How to Grow Kabocha Squash

Kabocha squash is one of our favorite squashes/pumpkins to enjoy in the fall! It has a lovely texture—almost like a cross between butternut squash and chestnuts. The skin is also edible, so you don’t have to peel it. Let’s talk about how to grow Kabocha Squash in your garden.

This post is part of our How to Grow Chinese Vegetables series, which is in its second season. In this series, we’re working with professional farmer Christina Chan of Choy Division, a regenerative Asian vegetable and herb farm in the Hudson Valley, who has generously offered to share her expertise with us and our readers!

What Is Kabocha Squash? Why Grow It?

Kabocha squash, also known as Japanese pumpkin in the U.S., is a sweet winter squash with dark green, slightly knobbly skin and bright orange flesh.

It is a long-season warm weather plant that grows much like other squashes and pumpkins. They can also be stored for months through the fall and winter.

We love it for several reasons:

• Sweet flavor: It’s often even sweeter than everyone’s favorite, butternut squash! Its water content isn’t as high as other varieties, which means that it has a really concentrated flavor.
• Texture: Rather than having a mushy texture, it has a little more density, heft, and starch to it. As I mentioned earlier, it’s like a cross between butternut squash and chestnuts. Some compare its texture to that of sweet potato.
• Edible skin: Intimidated by the need to peel/slice the skin off of other types of pumpkin? There is no need to peel a kabocha squash—just scrub it clean before slicing in half, scooping out the seeds, and cooking! Just take care when cutting it with your knife, as the squash can be quite hard/dense.
• Versatility: You can do a lot with a kabocha squash! Steam it as a side dish, or use it as a substitute for potatoes or other squashes to make a mash or roasted cubes. Kabocha squashes can also be hollowed out and used as a cooking vessel for hearty stews.
• Health factor: As a complex carbohydrate, kabocha is a healthier alternative to refined starches like white potatoes or rice. They’re also a good source of beta carotene and Vitamin C.

Because Kabocha can be stored for months, it’s a great crop to grow in your garden. You’ll be able to collect several squashes and enjoy them through the colder months, when fresh produce is less abundant.

Varieties of Kabocha Squash

There are several different types of kabocha squash available from heirloom seed sources, including Green Kabocha, Blue Kuri Kabocha, and Orange/Red Kabocha.

Here are some specific varieties from Christina, along with links to seed sources:

• Zuccuri (Oishi Nippon)
• Hokkori (Kitazawa)
• Stella Blue (Hudson Valley Seed)
• Black Forest (Hudson Valley Seed)
• Red Kuri (Johnny’s Selected Seeds)

How to Grow Kabocha Squash

Christina says that Kabocha squash does well either seeded directly into the ground, or when transplanted. We seeded many of our squash plants directly this year, and had great results. We grew loofah, birdhouse gourds, butternut squash, and Big Max pumpkins this way.

That said, Christina brought us young Kabocha Squash seedlings when she visited TWOL HQ back in May (check out our Spring Farm Update from that time), so for our Kabocha crop, we used those, also with good results!

Plant them into the ground after the last frost date in your area. Here in the Tri-state area, that is around late May/early June. That said, they are also warm-weather-loving plants, so if you have a chilly May, planting in June may help establish healthier plants.

While these are referred to as a “winter squash,” that’s actually referencing their storage capabilities and not the time period in which they grow. These squashes do best in hot summer weather and need an entire summer to mature.

In other words, you must plant your Kabocha squash by early summer, or they won’t have enough time to grow!

Direct seeding is easiest—space them about three feet apart. They are hungry plants that need space. They are a vining plant, that takes up a lot of room in the garden.

While last year, we grew them horizontally, across the ground, we actually grew them vertically this year to save space:

From Christina: “I would not recommend planting anything you need to access regularly right next to Kabocha squash.  Once the plants start vining, you really don’t want to be stepping on them or causing any damage. You want to let it do its thing until its time to harvest. These are very ‘set and forget,’ other than a few weedings at the start to let the plants establish.”

If starting in pots and transplanting, start indoors 2-3 weeks before the last frost date. Seedlings are large and grow quickly, so you don’t want them to spend too much time indoors, which can stress the plant. Harden off the seedlings in a protected area outside for 1 week before planting out.

Ideal Growing Conditions for Kabocha Squash

Climate/Weather

Winter squash do best in dry and hot climates. Plant seeds or seedlings when soil temperatures are consistently higher than 60°F/16°C.

Water

• Only use drip tape or water at the base of plant. Overhead watering onto leaves increases the likelihood of bacterial and fungal disease.
• They can be dry farmed as well (water in very heavily at the beginning, and then let the roots scavenge for water on their own).  Dry farming creates better flavor, as there is less water weight in the final squash.
• In a very wet year (like this one in our area), squash are more prone to rotting (even after curing) because they are just so waterlogged.

