There is a method to growing cold hardy annuals for bigger, better, and more beautiful blooms. We are incorporating some of these techniques in our zone 5 garden, where we grow many hardy annuals on the flower farm!
What Are Cold Hardy Annuals?
Cold hardy annuals are an interesting group of plants. Becoming familiar with these plants will allow you to take advantage of their year long lifespan, and if done the right way, grow them for a little longer than you may be used to.
Hardy annuals are plants and flowers that span a year long life cycle from the initial seed, to the bloom, and then again to the production of seed.
If allowed to follow this year long growth trajectory these wonderful plants will reward you with fabulous growth and blooms.
Many people may not take advantage of this knowledge( yes I was one) , or perhaps they are not fully aware of the life cycle of these plants, or perhaps they live in a cold climate and choose a different way to plant for a very good reason.
Many, like me, plant hardy annuals in the spring. The plants grow throughout the spring and summer, and then when they are finished blooming, they produce their seeds in the fall. They have then completed their life cycle, in less than a year.
The key to successfully growing hardy annuals is to know what they are, know what they like, and then to plant them accordingly.
List of Hardy Annuals
Some hardy annuals that we have grown in our garden include:
Bells Of Ireland
Agrostemma (corn cockle)
White and Green Mist Ammi
Dara (chocolate lace flower)
What Is A Hardy Annual Flower?
An annual flower is one that grows for one year only. It does not return year after year like perennials.
A hardy annual is an annual flower that is cold and frost tolerant, and actually grows best in cooler temperatures.
Hardy annuals are annual flowering plants which can have a 12 month lifespan from the initial seed, through plant and flower production, and then through reproduction, when they produce their own seed.
Here in zone 5 , most annual plants are planted in the spring. They grow, bloom, then produce their seed all within the same growing season. Then in the fall when the season is done, they succumb to the frosts and their life cycle is complete.
We have always planted our hardy annual flowers this way as well.
But there is another way!
What Flowers Can Survive A Freeze?
Hardy annuals can survive a freeze!
Plant cold hardy annuals in early spring, for earlier summer blooms.
In my first year of flower farming I became aware that hardy annuals were able to withstand cool temperatures and frost, and so these were the flowers that I planted first.
They were the first seeds to be planted and grown in our basement, and the first to go out the door in spring to be hardened off.
While waiting for the soil to warm up and the dangers of the frost to be over, so that we could to plant out our more tender heat loving plants, these cold hardy plants (also known as cool flowers ) were able to be nestled snugly into their little planting holes, giving us a head start on the season.
Being able to plant them early, knowing that a freeze would not wipe out the crop, was very reassuring.
Direct Seeding Versus Transplanting Hardy Annuals
The seed packets for many of the hardy annuals that we planted, such as Larkspur, Bells Of Ireland, and Bupleurum, recommended that the preferred method of planting was direct seeding into the ground, since many of these plants do not tolerate the transplanting process very well.
Unfortunately we have had issues with direct seeding into our garden in the past, and I knew that direct seeding into the garden in spring would probably not go very well.
I had already spent a few years trying to direct seed daylily hybrid seeds into the garden, however our immense annual and perennial weed pressure provided just too much competition for the small seedlings.
Given our previous experience with this practice, rather than direct seeding, we decided that we would take a chance on transplanting. So to give these cool flowers a head start, they were planted indoors in March, and grown under lights, with the intended plan to be transplanted out in May.
It’s important to note that the seeds of hardy annuals are often quite hard to germinate, until you learn the right techniques.
The Importance Of Stratification
They benefit from a period of cold chill, or stratification. This became an issue for us that first year, as we learned the needs of these cold hardy plants. Some germinated well, while others were really tough.
That first year, seeds of bupleurum barely germinated on the heat mat. We put the trays outside where they were exposed to freezing temperatures. Lo and behold, it was just what they needed. Outside in the cold they had their best germination.You could really see the difference.
The same thing happened with Bells Of Ireland. They were difficult to germinate until the seeds were finally placed in the freezer for several weeks.
Some of my failed trays of Bells Of Ireland were placed outside in the cold, and eventually replanted with other seeds. To my surprise many of these Bells also germinated along with the new seeds, after their cold chill, and then had to be replanted.
