Zucchini

Cucurbita pepo

The garden's most generous vegetable — direct-sow it into genuinely warm soil, let the bees at the flowers, and check the plants daily once fruit starts coming.

At a glance

Sun: Full sun
Water: Moderate
Soil pH: 6–6.5
Days to maturity: 50–65; Clemson ~55 from seed; UMD 50–65. Individual fruit is ready 3–5 days after its flower opens.
Spacing: 8–15 in; UMN thins to 8–12 in, Clemson 12–15 in; or 2 plants per mound, mounds 4 ft apart (Utah State)
Germination soil: 60–70°F

Mature size: Bush types (most zucchini) need only 2–3 feet between rows; vining summer squash wants 2–3 feet of run on each side.

Hardiness

A very tender warm-season annual everywhere in the US. Frost injures the top growth, and seed rots or stalls in cold soil — the calendar matters less than a soil thermometer.

Sun

Full sun — at least 6 hours of direct light a day; 8–10 hours preferred (UMD).

Water

About 1 inch a week (UMN; Utah State 1–2), at the base of the plant — keep the leaves dry, especially once fruit is forming.

Planting calendar

Timed to your own frost dates — look up yours by ZIP on the home page.

Transplant — Generally skip transplants — UMN warns squash started indoors is often set back by root damage. If you must (UMD allows it), start only ~3 weeks ahead in individual pots and disturb roots as little as possible. With black plastic and row covers, plants can go out 2–3 weeks before last frost (Utah State).
Direct sow — Sow after the last frost once soil reaches 60–70°F, about ½ inch deep (UMN/Clemson; Utah State plants deeper at 1–2 in).

Zucchini's reputation for burying gardeners in fruit is earned — but only when three things go right: warm soil at sowing, pollinators at flowering, and a daily harvest habit.

Male flowers falling off is not a problem

Squash carries separate male and female flowers on the same plant, and the males open first and drop naturally (UMN). Nothing is wrong. Fruit comes from female flowers (look for the tiny squash behind the bloom), and each needs bee visits — poorly pollinated fruit comes out stubby and misshapen (Clemson). Parthenocarpic varieties set fruit without any pollination (UMD).

Row covers off at first bloom

Floating row covers are the best early defense against cucumber beetles and vine borers — but they also exclude bees. The moment flowers appear, the covers come off (UMN).

The squash vine borer is the one that kills

Beetles and squash bugs weaken plants; the squash vine borer ends them — it tunnels into the crown and the whole plant wilts at once (UMN). Row covers until bloom, a watchful eye on the lower stem, and prompt removal of frass-oozing entry points are the home gardener's tools.

Harvest small, check daily

Zucchini is best at 7–8 inches; crookneck at 1½–2 inches across; scallop types at 3–4 inches (Clemson). Skin toughens within days (Utah State), and a plant left holding overgrown fruit slows production. Once bearing starts, check every day (UMD).

Cold soil is the false start

Seed sown into cold soil rots before it sprouts. Use a soil thermometer — 60–70°F at sowing depth — or cheat spring forward with black plastic mulch.

Common pests

Squash vine borer
Squash bugs
Striped cucumber beetle
Spotted cucumber beetle
Aphids
Pickleworms

Common diseases

Powdery mildew
Cucurbit mosaic viruses
Bacterial wilt
Downy mildew
Anthracnose
Angular leaf spot
Choanephora (blossom-end) rot