If you want to grow the sweetest, richest, creamiest, dreamiest winter squash on the planet, try planting kabocha squash. This Japanese winter squash puts regular ole’ pumpkins to shame. The delectable sweetness makes it far more desirable for pies and desserts. When roasted and pureed, the dense, luxurious texture is like a combination of mashed sweet potato and butternut squash.
Best of all, kabocha is ridiculously easy to grow in the garden. These vigorous vines practically take care of themselves! This squash is a delight in the garden as long as you have plenty of warm sunshine, water, and room to ramble. Let’s dig into everything you need to know about upgrading your pumpkin patch to gourmet Japanese squash.
Kabocha Squash ‘Cucurbita maxima’ Plant Overview
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History and Cultivation
Kabocha boasts a distinct culinary and agricultural heritage.
At first glance, kabocha looks like a funky, warty green pumpkin. As a varietal of the Cucurbita maxima species, it is closely related to ‘Hubbard’ squash and butternut, but its unique culinary and agricultural history has earned kabocha its own category. This lusciously rich squash has a hard exterior with bumpy green or orange skin and light green or white stripes. When cooked, the vibrant orange interior has a chestnut-like texture and a fluffy creaminess.
Best of all, it has a long storage period when it’s cured properly. Perhaps this is why Japanese pumpkins have become a hallmark of Asian cuisine. The plant’s rich history provides many clues on cultivating, storing, and cooking it!
What is Kabocha Squash?
The skin of this squash can be orange or green with subtle stripes and a rough, bumpy texture.
Kabocha squash, also known as kabocha pumpkin or Japanese pumpkin, is a variety of winter squash revered for its velvety, fluffy texture and exceptionally sweet flavor. Many describe it as a cross between sweet potatoes, pumpkins, and butternut squash.
Kabocha has vibrant orange or green skin, faint stripes, and a bumpy or warty texture. The flesh is bright yellow or orange and is delicious when roasted, boiled, steamed, or pureed.
The Japanese word kabocha literally translates to “Japanese pumpkin.” Some say the term comes from the Japanese root word kabu, which means “turnip,” a reference to the squash’s hearty, starchy sustenance. The crop is widely used in traditional dishes, like Kabocha no nimono, a simmered soy sauce-flavored side dish served nearly everywhere in Japan. In the Korean Danhobakbap, squash slices are stuffed with sweet black rice, peas, nuts, and chilis.
Where Does Kabocha Squash Originate?
These winter squash seeds were said to have reached Japan in the 16th century from Cambodia.
Despite its popularity in Japanese and Korean cuisines, kabocha squash originated in Central and South America with the rest of the squash family cousins. When the Portuguese colonized Brazil, they collected and transported many cucurbits to Asia, including the ancestors of this winter squash variety.
The first seeds reportedly arrived in Japan in the 16th century from Cambodia. Because it is suited to cooler climates than other squashes, it became especially popular in Hokkaido, a northern region of Japan.
What Does Kabocha Squash Taste Like?
Kabocha offers a unique taste, suitable for both sweet and savory dishes.
The unique flavor and texture of kabocha tastes like a combination of butternut squash and sweet potato, like an ultra-sweet creamy pumpkin. It can be used in sweet and savory dishes, from pies to roasts to soups to tempura.
Propagation
Like most winter squash, kabocha is planted in late spring or early summer when the weather has thoroughly settled and all chances of frost have passed. This cucurbit is sensitive to cold weather and will not tolerate temperatures under 55°F. You can propagate it by direct seeding, growing your own starts, or purchasing nursery seedlings.
Direct Seed
With its delicate taproots, squash thrives when seeded directly in garden soil.
Squash does best when sown directly in the garden soil. These frost-tender vines have fragile taproots that prefer to get established in place. However, this can be challenging for northern growers or anyone with erratic spring weather.
The soil temperature must be at least 70°F, preferably closer to 80-90°F. Use a soil thermometer probe to check before planting. Raised beds heat up faster than in-ground beds, so consider growing your squash on a mound or lasagna-style bed.
Move any mulch out of the way so the sun can quickly warm the soil. Straw mulch is amazing, but it can slow the warming of your soil in the spring. A black tarp or clear plastic can also help heat up the seed bed more quickly.
Depth and Spacing
It takes 7-12 days for the seedlings to emerge.
Sow seeds ½ to 1” deep, or at roughly a depth that measures twice the dimensions of the seed itself. I like to sow two seeds per hole at 18-48” apart in rows 6-12 feet apart. Bushy and short-vine varieties typically need 6’ spacing between rows, but longer vines may require up to 12’ to reach maximum potential.
