Frost charts, soil temperature, phase of the moon…gardeners have all kinds of methods for determining the best time to plant. There are no guarantees, since Mother Nature seems to have a mind of her own, but there are some guidelines you can follow to have the best chance of success…
Transplanted vegetables and annuals: after the last hard frost
Seeds for vegetables and annuals: plant so the seeds will sprout when the last frost date is past.
Spring flowering bulbs: 6 weeks before the ground freezes; when the soil temperatures falls below 60 degrees; after the first heavy frost; usually around Halloween.
Trees and shrubs: whenever the ground can be worked; after leaf drop or before bud break.
Perennials and wildflowers: in spring after the last hard frost; in fall before the ground freezes.
Cool grasses (such as fescue and rye): early spring or fall.
Warm grasses (such as Bermuda and Zoysia): when temperatures are 70-80 degrees.
Potted roses: spring or fall.
Bare root roses: after the last hard frost.
In USDA Hardiness Zone 8, where most of the Seattle area falls, the average last frost date is March 15 and the average first frost date is November 15th. You can also check the online Farmer’s Almanac for other areas.