Growing Watermelon on Trellises
If you've been avoiding growing watermelons because your garden is too small, wait no longer! You can grow a watermelon plant in a small 4′ x 4′ raised garden bed – if you use a trellis.
A single watermelon plant, given good growing conditions, can almost fill a 15-foot-wide circle on the ground. Yikes! There's no avoiding that they are large, vigorous plants. But if you select the right variety, take good care of them, and train them up a trellis, you can enjoy fresh melons from your own small garden beds.
1) Make sure these plants get full sunlight – 8 hours or more.
Watermelons thrive in full sunlight. However, a couple of years ago, I took a chance and planted a watermelon in a 50-square-foot bed (about 3′ x 16′) with two young 2-year-old espalier apple trees. It only received about 6 hours of sunlight, but I still harvested 3 large watermelons from that bed. So, sometimes you can succeed, even if you “break” the rules! Just don't count on a good harvest with less than full sunlight of 8 hours or more.
- 2) Give them the best soil, as deep as possible, in your raised bed.
Their root systems are massive. Just because they will be growing vertically up a trellis doesn't mean that their roots will remain in a small area at the base of the trellis. These roots will go down as deep as they can, and sidewise for a long distance. I've found the roots growing several feet outside the small garden bed they were planted in.
This is one reason that I don't put weed barrier under my raised garden beds. I want my plants to grow as large and vigorously as possible, to produce a big crop. Any time you restrict their root growth, the plant will become stunted and not produce as much.
Also, once their vines start taking off (maybe 3-4 feet long), I no longer grow other plants in the same bed with them. I give my watermelon plants the whole bed to themselves. But I still usually grow a spring crop before the watermelons, and a fall crop after them.
We built new garden beds last year, to make it easier for me to garden with my disability. These beds are made from concrete (cinder) blocks, and are 18 inches high, a little over 3 feet wide, and almost 16 feet long – for a total of 50 square feet each. These beds have the deepest soil I've ever used in my raised bed gardens, and I was frankly stunned at how large our harvests were last year.
Deep soil can have a huge difference on how well your plants grow. We planted 2 butternut squash plants and 3 watermelon plants in one of those beds. We used 4 trellises – two at each end – and grew the third watermelon plant on the soil in the middle.
We ended up harvesting 40 pounds of squash and 105 pounds of watermelon in just 50 square feet! Our friends and neighbors really loved us last year, as there was no way my sister and I could eat all that watermelon by ourselves.
3) Select a variety suited for trellising and your climate
Watermelons love hot weather and often take 90-100 days to mature. They generally don't thrive in cool, cloudy climates or short growing seasons. However, some varieties have been bred to mature quickly or tolerate cooler weather.
I like to grow “Blacktail Mountain.” It can ripen in just 75 days, and will grow well in both cool and hot weather. It usually produces icebox melons, about 10 pounds, which is a nice size to trellis. I will be planting one in late May and another in July, in order to extend the harvest.
But this variety really surprised us last year – one of the watermelons hanging on our trellis weighed 17 pounds! That one almost popped out of the sling we made out of nylons. I wouldn't normally try to trellis melons that large, but we weren't given a choice!
4) Don't Plant Until the Soil is Warm
Wait until both the weather and the soil is warm before you plant them. Our average last spring frost is around May 15th, but I'll often wait until late May for the best growing conditions. You can try babying your plants and starting them sooner under row cover, in a cold frame, or protected in a Wall-of-Water, but they simply don't thrive in those conditions. After all that effort, you will usually only harvest melons a week or two earlier at most.
However, if you live in an area with an extremely short growing season, it may be the only way to grow watermelon at all. I've generally had better luck growing a fast maturing variety instead of trying to start them early before the weather warms up.
I prefer to plant the seeds directly in the garden bed, instead of using transplants. This is because direct-seeded plants tend to grow very large, vigorous root systems with deep taproots. Transplants often fail to develop taproots, and end up needing to be watered more frequently.
5) Build sturdy trellises!
Given deep soil and good growing conditions, I normally expect to harvest 20-30 pounds of watermelon growing on a 4 foot wide and 7 foot tall trellis. That's a LOT of weight! Make sure your trellis is sturdy enough to hold that.
Our favorite trellis right now is made from a livestock panel cut in half and attached to two t-posts pounded into the soil. That will hold anything! I've also made trellises from wood frames and welded wire fencing, and have screwed these to the outside of small wooden garden beds.
I have learned that I can use trellises on both the north and south sides of my raised beds. The mid-summer sun is high in the sky, and will supply full sunlight to both trellises as it travels. Don't put the trellises on the east and west sides, as they will shade each other as the sun moves across the sky.
6) Train the plants up the trellis
Watermelon plants grow fast – as much as 1-2 feet per week! They will not climb a trellis by themselves, so you need to tie the vines to the trellis as they grow. Don't count on their tendrils to hold the plants secure – especially during wind storms or when they have heavy fruits hanging from them.
You can use any number of things to tie your plants to the trellis. My current favorite is surveyors tape. I like to use a loose figure-8 loop, wrapped just below a leaf joint, to hold the vines up.
Watermelon vine are continually sending out new vines at nearly every leaf. I will train 8-10 main vines up my trellis, but I prune off ALL the side shoots they are sending out. Otherwise, the trellis will become very overgrown. Your fruit will obtain all the energy they need from the leaves on the main vines.
7) Support your watermelon fruit with slings
Although butternut squash fruit never need to be supported, once the fruit of your watermelons start weighing more than a few pounds, they will fall off the vines and break. (Been there, done that!) You will need to support them by creating a sling attached to the trellis. You can make slings out of many different items. Some people use mesh onion bags, pieces of fabric, or even bird netting.
Last year, I used nylon stockings given to me by a friend. I cut two slings out of each leg, tied the bottoms closed and slit the top part of the nylons into two pieces so I could tie it to the trellis. You need to make sure that the sling will continue to support the watermelon as it grows. You don't want it to stretch and sag so much that the weight of the melon ends up hanging from the vine instead of the sling.
A few of your early-pollinated melons will grow at the base of the vine, and can be supported by a brick or other object underneath them, if they don't quite touch the ground.
8) Keep your melon plants well-watered
Vines growing on trellises are exposed to the wind, and lose more moisture than vines growing on the ground. Make sure you water your plants once or twice a week during dry weather. You want the water to soak deep into the soil. I also mulch the soil surface to slow evaporation.
This is the second reason I don't use weed barrier under my raised beds. I want my plant roots to grow as deep as possible. This will let them reach moisture deep in the soil, and reduce how often I need to water them. If these large vines are growing in shallow 6” deep soil, you might need to water the plants every single day.
9) Harvest the melons when they become ripe, and enjoy!
Each watermelon is attached to the vine, opposite of a leaf. Next to the base of the watermelon stem will be a tendril. When that tendril turns brown and starts drying up, the watermelon will be ripe.
Now, if you only have 6 inches of topsoil in your raised garden beds, don't worry! You can still grow watermelons on trellises. The plants just won't grow as big, may produce a smaller harvest, and will probably need watering more often. But they'll taste just as sweet! I've even grown watermelon in 20-gallon Smart Pots, and harvested 5 small watermelons from one pot.
Have fun growing your own watermelons in small garden beds, and enjoy your harvest!