Japanese squash, also known as Kabocha, kabocha squash, and Japanese pumpkin, makes a superb addition to any garden and plate! To grow it at home, it’s worth knowing a few tips and tricks.

In this guide, our experts reveal their secrets to ensure a bountiful harvest.

What is Japanese squash?

Japanese squash is a variety of winter squash popular in Japan. Like the buttercup squash, it produces large fruit, weighing between 2 and 3 pounds (0.9 to 1.4 kg), with a thick, dark green rind and yellow or orange flesh.

What makes kabocha so popular, not just in Japan but worldwide, is its unique sweetness and texture. Often, it has been compared to a mix between sweet potato and pumpkin.

– What’s the difference between summer and winter squash?

Why is it called Japanese winter squash? Unlike summer squash varieties, which can be eaten fresh, kabocha is harvested and allowed to ripen for at least one month, usually overwinter. By the time it is fully ripe, the outer skin is tough and coarse, which also helps preserve the squash for many months during the cold season.

– Japanese squash varieties

There are many Japanese squash varieties and hybrids you can pick from. They vary in shape, size, and color, as well as flavor and texture. Some hybrids can produce fruit that weighs up to 8 pounds (3.6 kg), while small Japanese squash varieties are more contained, weighing in at just 2 pounds (900 g).

Most varieties have a dark green rind with small bumps, although some hybrids, such as Kuri, can have blue-green skin or even bright orange. Delica and Tetsukabuto are some of the most popular hybrids in Japan. Other well-loved cultivars include Naguri, Ajihei, Miyako, Kofuki (noticeable nutty aroma), and Emiguri (very sweet and aromatic).

How to grow Japanese squash

Whichever variety or hybrid of Japan squash you go for, the growing conditions are the same. Two or three plants are more than enough to keep you and your family stocked with kabocha over winter.

So if you have some spare space in your garden, make sure you don’t miss out on this beautiful fruit.

Here’s what you need to get started.

– When to plant Japanese squash

Don’t let the name’ winter squash’ trick you: Japanese kabocha is a warm-season crop that needs lots of sun and heat. It also takes quite some time to mature, and in some cases, you will need to wait up to 5 months from sowing before your pumpkins are ready to harvest.

1. Sowing directly outdoors

Japanese squash seeds can be sown outdoors directly in late spring or when soil temperatures are consistently above 60 °F (15 °C). The seeds will germinate in about 7 to 10 days. The plants will spend the following months growing vines, leaves and flowering before producing fruit in late summer. This process can take quite a bit of time, and as a result, it’s best to get a head start early in the season.

We recommend germinating Japanese squash seeds indoors 2 or 3 weeks before the weather is warm enough to transplant the young plants outside.

2. How to germinate seeds indoors

Japanese squash seeds have tough skin, so it’s best to soak them in before sowing. It will soften the outer layer and speed up germination. You can soak them in lukewarm water for at least two hours, or best results, overnight.

Once the seeds are soaked, prepare a compostable seedling pot for each seed by filling it with a seed starter and soil mix. Plant each seed 1 inch (2.5 cm) deep and water well. The soil should be kept moist but not soaked, as this can cause the seeds to rot.

The ideal temperature range for germinating squash seeds is between 64 °F and 80 °F (18 °C to 27 °C). If possible, keep the bottom of the seedling pots warm. Once the seeds have germinated, remove the heat source to avoid damaging the roots.

3. When to transplant cucumber seedlings

The young Japanese squash plants are ready to move outdoors when soil temperatures are consistently above 60 °F (15 °C). Each plant has at least two sets of fully developed leaves.

– Outdoor Grow Tips

Plant your Japanese squash in a part of your garden that receives at least 6 hours of bright, direct sunlight each day. Prepare the garden soil by digging it up to a depth of 1 foot (30 cm) and turning it over, and make sure to incorporate plenty of compost. Japanese squash grows best in rich, well-draining soils, with a pH ranging from 6.0 to 6.8.

1. Does Japanese squash need support?

Kabocha is a vining plant producing vines that can be anywhere between 3 and 6 feet (90 cm to 180 cm) in length. Some gardeners recommend using trellises to grow these plants, although keeping it as a creeping vine works just as well. The main thing to check is the fruit’s weight, which differs from one hybrid to the other.

Varieties that produce smaller fruit, up to 2 pounds (900 grams), can be grown on trellises and the ground. They are also suitable for growing in containers. However, hybrids that produce heavy fruit (5 pounds/2.3 kg and above) are best grown as ground creepers, as the weight of the mature squash can damage the vines if left to hang.

