Annuals are a great way to add variety and color to the landscape and containers.
When temperatures cool in late summer into fall, many of the summer annuals like marigolds, coleus and impatiens are looking “tired.” Cool season annuals can be replaced by those that do well in the cooler temperatures of fall.
As winter subsides and gives way to spring, the temperatures are not quite warm enough for more familiar annuals like zinnias, impatiens, or geraniums. Cool season annuals can be planted early to provide early color before being replaced later in spring with those species that love the summer.
Learn more below about cool-season annuals and how to use them.
Definition | When to Plant | Removal | Suggested Species | Perennials as Cool-Season Annuals | Forced Bulbs as Cool-Season Annuals | FAQs | More Information
What are Cool-Season Annuals?
Cool-season annuals are annual plants that prefer cool temperatures, growing best in spring or fall. Many are tolerant of a light frost, often surviving down to 28°F or sometimes even 25°F with little damage to flowers or leaves. They are great additions to containers and garden beds in the shoulder seasons to add color late into fall or early in the spring season.
When to Plant
For the fall season in Iowa, cool-season annuals can be planted mid-to late September. For early spring color, plant cool-season annuals mid-March through early April, depending on the weather conditions.
Starting Transplants
Some species do best when directly sown but many need to be started indoors and transplanted outdoors. If starting from seed indoors, consult the seed packet to determine the length of time from seed to transplant. For many annuals it’s six to eight weeks. Count back from your projected planting date outdoors and sow seed at that time.
For many species this means sowing seed in late July through early August for cool-season annuals planted in fall and mid-January to early February for those planted in early spring.
Removing Cool-Season Annuals
Fall Planted
Cool-season annuals planted in fall can be left in the ground through the winter months, some species may even overwinter under the snow and begin growing again in early spring. They can be replaced with new cool-season annuals in early spring or left to bloom through the cool spring season and replaced with summer annuals after the danger of frost passes, in early to mid-May for much of Iowa.
Spring Planted
Since nearly all cool-season annuals do not grow well in warm temperatures, especially those that exceed 80 to 85°F, they can be replaced with summer annuals once the danger of frost passes.
Cool-Season Annuals for Iowa
- pansy (Viola)
- ornamental cabbage and kale (Brassica oleracea)
- snapdragons (Antirrhinum majus)
- stock (Matthiola incana)
- larkspur (Delphinium consolida)
- bachelor’s buttons (Centaura cyanus)
- pot marigold (Calendula officinalis)
- twinspur (Diascia)
- lobelia (Lobelia erinus)
- nasturtium (Tropaeloum majus)
- Nierembergia (Nierembergia)
- sweet alyssum (Lobularia maritima)
- cape daisy (Osteospermum)
- pinks and sweet William (Dianthus)
- swiss chard and beets (Beta vulgaris)
- dusty miller (Jacobaea maritima, aka Senecio cineraria)
- petunia (Petunia)
- sweet pea (Lathyrus odoratus)
- Nemesia (Nemesia)
- California poppy (Eschscholzia californica)
- bells of Ireland (Molucella laevis).
There are several species traditionally grown as perennials that can also be treated as annuals and grow well in the cool season including:
- mums (Chrysanthemum)
- coral bells (Heuchera)
- black-eyed Susan (Rudbeckia hirta)
Using Perennials as Cool-Season Annuals
Plants such as mums, coral bells, and black-eyed Susan are sometimes grown as perennials, but also grow well when treated as a cool-season annual. These species will not reliably over winter when planted in the fall. Fall planting does not allow sufficient time for root establishment, therefore they don’t overwinter well. They are best treated as annuals when planted late in the season.
Some species traditionally treated as annuals, like pansy, dianthus, and bachelor’s button, will frequently survive the cold winter temperatures when planted in fall and begin growing and blooming again in early spring. These plants often do not tolerate the warm temperatures of summer, however, often browning and dying in the heat. Because of this, they are not treated as perennials despite being winter hardy most years.
Using Forced Bulbs as Cool-Season Annuals
Tulips, hyacinth, daffodils, crocus, grape hyacinth and other forced spring-blooming bulbs make excellent cool season annuals, especially for containers. While showy and colorful, they do not remain in flower for more than a couple of weeks. To get the most out of your purchase, be sure to buy plants in bud, without any open blooms.
Forced potted bulbs can be purchased in succession and swapped out as the blooms fade so blooms can be enjoyed all spring.
With a little planning, bulbs purchased in the fall can be forced at home. Learn more in this article: How to Force Spring-Blooming Bulbs Indoors.
FAQs
- What cool-season annuals do well in Iowa?
- What are cool-season annuals?
- When should I plant cool-season annuals?
- Will perennials reliably come back each year if grown as cool-season annuals?
More Information
- Growing Annuals in Containers
- Selecting, Hardening, and Planting Bedding Plants
- Care of Plants Growing in Containers
- Early Spring Planting of Vegetables
- Fall Planting of Vegetables
- Cold and Freeze Damage to Garden Plants
- How to Protect Plants from Frost and Freeze
- Spring Garden Tasks
- Fall Garden Tasks
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