Heirloom

Blacktail Mountain Watermelon

Citrullus lanatus 'Blacktail Mountain'

Developed in Idaho for short-season growing, this remarkable heirloom produces full-sized, incredibly sweet watermelons in just 75 days even in cool climates. The round, dark green fruits with subtle stripes contain bright red flesh that rivals any long-season variety for flavor and sweetness. Perfect for northern gardeners who thought they couldn't grow watermelons.

Harvest

70-75d

Days to harvest

📅

Sun

Full sun

☀️

Zones

3–8

USDA hardiness

🗺️

Height

4-8 inches

📏

Planting Timeline

Zone:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Start Indoors

Transplant

Direct Sow

Harvest

Start Indoors

Transplant

Direct Sow

Harvest

Showing dates for Blacktail Mountain Watermelon in USDA Zone 7

All Zone 7 melon →

Zone Map

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Blacktail Mountain Watermelon · Zones 3–8

What grows well in Zone 7? →

Growing Details

Difficulty

Easy

Spacing36-48 inches

SoilWell-drained sandy loam, tolerates various soil types

pH6.0-7.5

Water1-2 inches per week, reduce as fruit ripens

SeasonWarm season

FlavorSweet and juicy with excellent watermelon flavor

ColorDark green skin with red flesh and black seeds

Size8-10 inches long, 6-12 pounds

Zone-by-Zone Planting Calendar

Zone	Indoor Start	Transplant	Direct Sow	Harvest
Zone 1	June – June	July – August	July – September	October – August
Zone 2	May – June	July – July	July – August	September – September
Zone 11	January – January	February – February	February – March	April – June
Zone 12	January – January	February – February	February – March	April – June
Zone 13	January – January	February – February	February – March	April – June
Zone 3	May – May	June – July	June – August	September – October
Zone 4	April – May	June – June	June – July	September – October
Zone 5	April – April	May – June	May – July	August – October
Zone 6	April – April	May – June	May – July	August – September
Zone 7	March – April	May – May	May – June	July – September
Zone 8	March – March	April – May	April – June	July – August
Zone 9	February – February	March – April	March – May	June – July
Zone 10	January – February	March – March	March – April	May – July

Complete Growing Guide

Blacktail Mountain demands warm soil (at least 70°F) and full sun exposure to hit its impressive 70-75 day maturity, so start seeds indoors 3-4 weeks before your last frost or direct sow only after soil warms thoroughly. Unlike longer-season watermelons, this cultivar cannot tolerate cool springs—premature planting will stunt growth rather than advance harvest. Plant in rich, well-draining soil amended with compost and space vines 3-4 feet apart to allow adequate air circulation, which prevents powdery mildew and wilt diseases that can spread quickly in dense plantings. While generally pest-resistant, monitor for cucumber beetles early in the season, as they vector bacterial wilt; row covers on young plants provide effective protection. One critical practice: thin developing fruit to one melon per vine, as Blacktail Mountain produces multiple flowers but concentrates its sugars better in single fruits, ensuring those prized sweet, full-sized melons rather than multiple undersized ones.

Light: Full sun (6 or more hours of direct sunlight a day). Soil: Loam (Silt). Soil pH: Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 0 ft. 4 in. - 0 ft. 8 in.. Spread: 5 ft. 0 in. - 10 ft. 0 in.. Growth rate: Medium. Maintenance: Medium. Propagation: Seed. Regions: Coastal, Mountains, Piedmont.

Harvesting

Blacktail Mountain watermelons reach peak harvest readiness when the dark green skin develops a dull, matte finish rather than a glossy sheen, and the fruit achieves a diameter of 6–8 inches with a firm, hollow sound when thumped. The underside should display a creamy yellow or pale orange spot indicating full maturity. These plants produce watermelons in a continuous pattern throughout the season rather than a single flush, allowing successive harvests as new fruits develop. Time your harvesting for early morning when temperatures are coolest, as this preserves the crisp, juicy texture and peak sugar content of these remarkably sweet melons. A ripe Blacktail Mountain will detach easily from the vine with gentle pressure—avoid pulling hard, as fruits ready for harvest should separate with minimal resistance.

