Bonbon Treated (F1) Buttercup Squash Seed

Scientific name

Cucurbita maxima

Soil and setup

Kabocha and other C. maxima squash want fertile, well-drained ground at pH 6.0–6.8. Plastic mulch plus a medium-weight row cover helps young plants get going and keeps insects off; take the cover off when flowers open so bees can do their work. Misshapen or undersized fruit usually means pollination fell short.

Days to maturity

Counted from direct sowing. Take off about two weeks for transplants.

Transplanting

Roughly 3 weeks before planting out, sow 2–3 seeds in each 2" pot or plug cell and snip off all but the best seedling. Harden plants off for 4–7 days, then set them out after the last frost at the spacing for the variety, disturbing the roots as little as you can.

Direct sowing

Plant 2 seeds, 1/2–1" deep, at each spot along the row, spaced for the variety's vine length, and thin to one plant once they are growing strongly.

Plant spacing

Bush and short-vine types need rows about 6' apart; long vines need about 12'. In the row, allow about 18–24" for small fruit, 24–36" for medium and 36–48" for large.

Disease

Powdery mildew, downy mildew, bacterial wilt and Phytophthora are the main diseases. Good drainage, open airflow, beetle control and rotation away from cucurbits prevent most trouble; ask your county Extension office about control options if needed.

Insect pests

Striped and spotted cucumber beetles, squash bugs and squash vine borers are the usual problems on this crop family. Floating row cover shields young plants. Look under the leaves for clusters of bronze squash bug eggs and crush them. If a borer gets into a vine, slit the stem to remove it and mound soil over the cut so the vine can reroot. Mowing field edges, clearing crop debris in fall and plowing in spring all cut down on overwintering pests; pyrethrin gives partial control.

Harvest and curing

Fruit is generally ready 50–55 days after it sets; get it in before a hard frost. Cut it from the vine and handle it gently. Cure it in the sun for 5–7 days, or indoors at 80–85°F (27–29°C) with good air movement.

Storage

Keep at 50–60°F (10–15°C) and 50–70% relative humidity with good ventilation. Repeated chilling below 50°F (10°C) damages the fruit. Most kabochas get sweeter after a few weeks in storage; how long each one keeps is given in the variety description.

Seeding rate

At 2 seeds per foot in rows 6' apart: about 1 oz. per 75 ft., 1 lb. per 1,250 ft. and 5¾ lb. per acre.

Seeds per lb.

About 1,900 on average.