Growing Watermelons... in Raised Beds?!

“You’re a little crazy,” they say when I plant eggplant in the middle of a 4ft. x 4ft. raised bed packed with peppers, garlic, flowers, and herbs. 

“There’s no space!” they say when I squeeze more herbs around the edge of the bed. 

“All right, now you’ve gone too far! Those plants will get too big,” they say when I plant four watermelon plants around the edge of that exact same raised bed. 

If there’s one thing I agree with these plant spacing police/social media trolls on, it’s that watermelon grows too large to be given your precious raised bed real estate. These are, after all, sprawling plants that will want each and every inch they can have.

I disagree, however, that watermelon can’t be grown in a raised bed, even one already planted intensively, for that matter. 

Here’s the thing: Watermelon plants do grow long vines, but the only part of the plant that needs to be inside the actual raised bed is the root structure. The rest of the plant can cascade over the side of the bed and trail along the garden pathway.  

If you want to grow mouthwatering watermelons in your raised beds without growing only watermelons in your raised beds, stick with me, folks. Here's how.

The Benefits of Growing Watermelon in a Raised Bed

The massive roots of the watermelon plant get to benefit from the added depth of the raised bed structure. Melons are hungry plants, so they’ll enjoy pulling nutrients from the great soil filling the raised bed, and they'll also appreciate the good drainage. The soil in your raised bed even heats up faster than the soil in the ground, and melons grow best in nice, warm soil.

These benefits you shall have without sacrificing your entire raised bed space to one watermelon plant. 

How to Prepare Your Raised Bed for Watermelon

If you've got multiple options, make sure you pick the raised bed that gets the absolute most sunlight. At minimum, a large fruiting plant like watermelon needs 8 hours of sunlight a day but will thrive with 10 to 12 plus hours of sun. 

Once you've picked the sunniest spot, you can lay a healthy foundation for your watermelon plants by adding a 2- to 3-inch-thick layer of compost to the top of the soil. I'm assuming your bed is already filled with nutrient-rich organic soil, so now you're just enhancing its fertility and drainage capabilities a bit more. I like to compare this to carb loading before running a marathon.

Watermelons thrive in slightly acidic soil, so you might need to test and adjust the pH level of your soil. In my experience, a raised bed filled with well-maintained soil will support these plants just great without needing adjustments.

Planting Watermelon Seeds or Seedlings

Watermelons need lots of long summer days to complete their growing stages. You're looking at 80 to 120 days before they reach full maturity.

If you live somewhere with a really long growing season, you can direct sow watermelon seeds in the raised bed as soon as the threat of frost has passed and your nighttime temps are staying above 50 degrees Fahrenheit (this ensures the soil is nice and warm, just the way watermelons like it).

If you live somewhere colder and barely have a hundred days of warm to hot weather, you can start watermelons by seed under lights indoors about 4 to 6 weeks before your last frost date. While I have started gourds and melons indoors before, I've found they often lag behind seeds sown right in the garden thanks to the shock of being moved. Transplant seedlings when they've developed a few true leaves, and make sure to keep an eye on them for the first couple weeks.

Add up to one cup of nitrogen-rich fertilizer below the seed or seedling the day of planting. Make sure to keep the soil moist while you're waiting on the seeds to sprout.

Tending Watermelon Growing in a Raised Bed

Once your watermelon plants begin sending out vines, your garden will feel a little wild! Make sure you don’t step (or trip!) on all those vines when you’re walking through your kitchen garden. Each vine will have little tendrils for grabbing onto a support structure. You could utilize these to grow your melons vertically if it weren’t for the size of each fruit. They’re just a tad too heavy to hang onto a trellis. Instead, let the vines and their tendrils sprawl over the garden path. 

Now, I will say, this is one reason I prefer to have gravel paths instead of using mulch or soil. If your pathway is covered in organic matter, there will be a higher likelihood of pests like cucumber beetles and squash vine borers getting onto the leaves and vines of the plant. 

I like to spread out the vines a bit to ensure each one is getting as much sunlight and fresh air as possible. Avoid vines crossing and tangling, at least in the beginning.

Other than looking out for the vines, your only tending tasks will be watering, replenishing nutrients, and pruning. 