The in-row spacing varies based on the fruit size:
- Small varieties: 18-24” between plants
- Medium: 24-36”
- Large squash: 36-48”
The seeds take 7-12 days to emerge. After germination, thin the seedlings to 1 plant per spacing interval. Double-check your seed packet for recommended spacing, as some kombucha varieties are more compact and can be grown closer together.
Use Row Cover
This row cover is a game-changer for early squash growth, reducing transplant shock significantly.
Immediately water the seeds and cover them with floating row fabric. Row cover dramatically improves early squash success and alleviates transplant shock.
It moderates the microclimate near the soil, keeping the seedlings warmer and buffering against nighttime temperature dips. It also physically excludes pests so your baby plants can get established in peace. Don’t forget to secure it with sandbags or smooth rocks.
Start Indoors
Beginning indoors allows you to employ a seed heating mat, promoting strong early growth.
Cold climates warrant transplanting your squash because the spring weather is too unpredictable. Kabocha doesn’t mind being transplanted as long as you handle them very carefully. Starting indoors allows you to use a seed heating mat to encourage robust early growth.
Ensure plenty of bright sunlight from a south-facing windowsill, greenhouse, or a grow light. The ambient temperature should be around 70°F or room temperature in your home.
Don’t Start Too Soon
Sowing squash seeds indoors should ideally happen three weeks before transplanting.
The best time to seed indoors is just three weeks before transplanting. I like to sow squash seeds on the last frost date, assuming the weather is thoroughly settled three weeks later. Winter squash should not be started indoors too soon. The seedlings establish rapidly and may suffer if they wait in their pots for too long before the weather settles outdoors.
Fill 3-4” pots with a quality well-drained potting mix. Sow 2-3 seeds per container and thin one plant each after germination. Grow at a consistent 70-75°F ambient air temperature. Maintain consistent moisture without making the soil soggy.
Don’t Forget to Harden Off Your Plants
If the nights are chilly, use row fabric to cover the plants.
Harden off the plants 4-7 days before transplanting. You can move them from your nursery or windowsill to a protected patio or porch. Cover with row fabric if the nights are still cool. Allowing the plants to acclimate to harsher outdoor conditions dramatically reduces the risk of transplant shock.
Nursery Seedlings
To ensure healthy growth in late spring, prioritize selecting the strongest seedlings.
Finding kabocha in standard nurseries may be difficult, but many specialty organic vegetable farmers grow the starts and sell them at spring plant sales. If you want to transplant from an established seedling, be very selective about which baby plants you take home.
Here’s what to look for when purchasing squash transplants:
- Growing in 3-4” pots (small cell plugs may not be strong enough to transplant)
- Bright green, healthy leaves
- Several true leaves (not just the rounded cotyledons)
- No signs of mold, mildew, or pests
- Thoroughly rooted in the container (roots fill out the pot)
- Not root-bound (roots shouldn’t be winding around in a circle)
- Not too large or overgrowing the container
- Hardened off (they have been acclimated to conditions outside of a greenhouse)
Remember that cucurbit-family crops are very sensitive to transplant because they have tender taproots. While it’s perfectly possible to grow successful squash crops from transplanted seedlings, you want to select the strongest and most vigorous plants and handle them carefully. Otherwise, you’ll have sad, wilted plants that fail to take off in the late spring properly.
Planting
After seeds are established, planting is a breeze. As long as you thoroughly aerate the soil and carefully handle the seedlings, your kabocha should take off with exponential growth!
The most important thing to do is monitor the weather. Don’t risk losing your winter squash by transplanting too soon. Nighttime temperatures should be reliably above 55°F. Anything colder warrants the use of a low tunnel or row cover.
How to Transplant
Consider using a row cover to keep the young plants warm during their transition to the garden.
Transplant kabocha just like any cucurbit: with extreme care! Cucumbers, melons, squash, and pumpkins all have sensitive taproots. If you cram seedlings into the soil, you risk disturbing their root zones and stunting or killing them.
First, make sure the soil is thoroughly aerated. Generously amend with compost and broad fork to lift any compaction. Use a shovel or hori hori knife to make a hole twice as deep and wide as the seedling root ball.
Gently massage the bottom of the container to loosen the roots. Grasp the plant from the base of its stem and shimmy it out of the pot. Place in the hole and carefully hold it up so the stem stays above ground.
The soil level should remain the same as when it was in the pot. Backfill the remaining soil under and around the plant until it is perfectly tucked in. Give it a gentle press, but don’t tamp down the soil and compact it. To minimize transplant shock, water in with a diluted kelp solution and a generous amount of irrigation.
