Heirloom Watermelon Planting Guide: From Seed to Harvest

Heirloom watermelons (Citrullus lanatus) have become increasingly popular for their intense flavor, vibrant colors, and rich history. Unlike hybrid varieties, which are often bred for characteristics like uniformity and shelf-life. Heirloom watermelons are open-pollinated. This means they have been carefully preserved and passed down through generations without genetic modifications, capturing the true essence of watermelon varieties enjoyed by our ancestors.

Growing heirloom watermelons offers a rewarding experience that reconnects gardeners to the origins of this beloved summer fruit. With their unique appearance and superior taste, these watermelons can turn any garden into a celebration of tradition and flavor. If you’re ready to bring a taste of the past to your table, this Heirloom Watermelon Planting Guide will walk you through the steps needed for a successful, bountiful harvest.

Quick Start Heirloom Watermelon Planting Guide – Complete Planting Guide Below

Heirloom / Open Pollinated Watermelon are heat loving plants that prefer well drained loose soil and an even amount of water. Plant heirloom watermelon in rows or hills but make sure the soil is well warmed. In cooler climates, you can start watermelon seeds indoors 2-4 wks. before last frost to extend the growing season. Plant seeds ½ – 1″ deep.

Plant seeds or set out heirloom watermelon transplants in full sun. For rows plant 6-12″ apart, in rows 6-10′ apart. For hills plant 4-6 seeds per hill, in 1′ diameter hills, with hills 6-10′ apart. Germination should occur in 3-10 days in soil 70-85°F. In hills thin to 2 plants per hill. In rows thin plants to or set out transplants 24-36″ apart. Harvest heirloom watermelon when fruit sounds hollow when thumped, when surface color turns dull, or underside turns yellow.

The Complete Planting Guide for Heirloom Watermelon: From Seed to Harvest

Why Choose Heirloom Watermelons?

Heirloom watermelons are special because they are true-to-type seeds, meaning the seeds collected from these watermelons can produce fruits with identical characteristics year after year. This differs from hybrid varieties, which are bred for uniformity, transport durability and are often seedless. Heirlooms focus on flavor, and many gardeners swear by the taste of heirloom watermelons. Some popular heirloom varieties include the “Moon and Stars,” “Charleston Gray,” “Sugar Baby,” and “Jubilee.” Each brings its unique flavor, size, and appearance to the garden.

How to Grow Heirloom Watermelon: The Basics

Before diving into the details, let’s go over the basics of how to grow heirloom watermelon. Heirloom watermelons thrive in warm, sunny conditions with plenty of space to sprawl. They are known for their relatively long growing season, so it’s essential to get a head start, especially in regions with shorter summers. Here’s a general overview:

1. Location: Full sun
2. Soil: Well-draining, loamy soil rich in organic matter
3. Temperature: Warm; ideal temperatures are between 70°F and 85°F
4. Spacing: 3-4 feet between plants
5. Watering: Deep watering weekly

Let’s break down each step in the planting heirloom watermelon process.

Step 1: Choosing the Right Variety

Different heirloom watermelon varieties have specific growing needs and characteristics, so choose one that suits your climate and taste preference. Here’s a quick overview of a few favorites:

• Moon and Stars: Known for its dark rind with bright yellow spots, this variety has a unique look and a sweet, classic watermelon flavor.
• Charleston Gray: A long, oblong watermelon with a grayish rind and deep red flesh, perfect for Southern climates.
• Sugar Baby: Small and compact, ideal for small gardens or container planting, producing a sweet, red-fleshed fruit.
• Jubilee: Weigh in at 25 to 35 lbs and have a tough rind for shipping. Have red flesh and good disease resistance.

Selecting the right heirloom variety will give you the best chance of a fruitful harvest, so do some research to ensure your choice suits your region.

Step 2: Preparing the Soil

Heirloom watermelons require nutrient-rich, well-draining soil to thrive. Here are a few tips on preparing the perfect soil:

1. Choose the Right Location: Select a spot in your garden that receives full sun, as watermelons need at least 8 hours of sunlight daily.
2. Soil Testing and pH: Watermelons prefer a slightly acidic to neutral soil pH of 6.0 to 6.8. A soil test can help you adjust the pH if needed.
3. Amend the Soil: Adding compost or well-rotted manure will enrich the soil with organic matter, improving both drainage and nutrient levels. Avoid fresh manure as it can be too high in nitrogen, promoting leafy growth over fruit production.
4. Create Mounds: Watermelons grow best in slightly raised mounds or hills. These improve drainage and allow the soil to warm up faster, which is crucial for germination. Each mound should be about 18 inches across and a foot high.

