Vegetable Planting Time
Vegetables can be divided into two general groups - cool season vegetables and warm season vegetables. Cool season vegetables are frost-hardy, thrive in cool weather, and do well in early spring. Some may be replanted in late summer and fall to take advantage of the cool fall weather and many can have their harvest extended into winter months by using season lengthening techniques (cold frames, row covers, etc.).
Warm season vegetables, such as tomatoes and peppers, are frost tender and require a warm growing season. These vegetables should not be planted outside until all danger of frost is past. They may also require ground warming techniques (black or infra-red ground covers, wall-o-water, etc.) for them to thrive in cooler climates.
The specific variety of plant selected for use should be based in part on the length of the growing season and the relative maturity rate of that variety. Varieties that develop slowly (require a long growing season) will not do well in an area with a short growing season unless season lengthening techniques are used. Areas with short growing seasons may be restricted to cold-hardy vegetables only. Seed catalogs typically provide the length of days required from seeding to harvest.
The charts below provide approximate times for the planting of vegetable seeds based on the average last spring frost and the average first fall frost.
Additional points to consider:
Elevation - higher elevations are generally colder than low-lying areas and prevailing winds and microclimes can alter this even further.
Proximity to water - especially large bodies of water - can alter the local climate. Notice that Seattle on Puget Sound, has her last frost three weeks earlier and first frost three weeks later than Olympia, further south but also further inland.
Length of day - Traditionally, Northwesterners have turned to Great Britain for garden guidance as the cool, wet Maritime Northwest climate bears some similarity to that of those islands. However, in terms of gardening, the Maritime Northwest is closer to France (Washington and Oregon both grow French grapes quite well.) - Paris is at latitude 48N50. Seattle is south of Paris at 47N37, and Portland is at 45N31. Latitude determines length of day and length of day determines how much sunlight is available - despite the clouds, Seattle and Portland have more available sunlight in winter than London, or even Paris. In summer, the lower latitudes have shorter days than the higher latitudes (remember the 24 hour days at the poles?), but this is more than made up for by the longer winter days. Research has shown that the minimum number of daylight hours needed for successful fall/winter growing is ten hours. Less than that the plants go dormant - this does not mean they cannot be harvested, they simply don't put on new growth.
This also means that with relatively simple season extending techniques (i.e., cold frames, row covers) to protect the plants from adverse temperatures, vegetable harvests in the Northwest can be year-round with little difficulty. To find out when the daylight in you area drops below the necessary ten hours per day, check out USNO data services and look up your city.(Where I'm at, my garden gets less than 10 hours per day between November 3rd and February 7th.)
Transplants are typically more cold sensitive than when the same plant is directly seeded into the garden. (In my garden, lettuce has been known to sprout from seed in late February.) Transplants should be set out into the garden after all danger of frost has past or hot caps or other protective devices can be used to shelter these tender transplants from the stresses of cold weather.
|Average Frost dates for Western Washington and Western Oregon.|
|Ave. Last Frost||Apr 6||Apr 30||Apr 26||Mar 25|
|Ave. First Frost||Nov 4||Oct 15||Oct 25||Nov 13|
|Ave. Last Frost||Apr 1||Apr 9||Apr 14||Apr 3|
|Ave. First Frost||Oct22||Oct 31||Oct 28||Nov 4|
|Cold-Hardy Plants for Early Spring Planting|
|Hardy (plant two to four weeks before the average last spring frost)- mid-March
||Not cold-hardy (plant after average last spring frost)|
Cold Hardy crops can also be planted in the late fall for a spring crop
|Cold-Tender or Heat Hardy Plants for |
Late Spring or Early Summer Planting
|Requiring hot weather (plant at least one week after average last spring frost)- April - May
||Medium heat-tolerant (good for summer planting; i.e. April-May in this area)
||Hardy plants for late summer or fall planting (plant approximately two months prior to average first killing fall frost)- August|
New Zealand spinach
|Beans (Lima & snap)|
New Zealand spinach
|Very hardy (plant approximately six (6) weeks prior to last killing spring frost) - Late February - early March