Flowering bulbs generally bloom within three to six months of planting, according to Cornell University. The most commonly planted bulbs are daffodils and tulips, which unfurl in spring and early summer. These are planted in the fall. Mid-summer flowering bulbs such as dahlias and gladiolas are planted in the spring after the danger of frost has passed.

On the Other: Know Your Growing Zone

The U.S. Department of Agriculture divides the country into 10 distinct growing zones based on the average minimum temperature at the coldest time of the year. Spring flowering bulbs must be planted before the first frost in order to establish roots. For example, gardens in northern zones 4 and 5 require bulbs to be planted between late September and early October. Southern gardens in zone 7 perform well when bulbs are planted in early November. Mid- and late-summer flower bulbs can be planted in any zone once the last threat of frost in the spring has passed.

Bottom Line

There is some flexibility in deciding when to plant flowering bulbs. Every gardener, however, should know the agricultural zone of his region since frost impacts timing.

Source:

Cornell University: Tips on flowering bulbs

U.S. National Arboretum, U.S. Department of Agriculture: USDA Plant Hardiness Zone Map