Step 3: Planting Heirloom Watermelon Seeds

To ensure success in planting heirloom watermelon seeds, it’s essential to start them early, especially in cooler climates. You can either start seeds indoors or plant directly outdoors if temperatures permit.

1. Indoor Starting: Start your seeds indoors 4-6 weeks before the last expected frost. Plant each seed about ½ inch deep in seed trays filled with a seed-starting mix. Keep the trays in a warm, sunny location or under grow lights.
2. Outdoor Direct Planting: Wait until the soil temperature is consistently above 70°F. Plant 3-4 seeds per mound, spacing each mound 3-4 feet apart to allow for vine spread. Cover seeds with about ½ inch of soil.
3. Thinning: Once the seedlings have developed a few leaves, thin them to one or two plants per mound, keeping the strongest seedlings to ensure robust growth.

Step 4: Watering and Feeding

Heirloom watermelons are relatively low-maintenance, but they need adequate water and nutrients, especially during key stages of growth.

1. Watering: Water deeply once a week, allowing moisture to penetrate the soil. Watermelons need about an inch of water per week. During hot, dry spells, increase watering frequency. Avoid overhead watering to reduce the risk of fungal diseases; instead, water at the base of each plant.
2. Mulching: Applying mulch around the base of the plants helps retain soil moisture, regulate temperature, and suppress weeds. Organic mulches, like straw or shredded leaves, work well.
3. Feeding: Once the plants start producing vines, switch to a phosphorus-rich fertilizer to promote flower and fruit production. Avoid high-nitrogen fertilizers as these can encourage leafy growth at the expense of fruit development.

Step 5: Pollination and Supporting Fruit Growth

Since heirloom watermelons rely on open pollination, bees and other pollinators are essential for fruit set. If you’re growing in an area with few pollinators, consider hand-pollinating to ensure a good yield.

1. Hand Pollination: Use a small paintbrush to transfer pollen from male flowers (long stems) to female flowers (with small fruit-like bulbs beneath the petals).
2. Supporting Vines: As the watermelons grow, ensure they have enough space to sprawl. Avoid disturbing vines as much as possible to prevent damage to the fruits.

Managing Diseases and Pests in Heirloom Watermelons

Like many garden plants, heirloom watermelons (Citrullus lanatus) are vulnerable to certain pests and diseases, which can impact growth and yield if not managed properly. To protect your plants and maximize harvest, a combination of preventative strategies and organic treatments can be highly effective. Here’s how to manage some of the most common pests and diseases encountered while growing heirloom watermelons.

Common Pests

1. Aphids: These small, soft-bodied insects feed on the undersides of leaves, sucking out sap and causing leaves to curl and yellow. They can also transmit diseases to the plants.
   • Control: Use a gentle spray of water to dislodge aphids from leaves, and introduce natural predators like ladybugs. Neem oil and insecticidal soap are also effective organic treatments.
2. Cucumber Beetles: Both striped and spotted cucumber beetles are common threats to heirloom watermelon plants. They feed on leaves and flowers and can transmit bacterial wilt.
   • Control: Row covers can protect young plants from cucumber beetles in the early stages. Remove covers once flowers appear to allow pollination. Handpick beetles if possible, or use a natural insecticidal spray in severe cases.
3. Squash Bugs: These bugs suck sap from the leaves, causing them to wilt, yellow, and die back. Large infestations can stunt plant growth.
   • Control: Inspect plants regularly for clusters of squash bug eggs (found on the undersides of leaves) and remove them manually. Neem oil can also help reduce squash bug populations if applied early.
4. Cutworms: These pests are known to cut young plants off at the soil level, leading to sudden plant death, especially in seedlings.
   • Control: Place collars around young plants (e.g., cardboard tubes pushed into the soil around stems) to deter cutworms. You can also sprinkle diatomaceous earth around plant bases to discourage them.

