Hardy annual flowers have become known as “cool flowers” in the flower farming industry, where these types of plants will withstand cold and actually prefer cooler temperatures. In fact, when warmer weather begins in the early summer, these annuals will fizzle out from the heat.
I have plants in my containers all year long and start in mid March after pulling out Christmas greens using the long list of early spring flowers that can tolerate and thrive in chilly weather. Violas and pansies are the stalwarts of cool weather flowers, but there are many others to try.
There are so many flowers that you can use before cold temps subside (below 35 degrees Fahrenheit at night) that I make up at least a bunch of containers to cheer me up after a long cold winter. Having hung up my winter coat and gotten out fleeces, I am ready to plant.
One year I had a cold snap in April where the nighttime temps went down to about 29 degrees Fahrenheit. I placed a frost blanket over my containers and they sailed through without any problems. These covers can increase the temperature inside by a critical 2-8 degrees Fahrenheit, depending on the weight of the row cover. The heavier the weight, the more expensive.
Spring or Fall
Hardy annual plants are cold tolerant annuals which separates them from heat lovers like zinnias, cosmos, and sunflowers. Handling a slight freeze, they are good choices for early fall. A sustained freeze though will do them in. Hardy annual plants will do much better in the ground, rather than in containers, since the ground will insulate roots better than the small amount of soil in a container.
And plants that have had time to adjust to increasingly cold weather will be hardier than those that suddenly encounter it. So, don’t buy plants that were in a greenhouse and set them outside without hardening them off. This just means acclimatizing them to cooler temperatures gradually. Place your plants in an unheated garage or other shelter before introducing them outdoors.
Here is my top most planted list of cold tolerant annuals:
- Pansies & Violas
- Sweet Alyssum
- Swiss Chard
- Culinary Sage
- Cerinthe or Honeywort
- Chinese Forget Me Not
- Bells of Ireland
- Sweet Peas
- Love in a Mist
This list is by no means inclusive of all annuals that thrive in cool temperatures, but it offers a good selection of colorful and easy-to-grow flowers. Go to Walter Reeves for a Handy Chart on both veggies and flowers to get the best timing.
When to Sow Outdoors
Winter is the time to sow your Cool Season Annuals as soon as the soil can be “worked”. This term is gardening slang for soil with a texture that is neither mud nor frozen! After determining that my soil was ready by drawing a rake through it, I gathered my cool season annual seeds together with plant stakes, sharpie for marking, and my favorite multi-bladed sowing rake. On the menu for sowing was Poppies, Bells of Ireland, Love-in-the-Mist, Cerinthe, and Calendula. That was February for me in zone 7 Maryland.
Cool Season Annuals differ from annuals that you sow after the danger of frost is past because the seeds need cold temperatures to germinate and cool temps to grow well in the garden. When hot weather hits, they fade away, and I pull them out to make way for annuals that relish the hot weather. Poppies are one of my all-time favorite flowers for cool weather, and I make sure to plant plenty.
Growing quickly in the cool temperatures of late winter and early spring, the cool season annuals are usually old-fashioned flowers that you would find scattered in an English cottage garden. Best sown outdoors, these flowers are frost tolerant and grow quickly to give you a much-needed dose of color after the long winter. If you want to plant edibles like brassicas, go to Pegplant who writes an excellent blog on gardening.
Raking the soil with my sowing rake is the only preparation needed. I broadcast sprinkle the seeds as evenly as possible, using dry hands, then tamp down the soil firmly with the rake, not adding any additional soil. Sprinkling the surface with bits of straw or leaves helps keep the soil moist and hopefully hides the seed from wandering birds. I spray a light mist of water on top to moisten the surface and wait with anticipation.
Popping up quickly through the leaf litter, weeding and sprinkling with water is necessary if we hit a dry spell. Then it is time for the color show! Cutting flowers from these early blooms make great arrangements in the house.
For a great video on planting cool flowers, go to Cool Flowers, a website by Lisa Ziegler.