2. Spacing and watering

Plant your Japanese squash 2 feet (60 cm) apart, in rows spaced out at least 3 feet (90 cm). After transplanting your seedlings, give the soil a thorough watering. Continue to water the soil each week after the plants are established. Japanese pumpkins need plenty of water to grow, but if the soil is soaked or poorly draining, it can cause root rot and even damage the fruit growing on the ground.

3. Fertilizer

For an abundant harvest, provide your Japanese squash with a monthly application of liquid fertilizer. Start feeding the plants one month after transplanting, and continue the application throughout summer and early autumn. Nitrogen-rich fertilizers can be used when the plants are still young to boost their growth.

It’s best to avoid using too much nitrogen as the plants enter the flowering stage. It will result in too much vegetative growth (such as leaves and vines) and not enough flowers. A nutrient ratio of 2-3-1 is best.

– Pollinating

Japanese squash plants produce separate male and female flowers, and they rely on pollination for the fruit to set. Plants grown outdoors are typically pollinated by insects such as bees and butterflies. Still, for squash grown in greenhouses, manual pollination is essential. We often recommend manually pollinating your squash plants regardless of where they grow. It will vastly improve the chance of fruit setting.

To manually pollinate Japanese squash, start by identifying the female flowers. They should have a small lump on the flower stem underneath the petals, which will develop into the squash fruit. Then, remove a male flower from the vine and gently rub it against the female flower to transfer the pollen. The best time to do this is early in the morning before 10 am.

If pollination is successful, the small lump on the female flower stem will slowly start swelling, growing into the squash fruit. When growing Japanese squash, patience is vital, so be prepared to wait at least 40 days once the fruit sets before it is ready to be harvested.

– Harvesting time

On average, it’s best to harvest your Japanese squash 45 – 50 days after the fruit has started forming on the vine. It means you will most likely begin harvesting your kabocha beginning in early autumn. Don’t leave the squash on the vine for too long, as the main plant will stop producing new fruit.

By this time, it’s ready to harvest. The fruit should have a thick, firm, and slightly ribbed skin and should weigh anywhere between 1.5 and 5 pounds (700g to 2.2 kg), depending on the hybrid. The fruit’s stem should be dry, brown, and thick, so use a pair of gardening scissors to cut it off the vine.

Try to harvest your Japanese squash before the seasonal autumn rains to reduce the risk of mold or damage to the rind. Although the fruit can survive a light frost, it’s best if you harvest your squash before temperatures drop too low.

Ripening Japanese squash

Like other buttercup squash varieties, kabocha needs to be allowed to ripen after it has been harvested. This way, the fruit’s starches will convert to sugars, giving the Japanese squash its well-loved flavor. After harvesting, keep the fruit in a warm and well-ventilated area, with temperatures around 77 °F (25 °C). After another two weeks, move the squash to a cool, dry place, where temperatures don’t go above 50 °F (10 °C).

When is Japanese squash ripe enough to eat? Well, it depends entirely on which hybrid you’re growing. Some varieties, such as red-skinned kabocha, should be allowed to ripen for about two months.

Tetsukabuto, the most popular type in Japan, is often left to mature for at least three months. What we recommend is that you leave your kabocha to ripen for two whole months so that it reaches its full flavor potential. The wait will be well worth it!

Uses for Japanese squash

Japanese squash is delicious and versatile, and you can use it in sweet and savory dishes. Its flavor is sweet and fragrant and can vary from one variety to the other. Often, it is sweet and fragrant, similar to that of melon or cantaloupe. Still, it can also have apricot, persimmon, or even banana notes. Some varieties, such as Kofuki, are grown for their nutty, chestnut-like flavor.

The best way to enjoy Japanese squash is by roasting it. The tender texture and buttery sweet aroma work perfectly in soups, curries, tempura-style deep-fried dishes, sauces, as well as cakes and other desserts.

Conclusion

Japanese squash has become increasingly popular in recent years. If you want to try it yourself, follow the steps in this grow guide, and you’ll have a bountiful harvest in no time!

Let’s go over the key points:

  • Japanese squash is a warm-season crop, meaning it should be planted in spring, ready for autumn harvest.
  • It’s best to germinate the seeds indoors before transplanting outside, especially if you live in an area with long, cold winters.
  • Most varieties can be grown as a creeping vine, just like a pumpkin. However, those that produce smaller fruits can also be raised on a trellis.
  • After harvesting Japanese squash, you’ll need to allow the fruit to ripen before it’s good to eat. Around two months is typically long enough.

Growing Japanese squash at home has never been easier, so why not grab a packet of seeds today and try it yourself?

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