Common Diseases

1. Powdery Mildew: This fungal disease appears as a white, powdery coating on leaves, eventually causing them to yellow and die. It thrives in humid conditions with poor airflow.
   • Control: Ensure plants are well-spaced and pruned to improve air circulation. Use organic fungicides like potassium bicarbonate or sulfur-based sprays as a preventative measure. Water plants at the base to reduce humidity around foliage.
2. Anthracnose: A common fungal disease in watermelons, anthracnose causes dark, sunken spots on leaves, stems, and fruits, reducing yield and quality.
   • Control: Avoid overhead watering and remove any infected plant material. Use copper-based fungicides as a treatment, especially during wet weather. Rotate crops annually to prevent soil buildup of anthracnose.
3. Fusarium Wilt: This soil-borne fungus causes wilting and yellowing of leaves, often leading to plant death. Once infected, plants cannot be saved.
   • Control: Practice crop rotation, avoiding planting watermelons in the same area for at least three years. Choose varieties with natural resistance to Fusarium wilt when possible, and solarize the soil if Fusarium wilt has been an issue in past seasons.
4. Downy Mildew: Downy mildew appears as yellow spots on leaves that turn brown and necrotic over time. It thrives in damp, humid environments.
   • Control: Improve airflow by spacing plants adequately and avoid overhead watering. Organic treatments, like neem oil or copper-based sprays, can help prevent downy mildew outbreaks.
5. Bacterial Wilt: This disease is spread by cucumber beetles and causes wilting and death of entire plants. Once infected, there is no cure for bacterial wilt.
   • Control: The best prevention for bacterial wilt is managing cucumber beetle populations. Remove infected plants immediately to prevent the spread of the bacteria.

Integrated Pest and Disease Management Tips

• Companion Planting: Planting certain herbs and flowers, such as marigolds, nasturtiums, and basil, around watermelon plants can help repel pests.
• Proper Watering: Water plants at the base rather than from above to prevent leaf wetness, which promotes fungal diseases.
• Sanitation: Remove plant debris from the garden at the end of each season to reduce overwintering pests and pathogens. Sterilize any gardening tools used on infected plants.
• Rotate Crops: Rotating your watermelon crop with unrelated plants (such as beans or corn) every year helps prevent soil-borne diseases from building up.
• Organic Sprays: Use organic sprays like neem oil, insecticidal soaps, and copper-based fungicides as a last resort. Always follow label instructions and apply during cool parts of the day to avoid damaging plants.

By following these steps to manage pests and diseases, you can protect your heirloom watermelons and enjoy a productive growing season. Proactive prevention and regular monitoring are key to keeping plants healthy and resilient.

Harvesting Heirloom Watermelons

One of the biggest challenges in planting heirloom watermelon is determining when they’re ripe. Unlike other fruits, watermelons don’t continue to ripen off the vine, so picking them at the right time is crucial.

1. Check the Tendril: Look at the tendril closest to the watermelon. When it turns brown and dries up, the fruit is likely ripe.
2. Surface Appearance: The rind of a ripe watermelon will have a slightly dull appearance, and the underside (the part touching the ground) will turn from white to yellowish.
3. Sound Test: Tap the watermelon; a deep, hollow sound typically indicates ripeness.

Cut the watermelon from the vine, leaving a short stem attached. Store watermelons in a cool, dry place or in the refrigerator until ready to eat.

Storing and Preserving Heirloom Watermelons

After a season of careful planting, tending, and harvesting, it’s time to make the most of your heirloom watermelons (Citrullus lanatus). Proper storage can keep your fresh watermelons in peak condition, while preservation techniques allow you to enjoy their flavor long after the growing season has ended. Here are some tips for storing and preserving your heirloom watermelons for maximum freshness and flavor.

Storing Fresh Heirloom Watermelons

Whole heirloom watermelons have a relatively long shelf life if stored properly. Here’s how to keep them fresh for as long as possible:

1. Room Temperature Storage: A whole, uncut watermelon can be stored at room temperature for up to two weeks. Keep it in a cool, dry place, away from direct sunlight to prevent it from ripening too quickly.
2. Refrigeration: If you need to store the watermelon longer, place it in the refrigerator. A whole watermelon can last up to three weeks in a fridge, although the flavor and sweetness may decrease slightly over time.
3. Cut Watermelon: Once cut, watermelon should always be stored in the refrigerator. Cover cut pieces tightly with plastic wrap or place them in airtight containers to prevent the flesh from drying out. Cut watermelon will stay fresh for 3-5 days when refrigerated.
4. Avoid Freezing Whole Watermelons: Freezing whole or uncut watermelon is not recommended, as it causes the fruit’s cells to burst, resulting in a mushy texture when thawed.

