How to Grow Watermelons From Seeds

By
Barbara Gillette
Barbara Gillette
Barbara Gillette
Barbara Gillette is a master gardener, herbalist, beekeeper, and journalist. She has 30 years of experience propagating and growing fruits, vegetables, herbs, and ornamentals.
Learn more about The Spruce's Editorial Process
Published on 02/16/23
Reviewed by
Julie Thompson-Adolf
Julie Thompson-Adolf
Reviewed by Julie Thompson-Adolf

Julie Thompson-Adolf is a Master Gardener and author. She has 30+ years of experience with year-round organic gardening; seed starting and saving; growing heirloom plants, perennials, and annuals; and sustainable and urban farming.

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how to grow watermelons from seed

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Project Overview
  • Working Time: 3 - 4 hrs
  • Total Time: 8 wks, 4 days - 12 wks, 6 days
  • Skill Level: Kid-friendly
  • Estimated Cost: $3 to $15

Watermelons are the iconic fruit of summer with sweet, juicy texture and flavor so popular it appears in everything from candy to beverages. Still, nothing quite compares to this large fruit, itself, and it's easy to grab a packet of seeds and grow your own watermelon.

The seeds of a watermelon (Citrullus lanatus) can be planted directly into the garden after the soil has warmed, or they can be started early indoors in pots or flats which can give you an earlier harvest or help ensure mature fruit if you live in a short-season climate. This is a great family project easy enough for children with the final result, a delicious treat everyone will enjoy.

When to Plant Seeds

Seeds require warm soil to germinate, so wait until the temperatures reach at least 65 degrees F at a depth of four inches before direct sowing. The seeds germinate faster if the soil is 70-95 degrees F. Many varieties are available from small, round, 'personal' types to large heirlooms like 'Black Diamond'. In most cases, the larger the melon, the longer the time until harvest, which ranges from 60 to 100 days. Watermelons are not cold hardy, so check the seed package and allow for plenty of growing time to ensure ripe fruit before first frost.

Where to Plant Watermelon Seeds

Watermelons grow on spreading vines that each produce two to three fruits. Vines grow rapidly and bear large, heavy fruits that don't adapt easily to trellising. Elevated vines will break under the weight, so you need to set aside plenty of garden space, up to 20 square feet per plant. Plant in nutrient-rich, well-draining soil that warms up early in spring and stays sunny all day throughout the growing season.

You can find small, individual-sized watermelon varieties, like 'Sugar Baby', that work on trellises for small-space gardens.

Spacing

For the home gardener, planting in mounds is the easiest, most effective space-saving technique. Small fruit varieties may need less space than larger fruits, but you still need adequate space for good air circulation and fruit development. Recommendations vary, but a good starting point is to create mounds 8 to 10 inches high, 3 feet apart, in rows with 5 feet on either side. It won't hurt vines to overlap, as long as developing fruits don't touch.

Tip

If space is limited or you want to try growing watermelon in a raised bed, look for small variety seeds. Vines still need space, but you can install specialized trellising with platforms to support fruits.

What You'll Need

Equipment / Tools

  • Shovel or hoe
  • Hand trowel
  • Gloves

Materials

  • Watermelon seeds
  • Fertilizer (30-10-10) and (5-10-10)

Instructions

How to Grow Watermelons From Seeds

Watermelons are one of the easiest fruits to grow from seeds. It's best to start with purchased seeds, since melons do cross-pollinate, and saved seed doesn't always produce the same watermelon you grew last season.

  1. Mound Soil

    Using a shovel or hoe, turn over enough garden soil to create a mound 8 to 10 inches tall at the peak and 10 to 12 inches across.

    If the soil lacks nutrients, use the hand trowel to work fertilizer into the soil according to label instructions. A nitrogen-rich formula such as 30-10-10 is sufficient.

    Use your gloved hands or the trowel to build the mound, loosely packing soil around the sides and creating a slight depression around the base of the mound.

  2. Plant Seeds

    Using your gloved index finger poke 3 holes 3/4 to 1 inch deep around the sides of the mound about halfway to the top. Place a seed in each hole and cover with loose soil. Pat down gently.

  3. Add Water

    A watering can with a rose spout or hose attachment with a sprinkler head work best for initial watering. You want to moisten the seeds but not wash them out or flatten out your mound. You can also fill the depression at the bottom of the mound with water to encourage root growth. Do not let the soil dry out while the seeds germinate.

    Watermelons require 1 to 2 inches of water per week. If rainfall amounts are insufficient prepare to give your plants an extra drink. Once the plants establish, watering with a sprinkler or spray hose attachment is okay.

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  4. Thin the Seedlings

    When the seedlings grow a few inches tall and have two sets of true leaves, thin the number down to one seedling per mound.

  5. Fertilize Monthly

    Watch for the vines to produce flower buds. This can occur anywhere from four to eight weeks after planting, depending on variety and growing conditions. Consult your seed package for information specific to your type.

    Apply a higher phosphorous fertilizer such as 5-10-10. Continue to fertilize once a month throughout the growing season.

  6. Train the Vines

    Unlike other vines that attach to surfaces with runners, watermelons only put down roots where the plant starts. This makes it easy to move vines and place them where you want them to grow. Do this only if necessary, before fruit develops, and when the vines are no more than 2 to 3 feet long.

  7. Support the Fruits

    You can prevent insect damage by creating a light barrier between the ripening melon and the soil. This can be accomplished by placing each fruit on a paper or plastic plate, a small piece of wood, or weed barrier. Heavy rain amounts may necessitate replacement if the material degrades. Make sure to water frequently. Watermelons are 92 percent water, and the plants need adequate moisture to produce.

  8. Harvest Ripe Melons

    Look for these signs that your watermelon is ready to pick. The stem will thin out and turn grayish brown and dry. A pale or faint yellow spot will appear where the melon contacts the soil.

    Use a sharp hand pruner to cut the stem close to the vine leaving about 2 inches attached to the fruit.

Starting Watermelon Seeds Indoors

Watermelon seeds germinate quickly and reliably, but they don't always transplant easily. If you want to get a head start on the season, plant seeds indoors in biodegradable pots or another biodegradable pot. This allows you to transplant the entire pot with the seedling without disturbing the roots. Start seeds indoors two to three weeks before your last frost and grow the seedlings out until soil temperatures reach 65 degrees F. Remember to harden off before planting out in the garden.

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