Watermelons prefer to grow on well-drained, deep sandy or sandy loam soil which, preferably, has been amended with organic matter. So, you want soil that holds moisture fairly well but not too well. They also prefer a slightly acidic soil (pH 5.5 to 6.5 or thereabouts) but will tolerate more alkaline soil than that.

When I have grown them in clay, they've done really well as long as they clay is very well amended with a lot of organic matter and in raised beds 6-8" above grade level. Any soil with a heavy clay component obviously must be well-mulched to help hold in the moisture in the summer and help prevent the clay from drying into hard concrete-like clay that restricts root movement. Loamy clay should have enough organic matter in it the clay doesn't dry up and become rock hard.

You can add sand as long as the clay has a loamy component. You wouldn't want pure sand + pure clay because that = adobe clay. As long as you have enough organic matter, whether it is compost or hugelkulture materials or whatever, the watermelons ought to be fine.

There are people here in our county who raise watermelons and melons of all kinds on deep river sand (near Thackerville I know the sand goes down at least 300') that does not look to me like it has any organic matter in it or added to it, but what it does have going for it is excellent drainage. They do irrigate quite a lot in the hot weather. One of the best local melons I've ever tasted (a Crane melon) was grown in the sandy soil of the usually rocky (but interspersed with sandy soil areas and probably clay areas as well) Criner Hills area. It had the most superb flavor but I forgot to ask my friend if he gardens in sand or clay when he gave me the melon.

Moisture is tricky with watermelons. You want them to have enough moisture to grow and produce watermelons, but not so much that the melons have poorly-colored, poorly-textured and poorly-flavored flesh. They are like tomatoes in the sense that too much water as the melons size up waters down the flavor and also ruins the texture. What I usually do is irrigate periodically until fruit sets and then I don't water the melons at all after fruit begins setting unless we are in some very advanced drought stage.

Sometimes hugelkultur beds can hold too much water if the big logs in the mounds become waterlogged (no pun intended) and deeply soaked, but the watermelons should be okay as long as the plant roots are slightly above grade level.

Perfect! Thank you. I know exactly what to do now. I'll leave the sand alone and be selective about organic materials.

This is helpful! I was intending to try a few "hills" in between my fruit trees this year. I was hoping the deep mulch will be the right amount of moisture for a few watermelon vines.. we'll see. I was going to try squash but I don't want to attract squash bugs and have them multiplying in the mulch like crazy. What a nightmare!

Bon, You're welcome.

Alexis, I agree that squash bugs hiding in mulch would be a total nightmare.

Dawn