Spacing
To ensure proper spacing, refer to the information on your seed packet.
As with direct seeding, transplanted kabocha must be spaced fairly far apart. The exact spacing depends on the variety. Check your seed packet and, when in doubt, widen the spacing. Plants should have too much room rather than too little.
I like to grow small ‘Kurinishiki’ kabocha in mounded rows 4 feet apart with plants 18-24” apart. Larger fruited varieties need more room to sprawl. If you live in a humid climate where squash regularly gets diseased, wider spacing is the best way to ensure airflow between the vines.
How to Grow
Kabocha thrives in the same conditions as your other summer and winter squash crops. The plants will yield abundantly as long as you provide ample sunlight, rich soil, and plenty of water.
Light
Avoid growing squash alongside tall companion plants; it doesn’t like being shaded.
Squash requires full sun to produce healthy fruits. Plant in an area that receives at least 6-8 hours of direct sunlight daily. These vines do not tolerate shade well unless you live in a southern climate where they need protection from extreme afternoon heat.
Avoid planting in the shadow of trees or other structures. You should also avoid growing with tall companion plants. Though some have succeeded with “three sisters” (corn, beans, and squash) interplanting, kabocha does best when it can vine out in the open.
Water
Always ensure the water reaches the lower layers of the soil without accumulating or creating soggy conditions.
Consistent moisture is essential for robust Japanese pumpkins. The soil should be regularly moist but never waterlogged. The plants enjoy deep watering at least once weekly or more frequently during dry periods.
Do not irrigate kabocha from above, which can lead to fungal diseases like powdery mildew. You don’t want moisture to sit on the leaf surface. Instead, use drip irrigation or soaker hoses to water from the base.
Remember that plants enjoy less frequent, deeper watering rather than constant shallow watering. Allow the irrigation to run for an hour or so, then stick your finger in the soil to check if the water has reached 4-6” down. These plants have extensive root systems with deep taproots and many shallow lateral roots. Always ensure that water reaches the lower soil layers but make sure that it isn’t pooling up or causing soggy conditions.
Soil
Ensure you don’t place the mulch too close to the plant stems to allow for proper airflow.
It’s best to grow kabocha in raised beds or mounds. Soil elevated off the ground warms up more quickly because a greater surface area is exposed to the sun. Moreover, the raised beds encourage faster drainage to prevent waterlogged or soggy conditions. A lasagna-garden-style bed (layers of sticks, straw, leaves, grass clippings, compost, and topsoil) works incredibly well for this plant.
Your classic loamy, well-drained, compost-rich garden soil is ideal for this winter squash. A slightly acidic pH between 6.0 and 6.8 is standard. Before planting, I always amend my squash beds with generous amounts of well-rotted compost or aged manure. Organic matter will improve fertility, drainage, and water-holding capacity on hot, dry summer days.
Mulch winter squash generously to reduce weeds and conserve water. Straw or dried deciduous leaves help keep the fruits off the soil surface, reducing the risk of rotting. I spread a 1-2” thick layer of mulch a week or so after transplanting. Avoid spreading the mulch too close to the base of the plants, as you want plenty of airflow by the stem.
Climate and Temperature
It is essential to verify that your area has sufficient frost-free days so the produce reaches maturity.
This is a warm-season crop that demands temperatures above 55-60°F. The ideal weather is 70-85°F, but you can use season extensions like row covers to keep the plants cozier into the fall. Kabocha is a long-maturity crop that takes 90-120 days to mature.
Zones 5-11 typically have no problem growing this pumpkin out in the elements without protection. Ensure your region has enough frost-free growing days. Otherwise, you’ll have to transplant or use low tunnels to ensure the plant can produce mature fruits before cold weather arrives.
Using and Removing Row Covers
Once the plants flower, row covers must be promptly removed to ensure proper pollination.
As we’ve mentioned several times, row cover is crucial for this crop because it keeps the tender plants warm and protected from pests. However, you MUST remove the row covers once the plants begin flowering!
If you leave the covers on, pollination will be severely reduced, and you may not get any Japanese pumpkins. Squash is predominantly pollinated by bees, and these buzzing pollinators will have trouble accessing your crop if the row fabric stays in place for too long.
You can hand-pollinate squash if you’re dealing with significant pest pressures and need to keep the row covers in place, but don’t forget to check every day to see which flowers are in need of pollination.
Fertilizing
To ensure optimal squash growth and fruit production, avoiding over-fertilizing is crucial.
