Rainline Garden
When to plant sweet corn in Cottage Grove, OR
Plant sweet corn from seed, directly in the garden in Cottage Grove, May 10 – Jun 14.
- Difficulty
- Moderate
- Sun
- Full sun
- Spacing
- 10 inches apart in a block of short rows
- Planting depth
- 1 inch deep
- Frost
- Killed by frost
- First harvest
- About 80 days after planting
Why these dates
Cottage Grove's typical last spring frost is April 24. Frost kills sweet corn, and warm-season crops also need warm soil. Soil here stays cold for weeks after the last frost, so planting waits until about May 10.
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 sweet corn in Cottage Grove
- Prepare the bed: loosen the soil and mix in an inch or two of compost.
- Plant seeds May 10 – Jun 14, 1 inch deep, 10 inches apart in a block of short rows.
- Keep the soil evenly moist until sprouts appear, which can take one to three weeks in cool soil.
- Harvest: Ready about three weeks after the silks appear, when the silks are brown and the kernels squirt milky juice.
Key numbers
- 60°F or warmerSoil to sprout
- 5.8–7.0Soil pH
- 1+ inch a week at silkingWater
- Cold soil, crowsBiggest risk
Growing notes
What makes the difference in Northwest gardens, in plain language.
Soil, warmth and feeding
Corn is a warm-season grass that sprouts poorly in soil below about 60°F, and seed often rots in cold, wet ground. West of the Cascades that usually means waiting until mid to late May, while hot eastern valleys can plant a bit earlier. Supersweet types are even fussier about cold soil. Corn is a heavy nitrogen feeder: work in compost and fertilizer before planting, then side-dress when plants are about knee high. A pH of roughly 5.8 to 7.0 is fine.
Pollination and why ears are half empty
Each kernel forms only if a grain of pollen lands on its own silk strand. Pollen falls from the tassels on top and drifts on the wind, which is why corn is planted in a block of short rows instead of one long row. Gappy ears usually mean poor pollination from too few plants, hot dry weather at silking, or drought. Water deeply when tassels and silks appear. Also keep sweet corn types apart: if a supersweet crosses with a regular sweet corn, the kernels can turn starchy.
Harvest, storage, and east vs west
Sweet corn's sugar starts turning to starch the moment you pick it, so harvest right before cooking or chill ears quickly in the fridge. Check ears about three weeks after silking: brown silks, a full rounded tip and milky juice in the kernels mean ready. West of the Cascades, choose quicker varieties like Early Sunglow and Golden Bantam that finish before cool fall weather. East of the Cascades, longer-season types like Bodacious ripen easily, but watch for raccoons as ears near ripeness.
Common questions
When is the last frost in Cottage Grove, OR?
Typically April 24. In 9 years out of 10, frost is over by May 10. These are 1991–2020 NOAA climate normals for Cottage Grove.
Is it too late to plant sweet corn in Cottage Grove?
The spring planting window runs through June 14. Later plantings may not have time to produce before the first fall frost, which usually arrives around October 25.
How long until I can harvest sweet corn?
About 80 days after planting. Ready about three weeks after the silks appear, when the silks are brown and the kernels squirt milky juice.
Why are there missing kernels on my corn?
Those kernels weren't pollinated. Plant in blocks of at least four short rows so pollen falls onto neighboring silks, and water well when plants tassel. Heat and drought at silking also cause gaps.
When should I plant corn in western Oregon or Washington?
Wait until the soil is at least 60°F, which is usually mid to late May. Seed planted earlier in cold, wet soil often rots before it sprouts. Black plastic or a clear cover for a week can warm the bed faster.
Why isn't my sweet corn sweet?
It may have been picked too late, stored too long, or crossed with another type of corn growing nearby. Pick at the milky stage and eat or chill it right away. Keep different sweet corn types apart or plant them to tassel at different times.
Also plant in Cottage Grove around the same time
Carrots
Beets
Swiss chard
Bush beans
Cucumbers
Zucchini and summer squash
Winter squash and pumpkins
Tomatoes
Planting dates for sweet corn in nearby areas
- Salem, OR May 10 – Jun 14
- Eugene, OR May 10 – Jun 14
- McMinnville and Newberg, OR May 10 – Jun 14
- Corvallis and Albany, OR May 10 – Jun 14
- Portland, OR May 10 – Jun 14
- Gresham, OR May 10 – Jun 14
Full planting calendar for Cottage Grove · Sweet corn in every city