Watermelons in pots

There are different watermelons, with different dates to maturity and so forth.  I can generalize instructions, but it would be helpful to know what watermelon variety you have, and whether they are adapted to your local conditions (do others grow them in Yorkshire).  I'm hoping you have a short-season melon with small ("bush") plants that can produce melons in as little as 75 days, similar to sugar baby.

Not knowing your exact location, I just looked up a month-long weather forecast for Hornsea.  You can probably get watermelons to crop there.  Try putting the strongest seedlings into half gallon or larger pots to grow on for a few weeks to a month (one seedling per pot; you can turn just about any container into a pot if you have drainage holes) .  Your goal is to get the best seedlings ready, to eventually end up in the ground, in well-drained soil.  Even the "bush" melons need room to sprawl.  If you have 32 seedlings, I would not try to plant all of them in your south-facing spot.  Look up spacing and growing directions for the variety you have.  For your spares, maybe your little one can share the extras with other little ones?  Or, if there is some spare corner of the yard, plant them in the ground and see what happens.

You can grow your seedlings in the larger pots in a sunny spot, close to a location where they can be pulled into protection if the weather turns too cold (shed or garage for example).  Like tomatoes, they will do best in warm conditions, poorly below 10 C.  June, July, and August might be good months to have them in the ground.

I would look for additional growing tips from seed companies, many have growing tip on their websites.  Melons are heavy feeders, provide moderate doses many times throughout the growing season.

A trick you need to remember for harvesting: Watermelons develop something called a "field spot" which is where the melon rests on the ground.  The field spot will develop as a white spot underneath the melon (the rest of the melon rind will be green of course).  Don't harvest if that field spot is white; wait for it to turn a strong yellow, the deeper the yellow, the better (sweeter) the melon will be.  Also, the tendrils closest to a ripe melon will begin to turn from green to yellow or brown.  People do all kinds of other things to check if a watermelon is ripe or not (thumping it, or balancing a broom straw on it to see if it will turn). I have tried them all, I think the field spot and tendrils are the best indicators.

I remember as a very young child (maybe 5 or 6)  that I really wanted to grow watermelons, green beans too.  The next door neighbor man always watched my gardening with some amusement.  I grew vines which eventually bloomed, and started making little melons.  Miraculously, I suddenly had watermelons overnight!  A little older, I figured out the secret . . . my neighbor put a few ripe watermelons into my garden overnight  .  They had come from his garden at his vacation home in southern Indiana.  He was a kind man, but sometimes tricky 

For Sugar Baby, I see recommendations for spacing HILLS at 4 x 4 ft to 4 x 6 ft spacing.  Nowhere near 60 sq ft.

Here is a more detailed growing guide I found for Sugar Baby (worth printing and saving). http://www.heirloom-organics.com/guide/va/1/guidetogrowingsugarbabywatermelon.html  Disclaimer: I'm neither a customer nor employee of Heirloom Organics.  Their growing guide seems reasonable to me.

BTW, a hill is a grouping of plants.  Since you already have plants, consider a hill to be 2 or 3 plants of this melon planted in a group.

Although I probably wouldn't try growing watermelons in a pot, if you do, make it a big one.  I grow squash in 10 gallon pots, I wouldn't go smaller than that.  Just my opinion.

Here's a pic of how some of them are doing

Nice and healthy. You should have no problem moving those to bigger pots.

I'm not sure about that one. You could try some where you remove all but the best, others where you leave them all on.  Either way, I would stoke up the coals.  Frequent liquid feed, frequent watering, moist but not soggy, never drying out, consistent with that growing guide.

You are doing well with them, sounds like your hard work is paying off!

I bet your little one was pleased!
How did they taste?

Someone on another thread posted asking if melons can really be grown in the UK at all. You proved that it can be done.

Well, I’ll eat my words. Were they grown inside or outside?  My neighbour here in London just got one grapefruit sized watermelon for his efforts.