Squash is a heavy feeder that needs plenty of fertility to fuel the growth of massive vines and pumpkin production. Before planting, incorporate 1-2” of compost. At the time of seeding or transplanting, add a nice handful of all-purpose granular fertilizer like Espoma Bio-Tone Starter Plus Organic Plant Food. As the plants begin flowering, side-dress with one more dose of balanced, all-purpose fertilizer like Espoma Garden-Tone Organic Plant Food or a seaweed-based liquid fertilizer.
Avoid over-fertilizing squash because too much nitrogen can lead to excessive foliage growth that may reduce fruit production. Balanced, slow-release organic fertilizers are ideal. Balanced means that the three numbers on the fertilizer packet (Nitrogen – Phosphorus – Potassium) are fairly close together, such as 4-3-3 or 3-4-4
Maintenance
Using straw or leaves as mulch can greatly reduce the need for weeding.
The only regular maintenance these plants ask for is regular weeding. Squash do not tolerate a lot of weed competition when they are young. Fortunately, as the plants mature, their large leaves naturally shade out many weeds.
Be very careful when hoeing or weeding near the plants so you don’t damage the shallow roots and vines. Mulching with straw or leaves significantly cuts down on weeding. Better yet, try no-till strategies to reduce your weed pressure.
If you live in a humid climate where plants are prone to disease, you may also want to prune away excess foliage to improve air circulation. Remove yellow, dying, or infected leaves promptly. Never leave squash debris in the field; it can become a reservoir for pests and diseases the following season.
Curing
Neglecting to cure your winter squash can cause a less satisfying taste when used in recipes.
When your kabocha squash has finally sized up into gorgeous orange or green pumpkins, it’s time to harvest and cure them! Curing is simply placing the freshly harvested fruits in a warm, dry place for a specific duration of time.
The curing process hardens the skins to ensure long-term storage through the winter. As squash cures, their sugars also become more concentrated because the moisture content is reduced. The result is a more flavorful culinary experience. If you don’t cure your winter squash, it may not last as long in storage or taste as good in the kitchen.
To properly cure your squash:
- Harvest at the Right Time: Wait until the squash turns a deep, rich color and the skins feel hard. You should not be able to scratch or pierce them with your fingernail.
- Trim the Vines: A few days before harvest, prune away the vines and leave 1-2 inches of stem attached to each squash. The stem prevents pathogens and moisture from contaminating your harvest during the curing stage.
- Clean the Squash: Use a brush or dry towel to remove excess dirt or debris. Never wash the squash with water, as this can cause rot or other issues. Keep them as dry as possible!
- Prepare a Warm, Dry, Ventilated Area: The best place to cure is in a warm area between 75-85°F. A garage, shed, or covered patio works great as long as it is dry and breezy. If there is no airflow, add a couple of fans.
- Spread Out the Squash: Lay your squash on a layer of dry newspaper or a slotted table. I always use a fine hardware cloth mesh laid over wooden sawhorse supports. Be sure there is plenty of space between each squash to allow for proper air circulation.
- Leave for 1-2 Weeks: Let your kombucha cure in peace and quiet!
- Rotate and Inspect: Check the squash every few days for signs of rot, mold, or pests. Remove any rotten or damaged squash right away to prevent spread to the others. Rotate and flip the squash to promote even curing.
- Store Properly: After curing is complete, keep the squash in a cool, dry area like a root cellar, pantry, garage, or barn. The best storage conditions are between 50-55°F and 50-70% relative humidity.
Avoid exposing the squash to direct sunlight because UV rays can scorch the fruits and reduce the storage time. Properly cured kabocha can be stored for 3-4 months or more!
Varieties
Kabocha is technically a whole category of Japanese squash that includes green and red (orange) varieties of many different sizes and specifications.
‘Kurinishiki’
These pumpkins can be stored for up to 5 months when appropriately cured.
This small, reliable variety yields 3-4 pound Japanese pumpkins with 4-12’ vines. The robust fruits store for up to 5 months when properly cured.
‘Marmalade’
‘Marmalade’ boasts superior storage life and a more vibrant color than other types.
The smaller premium 2-3 pound kombucha has incredibly high yields per plant. You may only need a few plants to keep you satisfied all winter! The storage life and vibrant color are notably better than other varieties.
‘Sweet Jade’
These squash make excellent soup bowls.
A gorgeous deep green personal-sized kabocha, ‘Sweet Jade’ is great for stuffing. You can use the skins as soup bowls with little to no wasted fruit. They average a micro 1-2 pounds and work great for compact gardens.
