I'd avoid growing watermelons in pots so planting in-ground gets my vote. The more direct sun exposure the better and digging out all roots (within the plot) from nearby plants is a good idea. No soil mix needed if the natural soil is good, just add/mix in some well balanced fertilizer and/or compost a few days prior to planting. Sprawling rather than trellising but keep weeds under control.

vgkg - Thank you! Will they sprawl over mulch?

Trellising watermelons is difficult if not impossible as the vines on the trellis cannot support the fruit weight. You would have to rig up some sort of slings for the fruit. Normally the vines are meant to sprawl for best results. Running out onto the surrounding lawn isn't a problems except for mowing the grass. Vines average 6' long but can grow even longer.

Trying to grow watermelon, with limited space available, is unusual and two vines will most likely only produce 4 fruit so are you sure the space couldn't be better used?

Also please note the soil temps required for direct seeding watermelon as it may still be too early in your zone.

Dave

digdirt - thank you, I think for 6' I can let them sprawl on mulch/grass. That space if not used by vine, will just be mulch area, so I think I will give it a try. I think my kids will be thrilled :)

I assume I should do a mound for these too? If too cold now, when is the right time to start seeds outdoors? Or should I start indoors now, but I heard they do not like to be transplanted.

Traveler000mkl, a slight mound is good for drainage. As for the melons on mulch that should be ok too but what type of mulch, pine bark? I generally mulch with compost or pine needles. Not a big fan of pine bark as I have found that termites like it too and sometimes come with the bag.. Watermelons have a thick tough rind that should be able to "sit" on just about anything ok though the dryer the better to avoid possible bottom rot (rare).

As a side note, Cantaloupes have a more tender rind so as they mature I'll put a hand full of pine needles under each one to keep the bottoms off of wet or muddy soil. In one instance I found a ripe cantaloupe with termites drilling into the bottom, ants do this too at times. The only critters that drill into my watermelons usually have 4 legs rather than 6 :)

< If too cold now, when is the right time to start seeds outdoors? Or
should I start indoors now, but I heard they do not like to be
transplanted.>

None of us can tell you the exact time for best planting in your garden. Weather plays a crucial role. As a general guide, watermelon is a warm weather crop, not a spring cool crop. But only your soil temps can tell you when to plant and so many factors affect that so even neighboring gardens are different. So you will need to learn how to take and monitor soil temps. There are many charts available on required soil temps for germination. Containers will warm faster than in ground beds but they will also cool off faster.

Watermelon can be started inside for transplant however it does best when direct seeded at the proper time as transplants are easily set-back or stunted.

Your obvious enthusiasm will see you through but it won't replace the research and homework to be done before planting and all kinds of "how to grow __________ in the home garden" info is available online. :)

http://bonnieplants.com/growing/growing-watermelons/

Dave