Preserving Heirloom Watermelon

If you have a large harvest or want to enjoy heirloom watermelon throughout the year, there are several ways to preserve it. While fresh watermelon doesn’t freeze well, other preservation methods can capture its flavor and make it a versatile ingredient for months to come.

How to Ferment Watermelon Rind: Place peeled watermelon rind pieces in a brine of water and salt, weighted down to keep them submerged. Leave at room temperature for 3-7 days, tasting as it ferments. Once it reaches the desired flavor, refrigerate the rind. Fermented watermelon rind can last up to 2 months when stored in the refrigerator.

Freezing Watermelon Cubes: While freezing whole watermelon doesn’t work well, freezing cut watermelon cubes is an excellent option for making smoothies, drinks, and desserts.

How to Freeze: Cut the watermelon flesh into 1-inch cubes, removing seeds as needed. Lay the cubes in a single layer on a baking sheet and freeze until solid. Once frozen, transfer them to a freezer-safe bag or container. Watermelon cubes can last up to 6 months in the freezer and work well for adding to smoothies or blending into refreshing drinks.

Watermelon Juice: Preserving watermelon as juice is a great way to enjoy its flavor year-round. Watermelon juice can be enjoyed as is, or added to cocktails, mocktails, and iced teas.

How to Make and Store Watermelon Juice: Blend the watermelon flesh in a blender until smooth, then strain through a fine-mesh sieve if you prefer a smoother juice. Pour the juice into glass jars, leaving some space at the top, and freeze. Frozen watermelon juice can last up to 12 months in the freezer.

Watermelon Jam: Watermelon jam is a unique and delicious way to preserve the fruit. The jam has a sweet, mild flavor that pairs well with toast, yogurt, and desserts.

How to Make Watermelon Jam: Cook pureed watermelon flesh with sugar and lemon juice until it reaches a jam-like consistency. Add pectin as a thickening agent if desired. Once cooked, pour the hot jam into sterilized jars and process in a water bath for long-term storage. Properly canned watermelon jam can last up to 1 year when stored in a cool, dark place.

Pickled Watermelon Rind: The rind, often discarded, can be pickled to make a tasty, tangy snack that’s also great in salads and sandwiches. This method uses the entire fruit, minimizing waste.

How to Make Pickled Watermelon Rind: Peel the outer green skin from the watermelon rind and cut the rind into small cubes or strips. Boil the rind briefly, then soak in a vinegar and sugar brine with spices like cloves, cinnamon, and mustard seeds. After pickling, store the rind in sterilized jars in the refrigerator or process the jars in a water bath for shelf-stable storage. Pickled watermelon rind can be stored in the fridge for up to 2 months, or up to 1 year if canned.

Dehydrated Watermelon: Dehydrated watermelon, often called “watermelon jerky,” is a chewy, sweet snack that captures the essence of watermelon in a concentrated form.

How to Dehydrate Watermelon: Slice watermelon into thin strips or small cubes, removing seeds as needed. Lay the pieces on dehydrator trays or a baking sheet if using an oven. Dehydrate at 135°F (57°C) in a dehydrator or the lowest setting in an oven until fully dried, which can take 8-12 hours. Store dehydrated watermelon in airtight containers for up to 6 months.

Fermented Watermelon Rind: For a probiotic-rich snack, try fermenting watermelon rind. This method creates a tangy, pickled flavor with health benefits similar to other fermented foods.

By storing and preserving your heirloom watermelons, you can extend their flavor and enjoy a taste of summer long after the growing season has passed. Whether you’re freezing cubes for smoothies, making watermelon jam, or pickling the rinds, these preservation methods allow you to make the most of your harvest and savor the fruits of your labor all year round.

Saving Seeds from Heirloom Watermelons

One of the great advantages of heirloom watermelons (Citrullus lanatus) is their open-pollinated nature, allowing gardeners to save seeds and grow true-to-type plants season after season. Saving seeds from your heirloom watermelon harvest can be a rewarding way to continue cultivating your favorite varieties and ensures you’ll have a reliable source of seeds. Follow these steps to save and store your heirloom watermelon seeds successfully.

Step 1: Choose the Right Watermelon

For the best quality seeds, select a fully mature watermelon from a healthy plant. Look for a fruit that has ripened naturally on the vine and displays the ideal characteristics of its variety in terms of color, shape, and size. Avoid saving seeds from a watermelon that shows signs of disease or pest damage, as these issues can carry over to the next generation.

