Gardening by zone is a tricky business in a region as where temperatures can vary by up to 10 degrees Fahrenheit to neighborhood. Under the 2012 U.S. Department of Agriculture plant hardiness zone map, which will be based solely on average minimum temperature, town itself and the area immediately ringing the bay drops in zone 10 — from 30 to 40 degrees Fahrenheit — with inland areas in zone 9 — by 20 to 30 F. Crocuses demand a certain number of days under 40 levels to break dormancy, but they may be increased in areas with temperatures equal to zone 9, provided that you choose and prepare the bulb-grown plant in line with the requirements in your yard.
Set standard hybrid crocus corms, the bulblike structures that make crocuses, in the refrigerator in a paper bag for approximately fourteen days. The kind found in many garden centers, common crocuses, need a chilling period. Blooms are stunted, when they don’t spend sufficient time under 40 degrees or so the plants might produce leaves.
Clear the coolest spot in your garden that has well-drained soil. The USDA map is based on averages and does not take into consideration microclimates created by hills and valleys, sheltered or reflected sunlight, color or exposed areas, or of course. Start looking for a place, away from a wall that reflects earth that does not collect water, and some other area that holds heat or light.
Dig a broad trench with a spoonful large enough to allow you to plant the corms 4 to 6 inches deep and 4 to 6 inches apart. Crocuses have the most impact when planted in drifts that are natural-looking, rather than soldier-straight rows.
Examine your crocus corms and discard any that are mushy or shriveled. Corms should be firm and plump. Crocus varieties adapted to warmer climates, for example Crocus chrysanthus, as well as some pre-chilled corms, may be planted in the fall once evening temperatures are reliably in the 50s, generally in October or November, according to the University of California Cooperative Extension.
Place the corms in the pit line 4 up to 6 inches apart. Fill the hole with soil and tamp the soil. Crocuses generally do not need fertilizer their first season as the corm contains all the nutrients necessary for the initial year of bloom.
Permit blossoms to fade and foliage to die back following your bloom, normally from February to April. Allowing the growth cycle of the plant to keep helps the crocus to store energy for next year’s flowers.
Apply an equal mix of fertilizer in the fall into the crocus patch in future seasons and bone meal. Follow up with fast-release fertilizer in the spring, implemented as shoots emerge.
Monitor the performance of your crocuses from year to year. If they don’t bloom the second year following planting, then your microclimate does not provide adequate chilling every fall and you have to treat them as annuals — replanting and frightening new corms. When they flourish, split the corms you want to dig them up and replant them to 6 inches apart to keep them performing well.