‘Sunshine’
You can enjoy this squash as soon as it reaches maturity without the need for curing.
The classic scarlet kabocha, these fruits are medium-sized with glowing, gorgeous skin. This F1 hybrid has a superior appearance and eating quality. You can eat the squash right at maturity (even before curing!) The vines are short and vigorous.
Pests and Diseases
Like many cucurbits, this squash is susceptible to the aggressive attack of aphids, cucumber beetles, and squash bugs. Powdery mildew and other diseases can also attack the vines if stressed, overcrowded, or exposed to high humidity. Fortunately, there are easy ways to cope with these issues organically, so you don’t have to resort to synthetic pesticides or fungicides.
Aphids
To prevent future infestations, employ a diluted neem spray.
These small, soft-bodied insects eat just about everything in the garden. They can be green, yellow, or black and tend to cluster on the undersides of leaves. You may notice a sticky sap that attracts ants.
To control them, spray a strong stream of water on your plants to dislodge the aphids. Do this in the morning so the squash has plenty of time to dry out in the sun. Use a diluted neem spray to repel future infestations. Companion planting with marigolds, white alyssum, and yarrow can attract ladybugs and lacewings, natural predators of aphids.
Cucumber Beetles
Row covers are highly recommended to safeguard your plants from cucumber beetles.
These little yellow-and-black striped or spotted beetles are a real pain for anyone who loves cucumber-family crops. They attack cucumbers, melons, zucchini, and winter squash with equal vengeance, so it’s best to keep these crops spread out in different garden areas. They most commonly go for the leaves and flower blossoms of kabocha.
Row covers are your best protection, especially for young plants. You can handpick and kill beetles. Diatomaceous earth is a natural powdery deterrent you can dust on leaf surfaces to keep cucumber beetles away.
Squash Bugs
If you spot these bugs, you can manually remove and squash them.
These gross-looking brown or gray flattened insects damage the leaves and stems, causing wilting. If you notice them around, hand remove and squash them (no pun intended). Neem oil and insecticidal soap can control severe infestations, but row covers are a more reliable way to exclude them from the crop physically.
Powdery Mildew
This fungal disease thrives in warm and humid conditions.
This annoying powdery white fluff tends to appear on squash in midsummer and fall. This fungal disease loves warmth and humidity, so circulation is a must to prevent infections. Properly space your plants and prune away any excess or dying foliage. Neem oil can be applied preventatively. Use an organic copper fungicide as a last resort. Always follow package instructions. Avoid overhead irrigation at all costs, as this can facilitate the rapid spread of the disease.
Downy Mildew
Avoid overhead irrigation for squash plants, as it can increase the likelihood of downy or powdery mildew.
This fungus manifests as angular, yellow spots on the top of leaves and grayish fluffy growth on the undersides. It can spread fairly quickly in wet conditions, which is why overhead irrigation is so bad for squash plants. Remove and destroy affected leaves to prevent them from spreading. Never compost mildew-infected plants! Copper-based fungicides can be used as a last resort.
Bacterial Wilt
Since no known remedy exists for bacterial wilt, you must promptly eliminate and dispose of affected plants.
If your plants suddenly wilt and die, you may be dealing with bacterial wilt. Cucumber beetles often spread this nasty disease. There is no cure, so you must remove and destroy infected plants and practice rigorous crop rotation to keep this bacterial infection at bay.
Plant Uses
Kabocha squash finds its way into sweet and savory dishes in various culinary traditions.
Kabocha squash is a remarkably versatile ingredient used in sweet and savory dishes across many cuisines. The best ways to use these gourmet pumpkins include:
- Roasting
- Steaming
- Pureeing in creamy soups
- Mashing like potatoes
- Pie filling (you’ll never want to use pie pumpkins again!)
- Curries
- Stir-fries
- Tempura
Is Kabocha Squash Skin Edible?
Roasting or steaming the whole pumpkins allows you to enjoy the skin.
The skin of kabocha is edible when cooked. You can roast or steam the pumpkins whole and enjoy the skin much like a Delicata squash. The beautiful orange rinds are gorgeous in roasts and add a nice dose of fiber. Better yet, the rinds are strong enough to act as a squash bowl that can be stuffed with vegetables or filled with soup.
Final Thoughts
Honestly, I wouldn’t even bother growing pumpkins anymore. Kabocha is just that good! The key to success with this crop is growing in warm weather, providing plenty of moisture, and using row cover during the early stages. However, don’t forget to remove the covers once plants begin flowering! They need to be pollinated by bees to produce abundant squash!