Step 2: Harvest the Seeds

Once you’ve selected a ripe watermelon, cut it open and remove the seeds. Here’s how to do it:

1. Scoop Out Seeds: Use a spoon to scoop out the seeds from the flesh, being careful to avoid breaking or damaging the seeds.
2. Separate Seeds from Pulp: Place the seeds and surrounding pulp in a bowl of water. Gently agitate the mixture with your hands to separate the seeds from the pulp. The healthy, viable seeds will sink to the bottom, while the pulp and any immature seeds will float.
3. Discard Immature Seeds: Remove any seeds that float to the surface, as they are likely underdeveloped and will not germinate well.

Step 3: Clean the Seeds

After separating the seeds, it’s essential to clean them thoroughly to prevent any remaining pulp from spoiling during storage.

1. Rinse Under Running Water: Place the seeds in a sieve and rinse them under cool running water to remove any remaining flesh.
2. Soak (Optional): For additional cleaning, you can soak the seeds in a weak vinegar solution (1 part vinegar to 10 parts water) for 10 minutes. This helps sanitize the seeds and reduces the risk of mold during storage. Rinse the seeds again after soaking.

Step 4: Dry the Seeds

Proper drying is crucial to avoid mold or rot during storage. Follow these steps to dry your seeds thoroughly:

1. Spread Out Seeds: Lay the seeds out in a single layer on a paper towel, cloth, or a fine mesh screen. Ensure they’re in a warm, well-ventilated area, out of direct sunlight.
2. Air Dry: Allow the seeds to dry for at least one week, stirring them every day to promote even drying. Seeds are dry when they are hard and brittle and break cleanly instead of bending.
3. Avoid Heat Sources: Do not use artificial heat sources like ovens or dryers to speed up the process, as high temperatures can damage the seeds’ viability.

Step 5: Store the Seeds

Once the seeds are completely dry, they’re ready for storage. Proper storage helps maintain their viability, so they’re ready to sprout when planting season arrives.

1. Choose a Container: Store the dried seeds in an airtight container, such as a glass jar or a resealable plastic bag. For added protection, place a small desiccant packet in the container to absorb any remaining moisture.
2. Label the Container: Label the container with the variety, harvest date, and any other notes you may want to remember about the plant. This information will be helpful when planting or sharing seeds in the future.
3. Find a Cool, Dark Location: Store the container in a cool, dark place, such as a cupboard, pantry, or refrigerator. The ideal storage temperature is around 32-41°F (0-5°C). Properly stored watermelon seeds can remain viable for up to 5 years.

Testing Seed Viability

To check whether your saved seeds are viable before planting, conduct a simple germination test:

1. Dampen a Paper Towel: Place a few seeds on a damp paper towel, fold it over, and place it inside a plastic bag or a container with a lid.
2. Wait and Observe: Place the bag in a warm, dark place, and check after a week. If the seeds begin to sprout, they are viable and ready for planting. If most seeds don’t sprout, consider discarding the batch and saving fresh seeds.

By saving seeds from your heirloom watermelons each year, you can ensure a continuous supply of your favorite varieties, tailored to the conditions in your garden. Seed saving not only helps you preserve heirloom varieties for future generations but also deepens your connection to the plants you grow.

Final Tips for Growing Heirloom Watermelons

• Rotate Crops: Avoid planting watermelons in the same spot each year. Rotating crops helps prevent soil-borne diseases from building up.
• Save Seeds: Heirloom varieties allow you to save seeds from season to season. To save seeds, allow a few watermelons to fully mature and collect seeds from the ripest fruits.
• Be Patient: Heirloom watermelons often take longer to grow and ripen than hybrid types, but their unique flavors are worth the wait.

Growing heirloom watermelons is a rewarding journey that brings history, flavor, and beauty to your garden. With the right preparation, patience, and a bit of care, you’ll enjoy delicious, home-grown heirloom watermelon all summer long.

Conclusion

This Heirloom Watermelon Planting Guide gives you all the knowledge you need to start growing these delightful fruits. By following these steps, you’ll be well on your way to a bountiful heirloom watermelon harvest. Enjoy the process and most importantly, savor the results of your labor!

FAQ: Heirloom Watermelon Planting Guide