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When to plant lettuce in Ontario, OR

Plant lettuce in the garden in Ontario Mar 20 – May 15, either as seeds or as young plants started indoors Feb 6–20. For a fall harvest, plant again Aug 19 – Sep 2.

Easy Plant seeds or young plants

Difficulty
Easy
Sun
Full sun in spring; afternoon shade in summer
Spacing
8 to 10 inches apart for heads
Planting depth
¼ inch deep (it needs light to sprout)
Frost
Handles light frost
First harvest
About 50 days after planting

Why these dates

Ontario's typical last spring frost is April 21. As a cool-season crop that handles light frost, this crop doesn't need to wait for that date. In the Columbia Basin and low eastern valleys, though, the soil usually isn't ready to work until about March 20.

Columbia Basin and low eastern valleys. Hot, dry summers and quick spring warm-up. Warm crops go in earlier than west of the Cascades, and irrigation matters more than rain.

How to grow lettuce in Ontario

  1. Start seeds indoors Feb 6–20 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 20 – May 15, 8 to 10 inches apart for heads. If you plant seeds instead, sow them ¼ inch deep (it needs light to sprout).
  4. Water deeply once or twice a week rather than a little every day, and mulch once the soil is warm.
  5. Plant again Aug 19 – Sep 2 for a fall harvest.
  6. Harvest: Pick outer leaves as needed, or cut whole heads when full. Harvest in the morning for the crispest leaves.

Key numbers

How it works

The plant biology behind the advice above, in plain language.

Getting seeds to sprout

Lettuce sprouts in soil as cool as 35 to 40°F and does best around 75°F. Many varieties also need some light to germinate, so sow seeds no more than about a quarter inch deep and keep the surface moist.

In summer, soil above about 80°F can make lettuce seeds go dormant, and they simply won't come up. To sow in July or August, water the bed to cool it, sow in the evening, shade the row with a board or shade cloth until seeds sprout, or start seeds indoors where it's cooler.

Bolting and bitterness

Lettuce bolts (sends up a flower stalk) in response to heat and long days. As it does, the leaves fill with a milky sap containing bitter compounds. Once the center starts to stretch up, the bitterness can't be reversed.

To delay it, grow slow-bolting varieties for summer, give afternoon shade, keep the soil moist, and sow small batches every two to three weeks so there's always a young planting coming along.

Soil and water

Lettuce has shallow roots and grows fast, so it needs steady moisture and fertile soil with a pH of about 6.0 to 7.0. Mix in compost before planting. Dry spells make leaves tough and bitter, and uneven watering can cause tipburn, the brown, crispy leaf edges caused by a short supply of calcium during fast growth.

Cold tolerance

Most lettuces handle light frost, and hardy types like Winter Density and Arctic King take nights into the mid-20s. West of the Cascades, fall-sown lettuce under a cold frame or row cover can keep going through much of winter. Leaves that freeze solid will thaw fine if left alone; don't pick them while frozen.

Harvest and storage

Pick in the morning, when leaves are fully hydrated and crisp. Lettuce keeps best right above freezing with high humidity, so store it in a bag or container in the coldest part of the fridge, where it lasts one to two weeks.

Common questions

When is the last frost in Ontario, OR?

Typically April 21. In 9 years out of 10, frost is over by May 8. These are 1991–2020 NOAA climate normals for Ontario Municipal Airport.

Is it too late to plant lettuce in Ontario?

The spring planting window runs through May 15. If you miss it, plant again for fall from August 19 to September 2.

When should I start lettuce from seed indoors in Ontario?

February 6 to February 20, which is 6 to 4 weeks before the March 20 planting date. Or buy young plants at a garden center instead.

Why won't my lettuce seeds sprout in summer?

Soil above about 80°F makes many lettuce seeds go dormant. Sow in the evening, water to cool the soil, shade the row until seedlings appear, or start seeds indoors and transplant.

Why is my lettuce bitter?

Bitterness comes as the plant starts to bolt in heat and long days, or after dry spells. Harvest before the center stretches up, grow slow-bolting varieties in summer, and keep the soil evenly moist.

Can lettuce survive frost?

Yes, most varieties handle light frost, and hardy types take nights into the mid-20s. With a cold frame or row cover, lettuce often lasts through much of winter west of the Cascades.

Also plant in Ontario around the same time

Planting dates for lettuce in nearby areas

Full planting calendar for Ontario · Lettuce in every city