temporary shade for soon-to-open flowers, and doing the hand-pollinating as early as possible after the flowers open, might help?

Too hot? We grew watermelon down here in the dead of summer and they loved it. Produced so many we had to give them away. Fertilized once with 10-10-10 or 6-6-6. Didn't water much either. No joke! Maybe it rained alot that year. They were in full sun also. Just a dab of shade from the grape vines they were growing under.

zzackey, you're showing as being in 8b, Georgia, which a Googling claims gets summer temperatures in the nineties. (F) The OP says that he is in 10b and can get to 113F. That is a good deal hotter.

Actually we get about thirty days over 100 degrees. Watermelon tolerates a lot more heat and drought than pumpkins or other squash so I doubt that is the problem. Disease could be the problem altho most watermelon diseases affect the squash family. Watermelons are not picky except for an extreme dislike of clay soils. I have seen them grow as volunteers on a sandbar. They do need a deep soil, is it possible that you have a hardpan under your soil ( soil depth less tha a half meter)? They are also very intolerant of wet feet, could you be putting too much water on them. Remember they originated in the subSahara.

It's never too hot for watermelon they originated in africa. Before I plant my melon starts I cover the whole patch with black plastic. Each plant has its own emitter and gets 3 gallons of water per day once melons are a little bigger than a football until 2 weeks before harvest. Less melons per vine means bigger melons.