Growing Watermelons in a Small Space
My family loves watermelons, especially the smaller varieties we get from the organic farmers markets we frequent. They're always sweet, fresh and juicy and just the right size to fit in the fridge. These smaller melons grow on plants that are well suited for trellis growing which makes them perfect for growing on the balcony.
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. My first attempt to grow watermelons in containers yielded a plant that had a couple of 12 foot vines and several shorter offshoot vines and over its lifespan it produced a dozen female flowers, of which 2 produced juicy sweet 4 pound Early Moonbeam watermelons. Since then I've grown others like Sugar Baby and Golden Midget and they all had similar growing habits.
The first few leaves at the base of my early moonbeam watermelon vine were damaged by a cold wind shortly after being transplanted.
Just a few weeks after pollination.
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 outside. Watermelon plants don't transplant too well but on that particular occasion I didn't have any trouble. Apparently they do best when transplanted after the soil temperature reaches the 18 to 20C range. 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.
My makeshift bamboo trellis held together with twine and masking tape.
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. Since then I've constructed a slightly larger self watering container using a pair of storage totes. I find this provides more than enough space to grow an icebox variety watermelon plant.
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 grow my melons on a trellis. I used to use nothing more than some bamboo "sticks" lashed together with twine and masking tape. It was very crude, very temporary and very cheap. Since then I've constructed something a little more substantial and permanent. The important thing is to make sure the structure can support the weight of the melons. Even so, I've grown large tomato plants that put much more stress on a trellis than these small watermelon plants.
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 have to resort to hand pollination. All I do is wait for a female flower to open and then pull off whatever male flowers are also open, pull the petals off the males and gently wipe them across the female flower's stigma to transfer the pollen. You can also transfer pollen with a small artists brush but I find the grains of pollen produced by these small watermelon flowers are harder to work with on the tip of a brush. It's best to perform this activity in the morning which is when I like to pollinate my melons. You can identify the female flowers by their ovary which looks like a small immature melon at the base of the flower.
One problem with using a trellis for watermelon plants is that the melons will need support once they get over a certain size. The vines and tendrils have a hard time supporting the weight of the melons themselves. I once had a melon pull away from the trellis and as it went crashing to the balcony floor it ripped away from the vine and severed it as well. I've used nylon onion sacks and old T-shirts tied to the trellis like hammocks to take the weight of the melons off the vines. It actually works quite well. When using old T-Shirts I found that they the areas of the melons covered with the shirt remained slightly green, even after the melon ripened. I didn't affect the taste of the melons.
This melon is supported in a hammock made from nylon onion sacks suspended from the trellis.
This was my first early moonbeam watermelon. A little overripe but still quite juicy and very very sweet.
I like to grow my watermelons in a potting mix that has compost and organic fertilizer added. I'll add 10-20% compost to the soil (I do this with all of my containers) as well as a good amount of extra perlite or vermiculite to keep the soil light and airy because the compost has a tendency to make the potting soil overly dense for container use. The composts I use contain a lot of peat moss. I also mix in a healthy amount of organic fertilizer. At one time I was mixing in different things but now I just use a general purpose well-balanced fertilizer suitable for growing vegetables. What I use changes from season to season. I mix it in with the soil at the start of the growing season following the instructions on whatever package I've purchased from the garden center.
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.
I've never been able to get anything out of tapping a watermelon and never see any tendrils on my plant turning brown. Ripe melons should also feel heavy for their size though. The first time I grew watermelons I just left them on the vine until I noticed the melons were starting to shrink, just a little. That's when we figured it was time to pick. If we had taken them a week earlier it might have been a bit better. It's a good idea to keep track of when you started your plants and when you transplanted them. Find out how long it should take your chosen variety to reach maturity and use this as a rough guide for when to pick that first melon. My first time growing Golden Midget watermelons yielded my first ripe melon after 70 days: exactly the number of days to maturity stated on the seed pack.
I suspended this melon from the trellis with the remains of an old shirt.
An almost perfect Golden Midget watermelon.
A couple of times I've attempted to grow Sugar Baby watermelons in a container and I have yet to reproduce the success I've had with others like Early Moonbeam or Golden Midet. I don't blame the watermelon through. There is nothing difficult or fussy about Sugar Baby watermelon plants. I just haven't had much luck with them.
The first time I grew sugar babies I found The seedlings were slow to start and did not grow as fast as I hoped they would. And when I got them outside they took a long time to start growing again. My belief is that I left them in their starter containers too long so when it came time to transplant them, the roots were easily disturbed and 'upset' by the transplant. I've since learned to be a bit more gentle with transplanting watermelons and to make sure my container soil is nice and warm so the plants are not overly shocked by the change.
Eventually the plant took off and I had to get it up on a trellis but the vines did not grow as long as I hoped they would. The leaves got big and dense but the plant just didn't want to grow. As the melons that formed on the plant grew, they quickly went from light green with stripes to an overall very dark green colour, just like you'd expect from a sugar baby melon. But once they reached large apple size I noticed they were lopsided with the distance from top stem to bottom dimple being shorter on one side. A likely cause: inconsistent pollination. Pollination isn't just about getting male pollen somewhere in the female flower. It's about getting the pollen spread consistently across all areas of the female stigma. If the flower is inadequately pollinated, you end up with lopsided fruit growth.
You can see the spider mite damage on the lower leaves.
This was about as big as my sugar baby watermelons got. About the size of a grapefruit. This is a month and a week after pollination.
The other major problem I had with my first Sugar Baby watermelon plant was spider mites. I started to notice some of the lower leaves on the plant turning yellow from the inside out. I couldn't see it easily at first but under really close observation I could see a number of very tiny insects covering some of the lower leaves. And they were slowing moving their way along the vines, sucking the life out of the plant as they went. The leaves on which they settled would turn yellow then brown and had a rough stippled texture before becoming brittle and dry. The backs of the dead leaves were covered with a very fine webbing. And it was spreading practically before my eyes. To combat the problem I started spraying the backs of the leave with water using a spray bottle in an attempt to blast them off the leaves. If only I had known then that a little bit of dish soap in the water would have killed them instantly. It only took a few minutes and about half a gallon of water every other morning. I was able to slow the spread of the mites but it was not a permanent solution. I was not able to completely eradicate them, only slow them down temporarily.
Immature sugar baby watermelon that is lopsided due to improper pollination.
At that point I pretty much gave up. It was almost September and I didn't think there was any way my lopsided melons were going to reach a mature size before the spider mites killed the plant completely. I left the pair of melons the plant was supporting on the vines for a few weeks to at least give them a chance to mature. They barely weighted half a pound. Inside they were mostly white with lots of immature seeds. I learned quite a bit from the experience, about spider mites, hand pollination and transplanting.
If you can find it, 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.