Cold hardy annuals for earlier flowers
Icelandic Poppies
My fresh flower season can be painfully short here in Zone 3 Alberta. Many years we have frost in early June and then again in late August. I remember a year with frost in early July and another year with snow on the first weekend in August! It can be next to impossible to get good crop of zinnias, celosia or other heat loving annual flowers. Thankfully, there is a whole host of other annual flowers that love cold weather and don’t blink at a light frost. The traditional wisdom around here is to not put transplants in the garden until the Victoria day long weekend, the third weekend in May, in order to avoid frost. This gives you your first blooms 7-8 weeks later. While this is definitely what I do with tender plants like zinnias or amaranthus, the group of cold hardy annuals can go in the ground much earlier. In fact, this group of plants performs much better when planted in cold weather. They grow into a much stronger and taller plant than those planted after our season and soil has warmed up. In growing zones with milder winters, the best strategy for success with cold hardy annuals is to fall plant them as young seedlings a month before the first expected frost, then give them some frost fabric protection if good snow cover is not available. I have had success with this method on some cultivars, even here in Zone 3, but there are other ways of working with a plants internal clock to produce strong, early flowers. Here are the methods I’ve tried in my gardens, with varying success:
1) Direct seed plants in fall. In early to mid autumn, depending on what kind of weather we’re having, I have direct sown things like Nigella, Bupleurum, Ammi, Calendula and Larkspur. I am completely addicted to weather forecasts, as they run my life as a flower grower, but if I’m fall seeding I watch even more carefully. I don’t want to seed at the first sign of frost. I don’t want to seed before the first snow either. I wait to sow until the ground is almost frozen, usually early November. If the temperatures look like they will drop before then and stay cold, I will seed a little earlier in late October. I don’t want to seed when there is a chance the seeds could germinate because the deep cold will kill the little seedlings. I want to mimic nature, where the plants drop seed in late fall, snow arrives and buries the seeds where they stay dormant until spring. I sow thickly when I direct seed to compensate for the risk factors of mice and unpredictable Alberta springs. This method produces some of the best looking, early annuals I have grown. It can be a risky strategy though, as sometimes we lose our snow cover in mid winter, get an extended warm spell, seed germinate too early and then die when winter returns. How many months of March have I lived through here where we experienced -25C at the end of the month? Too many!! When it works though, it gives spectacular results with very little effort.
2) Direct seed in spring. A less risky option is to wait until winter has truly left, but the ground is still very cold. I direct seed all the above list(Larkpsur, Nigella, Ammi, Bupleurum and Calendula) in April, as soon as the snow is gone. This method produces beautiful plants as well. In fact it is my preferred method for all of the above. I never start Larkspur, Bupleurum or Nigella indoors because the results are so inferior to direct seeding. Ammi and Calendula seem to be a little more heat tolerant when it comes to transplanting. I sow a generous amount of seed and don’t thin plants when they pop up. The catch with this method is moisture. In 2019, when most of Alberta experienced a cold, very rainy spring and summer, I had my best crops ever of these annuals. I had 5 foot tall Larkspur, it was insane. Last summer, in 2021, it was hot and dry. The seeds sown in early spring were established enough to do well, but later successions were total garbage. Even with us watering regularly, those little seeds just said “nope!” The take away message then is get those seeds sown early, when the soil still has moisture.
3) Transplant seedlings in spring. This is my preferred method for cold hardy annuals like Sweet peas, Agrostemma, Feverfew, Campanula, Lisianthus, Mattiola, Pansy, Snapdragon, and Strawflower. These cultivars transplant well and knowing I have enough of each specific plant in different colors means I’m willing to do the extra work of starting them indoors. Some of these seeds are getting difficult to source as well, so I’m not willing to risk wasting sweet pea seed(to a hungry mouse) when I know only a few sources have the varieties I want. Expensive, hard to find seed is worth starting indoors. It’s also easier for my record keeping and crop planning. When I direct sow seeds, I never really know how many plants I will end up with. Transplanting 200 Agrostemma plants and recording my harvest gives me more precise information on profitability and production costs. If I am planting these annuals in one of my tunnels, I aim to have them in the ground the first week of April. If they are going outside in the field, I plant as soon as the soil can be worked. Some years that’s the third week of April, other years it’s the first week of May. This method is still subject to weather concerns like a prolonged cold snap, or the equally likely scenario in Alberta, an extremely hot spring. Cold is much less of a concern because these annuals are capable of handling temperatures much lower than you would expect. I cover transplants with a layer of frost cloth if it’s expected to get colder than -6C. I’ve uncovered plants in the morning to find them frozen and by a few hours later, they are green and unbothered! Heat is a greater threat to little spring seedling than cold in my experience. Most of my cold hardy transplants last year either died or struggled all season due to our extreme heat.
Agrostemma seedlings thriving outside with no cover on October 8th 2021
4) Transplant seedlings in fall. I have experimented more with this method in my growing plan in the last two years. I see the potential it has to produce better, earlier flowers than spring transplants, but I’m still learning how many of the cold hardy annuals can actually handle my -40C winters. The two flowers I have the most experience with fall planting are Icelandic poppies and Feverfew. I sow these seeds in early June and plant them out in mid August to early September. The idea is to get them in the ground four weeks before the expected killing frost. This is a moving target now with climate change. In just the last 9 years I’ve been a flower farmer, I’ve seen our killing frost date jump five to six weeks later, from mid September to mid or even end of October. A different metric to use when trying to time fall planting is the last ten hour day of the year. Transplanting a month before the last ten hour day in your location gives seedlings time to grow strong roots, but the declining sunlight slows foliage growth. This timing gives me a planting date of no later than September 15th, as mid October is when we start getting days with less than ten hours of sunlight. Last season, I transplanted five different annuals the first week of September to see how they would overwinter: Sweet peas, Feverfew, Ammi. Daucus and Agrostemma. I covered them with a layer of leaves, then a layer of frost cloth and then a mini tunnel of 4 mm plastic on quick hoops at the end of October when the temperatures dipped to killing frost. I am curious to see what, if anything survives! In my previous overwintering experiments, I did not provide cover other than snow. This poses the risk of early snow melt and winter temperatures killing even established plants. I’ve experienced loss of my Icelandic poppies and Feverfew when this happens. I’m hoping with the extra protection of frost cloth and plastic, these seedlings will do well. The crop planning required to do this on a larger scale, or in a tunnel, is no small feat. This may limit the usefulness of this approach. I had to set a reminder on my phone to start seeds (again!) right in the middle of my fresh flower season, and I needed a bed that could be prepped and ready to plant at the beginning of September. I may become a convert though if it works. To be determined!
Remember to check your seed packages or do a quick Google search if you are unsure whether something is a cold hardy annual. Phrases like “sow as soon as the soil can be worked” or “prefers cool growing conditions” means you don’t have to wait until the traditional frost free date in your area to plant that cultivar outside.
The resources I find helpful for cold hardy plants are:
The Winter Harvest Handbook by Eliot Coleman
Cool Flowers by Lisa Mason Zeigler
Overwintering Flowers resources in the Johnny Seeds growers library