Growing watermelon in containers from seed to harvest

Unless you have a large vegetable garden, it’s tough to find room to grow everything you’d like to, especially when it comes to vine crops that take up a lot of room. Containers are a great way to grow whatever fruits and veggies you don’t have space for in an in-ground or raised bed garden. They’re also great if you have no garden at all. For me, one crop I love to grow but never seem to have enough room for, is watermelons. This article introduces the ins and outs of growing watermelon in containers. Yes, you can grow watermelon in pots. But there are some important guidelines you’ll want to follow to set yourself up for success.

The benefits of growing watermelon in containers

Aside from saving space, there are several other reasons why growing watermelon in pots is a smart idea. First, watermelons love warm soil. If you plant the seeds or transplants in cool soil, they’ll languish, and the seeds may even rot before they germinate. Typically, soil in containers warms up much faster in the spring than the soil in the ground. If you grow in dark-colored pots or black grow bags, they absorb the sun’s rays, warming up the soil inside even faster. This means you can plant your watermelon seeds or transplants a few weeks in advance of planting in the ground.

Another benefit of growing watermelons in containers is the ability to control the moisture they receive. Watermelons are very thirsty plants that require a lot of water. Irrigation amounts can be tough to track in-ground, but the opposite is true in containers. However, it’s also very easy to forget to water or to short-change your plants when growing in pots. Later in this article, I’ll share some very useful tips for making sure your container watermelons get enough water.

One final benefit: pest prevention. Watermelons grown in containers ripen sitting on a deck, patio, or porch, instead of sitting on bare soil. This means that slugs, pill bugs, wireworms, and other ground-level pests don’t come in contact with the fruits.

Now that you know the perks of growing watermelons in pots, let’s discuss how to select the right variety for the job.

The best watermelon varieties for growing in containers

The vines of standard watermelon varieties can grow up to 10 feet in length, making them difficult to manage in containers. They are particularly difficult for gardeners who grow in small spaces. Plus, despite their crazy length, each vine only produces one or two fruits. If you’re lacking space, those low yields from such big plants are nothing to write home about. So, what’s a container gardener to do? Turn to a watermelon variety bred specifically for containers, of course!

When it comes to growing watermelon in containers, there’s no better choice than ‘Bush Sugar Baby’ watermelons. The vines of this container watermelon are compact. They reach only 24 to 36 inches in length. But don’t assume that means the fruits are puny. Each vine produces two or three 10- to 12-pound watermelons. The rind is dark green, and the interior flesh is red with a great flavor. I highly recommend ‘Bush Sugar Baby’ for the job. ‘Sugar Pot’ is another great alternative, but the seeds have been difficult to find the last few years. If you decide to grow a standard-sized variety, just be prepared to water them A LOT and give them plenty of room to ramble.

Regardless of what variety you grow in your pots, be sure to site the containers in a location where they receive a minimum of 8 hours of full sun per day. Watermelons will not form flowers or fruits if they don’t get enough sun.

What size pot is best for growing watermelon in containers

For growing watermelon in containers successfully, pot size is key. If you choose a container that’s too small, the roots won’t have enough room to spread. You’ll also be watering constantly. Choose a pot that holds at least 7 to 10 gallons of soil per plant if you’re growing ‘Bush Sugar Baby’ or ‘Sugar Pot’. An approximate dimension is at least 18 to 24 inches across and 20 to 24 inches deep. They’ll need to be almost twice as big if you’re growing a standard watermelon variety. Remember, that’s a minimum. The glazed ceramic pot shown in this article holds around 13 gallons of potting mix. I grow two ‘Sugar Pot’ or ‘Bush Sugar Baby’ melons in it.

Be sure that whatever pot you choose has multiple drainage holes in the bottom. If holes aren’t present, use a drill to make them.

The best soil for growing watermelon in containers

Aside from the size of the container and choosing the right variety, the next important factor in growing watermelons in containers is the soil. It’s important to fill the container with the right soil blend or you might as well chain yourself to your garden hose or watering can all summer long. If you opt for a mix that’s too well-draining, it will dry out too quickly and affect plant health and fruit production. If you opt for a mix that’s not well-draining enough, the soil will stay waterlogged, starving the roots of oxygen and potentially causing root rot.

Watermelons are heavy feeders that don’t like to dry out. Choose a high-quality potting mix and blend it with compost. I mix organic potting soil half-and-half with finished compost. The compost absorbs and retains water, and the potting soil keeps the mix light and well-draining. Plus, the compost adds beneficial soil microbes to the container, along with nutrients.

Should you grow from seed or transplants?

There are two ways to plant watermelons in pots. The first is from seed and the second is from transplants. Before I tell you how to do both, there are pros and cons of each method that are worth discussing.

Planting from seed is inexpensive, and it’s easier to make sure you’re growing the specific variety you want (‘Bush Sugar Baby’ in this instance – seeds are available here). The seedlings are not subjected to transplant shock since they will live where they were originally planted and never have to be moved. The main downside when growing watermelon in containers from seed is the length of the growing season. ‘Bush Sugar Baby’ requires 80 to 85 days to go from seed to mature fruits. If you live in a northern growing zone with a shorter growing season, this might not be enough time. If that’s the case, you should opt for planting transplants instead of seeds because it gives you a few weeks’ worth of a head start.