The plant produces melons which are large modified berries called a pepo. They are rounded to oval mottled green with darker green rind. Black, cream or mottled colored elliptic seeds. Flesh general red or pink but can also be yellowish.

Color: Green. Type: Berry. Length: > 3 inches. Width: > 3 inches.

Garden value: Edible

Harvest time: Summer

Edibility: The fruit can be eaten raw or pickled. The rind is edible after cooking.

Storage & Preservation

Store freshly harvested Blacktail Mountain watermelons at 50–70°F with 80–90% humidity in a well-ventilated space, away from ethylene-producing fruits. Whole melons keep for 2–3 weeks under these conditions; cut fruit lasts 3–5 days when refrigerated in airtight containers. For longer preservation, freeze cubed flesh in airtight bags or containers for up to three months—ideal for smoothies and juices. Canning is viable using established tested recipes for watermelon preserves or jams, though the high water content makes whole-fruit canning impractical. Drying thin slices at low temperature (135–145°F) yields chewy snacks with concentrated sweetness. This variety's thin rind means it bruises more easily than thick-skinned types, so handle carefully during harvest and storage to avoid cracking and premature spoilage.

History & Origin

Developed in Idaho during the mid-20th century, Blacktail Mountain emerged from breeding programs focused on creating short-season watermelon varieties suited to northern climates with limited growing windows. The variety represents a deliberate selection within heirloom watermelon lineages, prioritizing early maturity and cold tolerance while maintaining the sweetness and fruit quality of longer-season types. While specific breeder attribution remains unclear in available documentation, Blacktail Mountain became an iconic regional variety distributed primarily through seed companies serving mountain and northern states. Its success established it as a foundational heirloom for cool-climate gardeners, and the variety remains widely cultivated today through heritage seed networks and commercial seed producers.

Origin: Africa

Advantages

+Exceptionally short 70-75 day maturity enables northern gardeners to grow watermelons successfully.
+Produces full-sized melons with excellent sweetness rivaling traditional long-season varieties.
+Dark green striped skin and bright red flesh create visually striking, attractive fruits.
+Developed specifically for cool climates and short growing seasons in Idaho.
+Easy difficulty level makes it accessible for beginner and experienced gardeners alike.

Considerations

-Susceptible to anthracnose and fusarium wilt, requiring careful disease management practices.
-Vulnerable to cucumber beetles and squash vine borers that damage vines and fruits.
-Requires consistent moisture and warm soil temperatures despite cool-climate adaptation.
-May produce smaller yields compared to traditional long-season watermelon varieties in suboptimal conditions.

Companion Plants

Nasturtiums and marigolds work near watermelons by masking the scent cues that cucumber beetles (Diabrotica spp.) use to locate cucurbit seedlings — not foolproof, but worth the bed space. Radishes tucked at the edges pull double duty: they act as a trap crop for the same beetles and break up any surface crust that can impede water infiltration around shallow transplants. Beans fix nitrogen at a root depth that doesn't compete with watermelon's sprawling lateral roots. Fennel is the one to skip entirely — it releases allelopathic compounds that suppress neighboring vegetables, and tomatoes and potatoes share fusarium wilt strains that will keep that pathogen cycling in your soil long after the season ends.

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

Nutrition Facts

Calories

30kcal(2%)

Protein

0.61g(1%)

Fiber

0.4g(1%)

Carbs

7.55g(3%)

Fat

0.15g(0%)

Vitamin C

8.1mg(9%)

Vitamin A

28mcg(3%)

Vitamin K

0.1mcg(0%)

Iron

0.24mg(1%)

Calcium

7mg(1%)

Potassium

112mg(2%)

Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #167765)

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

Troubleshooting Blacktail Mountain Watermelon

What you'll see, why it happens, and what to do about it.

