Depending on your area, spring flowers that you plan to grow from bulbs are usually best planted in early to mid fall. If you want to plant spring flowers that have already been started, waiting until after the last frost is probably the best idea. Planting flowers in suitable weather can help them to grow to their full potential.
While many people believe that flowers are planted in the spring, flower bulbs actually do best with a fall planting. The key to planting spring flowers is to wait until the temperature of the soil is below 60° Fahrenheit (15° Celsius). For most gardeners, this happens sometime between September and October, although it can occur as late as December in very warm climates.
When you plant spring flowers in the fall, you give the bulbs a chance to develop roots before winter. The freezing of the ground, common in most areas during the winter season, actually helps to establish the roots of the bulbs because freezing is a natural part of the life cycle. While bulbs can be planted at the end of winter or the beginning of spring, they may not grow or bloom as well as they would with a fall planting; in fact, they often won't grow at all. When you plant spring flowers in the fall, you will have the best chance of getting healthy, long lasting spring flowers.
Planting spring flowers that have already been started is best done after the last frost. This time frame can vary greatly by region. In some places, you can plant spring flowers as early as March, while in others you may have to wait until the end of April or beginning of May. To determine when you should plant, talk to those the local nursery operator or any friends who are experienced in flower gardening. If all else fails, pay close attention to your local weather forecaster who can typically estimate when the last frost of the season will occur.
Once winter is over and the threat of frost has passed, you can begin to plant your spring flowers. This is best done on a day that is cloudy and below 75° Fahrenheit (23° Celsius). Moving a plant from a container to the ground can be stressful on the plant; too much heat or sunshine can actually fry the plant or hinder its growth. Waiting for a cloudy, cool day to plant spring flowers typically provides the best results. If you want to save yourself some work, try planting spring flowers right before it's expected to rain; newly planted flowers require a good soaking to thrive, which can mean a lot of time standing over them with a hose.