Korean Zucchini (Aehobak)

At a glance

Tip for beginners: Put up a 5-foot trellis before you plant, transplant 1 week after your last frost into warm soil, and check for fruit every day or two once flowering starts

Main challenge: The vines need a trellis or a lot of ground, and the fruit has to be picked within a few days of reaching 5–6 inches; powdery mildew usually slows the plants in late summer

When to plant

• Start seeds indoors 3 weeks before your last frost.
• Transplant outdoors 1 week after your last frost.
• First harvest about 8 weeks after transplanting.

What can go wrong

• Powdery mildew. White, powdery patches on the older leaves in late summer, spreading until the leaves yellow and production drops. Trellising, good spacing and watering at the base slow it down; keep picking until frost.
• Squash vine borer. Less common on aehobak than on zucchini, but still possible. Look for sawdust-like frass at the stem base and a section of vine that wilts in the afternoon. Bury a few nodes along the vine so it has backup roots.
• Fruit grows too big and hard. Aehobak passes its best size within days. Fruit left on the vine develops a hard rind and slows new fruit set. Check every day or two and pick at 5–6 inches.
• Small fruit that shrivels. Young female flowers that turn yellow and drop. Usually poor pollination early in the season, when male flowers outnumber female ones or bees are scarce. Hand-pollinate with a small brush in the morning.
• Squash bugs. Gray-brown, flat-backed bugs and clusters of bronze eggs on the undersides of leaves. Check leaves every few days, crush the egg clusters, and knock adults into soapy water.

Growing guide

Aehobak and zucchini get swapped for each other in recipes, but in the garden they are different plants. Italian zucchini is Cucurbita pepo, usually grown as a compact bush. Korean aehobak is Cucurbita moschata, the same species as butternut squash, and most varieties sold in the US grow as long vines. The fruit is pale to glossy green, club- or avocado-shaped, and picked small, often about a week after the flower opens. Plant it where you would put a zucchini and you may find it climbing the fence by midsummer.

It wants the same warmth zucchini does. Start seeds indoors 3 weeks before your last frost in individual pots, since squash roots resent disturbance, and transplant 1 week after your last frost once the soil is at least 60°F. You can also sow directly, 1 inch deep with two seeds per spot, once the soil has warmed. Give each plant about 3 feet along a trellis, or 3 to 4 feet between hills if it sprawls. A sturdy trellis or cattle panel about 5 feet tall keeps fruit clean and straight and makes it far harder to miss one under the leaves.

On a trellis, the vines need tying every few days at first; once the tendrils catch, they mostly climb on their own. Water deeply at the base and mulch, because uneven moisture tends to give misshapen fruit. Early in the season the plant often makes only male flowers, and the first female flowers, the ones with a tiny squash behind them, may drop without setting. That usually settles within a couple of weeks. Bees do the pollinating; if they are scarce, moving pollen from a male flower to a female one with a small brush in the morning can help.

The species difference matters most with squash vine borer. Extension research ranks C. moschata as the least susceptible squash species: the moths lay fewer eggs on it and the larvae have a harder time getting established in the stems. It is not immune, so still check the base of the vine for sawdust-like frass and sudden wilting. Vining plants also root where a leaf node touches soil, and burying a few nodes along the vine gives the plant backup roots if one section is attacked. Powdery mildew tends to be the bigger problem: white, flour-like patches that start on older leaves in late summer and spread until production slows. Squash bugs and cucumber beetles feed on aehobak as they do on any squash.

Pick when the fruit is about 5 to 6 inches long and the skin is still glossy and thin. Check every day or two in peak season. A fruit left on the vine keeps growing into a mature squash with a hard rind and full-sized seeds, and the plant tends to set fewer new fruit while it carries one. In Korea, growers often slip young fruit into plastic sleeves so they grow straight and uniform for market; that is optional at home, and a trellis does much of the same work. Most aehobak sold in the US is an F1 hybrid, and it crosses with butternut, so saved seed is unlikely to grow true.

Harvest and keep