Fertilizing Watermelon in a Raised Bed

Watermelon plants are like super hungry teenagers. They need nitrogen to start off, then potassium, and finally, regular doses of phosphorus as they flower and fruit. I recommend setting a weekly or biweekly feeding schedule to keep these nutrient-guzzlers happy.

Again, use a nitrogen-rich fertilizer in the first month of growing, and then switch to a phosphorus-rich one once the plant starts blooming. I recommend fish- or kelp-based fertilizers, though bone meal and rock phosphate are also great sources of phosphorus for your fruiting vines. You'll just add a little bit around the base of each plant and water it in well. You'll especially want to add one of these fertilizers if your plant isn't forming as many flowers as you'd expect.

Note that you'll slow down the fertilization process as the time to harvest draws near. When your melons are one to two weeks away from harvest, stop adding any fertilizers so that the plant can store its nutrients, sweeten its fruit, and be ready to pick. 

Watering Watermelon in a Raised Bed

They don't call it watermelon for nothing, you know? The seeds will need to stay moist until they sprout, and then the plants will require consistent moisture throughout their growing period. I like to give my watermelons at least one heavy watering a week. Deep but infrequent watering encourages the root systems to dig down deep to reach for water when they start to run dry. You might need to up your watering in the heat of summer if you live someplace really warm.

As far as how much to water, you'll need to give each plant one inch of water per square foot of plant growth to meet its H2O needs. Make sure you never see the leaves wilting or showing signs of stress in the middle of the day.

When watering these plants, be sure the water reaches the roots, not the leaves. 

You'll slow down your watering before harvest time just as you slowed down your fertilizing. Water less two weeks before, and then stop watering altogether for the final week before harvesting. The inside of the fruits will become sweeter, and the flesh will stay nice and crisp this way.

Pruning Watermelon in a Raised Bed

You may notice that several vines will emerge from the same root node. You've got a decision to make once the plant's been growing for about 40 days. Generally speaking, pruning to just one main vine will focus the plant’s energy and result in bigger watermelons. Keeping the extra vines will get you more melons, but they’ll be smaller. I prefer smaller fruits because I've found that more things can go wrong the bigger each fruit gets.

In addition to perhaps pruning down to one main vine, you'll also want to remove any leaves that are browning or yellowing or just showing signs of wear. Cutting these leaves frees up the plant's energy to put toward flowering and fruiting. Avoid pruning too much because you'll want to use the leaves to keep the fruits covered up. Do this type of light pruning about once a week.

Pollination and Watermelon Fruit Development 

Watermelons require pollination to successfully set fruit, and our friendly neighborhood pollinators play a vital role in this process. Encourage pollinators to visit your garden by planting lots of colorful flowers throughout your raised beds and by avoiding the use of pesticides. If you haven't noticed any bees buzzing or butterflies flitting, you can hand pollinate by transferring pollen from the male flower to the female flowers using a little paint brush or cotton swab.

Once your fruits are forming, you can prevent rotting by gently lifting them and turning them every week or two. Cover them back up with leaves when you're done.

Watermelon Harvest Time

Is it finally time to enjoy the fruits of your labor? Melons seem to have a special way to say, "I’m ready!" Here are a couple signs harvest time has arrived:

• The netting pattern is more visible, and the fruit's skin has turned dull.
• The underside has turned yellow or cream colored.
• A crack appears at the base of the stem.
• The melon sounds hollow when tapped.
• The tendril closest to the fruit dries up.

Don't forget: One week before harvesting, stop watering and fertilizing your plants.

Use a sharp knife or pruning shears to cut the watermelon from the vine, leaving a couple inches of the stem attached for storage. You can typically expect between 2 and 4 fruits per plant.

Make sure to harvest any remaining melons before frost arrives.

Homegrown Watermelon Right in Your Raised-Bed Garden

My daughter told me the other day that my garden was starting to look like a jungle thanks to all the watermelon vines! When I say these vines can grow wild, I mean it. I even found baby rabbits nestled underneath my watermelon vines back in Chicago (they were so cute!).

If you can handle the wildness, then you'll be on your way to slicing open homegrown organic watermelons—the juiciest, most flavor-packed melons you've ever tasted!

Thanks for being here and making the kitchen garden a normal part of life once again!