Dark, sunken, water-soaked spot on the blossom end of the fruit — sometimes with a moldy secondary growth on the rotted area

Likely Causes

Blossom-end rot — calcium deficiency in the developing fruit caused by uneven soil moisture
Overfertilization with high-nitrogen fertilizer, which disrupts calcium uptake
Soil pH outside the 6.5–6.8 range, reducing calcium availability

What to Do

1.Mulch heavily and water on a consistent schedule — 1 to 2 inches per week — to avoid the wet-dry swings that trigger this
2.Pull back on any nitrogen-heavy fertilizer once vines are running; side-dress with compost instead
3.Soil-test and lime to bring pH up to 6.5–6.8 as NC State Extension recommends; correct pH does more than any foliar spray

Small, circular tan spots with dark purple borders appearing on leaves, then sunken lesions developing on the fruit skin as it sizes up

Likely Causes

Anthracnose (Colletotrichum orbiculare) — a fungal disease that spreads quickly in warm, wet weather above 70°F
Rain or overhead irrigation splashing spores from infected soil and debris onto the canopy

What to Do

1.Strip and trash (not compost) infected leaves and any visibly lesioned fruit the moment you see them
2.Switch to drip irrigation or water at ground level — keeping foliage dry cuts transmission significantly
3.Don't plant cucurbits in the same bed for at least 2 seasons; Colletotrichum overwinters in crop debris and comes back ready

Frequently Asked Questions

How long does Blacktail Mountain watermelon take to grow from seed to harvest?▼

Blacktail Mountain watermelons mature in 70-75 days from seed to harvest, making them one of the fastest-ripening watermelon varieties available. This quick maturity is specifically bred for northern climates with short growing seasons. In zones 3-5, start seeds indoors in late April for transplanting after last frost to ensure full maturation before fall temperatures drop.

Can you grow Blacktail Mountain watermelon in containers?▼

Yes, Blacktail Mountain's compact vine structure makes it suitable for large containers (minimum 20 gallons) or raised beds. Choose containers at least 18 inches deep with excellent drainage. The variety's smaller fruit size (6-12 lbs) won't overwhelm container supports, and the shorter vines can be trained around container edges. Ensure full sun exposure and consistent watering for container success.

What does Blacktail Mountain watermelon taste like compared to store-bought?▼

Blacktail Mountain delivers exceptionally sweet, juicy red flesh with classic watermelon flavor that rivals or exceeds commercial varieties. Despite being bred for cool climates, it maintains high sugar content and crisp texture. The flesh is less dense than shipping varieties, giving it a more refreshing, melt-in-your-mouth quality. Many gardeners report superior flavor compared to grocery store watermelons.

When should I plant Blacktail Mountain watermelon seeds?▼

Direct sow Blacktail Mountain seeds when soil temperature reaches 65°F consistently, typically 2-3 weeks after your last frost date. In northern climates (zones 3-6), start seeds indoors 2-3 weeks before last frost for transplanting outside. Use soil thermometers rather than air temperature—soil stays cooler longer. Black plastic mulch can warm soil faster for earlier planting dates.

Is Blacktail Mountain watermelon good for beginners?▼

Absolutely—Blacktail Mountain is excellent for beginning gardeners, especially those in northern climates. Its cold tolerance forgives temperature fluctuations, compact size requires less space management, and reliable 75-day maturity removes guesswork about harvest timing. The variety's disease resistance and ability to produce quality fruit in challenging conditions makes it more forgiving than heat-dependent southern varieties.

How big do Blacktail Mountain watermelons get?▼

Blacktail Mountain watermelons typically weigh 6-12 pounds when fully mature, roughly the size of a basketball. This smaller size is intentional—larger fruits wouldn't ripen reliably in the short, cool seasons this variety was bred for. The compact size actually concentrates flavors while ensuring complete ripening, and makes harvesting and handling much easier for home gardeners.