Possibly not enough fertilizer especially nitrogen. The vines need lots of leaves and vigorous growth. A good patch should have at least this many leaves.

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They tend to do better on sandy well drained soils. But well drained loamy and clay loam soils like mine work well also.

For max brix the water and fertility need to be at proper levels. Plus lots of sun, heat, and few weeds. I grow mine on black weed barrier.

Do a soil test to see what you may need to add and get rid of the wood chips. They rob the soil of nitrogen. Watermelons don't need to be mulched, but they need loose soil, water and full all day sun.

By now the chips are not robbing anything anymore. Just add urea next year. If you don't see a jungle like in the picture above, add more urea. Or blood meal. They only need to be watered up to a point. In the last 15-20 days before harvest, no water for max sweetness.

Wood chips use up available nitrogen in order to decompose.

I love Steve Solomon's book on compost. Composting is more complicated than one would imagine. I've linked to his book, and specifically the page where he talks about wood chips.

Here is a link that might be useful: CHAPTER TWO Composting Basics

.. and eventually they give it back. They act like nitrogen banks, first withdrawing, then releasing. Nothing gets destroyed and in fact high wood beds preserve nitrogen better than normal soil. The chips went in, I suppose, in spring and were already half composted as per the PO. Possibly, his chips, spread as mulch, kept the soil somewhat cool. Watermelons like it hot everywhere. But for next year it should be fine. Also, I don't know about the East Coast, but this summer was cold in Michigan, not at all a summer to grow melons.

The wood chips are 5 years old, half composted. The pumpkins/kabocha close-by were dong fine. It is true that I did not feed the plants since I was reluctant to put on the fertilizers I'm not familiar with.

I think the reasons are: late planting (end of May); no feeding. I did not see any bugs. Some say the wood chips can bring some diseases. But I did not see.

I think next year, I'll plant them a little early. And use other things as mulch, such as mulched leaves, hay/straw, etc. I may learn how to use plastic cover....

RedSun,

Here's a link that discusses using plastic to get the soil warmer more quickly. Mulch keeps the soil cool.

Here is a link that might be useful: Getting melons up early: black+clear poly results

Yes, the heat would certainly help. But what made the plants die in the summer? They were watered, but not clogged... Just out of energy?

The thing I battle most is powdery mildew on melons. Seems everybody got it this year around here. I did too.
Did they develop a disease? Did they get powdery mildew?
I don't see how lack of food would kill them? Just stop them from producing.

I tried to spot pest and diseases, but I did not see any. I may have missed powdery mildew. Not sure.

The pumpkins were next to the watermelons. They had vine borers and some have powdery mildew. But the pumpkin plants still produced 2 fruits on each vine.

Well you have more info now. Try again, see what happens.

I am a bit confused. What is wrong? Is it only that the vines died off? You have 8" fruit. Is that a problem? Maybe the cultivar only produces 8" fruit. How was the flavor? Did they develop to mature melons? The die off could just be the vine saying "Ok, I am done..." I have seen this with pumpkins and gourds.

Check very closely for any evidence affecting the vine from the root to the first leaf. Insects burrow in at the soil level, lay eggs in the stem, and then the larva invades the plant killing the vine. This is what killed off my cucumber vines once.

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This following anecdote has nothing to do with your situation but I enjoy telling the story:

I once found mature seeds in a "seedless" watermelon and planted them. Vines grew very well and I clipped them to produce one watermelon. It grew to size and I left it on the vine for another month or so.

Late that summer I decided to open it. I found a very thick rind (green) section a very small pulp (red) section. Not only did the pulp have very little flavor but there were more seeds than pulp.

Since the seeds are not true to the parent, I wonder how they grow them in the first place...

The melons were not mature. There are many small fruits. I collected a total of 14 of them. Some of the fruits developed some kind of molds (or rot) and had to be thrown away. So I think maybe there is some kind of diseases.

One or two of the vines were still alive last week when I cleaned the melon bed.

This is my first year. So not much disappointment. But just something to learn. Next year, I'll grow my own seedlings, then pot them to bigger sizes. May use black plastic cover.....

I am trying to think of any other reasons that might be afoot here.

Have a soil test done right now and maybe you can prepare the bed for next year. Be sure to inform the tester what you plant to grow.

I grew them in both zone 4 and 5 and have never used black plastic. I believe it does more damage than any benefit from the heat it gathers. Kills nematodes, cooks worms, blocks water, etc... I wonder if, in zone 6, if it may cook the roots. Don't use landscapers fabric. It is almost as bad as plastic even though it lets water through.

If I were to grow them again, I would put down 5 sheets of newspaper covered with straw. I use that with my annual beds and it seriously stops weeds the first year. If you want a more cosmetic finish, use cooked/chopped hay for 2x the price. If you want to know how to do this and not have to fight the wind, let me know. I will explain.

You can get larger fruit if you trim the vines after two to three melons are set then later thin out to the best one per vine.

How large of an area? If you have enough room, let several melons set and check to see that the vines have rooted between them then cut right after each melon. Effectively, you have separate plants from one.

Was the rot on the bottom in contact with the soil or was it at the blossom end? Blossom-End Rot may be caused by lack of nutrients. Some people will claim that BER is only on tomatoes but I have seen it on any vine fruit plant.

Did the vines rot or just dry up?
Did the leaves turn yellow (could be too much water).

Starting seeds too early can be a mess with long unmanageable vines before it is warm enough to set outside. You also have to condition house-grown plants to the wind and sun (hardening off) before they will tolerate being outside. Use pro-mix soil to assure a good start.

May to Sept should be long enough to plant seeds directly in the soil.

Did you set the seeds in hills? It works better as they will be warmer.

Did you water at night or continuously? Either one can be bad for the plant and may cause rot. Soaker hoses work better but be sure to let the soil dry between watering cycles. Design something that only waters the main root. The rest of the plant should fend for itself.

Enough already? (:

We put down the seedlings, about 4" to 5", in the ground in late May/early June. The bed is about 7'x30' or so. The bed is newly dug. We put on the chip mulch two weeks later.

From the beginning, the plants put on very good growth. Many flowers. We let each vine to grow about 3 melons. We did not remove other flowers, but the vines stopping forming new fruits.

Then the vines stay there, not doing much. We just saw the melons getting larger. Then somehow the melons stopped growing, or growing very slowly. The leaves did not wilt. Then the leaves got dry and the vines died. As i said, one or two vines were still alive last week, but has not done anything after.

I had pumpkin vine borers close-by. I did not see the watermelons get infected. The pumpkins also have mildew, but I did not see that on the watermelon vines. The plants were watered regularly, but not clogged. I tried not to water on the leaves.

As for the mold on the fruits. The mold was like nickle size, several on the underneath of the fruits. But that happened to only two fruits. We threw them away.

We still have some melons. They are edible, but not mature and not very sweet.