Transplants have additional benefits, too. You’ll be harvesting earlier, and there is no chance the seeds will rot in soil that’s too wet or too cold. The main downsides are that it’s more costly, there is an increased chance of slow or stunted growth due to transplant shock (especially if the seedlings were pot-bound), and you may not be able to get the specific variety you’re looking for. If your local nursery doesn’t grow ‘Bush Sugar Baby’ or ‘Sugar Pot’, start your own seeds indoors under grow lights about 4 to 6 weeks before your last average spring frost date. Here in Pennsylvania, I sow the seeds indoors in peat pellets in mid-April for planting outdoors in late May or early June.

How to plant watermelons in containers from seed

If you opt for growing watermelon in containers by seed, head outside a week or two after the danger of frost has passed. For me, that’s around Memorial Day. Don’t get excited and plant too early. With watermelons, it’s always better to wait until the soil is good and warm, and there’s absolutely no chance of a freeze.

Bury each seed to a depth of about one inch. Follow the guidelines presented in the section on selecting a pot to know how many seeds to plant in your container. Do not over plant. If you want to grow more watermelons, buy more pots. Don’t cram more plants into the pots you already have. Give them oodles of room.

Growing watermelon in containers from transplants

When growing from transplants, regardless of whether you’ve grown them yourself or purchased them at the nursery, be mindful of following the pot-size guidelines above. Plant them to the exact same depth they were in the nursery pack or peat pellet. No deeper. If you grew in peat pellets, remember to peel off the outer layer of fine plastic mesh before planting them. If the transplants were grown in nursery packs or pots, try not to disturb the roots when planting them. Melons do not like to have their roots messed with, so don’t loosen them like you would for tomatoes or peppers.

Watering container watermelon plants

Immediately after planting your watermelon seeds or transplants, water them in thoroughly. It’s essential that the soil is kept continually moist all the way through harvest time. Never allow the soil to become completely dry. That means on hot days (over 85 degrees F), you’ll have to water in the morning and again in the late afternoon. And don’t be a wimp when you water. Water like you mean it. Aim the hose nozzle directly on the soil and apply lots of water, soaking the soil completely and repeatedly. Excess water should be freely running out the drainage holes in the bottom of the pot. For my 13-gallon pot, I add about 3 to 5 gallons of water each time I water.

That being said, make sure there is no water left standing in a saucer beneath the pot when you’re done watering. This can lead to root rot and starve the plant roots of oxygen. I don’t use any saucers beneath my outdoor plants to prevent this exact thing from happening.

Do not subject the vines to extended dry periods followed by lots of irrigation, especially when the fruits are close to being ripe. This causes the skin to crack open and/or the flavor to be watery.

The best fertilizer for container watermelons

Though the compost you added to the container provides some nutrients when growing watermelons in containers, it’s not enough. Watermelons are heavy feeders. Work two tablespoons of granular organic fertilizer that’s slightly higher in phosphorus into the soil every month throughout the growing season. Alternatively, use a liquid organic fertilizer with a slightly higher amount of phosphorous in it to feed your container watermelons every three weeks, starting when the seedlings develop their first true leaves.

How do you know when your watermelon is ripe?

Waiting too long to pick your melon means a mealy texture, but not waiting long enough might mean throwing an unripe treasure into the compost bin. Commercial melon farmers rely on a brix refractometer, a tool used to measure soluble sugar content of the fruits. While you can purchase a brix meter if you’d like, most home gardeners look for other ways to tell when their melons are ripe for the picking.

Since you know that ‘Bush Sugar Baby’ requires about 80 to 85 days to mature, mark your calendar to check for melon ripeness around that time. Do not harvest too early because watermelons picked before they are ripe will not ripen after they’ve been severed from the vine.

Clues you’ll want to watch for:
• Look for a yellow spot on the underside of the fruit, where it sits on the deck or patio. If the spot is light green or white, it’s not ready yet.
• Check the tendril closes to where the fruit stem attaches to the vine. The tendril starts to shrivel and turn brown when the melon is ready to be harvested.
• Some gardeners can tell ripeness by thumping the melons with their fist. It’s something I’ve never perfected, so I’ll offer no advice on that!

Unlike cantaloupes, ripe watermelons will not naturally separate from their stem. You have to cut the ripe melon from the vine with a knife or a pair of pruners.

Extra tips for growing watermelon in a pot

• Avoid using fertilizers high in nitrogen. They generate a lot of vine growth at the expense of fruit.
• For the best results, don’t plant watermelons until the soil is at least 70 degrees F, regardless of whether you’re growing in pots or in the ground.
• Add a layer of shredded leaves or straw to the top of the pot to serve as a mulch. It prevents moisture loss and stabilizes the soil temperature in the pot.
• For the sweetest flavor, stop watering your watermelons two weeks before harvest. The dryer soil causes the sugars to concentrate in the melon, giving it an even sweeter flavor.

As you can see, growing watermelon in containers is a fun endeavor, if you choose the right variety and pay attention to the plant’s care. Tasting your first homegrown melon is something you won’t soon forget!

For more on growing melons and other vine crops, check out the following articles:
• Mini melons for small gardens
• Growing cucamelons
• Cucumber trellising ideas
• Spaghetti squash growing tips
• When to harvest winter squash