Cool-season flowers play a special role because the peak growing season ends in fall or peaks in spring. Cool-season flowers thrive in cooler temperatures—not too hot or too cold. They are “shoulder season” growers, after the summer heat subsides and into the New Year when winter’s end blooms. Which cooler pants to choose and when depends on your region and growing conditions.
Annuals
When gardeners talk about cool-season flowers, we’re usually referring to annuals that bring colorful color through the transitional seasons. These include hardy annuals that grow in fall and spring and are frost tolerant. Planted in late summer and fall, they overwinter and continue to flower until warm weather.
Cooler climates also include tender annuals that serve as single-season color. They usually fall with cold winter temperatures (for fall planting) or rising temperatures (for spring planting). They flower and can drop seeds before being exposed to temperature extremes.
Both tender and cold-hardy annuals extend the flower display for weeks or months. In the fall, they add color for fall enjoyment and winter interest. In late winter and early spring, they bring an early show to welcome the season before heat-loving plants emerge. They provide sources of pollen and nectar for bees, butterflies and birds when many other plants are not in flower.
Perennials
In addition to cool-season annuals, many perennials bloom in fall and late winter/early spring for a variety of interest. Cold hardy perennials winter and are evergreen or enter winter dormancy depending on the plant and climate.
Rudbeckia, aster, coreopsis, and hardy garden mums are perennials that bloom in late summer and fall.
Bulbs
Flower bulbs, whether annuals or perennials, do best with fall or spring planting times, depending on their bloom cycle. Plant spring flowering bulbs in fall. Colder temperatures give the bulbs the chilling time they need for optimal flowering. They emerge in late winter/early spring. Fall planting bulbs for a spring display include tulips, daffodils, crocuses, snowdrops, bluebells and snowdrops.
Plant fall flower bulbs in the spring so they can be established in the summer. Blooms emerge when temperatures cool. Fall flowering bulbs include the hurricane lily and the fall-blooming crocus.
Growing Zones
Growing zones are a guide to determining which plants thrive in an area, depending on average extreme winter low temperatures.
When it comes to cool-season flowers, our growing zone tells us which plants will overwinter or which won’t cope with winter conditions. For fall planting, we will know if they are single bloomers or will repeat in the spring. Cold climate plants experiment and follow zonal guidelines to determine what works best in a given garden space.
Frost Dates
Estimated frost dates are as important as growing zones in determining when to plant a cold selection. The expected first frost is the approximate time frame for the initial heavy freeze in the fall, which affects tender annuals and perennials.
Cool-season plants that are not frost tolerant or hardy in your zone will die back at this point. Freeze-tolerant annuals withstand colder temperatures to a greater extent than each species and cultivar. Some hardy plants may enter winter dormancy after a deep freeze below 28°F.
The first frost of fall helps determine this How long do we have to enjoy the flowers before the freeze affects them? Tropical and subtropical climates enjoy growing year-round, and many cool-season crops grow throughout winter in milder regions.
The last frost date is in the spring when winter temperatures warm up and the warm growing season begins. Soil temperatures are warm, and conditions are ideal for transplanting and growing many edible and ornamental crops.
Seed or not to Seed
With estimated dates, we can decide if it’s time to grow cool-season selections from seed or if we should start with nursery-grown plants. The advantage of nursery starts is that the plants are growing along and possibly already in flower. Sold as bedding plants, it’s easy to get instant color when the growing season is short.
However, many cool-temperature annuals grow quickly and easily from seed and can be sown indoors prior to transplanting or direct sown for on-site development. Check variety information or seed packet on Days to Maturity (DTM). DTM is the number of days it takes from sowing or transplanting to flowering. ۔
Fall Planting
When sowing seeds in the fall, use DTM to ensure time to enjoy the flowering stage before frost. The long, warm days of late summer are perfect for starting many choices. In mid- to late summer, sow seeds indoors or in a cool, partially shaded location as temperatures moderate. Or, sow them directly into the ground if garden conditions are mild. Generally, six to eight weeks before the first frost date is ideal for most plants.
If your area gets hot in late summer and early fall, wait until cooler temperatures to plant. In cold weather, you may choose to start a nursery if a freeze is just around the corner.
Even frost-tolerant plants need to be established before cold weather begins. Hardy annuals and perennials planted in the fall are established to bloom again in the spring. Established plants have strong root systems for better disease resistance and the ability to withstand temperature fluctuations. Pest populations are generally lower in the fall, and disease problems are reduced as the humidity and temperature drop.
Spring Planting
Most cool-season flowers are ready to plant four to six weeks before the last frost date in the spring. Direct sowing or transplanting of seedlings. To start seeds indoors, allow eight to ten weeks before frost, depending on the variety. Harden off the plants outside for a few days before planting indoors. If freezing conditions increase, use crop covers, burlap or sheets to cover young plants until they are established.
