When To Plant Cool Season Flowers To Prolong Your Garden Blooms

Certain flowers specialize in bridging warm and cool seasons with a profusion of color. They delight in the cool conditions of autumn and spring and extend the flowering time of both.

Many gardeners can start planting these flowers in late summer and early autumn so they can establish and bloom before frost. In some areas, they’ll bloom through winter or overwinter to bloom again the following year. Late summer plants start rooting to gain a headstart on growing and flowering as the weather cools. Spring-planted flowers transform the winter garden into a warm-season spectacle.

Rely on hardy annuals to bring a flourishing display in autumn and spring. They provide color, fragrance, and pollinator interest to brighten chilly days.

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What Are Cool Season Flowers?

Cool-season flowers hit their growth and blooming stride in cool temperatures —not too hot or cold, but just right. They are “shoulder-season” growers, flowering after the summer heat mellows and in the new year when winter ends. Which cool-season selections to plant and when depends on your region and growing conditions.

Annuals

When gardeners talk about cool-season flowers, we usually refer to annuals that bring a burst of color in transitional seasons. These include hardy annuals that thrive in autumn and spring and tolerate frost. Planted in late summer and fall, they overwinter and continue flowering until the weather heats up.

The cool season also includes tender annuals that serve as single-season color. These usually decline with cold winter temperatures (for fall plantings) or rising heat (for spring plantings). They flower and may drop seeds before succumbing to temperature extremes.

Both tender and cold-hardy annuals lengthen the bloom display for weeks or months. In the autumn, they extend color for autumnal 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 supply pollen and nectar sources for bees, butterflies, and birds when many other plants aren’t in flower.

Chill-loving annuals include pansies, snapdragons, violas, calendula, wallflowers, sweet alyssum, and sweet william.

Perennials

Aside from cool-weather annuals, many perennials bloom in the autumn and late winter/early spring for varying interest. Cold-hardy perennials overwinter and are evergreen or enter winter dormancy, depending on the plant and climate.

Rudbeckia, aster, coreopsis, and hardy garden mums are late summer and fall-blooming perennials. For early color, look to larkspur, poppies, foxgloves, and phlox.

Bulbs

Flowering bulbs, whether annual or perennial, do best with fall or spring planting times, depending on their bloom cycle. Plant spring-flowering bulbs in the fall. Overwintering gives the bulbs a necessary chill period for best flowering. They emerge in late winter/early spring. Bulbs to plant in the fall for a spring display include tulips, daffodils, crocus, snowdrops, bluebells, and glory of the snow.

Plant fall-flowering bulbs in the spring to establish them over the summer. The bloom show emerges as temperatures cool. Fall-flowering bulbs include hurricane lily and fall-blooming crocus.

Growing Zones

Growing zones are guides to determine which plants thrive in a region, depending on average extreme winter low temperatures. The USDA updated growing zone classifications in 2023 to reflect current minimum temperatures. 

When it comes to cool-season flowers, our growing zone tells us which plants will overwinter or which won’t withstand winter conditions. For fall plantings, we’ll know if they are single-bloomers or will recur in spring. Cold-climate plants take experimenting and following zonal guidelines to find what does best in a given garden site.

Frost Dates

Estimated frost dates are as important as growing zones for determining when to plant cool selections. The anticipated first frost is the estimated time frame for the initial heavy freeze in the fall, which affects tender annuals and perennials.

Cool-weather plants that aren’t frost-tolerant or hardy in your zone will likely die back at this point. Freeze-tolerant annuals withstand cold temperatures to a point relative to each species and cultivar. Some hardy plants may enter winter dormancy after a deep freeze below 28°F.

The first fall frost helps determine how long we have to enjoy blooms before freeze affects them. Tropical and subtropical climates enjoy year-round growing, and many cool-weather crops grow throughout the winter in mild regions.

The last frost date is in spring when winter temperatures roll out for good and the warm growing time begins. Soil temperatures warm, and conditions are optimal for transplanting and growing many edibles and ornamentals. 

The final freeze in spring lets us plan when to plant new additions. Cool-weather selections span freezing and warming conditions and are viable planting as the soil is workable. 

To Seed Or Not To Seed

With estimated dates in hand, we can decide if there is time to grow cool-season selections from seed or if we should start with nursery-grown plants. The advantage of nursery starts is that plants are further along in development and likely already in flower. Sold as bedding plants, they’re easy to get in the ground for instant color when growing seasons are short.

However, many cool-temperature annuals grow quickly and easily from seed and can be sown indoors before transplanting or directly sown to develop on-site. Check the varietal information or seed packet on days to maturity (DTM). DTM is the amount of days it takes from seeding or transplanting to flowering. Count out the days to maturity related to your frost dates to ensure viable bloom time.

In northern zones, opt for dwarf cultivars, early-maturing varieties, or those with a short seed-to-flower window. Faster development means more blooming and less waiting as seasons change quickly.

Fall Planting

When sowing seeds in the fall, use the DTM to ensure time to enjoy the flowering phase before freezing. The long, warm days of late summer are ideal for starting many selections. In mid-to-late summer, sow seeds indoors or in a cool, partially shaded spot for transplanting as temperatures moderate. Or, sow them directly in the ground if garden conditions are mild. Generally, six to eight weeks before the first frost date suits most plants.

If your area experiences high heat in late summer and early fall, wait until cooler temperatures to plant. In cold climates, you may opt for nursery starts if freeze is around the corner.

Even frost-tolerant plants need to get established before frigid weather sets in. Hardy annuals and perennials planted in the fall become established for repeat flowering in the spring. Established plants have sturdy root systems for better disease resistance and the ability to withstand temperature fluctuations. There are generally fewer pests in the fall, and disease problems lessen as humidity and heat drop.

Spring Planting

Most cool-season flowers are ready to plant four to six weeks before the final frost date in the spring. Direct sow or transplant seedlings. To start seeds indoors, allow eight to ten weeks before frost, depending on the variety. Harden off seedlings for a few days outside before in-ground planting. If subfreezing conditions creep up, use a crop cover, burlap, or sheets to cover young plants until they get established.