Zucchini and summer squash

Summer squash types

Maryland describes the plants as non-vining bushes; Minnesota notes that some varieties form long vines and that bush types suit small gardens.

When to plant

For local dates, start from frost dates explained and the planting calendar.

How much space

A few plants go a long way: Virginia Tech suggests 1–2 plants per person per planting and expects 20–80 lb per 10-ft row; Maryland gives 20–40 lb. Sow seed ½ in deep (Clemson, UMN) in soil of pH 6.0–6.5 (Clemson, UMN), in full sun of at least 6 hours, 8–10 preferred (UMD).

To grow upward, Virginia Extension suggests cages rather than a trellis, since squash can overburden one, with slings for heavy fruit. Grid-bed counts are on square foot gardening spacing.

Containers

UW–Madison's container variety list names Astia, Golden Scallopini Bush, Golden Zebra, Multipik, Supersett, Sweet Zuke and Zebra Zuke under "squash". Other crops: container sizes for vegetables.

Flowers and pollination

• Two kinds of flower. Each plant carries separate male and female flowers (Clemson, UNH). Female flowers have a small immature fruit at the base; male flowers sit on long, thin stems (UNH, UMN).
• Males come first. They open 1–2 weeks before the females (UMD); the first blossoms are male and often drop, which is normal (UMN). Fruit sets only when both are open at once (UNH); parthenocarpic cultivars need no pollination (UMD).
• Bees do the moving. Bees and wasps carry the pollen (Clemson). Fruit set suffers in cold, rainy or cloudy weather (UMN, UMD) and where bees are scarce (UNH).
• Hand pollination. Early in the morning, since flowers open early and last one day, move the sticky pollen from the center of a male flower to the stigma of a female flower with a small paintbrush, or pick the male flower and roll its pollen onto the stigma (UNH).

Squash vine borer

The adult is a wasp-like, day-flying moth about ½ in long with an orange abdomen and metallic green front wings; it lays flat brown eggs singly at the plant base, and the cream, brown-headed larva tunnels into the stem (UMN). The first sign is wilting, often in strong sun, then holes at the stem base with moist, sawdust-like frass (UMN). UNH rates zucchini and summer squash very susceptible and butternut resistant; bush types suffer more than vining types, which root at the nodes, and small plantings more than large ones.

Sprays work only while eggs are hatching, before larvae enter the stem (UMN); to protect bees, UNH advises late-day application after blossoms close. Sprayed Bt does not reach larvae inside stems (UMN), while Virginia Extension describes injecting it into entry holes.

This page gives no pesticide or fertilizer rates. The UMN, UNH and Virginia Extension pages linked below discuss products; follow the label and ask your county extension office to confirm a diagnosis.

Where sources disagree

Watering and harvest

Give about 1 in of water a week (UMN), wetting the soil 6 in deep in the morning (Clemson). Once plants bear, check them daily (UMD). A rind too hard to mark with a thumbnail means the fruit is over-mature; remove such fruit, because leaving it reduces yield (UMD, UMN).

Small-space checklist

• Plan 1–2 plants per person, 2–3 ft apart.
• Sow after the last frost in soil of 60–70°F.
• For a pot, choose a bush variety and at least 5 gallons.
• Hand-pollinate in the morning if fruit is not setting.
• From the last week of June, check stem bases for frass and wilting (UMN); cover plants until flowering.
• Sow a second round in early July.
• Pick daily, before the rind hardens.

More crop pages: cucumbers, bush and pole beans, tomatoes, peppers, peas and lettuce.