From Seed to Harvest: A guide to growing Watermelons In Containers

Despite being an avid gardener, I never considered watermelons to be a container crop. With their sprawling vines and huge fruits, growing watermelons in containers seemed impractical at best.

Yet for those of us with only small yards or balconies to work with, container growing may be our only option if we want to taste ripe, succulent, homegrown watermelons.

As it turns out, growing watermelons in containers is more than just a way to deal with limited space.

There are actually quite a few advantages to growing watermelons in containers, so regardless of the size of your garden, you might want to give it a try.

Growing watermelons in pots or containers are as easy as growing them in the garden. Keep reading for tips on how to plant, grow and harvest your container grown watermelons.

The Advantages of Growing Watermelons in Containers

The Advantages of Growing Watermelons in Containers

Watermelons love heat, and the soil in containers warms up much faster than soil in in-ground or raised beds, which means you can plant watermelons in containers weeks earlier than other locations.

Warmer soil also means better germination rates, as watermelon seeds tend to rot in cold, wet soil.

Containers, being off the ground, also create distance between your watermelon plants and common garden pests.

Not only that, but you’ll be able to more easily keep track of how much water your plants are getting, which is important since watermelons require a great deal of water to grow well.

Choose a Compact Watermelon Variety That Will Thrive In Pots

Choose a Compact Watermelon Variety

While there are benefits to growing watermelons in containers, you still must choose the right varieties in order to have a successful harvest.

Conventional watermelon varieties have vines that grow ten feet or longer while only producing a couple fruits per plant; clearly this is impractical for container gardening.

Types that do well in containers are compact, with vines that grow only 2-3’ long, while producing 2-3 fruits per plant. Some examples include “Bush Sugar Baby,” “Sugar Pot,” and “Mini Love.”

The Right Container for Growing Watermelons

The Right Container for Growing Watermelons

Even compact watermelon plants require a pretty hefty container. Watermelons need a lot of space to develop a strong root system, so choose a container that provides at least 7-10 gallons of soil per plant.

You’ll be watering these plants quite a bit, so make sure that your container has an abundance of drainage holes, and add gravel or a screen to the bottom of the pot to reduce soil loss.

Soil Requirements for Watermelons

Soil Requirements for Watermelons

Your container watermelon need a soil that provides great drainage without drying out, and retains moisture without getting waterlogged.

The perfect blend for them is equal parts high quality potting mix and finished compost. Potting mix is light and airy, and will provide drainage, while the compost will retain moisture and provide beneficial microorganisms and nutrients.

How to Plant Watermelons in Containers

How to Plant Watermelons in Containers

When planting watermelons in containers, you can direct sow seeds, grow your own starts, or buy starts. Each option has its unique advantages and disadvantages.

When buying starts, your variety choices will be limited to what you can find at your local garden store or farmers’ market, and you may not be able to find a variety suitable for container growing. Buying starts is also more expensive than purchasing seeds.

Growing your own starts is more work, but may be your only option if you live in an area with a short growing season.

Transplants can give you an earlier harvest, and you won’t risk your seeds rotting in cold, wet soil or being eaten by pests.

If your growing season is long enough, try direct sowing seeds. It’s far less work than growing your own starts, and since your plants will not suffer transplant shock, they’ll experience smoother growth and less stress.

Before planting starts or seeds, make sure that the danger of frost has passed and soil temperatures are at least 70℉.

To Grow Your Own Watermelon Starts:

  • Begin 4-5 weeks before the last frost date in your area.
  • Plant 1-2 seeds per pot, to a depth of one inch.
  • Use a heat mat to help seeds germinate (remove the mat after germination).
  • Use supplemental lighting to promote good growth: hang lights 6-12 inches above plants, and keep lights on for 14 hours a day.
  • Keep soil moist by misting regularly.

To Transplant Watermelon Seedlings:

  • Before planting, harden off seedlings.
  • Transplant to your container 1-2 weeks after last frost date.
  • Plant to the same depth plants were in pot, not deeper.
  • Do not loosen roots before planting as you would do with tomatoes, as melons do not like their root systems to be disturbed.
  • Water plants in, immediately and thoroughly.

To Direct Sow Watermelon Seeds:

  • Sow seeds 1-2 weeks after the last frost date.
  • Sow twice as many seeds as plants the container can hold.
  • Plant seeds to a depth of one inch.
  • Water in, immediately and thoroughly.
  • After germination, thin to 1 plant per 7-10 gallons of soil.

Caring for Your Watermelon Container Plants

1: Provide Full Sun

Provide Full Sun

Watermelon plants require at least eight hours of sun per day in order to flower and fruit, so make sure your plants are in an area that gets full sun.

If possible, rotate your container every couple of days so that the whole plant receives adequate sun.

2: Water Container Watermelon Plants Thoroughly and Often

Water Thoroughly and Often

It’s no secret that these juicy fruits need a lot of water, even more so when they are grown in containers.

Watermelon plants require constantly moist soil, so the soil should never dry out between waterings.

During hot weather, this may mean watering in both the morning and the afternoon. Adding a layer of mulch to your container will help retain moisture.

