Gardening in Oregon: zones, frost dates and when to plant

Oregon’s four vegetable regions

OSU Extension’s Growing Your Own (EM 9027) splits Oregon into four regions. Its planting table gives each one its own column.

• The coast, Astoria to Brookings. The season is long but cool. Wind, fog and low temperatures are the main obstacles, and heavy spring rain leaves slow-draining soils soggy. Many coastal soils are sandy, so they dry out fast in summer.
• The western valleys, Portland to Roseburg. The season varies in length from year to year. Days are warm and nights are cool. The Medford area can usually plant 7 to 10 days earlier than the table’s western valley dates and keep going 7 to 10 days later.
• The high elevations of central and eastern Oregon. The season is short, and frost can come in any month. Day-to-night swings of 40°F to 45°F are common. Soils range from light ground low in organic matter to heavy soils high in soluble salts that cause alkalinity problems.
• The Columbia and Snake River valleys, around Hermiston, Pendleton and Ontario. Days are hot, nights are warm, and the season’s length is fairly predictable. In the Columbia Gorge, steady winds of 20 mph or more blow from mid-spring through summer, and summer temperatures can top 100°F.

Go by soil temperature, not the date

OSU Extension’s main spring advice is patience. One of the most common mistakes, OSU says, is planting too early, when cold, wet soil can rot seeds or leave seedlings stressed all season. Peas, radishes, turnips, carrots and beets can go in once the soil is about 50°F. Tomatoes, peppers, cucumbers, corn and basil need at least 60°F, and tomatoes do best at 65°F to 70°F. Gardeners on the coast and in central and eastern Oregon often wait several weeks longer than those in the western valleys for soil to warm. A cheap soil thermometer is the most reliable tool. Use the frost dates for your city above as a backstop, not a starting gun.

Advice for each region

For the coast, Growing Your Own suggests cole crops, root crops, lettuce, peas, spinach, zucchini, leeks and onions. Short-season tomatoes and corn can work under row covers. Plant on the south side of a wall or building, run rows north to south, and put up fences or shade cloth against the wind. Work organic matter into sandy soil and water often in summer.

In the high country of Crook, Deschutes and Jefferson counties, OSU’s Central Oregon Vegetable Garden Calendar (EM 9473) is built around a short season and the chance of frost even in summer. The calendar holds tomatoes, squash and cucumbers until late May or early June and puts sweet corn in from mid-May to mid-June. Stick with root crops and cold-tolerant crops like cabbage, chard, leaf lettuce and kohlrabi, and choose short-season varieties. Expect cool nights to stretch a 65-day tomato to 75 or 80 days or more. Row covers, hotcaps and water-filled plant protectors buy extra warmth.

In the Columbia Basin, the problems are heat and wind. Water seedlings lightly and often so they don’t dry out, and shield them on the windward side with rocks or shingles. In extreme heat, mature plants may need deep watering three times a week. A 4- to 5-foot hedge on the west side of the garden blocks wind all season.

Tomatoes and winter crops

For tomatoes, OSU horticulturist Amy Jo Detweiler suggests varieties that mature in 60 to 70 days, including ‘Legend’ and ‘Siletz’, both bred at Oregon State. Early cherry tomatoes such as ‘Sun Gold’, ‘Gold Nugget’ and ‘Sweet Million’ are good choices for beginners. Big beefsteaks are harder to ripen in Oregon. In central and eastern Oregon, she recommends a cloche or row cover.

West of the Cascades, winter is a real growing season. OSU’s guide Winter Vegetable Production on Small Farms and Gardens West of the Cascades (PNW 548) says winter vegetables are usually very productive there. About three-quarters of the year’s rain falls between October and March, so a sunny, well-drained site is essential. Raised beds help drainage, but OSU warns they can also make crops more prone to cold injury. Winter brassicas are commonly transplanted in July or August. Cultivars named in the guide include ‘January King’ cabbage and ‘Rudolph’ sprouting broccoli.

Soil testing

Growing Your Own says to test the soil before you fertilize, so you add only the nutrients that are actually short. County Extension offices and soil testing laboratories can provide the detailed analysis behind fertilizer recommendations. This matters most in the high desert, where some soils already carry salts and alkalinity.