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A head of broccoli growing among its large leaves
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When to plant broccoli in St. Helens and Scappoose, OR

Start broccoli from seed indoors Jan 25 – Feb 8, then plant the young plants in the garden in St. Helens and Scappoose Mar 15 – Apr 19. For a fall harvest, plant again Jul 23 – Aug 6.

Moderate Plant young plants (starts)

Difficulty
Moderate
Sun
Full sun
Spacing
18 inches apart
Planting depth
Plant starts at the depth they grew in the pot
Frost
Handles light frost
First harvest
About 70 days after planting

Why these dates

St. Helens and Scappoose's typical last spring frost is April 10. As a cool-season crop that handles light frost, this crop doesn't need to wait for that date. In the west-side valleys, though, the soil usually isn't ready to work until about March 15.

West-side valleys. The Willamette Valley, Puget Sound and southern Oregon valleys. Long frost-free seasons, but soil stays cold and wet into May, so warm crops wait for warm soil, not just the last frost.

How to grow broccoli in St. Helens and Scappoose

  1. Start seeds indoors Jan 25 – Feb 8 in trays or small pots under a grow light or in your sunniest window. Or skip this step and buy young plants (starts) at a garden center.
  2. Harden off the young plants: about a week before planting, set them outside for a few hours a day, a little longer each day.
  3. Plant them in the garden Mar 15 – Apr 19, 18 inches apart. Plant starts at the depth they grew in the pot.
  4. Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
  5. Plant again Jul 23 – Aug 6 for a fall harvest.
  6. Harvest: Cut the main head while the buds are tight and dark green. Side shoots follow for weeks.

Key numbers

Growing notes

What makes the difference in Northwest gardens, in plain language.

Soil and feeding

Broccoli is a hungry plant. Give it rich soil with a few inches of compost and a balanced vegetable fertilizer at planting, then a light side-dressing of nitrogen about a month later as heads begin to form. Aim for a pH of 6.0 to 7.0. Many Northwest soils west of the Cascades are naturally acidic, and liming toward the upper end of that range also helps discourage clubroot, a soil disease that causes swollen, knotted roots and wilting plants.

Why broccoli flowers early or makes tiny heads

Broccoli heads are flower buds, so anything that pushes the plant to bloom early ruins the crop. Stress is the usual cause: transplants left too long in small pots, a hard cold snap right after planting, or dry soil. The plant gives up on growing big and makes a small, early head that quickly opens into yellow flowers. Plant young, healthy starts, keep them watered, and harvest as soon as the head looks full with buds still tight. Fall crops planted in mid to late summer often give the best heads in the Northwest, because they mature in cool weather.

Worms, aphids, and harvest

The green caterpillars on broccoli come from the small white butterflies seen all summer. Insect netting stops them from laying eggs, and that's easier than picking worms out of the florets later. Gray aphids hide in the heads in late summer; check often and spray them off with water. After cutting the main head, leave the plant in place, since side shoots keep coming for weeks. Purple Sprouting is planted in summer and overwinters west of the Cascades for a spring harvest. Store broccoli unwashed in a bag in the fridge for about a week.

Common questions

When is the last frost in St. Helens and Scappoose, OR?

Typically April 10. In 9 years out of 10, frost is over by May 1. These are 1991–2020 NOAA climate normals for Scappoose Industrial Airpark.

Is it too late to plant broccoli in St. Helens and Scappoose?

The spring planting window runs through April 19. If you miss it, plant again for fall from July 23 to August 6.

When should I start broccoli from seed indoors in St. Helens and Scappoose?

January 25 to February 8, which is 7 to 5 weeks before the March 15 planting date. Or buy young plants at a garden center instead.

Why is my broccoli flowering before the head gets big?

The plant was stressed, usually by heat, dry soil, or being root-bound in its pot before planting. Once the yellow flowers open, the head won't improve, so cut it and eat what you can. Next time plant younger starts and keep the soil evenly moist.

Does broccoli grow back after you cut it?

Not a new main head, but most varieties send up smaller side shoots for several weeks. Cut the main head with a slanted cut, leaving the plant and its leaves in place. Keep watering and the shoots will keep coming.

How do I get rid of worms in my broccoli?

Soak cut heads in cool salty water for 15 minutes and the caterpillars float out. To prevent them, cover plants with insect netting from planting day. Organic sprays made from Bt (Bacillus thuringiensis) also work on small caterpillars without harming people or pets.

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