We had also put some of the unused soil from the ungerminated trays back into the soil container outside. We used this soil to plant other seeds, and had little Bells Of Ireland popping up everywhere that year!
Winter Sowing Hardy Annuals
The seeds of hardy annuals are well adapted for winter sowing.
In fact, today I recycled a handy milk container for the first winter sown garden of bupleurum.
Plant cold hardy annuals in winter, for earlier summer blooms.
Since this hardy annual (Bupleurum) is so difficult to germinate without the cold, and is absolutely essential in my garden as a filler (very true, I love it), I will go to great lengths to grow it.
Winter sowing though is really pretty simple. I used a recycled 4L milk container washed and cleaned, and cut holes in the bottom for drainage.
Here’s The Process For Winter Sowing
Cut the container in half with a knife, with the lower portion being the planting bed, and the upper portion being the protective greenhouse. Since it’s a white container the sunlight will be able to shine through the walls for those plants that require light for germination, like Bupleurum.
Next fill the lower portion of the container with a good amount of moistened seed starting mix. I use Sunshine Mix 4, aggregate plus which I really love as a starting mix.
Press the soil down slightly in the container.
Sprinkle the seeds over the the soil.
If the seeds need darkness to germinate, cover with a thin layer of vermiculite or soil. If they require light for germination, just leave them on top of the soil.
Next it’s time to put the container back together. Tape the top half snugly to the bottom half with duct tape. Leave the pouring spout open on top to allow for natural precipitation and watering from the rain and snow. This hole will also allow for ventilation on warm days and allow for some evaporation.
Make sure you label what you’ve planted, and also date your planting day on the outside of the container. It’s also a good idea to place a plant label inside the container, just in case the outside markings get washed off (which happens all the time at our farm!).
When To Plant Hardy Annuals
In early May, when we planted out the hardy annuals, they actually transplanted well, considering that they do better with direct sowing. They survived the transplant, but they were slow to take off, as the weather was cold, and we had many frosts that spring.
When the weather finally warmed up, and we were starting to plant our heat loving flowers, the growth of the hardy annuals started to really take off, and many put on a great display. There were others however, that did not.
Some were beautiful, like the various types of Ammi, and Agrostemma, and Bachelor Buttons.They were early, and tall, and robust.
However some of the plants did not grow as well as I had hoped. Some were smaller than expected. Others lagged quite a bit. Our Bells Of Ireland did not grow very tall. Our Larkspur was hit and miss.
This is the issue with the hardy annuals.
Yes, you can plant them in the spring, in the cold, and even transplant them, and they will do okay. But they have not been given the full advantage of their complete growth cycle.
Sometimes when they finally get going in the spring the weather is too warm for them and they are not able to put on as great a show that they could have.
Direct Seed Hardy Annuals In The Fall
Plant cold hardy annuals in the fall, as it is a great way to naturally stratify the seeds.
If you want to have an amazing crop of hardy annuals, consider direct seeding them in the fall. To take full advantage of the hardy annual growth cycle, you can actually plant these seeds in the fall, 6-8 weeks before the first fall frost.
In milder climates, they should be able to survive the winter. In colder climates, you may be taking a chance, and they may need to be planted in early spring or winter sown.
Planting 6-8 weeks before the frost gives the plants a good head start before the freeze, and a chance to put down roots and establish their place, then overwinter until the following spring.
Hardy annual plants and blooms , if planted with this technique, are even more robust and beautiful in the spring than if grown early indoors under grow lights and then transplanted out in spring.
For us, the weed pressure in our garden in fall is much less compared to that in spring. This may be due to the cooler temperatures, or perhaps our summer weed management.
If we were to direct seed it would be a better option in the fall, versus the spring.
Although we are zone 5 and have frigid coastal winds in winter, there is a possibility that overwintering our hardy annuals may work for us, with the right techniques.
We will be growing and transplanting hardy annuals again this year, to ensure that we will have them available for our farmhouse bouquets.
However, we will also be finding a place to direct sow and plant some of our favorite hardy annuals this fall, and fingers crossed be able to enjoy earlier and more robust and beautiful blooms the following year.
Have you tried to plant cold hardy annuals indoors for earlier summer blooms? Be sure to leave a comment below to share your experience.