Growing Watermelons in a Greenhouse

Growing watermelon hanging hammock for beginners, Fruit is big and sweet

Choosing the Right Variety

The first step in growing watermelons in a greenhouse is selecting the appropriate variety. Different watermelon cultivars have unique characteristics, such as size, flavor, and disease resistance, making them better suited for specific growing conditions. Some popular greenhouse watermelon varieties include:

VarietySizeRind ColorFlesh ColorDisease ResistanceNotes

Crimson Sweet	Large (16-25 lbs)	Light green with dark stripes	Deep red	Fusarium Wilt, Anthracnose	Sweet, crisp flesh
Sugar Baby	Small (6-10 lbs)	Dark green with lighter stripes	Deep red	Fusarium Wilt, Anthracnose	Compact vines, early maturing
Millionaire	Medium (12-18 lbs)	Striped dark and light green	Bright red	Powdery Mildew, Anthracnose	High sugar content, crisp texture
Yellow Doll	Small (5-8 lbs)	Bright yellow	Yellow	Fusarium Wilt, Anthracnose	Unique sweet flavor

Seeded vs. Seedless Varieties

When choosing a watermelon variety, you'll also need to decide between seeded and seedless cultivars. Seeded watermelons are generally easier to grow and have a more robust flavor, but seedless varieties are more convenient for consumption. Seedless watermelons are typically more challenging to cultivate and may require special growing techniques, such as applying growth regulators or using seed from triploid hybrids.

Disease-Resistant Varieties

In the confined space of a greenhouse, disease prevention is crucial. Choose watermelon varieties that are resistant to common diseases, such as Fusarium wilt, Anthracnose, and Powdery mildew. These disease-resistant cultivars can help minimize the risk of crop failure and reduce the need for chemical interventions.

Greenhouse Setup and Conditions

Providing the right growing conditions is essential for successful watermelon cultivation in a greenhouse. The ideal greenhouse environment for growing watermelons in a greenhouse should have the following characteristics:

• Temperature: Watermelons thrive in warm temperatures, typically between 70°F and 85°F (21°C and 29°C) during the day and 65°F to 75°F (18°C to 24°C) at night.
• Humidity: Maintain a relative humidity level between 60% and 80% to prevent moisture stress and disease development.
• Ventilation: Proper air circulation is crucial for pollination, disease prevention, and temperature regulation. Install fans or open vents to maintain good airflow.

Temperature and Humidity

Watermelons are warm-season crops that require consistent high temperatures and moderate humidity levels for optimal growth and fruit development. In a greenhouse setting, you can maintain these conditions through various techniques, such as:

• Heating systems: Install a reliable heating system to keep the greenhouse warm during cooler periods or at night.
• Evaporative coolers or misting systems: Use evaporative coolers or misting systems to increase humidity levels and lower temperatures on hot, dry days.
• Automated climate control systems: Consider investing in automated climate control systems that can monitor and adjust temperature and humidity levels automatically.

Lighting and Ventilation

Watermelons require abundant sunlight for photosynthesis and fruit production. In a greenhouse, ensure that your plants receive at least 6 to 8 hours of direct sunlight daily. If natural light is insufficient, supplement with grow lights or high-intensity discharge (HID) lamps.

Proper ventilation is also crucial for watermelon growth in a greenhouse. Stagnant air can lead to disease problems and poor pollination. Install exhaust fans or open vents to facilitate air circulation and exchange with the outside environment.

Soil Preparation and Planting

Creating an optimal growing environment starts with proper soil preparation and planting techniques. Watermelons have specific soil requirements and benefit from careful planting methods to ensure vigorous growth and high yields.

• Watermelons prefer well-draining, nutrient-rich soil with a slightly acidic to neutral pH range of 6.0 to 7.0.
• Incorporate organic matter, such as compost or well-rotted manure, to improve soil structure and fertility.
• Provide adequate space between plants, typically 2 to 3 feet apart in rows spaced 6 to 8 feet apart.
• Plant seeds or transplants 1 to 2 inches deep, and water thoroughly after planting.

Soil pH and Nutrient Requirements

Watermelons grow best in soils with a pH range of 6.0 to 7.0. If your soil is too acidic or alkaline, consider adjusting the pH with lime or sulfur amendments. Proper nutrient management is also essential for healthy watermelon growth. The table below shows the recommended fertilizer ratios for watermelons:

NutrientRatio

Nitrogen (N)	1
Phosphorus (P)	1
Potassium (K)	2

Applying a balanced fertilizer with these ratios, along with micronutrients like calcium, magnesium, and boron, can help ensure optimal plant growth and fruit development.

Planting Techniques

When planting watermelon seeds or transplants, proper spacing and depth are crucial for successful germination and establishment. Here are some key planting techniques:

• Sow seeds 1 to 2 inches deep, spacing them 2 to 3 feet apart in rows that are 6 to 8 feet apart.
• If using transplants, plant them at the same depth as they were growing in their containers, and water thoroughly after planting.
• Consider using raised beds or mounding soil to improve drainage and root development.
• Provide support for vines as they grow, using trellises or cages to prevent fruit from resting on the ground.

Watering and Fertilizing

Proper watering and fertilization are essential for promoting vigorous growth, fruit development, and overall plant health when growing watermelons in a greenhouse.

• Watermelons have a shallow root system, so they require consistent moisture throughout the growing season.
• Water deeply and infrequently, allowing the soil to partially dry out between waterings to prevent root rot and disease problems.
• Adjust watering schedules based on plant growth stages, with more frequent watering needed during fruit development and ripening.

Watering Schedules and Techniques

Watermelons have specific watering needs throughout their growth stages:

1. Seedling stage: Water lightly and frequently to keep the soil moist but not waterlogged.
2. Vegetative growth: Water deeply once or twice a week, allowing the soil to partially dry out between waterings.
3. Flowering and fruit development: Increase watering frequency to maintain consistent soil moisture, as this is the most critical stage for fruit growth.
4. Ripening: Reduce watering gradually as fruits mature to concentrate sugars and enhance flavor.

Consider using drip irrigation or soaker hoses to deliver water directly to the root zone, minimizing water waste and preventing excess moisture on foliage.

Fertilizer Application

In addition to providing the right soil nutrients, watermelons may benefit from supplemental fertilization throughout the growing season. Here are some recommended fertilizer application practices:

• Apply a balanced fertilizer (such as 10-10-10 or similar ratio) at planting time and again when vines begin to run.
• Sidedress with a nitrogen-rich fertilizer (such as ammonium nitrate or calcium nitrate) when vines are actively growing and setting fruit.
• Consider foliar feeding with a water-soluble fertilizer or micronutrient solution during fruiting to ensure adequate nutrient uptake.
• Avoid over-fertilizing, as excessive nitrogen can lead to excessive foliage growth at the expense of fruit production.