Growing Watermelons in a Small Space

My family loves watermelons, especially the smaller variety we get from the organic farmers market we frequent. They're always sweet, fresh and juicy and just the right size to fit in the fridge. I searched all over the internet to see if anyone had grown them in a container and eventually found a couple of people who said it was possible using a trellis. Sounded like my kind of project...

The first few leaves at the base of my early moonbeam watermelon vine were damaged by a cold wind shortly after being transplanted.

For best results you have to select an icebox or midget variety like Sugar Baby, Golden Midget, or Early Moonbeam. They produce melons under 10 lbs on manageable vines. The Early Moonbeam I planted had a pair of 10 foot vines and some shorter offshoot vines and it produced 8 female flowers of which 2 produced juicy sweet 4 pound melons.

I started my Early Moonbeam from seeds indoors, probably a little too early and the vines were rather long and skinny when it was finally warm enough to transplant them. I've read that watermelon plant don't transplant too well but I didn't have any problems with mine. Apparently they do best when transplanted after the soil temperature is in the 18 to 20C range - a few weeks after the last frost date. I think the night time temps were half that when I transplanted mine. Watermelon plants hate the cold and get damaged easily by strong winds. If you start them from seed don't start them too early and when small, protect them from the wind and cold.

Just a few weeks after pollination.

You need a big container to grow watermelons, but not as big as you might think. I grew my moonbeam in a square 15x15x15 inch self-watering container that I made myself and it held about 10 gallons of soil with a water reservoir underneath that held maybe a gallon of water. The root ball grew to fill the container but I don't think it overgrew it. I've successfully grown tomatoes with root balls much denser in similar sized containers.

It really is impractical to let the vines trail on the ground, especially on a balcony. There just isn't enough space and the vines will get trampled. The sun hits my balcony from the west and never overhead. So to make the most of the available sunlight, I used a trellis made from bamboo "sticks" lashed together with twine and masking tape. It was very crude, very temporary and very cheap. I had planned to construct something from 2x2's and a heavy wire mesh but I didn't have the time and wasn't prepared to commit resources to creating a massive structure for holding a plant I wasn't sure would survive the season. I was lucky though. Under the weight of the two melons (4 lbs each) some of the bamboo in the trellis snapped but I had so much twine holding it all together it didn't collapse.

My makeshift bamboo trellis held together with twine and masking tape.

I don't see many insects buzzing around my balcony and rarely bees. Certainly not enough to pollinate a few flowers. Watermelon flowers don't open for long. Female flowers only stay open for a day so I had to resort to hand pollination. All I did was wait for a female flower to open and then pull off whatever male flowers were also open, pull the petals off the male flowers and gently wipe them across the female flower's stigma to transfer the pollen. I've read that you can also transfer the pollen with a small artists brush and next time I might try that. Apparently it's best to do this in the morning which is when I did mine. You can identify the female flowers by their ovary which looks like a small immature melon at the base of the flower.

From the back. In the middle of the season I moved the whole thing closer to the balcony railing to let the vines get a little more sunlight.

One problem with using a trellis for watermelons is that the melons will need support once they get over a certain size. The vines and tendrils can't support the weight of the melons themselves. I used nylon onion sacks tied to the trellis like hammocks to take the weight of the melons off the vines. It actually worked out quite nicely. I've also heard of people using nylon stockings and old t-shirts also. Whatever works. Just make sure the melon is free to grow.

I applied a liquid fertilizer to the soil every now and then. The potting mix I started out with was a premium organically certified mix with compost added. I added some extra nitrogen (in the form of seabird guano) at the beginning of the season to promote plant development. Occasionally I applied some calcium and micro nutrient supplements to the soil and once the plant started to bloom I applied a liquid fertilizer that was high in phosphorus and potassium to promote fruiting. I'm sure it would have worked just as well with a few applications of a liquid all-in-one (5-5-5 or something) or a one time application of a dry fertilizer added to the soil surface when I transplanted.

The melons were supported in hammocks or slings made from nylon onion sacks suspended from the trellis.

Apparently there are a few indicators you can use to tell when a melon is ready to pick. None of them work for me. When tapped, the sound of a ripe melon is suppose to sound like a dull thud, not hollow sounding. Another indicator is the colour of the spot where the melon rests on the ground should be yellow when ripe, not green or white. And finally, when ripe, the tendril on the vine nearest the melons stem is suppose to dry out and turn brown.

This was the first melon. A little overripe but still quite juicy and very very sweet.

I've never been able to get anything out of tapping a watermelon and didn't see any tendrils on my plant turning brown. Melons did feel heavy for their size though. There was a period when the first melon stopped growing for a couple of weeks and after that it started to shrink, just a little. That's when we figured it was time to pick it. If we had taken it a week earlier it might have been a bit better. The second melon I picked a couple of weeks later figuring at that point it had been on the vine as long as the first. It was juicy but not quite as sweet as the first. With the limited amount of sunlight my plant was getting, it's likely that the second melon would never have gotten much sweeter.

Although not just about watermelons, Amy Goldman's Melons for the Passionate Grower offers some additional information about growing several melon varieties but it's mostly just a picture book meant to inspire (which it certainly does). It doesn't give any information about growing melons in containers. The best source for information is the internet. There are a few threads on the GardenWeb forums that I highly recommend for anyone wishing to grow watermelons in containers.

After the success I had with the Early Moonbeam, I decided to try another watermelon the following season. This time it was a Sugar Baby in a larger container. This didn't go as smoothly with that one. You can read about it here.