Planting Timeline
Showing dates for Blacktail Mountain Watermelon in USDA Zone 7
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Blacktail Mountain Watermelon · Zones 3–8
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | April – May | May – June | June – June | August – September |
| Zone 4 | April – May | May – June | May – June | August – September |
| Zone 5 | April – May | May – June | May – June | July – September |
| Zone 6 | March – April | April – June | May – June | July – September |
| Zone 7 | March – April | April – June | April – July | June – September |
| Zone 8 | February – March | March – June | April – July | June – October |
Complete Growing Guide
Start preparing your Blacktail Mountain watermelon site in early spring by choosing the warmest, most protected spot in your garden. This variety thrives in raised beds or mounded soil that warms faster than ground level—critical for success in northern climates. Amend heavy clay soils with coarse sand and compost to improve drainage, as waterlogged roots will stunt growth even in this cold-tolerant variety.
For direct sowing, wait until soil consistently reaches 65°F at 4-inch depth, typically 2-3 weeks after your last frost date. In zones 3-6, consider using black plastic mulch or row covers for the first month to boost soil temperature. Plant seeds 1 inch deep in hills spaced 6 feet apart, sowing 4-5 seeds per hill and thinning to the strongest 2 plants.
Starting indoors gives you a crucial 2-3 week head start in short-season areas. Use large 4-inch pots to minimize root disturbance, as watermelons hate transplant shock. Harden off seedlings gradually over 7-10 days before transplanting when nighttime temperatures stay above 50°F.
Fertilize at planting with a balanced 10-10-10 fertilizer, then side-dress with compost when vines begin running. Avoid high-nitrogen fertilizers after flowering starts, as they'll produce leaves at the expense of fruit development. Water deeply once weekly, providing 1-2 inches total, but reduce watering as fruits approach maturity to concentrate sugars.
Train vines in one direction to maximize sun exposure and air circulation. Unlike heat-loving varieties, Blacktail Mountain actually benefits from some afternoon shade in very hot climates. Avoid the common mistake of overwatering—this variety's Montana heritage means it performs better with moderate moisture than constant irrigation.
Harvesting
Blacktail Mountain watermelons signal ripeness through several reliable indicators that develop over 7-10 days. The ground spot (where the melon rests) transforms from white to creamy yellow or pale orange. The tendrils nearest the fruit stem turn brown and crispy, while the fruit's surface develops a dull, matte finish rather than glossy shine.
Perform the thump test by tapping the melon—ripe fruits produce a deep, hollow sound versus the higher-pitched ping of unripe melons. The stem end should feel slightly soft when pressed gently. Due to this variety's compact 6-12 pound size, you'll notice the melon stops growing and may develop subtle striping changes.
Harvest in early morning when temperatures are cool and sugar content peaks. Cut the stem with sharp pruners rather than pulling, leaving a 2-inch stub to prevent rot. Since Blacktail Mountain doesn't continue ripening after harvest like some varieties, timing is crucial—wait for multiple ripeness indicators rather than rushing based on calendar days alone.
Storage & Preservation
Whole Blacktail Mountain watermelons store best at room temperature (70-75°F) for up to one week, developing optimal flavor and texture. Refrigeration before cutting actually diminishes the sweet flavor this variety is prized for. Once cut, wrap pieces tightly in plastic wrap and refrigerate for up to 5 days.
For preservation, the sweet flesh freezes exceptionally well when cubed and frozen on baking sheets before transferring to freezer bags—perfect for smoothies and agua frescas. The high sugar content makes excellent watermelon juice that can be frozen in ice cube trays for concentrated flavor additions. Dehydrated watermelon leather preserves the variety's distinctive sweetness, while pickled watermelon rind creates a traditional preserve that takes advantage of the fruit's tender, thin rind. Avoid canning the flesh as it becomes mushy and loses the variety's prized texture.
History & Origin
Blacktail Mountain watermelon was developed in the 1990s by Glenn Drowns of Sand Hill Preservation Center in Iowa, specifically bred for northern gardeners struggling with short seasons and cool nights. Drowns selected parent varieties based on cold tolerance and early maturity, crossing short-season melons from Montana gardens with hardy varieties that could set fruit reliably in temperatures that stopped other watermelons.
The variety gets its name from the Blacktail Mountains of southwestern Montana, where some of the original breeding material originated from homestead gardens. These mountain gardens, with their extreme temperature swings and short frost-free periods, provided the perfect proving ground for developing this remarkable cold tolerance.
As an open-pollinated heirloom, Blacktail Mountain represents a successful modern breeding effort focused on climate adaptation rather than commercial shipping qualities. It quickly gained popularity among northern gardeners and seed savers who had previously been unable to grow quality watermelons, making homegrown watermelons possible in previously impossible climates.
Advantages
- +Exceptional cold tolerance allows fruit set and ripening with nighttime temperatures down to 45°F
- +Reliable 70-75 day maturity even in short-season climates where other varieties fail
- +Compact vine size requires 30% less garden space than traditional watermelon varieties
- +Outstanding flavor development despite cool growing conditions maintains true watermelon sweetness
- +Performs well in high-altitude gardens up to 5,000 feet elevation
- +Disease resistance bred for northern climates with naturally fewer pest pressures
- +Excellent germination rates in cooler soils where other varieties rot
Considerations
- -Smaller fruit size (6-12 lbs) disappoints gardeners expecting large traditional watermelons
- -Thin rind makes fruits more susceptible to cracking during heavy rain periods
- -Limited heat tolerance—struggles in zones 9-10 during hot summers
- -Shorter storage life than thick-rind commercial varieties
- -Seeds can be difficult to source compared to mainstream varieties
Companion Plants
Plant Together
Nasturtiums
Trap crop for cucumber beetles and squash bugs, repels aphids
Marigolds
Repel nematodes and cucumber beetles with their strong scent
Radishes
Deter cucumber beetles and squash vine borers, mature quickly without competing
Beans
Fix nitrogen in soil to benefit heavy-feeding watermelons
Catnip
Repels ants, aphids, and cucumber beetles more effectively than DEET
Oregano
Repels cucumber beetles and provides ground cover to retain soil moisture
Corn
Provides vertical structure and shade, traditional Three Sisters companion
Sunflowers
Attract beneficial insects and provide windbreak protection
Keep Apart
Fennel
Allelopathic compounds inhibit germination and growth of melons
Tomatoes
Compete for similar nutrients and space, both susceptible to similar fungal diseases
Potatoes
May stunt melon growth and both crops attract similar harmful insects
Pests & Disease Resistance
Resistance
Good cold tolerance, moderate disease resistance
Common Pests
Cucumber beetles, aphids, squash vine borers
Diseases
Anthracnose, fusarium wilt, bacterial fruit blotch