How to Grow Watermelon Indoors

Growing Watermelons! Seed Sowing Indoors, Soil Amendments, Clay Soil, Container Growing And More

Growing watermelons indoors may seem like a daunting task, but with the right knowledge and techniques, it's entirely possible to enjoy fresh, juicy watermelons right from your own home. By following these steps, you can successfully grow watermelon indoors, ensuring a bountiful and delicious harvest.

Choose the Right Variety

Selecting the appropriate watermelon variety is crucial for successful indoor cultivation. While traditional large watermelon varieties can be challenging to grow indoors, several compact and dwarf varieties are well-suited for indoor growing. These varieties typically have smaller fruit sizes, making them easier to manage in limited indoor spaces.

Here's a table comparing some popular watermelon varieties suitable for indoor growing:

VarietyFruit SizeGrowth HabitDays to Maturity

Sugar Baby	6-10 lbs	Bush	70-85 days
Yellow Doll	5-8 lbs	Bush	70-80 days
Bush Sugar Baby	8-10 lbs	Bush	75-90 days
Jade Star	6-8 lbs	Dwarf Vine	70-80 days
Golden Midget	3-5 lbs	Bush	70-75 days

Dwarf or Bush Varieties

Dwarf or bush watermelon varieties are ideal for indoor growing because they have a compact growth habit and require less space. Examples of popular dwarf or bush varieties include Sugar Baby, Bush Sugar Baby, and Golden Midget. These varieties produce smaller fruits, typically ranging from 3 to 10 pounds, making them easier to manage in containers or small indoor spaces.

Soil Requirements

Watermelons thrive in well-draining, nutrient-rich soil with a slightly acidic pH between 6.0 and 6.8. To prepare the ideal soil mix for indoor watermelon growing, combine equal parts of high-quality potting mix, compost, and perlite or vermiculite. This combination will provide the necessary drainage, aeration, and nutrients for optimal growth.

Planting and Germination

Proper planting and germination techniques are essential for successful indoor watermelon cultivation. Starting with high-quality seeds and providing the right conditions will ensure a strong start for your watermelon plants.

Watermelon seeds germinate best when the soil temperature is between 75°F and 90°F (24°C and 32°C). To achieve this, use a seed-starting tray or container with a plastic dome or cover to maintain consistent moisture and warmth during the germination process.

Container Selection

Choose a container that is at least 18 inches wide and 12 inches deep to accommodate the watermelon plant's extensive root system. Larger containers, such as half-barrel planters or grow bags, can work well for indoor watermelon growing. Make sure the container has adequate drainage holes to prevent waterlogging.

Seed Planting and Germination

Plant watermelon seeds 1 inch deep and 12 to 18 inches apart. Water the soil thoroughly and cover the container with a plastic dome or clear plastic wrap to create a greenhouse effect. Place the container in a warm location with temperatures between 75°F and 90°F (24°C and 32°C). Seeds should germinate within 5 to 10 days. Remove the plastic cover once the seedlings emerge, and gradually introduce them to direct sunlight or grow lights.

Growing Conditions

Providing the right growing conditions is crucial for successful indoor watermelon cultivation. Watermelons require ample light, warm temperatures, and consistent moisture levels to thrive.

Watermelons are sun-loving plants that require at least 6 to 8 hours of direct sunlight per day or equivalent artificial light. If you're growing them indoors without access to direct sunlight, you'll need to supplement with grow lights.

Light Requirements

Watermelons require high levels of light for optimal growth and fruit production. Ideally, they should receive at least 6 to 8 hours of direct sunlight per day. If growing indoors without access to sufficient natural light, you'll need to provide supplemental lighting using grow lights.

High-intensity discharge (HID) grow lights, such as metal halide or high-pressure sodium lamps, are ideal for watermelon plants. Alternatively, you can use full-spectrum LED grow lights designed for fruiting plants. Position the grow lights approximately 12 to 18 inches above the plant canopy and adjust the height as the plants grow taller.

Temperature and Humidity

Watermelons thrive in warm temperatures between 70°F and 85°F (21°C and 29°C) during the day and slightly cooler temperatures around 65°F (18°C) at night. Maintain consistent temperatures to prevent issues like stunted growth or poor fruit set.

Humidity levels should be kept between 50% and 70% for optimal growth. Use a humidifier or place trays of water near the plants to increase humidity levels if necessary. Proper humidity levels will help prevent issues like blossom end rot and promote healthy vine growth.

Watering and Fertilizing

Watermelons have high water requirements, especially during the fruiting stage. Water the plants deeply, ensuring the soil is consistently moist but not waterlogged. Check the soil moisture level regularly and water when the top inch of soil feels dry.

Feed your watermelon plants with a balanced, water-soluble fertilizer every two to three weeks during the growing season. Look for a fertilizer specifically formulated for fruiting plants or a balanced fertilizer with an equal ratio of nitrogen, phosphorus, and potassium (such as a 10-10-10 or 20-20-20 formula).

Pollination and Fruit Set

Pollination is crucial for watermelon fruit development, and indoor growers may need to hand-pollinate their plants to ensure successful fruit set. Watermelons have separate male and female flowers, and pollen must be transferred from the male to the female flowers for fruit to develop.

Watermelon plants produce male flowers first, followed by female flowers a few weeks later. Female flowers can be identified by the presence of a small, immature fruit (ovary) behind the flower petals.

Here are the steps to hand-pollinate watermelon flowers indoors:

• Identify a fully opened male flower with visible pollen
• Gently remove the male flower from the plant
• Locate a female flower with a small ovary behind the petals
• Carefully transfer the pollen from the male flower to the stigma (the sticky, central part) of the female flower
• Repeat this process for several female flowers to increase the chances of successful fruit set

Understanding Pollination

Pollination is a critical process that enables the fertilization of watermelon flowers, leading to fruit development. Watermelons have separate male and female flowers on the same plant. The male flowers produce pollen, while the female flowers contain the ovary, which, when pollinated, develops into the watermelon fruit.

Without proper pollination, watermelon plants may produce flowers, but no fruit will form. This is why hand-pollination is often necessary for indoor watermelon growers, as there are no natural pollinators present in an indoor environment.

Hand-Pollination Techniques

Hand-pollinating watermelon flowers indoors is a straightforward process, but it requires patience and careful observation. Here are the steps to follow:

1. Identify male and female flowers: Male flowers are smaller and grow on a thin stem, while female flowers have a small, immature fruit (ovary) behind the petals.
2. Collect pollen: Use a soft-bristled brush or cotton swab to gently collect pollen from a fully opened male flower.
3. Transfer pollen: Locate a freshly opened female flower and carefully transfer the collected pollen to the sticky stigma in the center of the flower.
4. Repeat the process: Hand-pollinate multiple female flowers to increase the chances of successful fruit set.
5. Mark pollinated flowers: Use a small tie or marker to identify the hand-pollinated flowers for easier tracking.

It's essential to hand-pollinate watermelon flowers in the morning when they are fully opened and receptive to pollen. Repeat the process every few days until you see evidence of fruit development.

Pruning and Training

Pruning and training watermelon vines are essential practices for indoor cultivation, as they help manage plant growth, promote air circulation, and improve fruit production.

Watermelon plants have a naturally vining growth habit, which can quickly become unruly in an indoor setting. Regular pruning and training will ensure your plants remain manageable and direct their energy toward fruit production.

To begin pruning, wait until the plant has established itself and developed several sets of leaves and runners.