Water the soil directly with a watering can or hose nozzle on a gentle setting. Do your best to avoid getting the foliage wet as this promotes mildew.

A good rule of thumb when watering is to add about a third as much water as there is soil in your container at each watering. For example, add three gallons of water to a ten gallon container each time you water.

Or, simply water until the soil is moistened throughout and water is freely running through the drainage holes.

Just make sure not to leave your pot in standing water, because this can cause root rot. Empty your pot’s drainage tray elsewhere in the garden, or dispense with using a drainage tray entirely. As harvest time approaches, be especially careful not to let the soil dry out completely.

Dry soil followed by intense irrigation can lead to cracked or watery tasting fruits. However, watering less overall in the week leading up to harvest will concentrate sweetness and create better tasting fruits; just don’t let your soil dry out completely.

3: Fertilizer Plants Regularly: 

Fertilizer Plants Regularly:

Watermelons are heavy feeders and need to be fertilized. To promote flowering and fruit set, use an organic fertilizer that’s slightly higher in phosphorus every 3-4 weeks after the first true leaves appear.

Avoid fertilizers that are high in nitrogen, as these will cause your plants to direct too much of their energy toward foliage instead of fruit.

Harvest Time: When are Watermelons Ripe?

Timing is key when harvesting watermelons. Overripe watermelons will be mushy in texture, and unripe watermelons are flavorless and lower in nutrients.

Since watermelons will not ripen further once off the vine, it’s essential that you know how to identify a ripe watermelon in order to harvest at the optimal time.

Container grown watermelons can take anywhere from 70-90 days to mature, depending on the variety, so mark your calendar with an estimated ripeness date based on the type you planted. As this date approaches, check your watermelons for the telltale signs of peak ripeness:

  • A yellow spot develops on the underside of the fruit (if this spot is green or white, your melon isn’t ripe yet!).
  • The tendrils where the stem attaches to the vine are brown and dry.
  • The watermelon sounds hollow when smacked like a drum.
  • The skin of the watermelon is green and dull, not shiny.
  • The exterior of the melon is hard, and difficult to pierce with a fingernail.

Once your watermelon is ripe, harvest by cutting off the vine, leaving two inches of stem attached to the fruit.

After harvest, watermelons can be stored for about two weeks at temperatures under 60 degrees, and will stay fresh for up to 7-10 days. Refrigerate prior to eating for the best flavor.

Dealing with Watermelon Pests and Diseases

Dealing with Watermelon Pests and Diseases

While growing in containers can reduce your watermelon plants’ exposure to pests and disease, it’s still important to practice good management in order to prevent your plants from succumbing to either.

If you plant your watermelons in quality, nutrient rich soil, give them plenty of space, and water appropriately, your plants won’t be stressed–and will be far less vulnerable.

Let’s take a look at some common watermelon pests and diseases, their causes, and how to prevent them.

Powdery Mildew

This disease is caused by a fungus and presents as a powdery white growth on the leaves of the plant. Powdery mildew is discouraged by good air circulation and sun exposure, so make sure to give your plants the space they need.

If you do find powdery mildew on your plants, mix 1 part milk and 2 parts water and spray liberally on leaves; this home remedy is surprisingly effective.

Blossom End Rot

Blossom end rot is a nutritional disorder. It appears in young fruits as a light brown spot at the blossom end of the plant.

As the fruits mature, the spot grows into a large, leathery spot sunken into the fruit. Blossom end rot is caused by a lack of calcium in growing fruit.

If this deficiency occurs in container grown fruits, the most likely culprits are drought or excess nitrogen. Make sure to water thoroughly and regularly, and avoid fertilizers that are high in nitrogen.

Cucumber Mosaic

Cucumber mosaic is caused by a virus spread by aphids, so preventing an aphid infestation is the best way to keep this disease at bay.

Use reflective mulches to keep aphids from your plants. In the event of an aphid outbreak, treat your plants with insecticidal soap or neem oil.

Aphids

Aphids can be found on the underside of leaves. These insects do more than cause cucumber mosaic disease.

A heavy aphid infestation can cause yellow leaves or dead spots on watermelon leaves, as well as stunted growth.

If the aphid population is limited, they can be eliminated by pruning the affected area. If the entire plant is affected, insecticidal soap and neem oil are your best options.

Cucumber beetles

Established plants should be able to withstand some amount of cucumber beetle damage, so seeing a few beetles isn’t cause for alarm.

However, a cucumber beetle infestation can be treated with insecticidal soap as well. Preventative measures include using floating row cover until plants begin to flower, or regular applications of kaolin clay.

Spider Mites

Spider mites are almost impossible to see, but the evidence of their presence is unmistakable: spider mites leave yellow spots all over your plant’s foliage as they suck out the leaves’ juices, as well as telltale strings of their own silk. To treat a spider mite infestation, spray with neem until your plants have recovered.

Final Thoughts

While it might seem impractical to grow watermelons in containers, there are some clear advantages to doing so. Not only that, but it’s easy.

With just a little bit of effort, you’ll be able to harvest sweet, succulent, juicy fruits, whether your garden is part of a sprawling acreage or just a few pots on a balcony.

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