A freshly cut open Kurobe Watermelon revels deep red flesh glistening in the California setting sun.

Watermelon Seeds,
Kurobe

3.84 ReviewsSKU: #WM215Min. seed count: 25
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Description

(Citrullus lanatus). An extra-jumbo watermelon that can be found individually wrapped in rope ‘baskets’ in Japanese markets and sold for up to 7000 yen each! This iconic variety makes a popular gift in Japan and can often be found at summer picnics. This variety was selected from a U.S. variety called Rattlesnake, which was brought to Japan during the Meiji Era and cultivated in the town of Nyuzen and along the Kurobe River since the 1930s. This variety is presented to the Imperial family every year, and the super sweet mammoth fruit is a popular and expensive gift, up to 70 US dollars each. A giant cartoon watermelon is also a popular Japanese mascot, a nod to this beloved Japanese variety.

Growing Tips: Kurobe watermelon thrives in warm, sunny locations with fertile, sandy loam soil. Use mulch to maintain moisture and suppress weeds, and water consistently to avoid stress. Fertilize moderately with compost or a balanced organic blend at planting and during early fruit development.

Plant Details

Botanical Name
Citrullus lanatus
Life Cycle
Annual
Sun Requirement
Full sun
Days to Germinate
5–10
Days to Maturity
90–100
Planting Depth
1 in.
Plant Spacing
36–48 in.
Ideal Temperature
70 to 95°F
Frost Hardy
No

When to Grow

Start seeds indoors 3–4 weeks before your last expected frost date or direct sow once soil temperatures are consistently above 70°F. Transplant only after all danger of frost has passed. If you’re not sure how to find your first and last frost dates, consult our blog post 'Our Experts Answer Questions, Share Resources.'

How to Sow and Plant

  • Watermelon loves heat. In most climates, watermelon can be direct sown into the garden after frost season ends and soil is warm.
  • Soil should be rich and well amended with compost or manure.
  • Sow in full sun, preferably where no other melons, squashes or cucumbers have grown for at least three years, to reduce the likelihood of diseases.
  • Sow one-half inch deep and 12 inches apart, in rows 6 feet apart. If the soil temperature is right, sprouts appear in just a few days.
  • In shorter-summer climates, or to get an earlier harvest, seeds may be started indoors, 3-4 weeks prior to setting-out date.
  • Warm conditions yield fast germination; hold at 80 degrees or so. (Use a heating mat if necessary.)
  • Once seedlings appear, they need good light—at least half-day direct sun through a south-facing window or good artificial lighting.
  • Timing is critical—held in pots for too long the seedlings may become root-bound, which slows the plants down.

How to Grow

  • Thin if necessary to stand 2-3 feet apart in the row.
  • The vines soon begin to “run” and easily travel 6 feet from the roots as they grow. During this time, control weeds, keep the patch well watered, and watch for watermelon pests.

PESTS/SPECIAL CONSIDERATIONS

  • Cucumber beetle is possibly the most common pest. Spray with Spinosad as needed.
  • Watermelon plants also attract squash bugs. Pyganic or other pyrethrum-based insecticide is a good organic control.

How to Save Seeds

  • Allow fruit to fully ripen and cure on the vine before harvesting .
  • Scoop seeds from the flesh and rinse in a strainer to remove pulp.
  • Spread seeds on a screen or paper towel in a warm, dry place out of direct sunlight for 7-10 days.
  • Stir daily to ensure even drying.
  • Once completely dry, store in an labeled, airtight container in a cool, dark place.

FAQ

How long does Kurobe watermelon take to mature?

Allow 90 to 100 days from planting to harvest for this extra-jumbo watermelon. Seeds sprout in about 5 to 10 days.

What soil and feeding does Kurobe prefer?

It thrives in a warm, sunny spot with fertile, sandy loam soil. Mulch to hold moisture and suppress weeds, water consistently so the vines are never stressed, and fertilize moderately with compost or a balanced organic blend at planting and again during early fruit development.

Can I start Kurobe indoors?

Yes. In shorter-summer climates, or to get an earlier harvest, sow indoors 3 to 4 weeks before your set-out date and hold the flats at around 80°F for fast germination, using a heating mat if needed. Once seedlings appear give them at least half a day of direct sun or good artificial light, and do not hold them in pots too long, because root-bound transplants are slow to recover.
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