Sunlight

Full sun!

Soil Conditions 

Squash plants are heavy feeders and need nutrient-rich soil. Amend the soil with a 2-3 inch layer of compost before planting. We find there is no need to dig in the compost—just a layer on top feeds the plants without destroying the soil structure underneath.

Drainage is also important, so if your soil is a very heavy, wet clay type, it may help to add not just organic matter, but also sand for drainage.

Harvesting Kabocha

You’ll know Kabocha is ready for harvest when the skins have changed from shiny to matte and have a toughened exterior. The skin should not break easily (should not be scratched or damaged by a fingernail). The stem will have started drying out and become woody.

If you notice small fruit setting late in the season, prune these off. They will not reach maturity before the growing season ends and are drawing energy away from the plant. If you remove them, more energy will be available to help the larger fruit mature.

To harvest, snap squash off at the top of the stem. Keep the stem long-ish. Do not create breakage between the stem and the fruit—this open wound can lead to rotting.

After harvest, cure your squash by placing it in a warm place (sunny is okay—Choy Division cures their squashes in their greenhouse) ensuring there is good circulation around the squash, including underneath.

Make sure the squashes are in a single layer and not touching too much. Air flow and circulation is key!  Wire shelving units are great for curing squash.

Curing is necessary to prolong storage life and improve flavor. This process removes moisture and concentrates sugars. They are often stored this way for a several months to foster nutrient development and a more complex flavor.

In Japan, growers harvest them between summer and fall, but after curing, they are usually eaten in the wintertime. (A traditional Japanese winter solstice dish is a sweet kabocha soup with red bean.) The squash is in in season from September to December.

Pests & Diseases affecting Kabocha Squash

Pests

Cucumber beetles: There are a few different species of this insect, but our most common one is a small oblong yellow and black striped flying beetle. They and their larvae can feed heavily on the leaves, vines and fruit of the cucurbit (gourd) family. 

In addition to physically decimating a plant, they’re also responsible for disease transfer. We have seen these little beetles in our garden, browsing around our cucumber, squash, and pumpkin plants!

To prevent cucumber beetle damage, use a row cover after planting until you see flowers start to set or the plant starting to vine vigorously.  At this point, the plant should be strong enough to withstand any insect damage.

Diseases

If disease appears late, and your squash are almost ready to harvest, the recommendation is to harvest everything and cure. Here are some of the diseases that Kabocha is susceptible to:

• Bacterial wilt: One of the primary causes of death in Choy Division’s squash fields, this disease is transferred by cucumber beetles among other sources. Leaves first appear dull green, wilt during the day, and recover at night. The leaves eventually yellow and brown at the margins, completely wither, and die. 

• Phytophthora: In squash fields, Phytophthora capsici causes wilting, crown, root, and fruit rot, plant stunting, and the eventual death of the plant. Since the disease results in a range of symptoms in squash, it is often referred to as Phytophthora blight. Sporangia are formed on infected fruit and have a powdered sugar appearance.  If you see this, unfortunately it’s a lost cause and can’t be saved. 

• Powdery mildew: One of the most common plant diseases, and easy to identify due to its distinct appearance. Powdery mildew  makes the leaves look like they’ve been dusted with white/gray talcum powder. Most of that white dust consists of spores, which the wind easily carries to other nearby leaves.

We got relatively lucky with our squash plants this year, which were able to set small fruit despite the wet weather we had. While we did see some disease damage on our plants later in the season, we quickly harvested our Kabocha squash at a relatively small size and were able to enjoy them!

Last year, we had drier, sunnier weather, and our Kabocha squash grew to almost twice the size they did this year!

Origins & Migration

All squash types were domesticated in Mesoamerica. Seeds dating back several thousands of years have been found in Mexico and Peru! It is believed that the Portuguese brought squash plants to Japan in the 1500s, by way of Cambodia.

The Japanese mistakenly believed, therefore, that the squash came from Cambodia. The Japanese characters for the word translate to “southern melon,” referring to Southeast Asia/Cambodia. The word Kabocha now translates simply to “pumpkin” in Japanese.

While saying “Kabocha squash” in English essentially amounts to saying “pumpkin pumpkin,” we use the term to refer to this Japanese variety. You can now find them around the world, from Asia to North and South America, Europe, Africa, and Australia/New Zealand.

In World War II Japan, Kabocha was an important crop that people grew in backyard gardens and schoolyards to help mitigate food shortages. It lost its popularity after the war due to this association with lean times, but has since regained popularity.

Conclusion

We hope you enjoyed this post on how to grow Kabocha squash. We will have a bonus post for you in November: how to grow watercress! Stay tuned for that one.

We hope that our how to grow Chinese vegetables series has inspired you with some new ideas! Here’s a full list of what we’ve covered so far: