Oregon Frost Dates & Growing Season Guide

Oregon City Frost Dates

The table below shows the average last spring frost date, first fall frost date, growing season length, and USDA hardiness zone for each city. Click a city name for detailed planting calendars and zone information.

Planting Windows for Oregon

Based on average frost dates, here are the recommended planting windows for each city. The indoor seed start date is approximately seven weeks before the last spring frost. Transplanting should occur about two weeks after the last frost. The last direct sow date for fall crops is ten weeks before the first fall frost.

Gardening in Oregon

Oregon is really two states for gardeners: the mild, wet Willamette Valley and coast west of the Cascades, and the dry, temperature-extreme high desert to the east. Portland in zone 8b enjoys a long 232-day growing season with mild winters that allow overwintering of many crops. Bend on the east side at 3,623 feet has only 99 frost-free days. Western Oregon's cool, wet springs can delay warm-season planting, and gardeners often use raised beds and black plastic mulch to warm soil faster. The maritime climate grows world-class berries, hazelnuts, and brassicas. Eastern Oregon gardeners rely on irrigation and season extension. Slug management is a constant task in western Oregon's damp conditions.

Understanding Oregon's Hardiness Zones

Oregon includes USDA hardiness zones 6a, 8b. These zones indicate the average annual extreme minimum winter temperature for each area, which determines which perennial plants, trees, and shrubs can survive winter without protection. When purchasing trees, shrubs, or perennial flowers, always check that the plant is rated for your hardiness zone or a lower (colder) zone number.

Tips for Using Oregon Frost Dates

These frost dates represent long-term averages and should be treated as guidelines rather than guarantees. In any given year, the actual last spring frost or first fall frost may arrive one to three weeks earlier or later than the average. Factors that affect your specific location include elevation above the city center, proximity to water, slope direction, and whether you are in an urban or rural area. South-facing slopes and areas near large pavement or building masses tend to be warmer than surrounding open land. Low-lying valleys and exposed hilltops are often colder than mid-slope positions.

To protect against late spring frosts, keep row cover fabric, old bed sheets, or frost blankets on hand. Monitor your local weather forecast daily as the average frost date approaches. When frost is predicted after you have transplanted, covering plants in the late afternoon traps ground heat and can protect against temperatures down to about 28 degrees Fahrenheit. For fall season extension, the same covers protect mature plants from early frosts, often buying several additional weeks of harvest.