“Cool Flowers,” Cold temps & “Hardening Off” !

If you are interested in growing cut flowers or having a flower farm, you’ve probably heard about Lisa Mason Ziegler’s book “Cool Flowers” in which she discuses those hardy, cold tolerant annual flowers that can sometimes (in some zones) be planted in fall, overwintered, and provide early spring blooms that can often be harvested before we can normally even plant!

Since I’m growing cut flowers for the “Growing Kindness” project, I want earlier blooms for earlier bouquets. And since my space is small, if I can get an early crop to grow, flower and harvest it, an extra succession crop can be squeezed in. For a business, that would mean an extra round of bouquets and income! So, I studied Ziegler’s guide, but determined that in my area (Zone 5b, north central Indiana, last frost date around May 5-10) many of the flowers she suggests (that do well in her more southern area) would not survive our harsher winters and colder temperatures. But, I was interested in finding out what works early here, so I’m growing lots of small batches of different things with the intention of pushing my “normal” envelope. Some things may work, some things may not but the only way to find out is to try!

On March 1st, two varieties of dianthus (“Bodestoltz” and “Summer Mix”) I’d grown from seed in plug flats were planted out in a raised bed. I also direct seeded some bachelor buttons, bupleurum, dara, bells of Ireland, and nigella “Midnight” into another bed with some snapdragon plugs. Wire hoops and a layer of floating row cover were installed over them. This was not only for cold protection, but Ziegler also uses the hoops & row cover to eliminate the hardening off process. The cover protects them from too much wind and too much sun, but allows air movement and rain to penetrate. I’ve always used the standard hardening off process of moving plants outdoors for an hour, then two, then three, etc. but that’s a lot of work moving plants in and out, in and out! So, I was interested in giving row cover a try. After two weeks the plants looked fine, even though the night-time temps were usually in the mid-to upper 20’s. An additional layer of heavier frost cover was added for the night when it dropped to 12 degrees, and that worked. The plants still look happy.

Ranunculus newly planted

Feeling more confident, on March 14th more plugs were planted out. This time it was “Cantaloupe” calendula, “Anytime” stock, ranunculus, “Benary Princess” asters, “Madame Butterfly” and “Liberty” snapdragons. They also got the hoops and row cover instead of a hardening off process. Since then, the winds have howled repeatedly, the temperatures have fluctuated from 73 one day to 14 degrees one night, with 17 and 20 degrees included in that cold spell. I do open the tunnel ends when the temps are mid-fifties or higher, and add additional layers of frost cloth to the tunnels if the temps are going below 25 degrees. This bit of frost cloth not only adds night time protection from cold, but increased the daytime temps and retains warmer soil temps so plants are able to grow a bit faster. Most of the plants doubled in size before the end of the month.

Same ranunculus with two weeks growth during very cold weather, under floating row cover and hoops,

This is much easier than carrying flats in and out of the basement to harden off, so I will be using hoops and row cover from now on on all my crops in the potager and Cutting Garden. Plus it is definitely allowing plants to grow faster in adverse weather.

Two varieties of sweet peas (“Mammoth Choice” and “Old Spice”grown in 2” pots in my basement) were planted under four of the metal trellises. The only protection they were given was a plastic web flat to provide a bit of shade protection…no hoops, no row cover. They are not only happy, but showing new shoots at the base.

On March 30th, a row of “Wedding Bells” penstemon and a row of “Lace Perfume” dianthus plugs were planted in another raised bed. I was out of floating row cover, so I used a layer of shade cloth to help protect them from a day of sun and wind. That night, the forecast was for 24 degrees, so an old blanket was added on top. They seemed not to mind the cold at all, even though it went to 20 degrees.

And, I’m happy to report that all the direct seeded crops have germinated and are growing nicely, which encourages me to do lots more planting.

I hope this information from Zone 5b, north central Indiana may help other flower growers. These plants are a lot tougher than I thought as babies! And, I think that the row cover method should work on plants coming from a big box greenhouse, to provide that much-needed transition from magical greenhouse environment to reality. Plants can be placed in their pots or flats on the lawn, hoops and row cover added and after a week or two, they are hardened off sufficiently to be planted. No more carrying in and out! I just need more hoops!!!

About carolee

A former professional herb and lavender grower, now just growing for joy in my new potager. When I'm not in the garden, I'm in the kitchen, writing, or traveling to great gardens.
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5 Responses to “Cool Flowers,” Cold temps & “Hardening Off” !

  1. bcparkison says:

    Pray for me. I just signed up for the kindness project. I’m along way off from making vary many but maybe it will kick me into production. I think I need a project.. We will see..ps. I did give you credit for this jump.

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  2. Su says:

    I’m so pleased to see your results from using hoops and row covers. It kills my back to move plants in and out, so I’ll be trying this for my much smaller garden in Zone 4B. I’m building raised beds, and will use one of them as a nursery for all the babies I plan to raise. We are FINALLY going to be getting almost a week with no frost expected, so it’s timely. And a tunnel will protect them when night temps drop below freezing (as foercast for late next week). Thank you!

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  3. Jo+Shafer says:

    In my area of Central Washington’s Zone 6B, I don’t dare set out annuals until they appear in the garden centers. Petunias seem to weather those late frosts in May, and pansies, but nothing else, especially the tender herbs. I can add perennials to my beds, however, and of course roses to the enclosed English Garden (the fenced back yard with nearly full sun exposure). This year we’re experiencing a cold spring, seemingly switching March and April, as often occurs here. Mother used to call it the “pre-Easter chill.”

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  4. Bonnie Carrell says:

    Your experiments and success are interesting and encouraging. You’re a lot braver than I am, but then you’re a darn sight more experienced than I am also! The information you have given in this blog is wonderful. I checked on some of the short annual snaps that I planted last year and was going to pull them out and start cleaning my garden. However, I noticed that they were still green and viable once I removed leaf debree. I guess they stay for now and I’ll have to find another place to plant my new perennials that I just got in a shipment. Best to you on your new endeavor. Can’t wait to see the explosion of color you will have in a couple of months, or a little sooner by the sounds.

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  5. jorjagrael says:

    I’m in zone 7, in western North Carolina, so not as cold, but I’m going to try some of your tips! Thanks for all the great info!

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