May 2025: Black Diamond Watermelon

This month’s seed kit features Black Diamond Watermelon! To support our environment, some seed kit materials are now available digitally. Follow the link to download a planting log.

Black Diamond Watermelon

This heirloom variety is named for its deep, green-black skin color, which contrasts dramatically with a bright, cherry-red flesh. Non-GMO and open-pollinated, this giant typically weighs in at 35–50 pounds when mature.

Planting Instructions

Culture: Watermelons require warmth and full sun and can be directly seeded in the garden once temperatures are regularly over 75°F. Build soil mounds 12 inches high and 6 feet apart. Sow 3-4 seeds ½ inch deep into each hill. Watermelon vines need plenty of space and can be trellised with proper support, including slings for the melons. Avoid letting watermelons sit directly on the soil by placing mulch or supports underneath to reduce the chances of damage from moisture or insects. If temperatures drop, cover vines with floating row cover to retain warmth.  Once there are flowers, consider hand-pollinating to increase the chances of fertilization.   

Water: Keep soil moist, and ensure it does not dry out during flowering and as the fruit grows—taper watering before harvesting.  

Harvest: Black Diamond watermelons reach maturity in 80-95 days. When they are ripe, they will have dark green skin and a yellow spot on the underside. Look for the tendril nearest the melon to brown and shrivel as an indicator of ripeness. Watermelons can be stored in a cool, dark place for up to a few weeks.   

More About Black Diamond Watermelon

It will not be a surprise to learn that the watermelon was prized in ancient times as a source of water, but it will surprise those familiar with this delightful food that its flesh was not always sweet, or even red! The ancestor of the modern watermelon had yellowish-white flesh that was quite bitter. Watermelons are thought to have originated in the Kalahari Desert region of southern Africa, where they were used by the indigenous people as a source of both moisture and nutrition.

Seeds and paintings of watermelons have been found in Egyptian tombs dating from about 4,000 years ago, by which time the development of a sweeter fruit had begun. By the 600s, watermelons were being cultivated in India, and they reached China by the 900s. By the 1600s, watermelons were found throughout Europe and had been brought to the Americas.

Today, there are more than 1,200 varieties of watermelon grown throughout the world, ranging in size from the small “personal” watermelons weighing around 2 pounds to giants weighing over 100 pounds. The varieties may vary in size and sweetness, but all have the trademark high water content, making them the perfect snack for summer.

Source: University of Missouri, Division of Plant Science and Technology

Watermelon Gazpacho

 Serves: 4    Prep time: 15 minutes   Chill Time: 1 hour 

Ingredients:

• 2 ½ cups of watermelon, seeded and cubed
• 3 Roma or plum tomatoes, diced 
• 1 English cucumber peeled, seeded, and diced 
• 1 red bell pepper, cored, seeded, and diced 
• 1/2 red onion, diced  
• 2 cloves of garlic, chopped 
• 3 tbsp. of red wine vinegar 
• 3 tbsp. of extra virgin olive oil 
• 1 tsp. of kosher salt 
• ¼ tsp. of ground black pepper
• Garnish (optional)
  • 1 tbsp. of extra virgin olive oil
  • 1 tbsp. of chopped mint or basil 
  • 1/4 cup of crumbled feta

Instructions:

1. Combine watermelon, tomatoes, cucumbers, red bell peppers, red onions, and garlic into a blender. Puree on high speed until smooth. Add in red wine vinegar, extra virgin olive oil, salt, and pulse to combine. Season with additional salt and pepper to taste.
2. Transfer the gazpacho to a large bowl or pitcher. Cover and refrigerate until chilled, at least 1 hour or overnight.
3. Pour soup into a bowl, drizzle with extra virgin olive oil, and garnish with mint or basil and feta cheese

Craft: Watermelon Fruit Roll Up

You’ll Need:

• 8 cups of cubed watermelon
• ½ cup of granulated sugar
• ½ cup of lemon or lime juice 
• Parchment paper 
• Cheesecloth 

 Instructions:

1. Line two baking sheets with parchment paper and preheat oven to 170F°. 
2. Purée watermelon and drain liquid using cheesecloth over a fine mesh strainer or large bowl. You might save the juice for another use (e.g., making watermelon lemonade). 
3. Mix the watermelon solids, sugar, and lemon or lime juice in a bowl. 
4. Spread the watermelon mixture into a thin layer on the parchment-lined baking sheets. Bake for 3–4 hours, or until dry. 
5. Cut the resulting fruit leather into strips and roll them. Store roll-ups in an airtight container.