Plant hardy annuals. Plant cool flowers. Uhh, I loved reading all sorts of resources on planting cut flowers early in the season that could handle the cooler temperatures. Floret has a chapter in her book “Cut Flower Garden” on hardy annuals. She suggests planting these about a month before your average last frost. Gardener’s Workshop has a book “Cool Flowers,” which I devoured reading last summer. Although both share the hard work involved, I was so focused on the magic of gardening 6 to 8 weeks before when I usually start, that I found myself only half prepared for my first cool flower planting season. I overcame the great learning curves of covering cool flowers for hard frosts in my unheated greenhouse, and outdoors in the garden fields.
Coverings in an Unheated Greenhouse
Our greenhouse build has been more than a weekend project. We thought it was going to be weekend project, but nope. From mid-October to spring, we were able to build it structurally. Not quite finished, but it still works for this spring growing season. The one thing it lacks still is a heating system.
With plants that can survive cooler temperatures, but may die or be stunted under 28 degrees Fahrenheit, I wanted to make sure these plants had some extra protection, and extra warmth.
On the greenhouse table, my husband added hoops that would support either a frost cloth or some plastic. I’ve tried both at different times, and some of those cold nights I tried both. Both do the job well within the greenhouse. Covering my cool flowers in the greenhouse was my security blanket to reassuring myself my plants would survive.
Both do best when they are draped over hoops. We only installed enough hoops for the center of the greenhouse table. Hey, it’s what we needed in those first weeks. When some of the taller plants were layered with just the frost cloth, they became droopy. They did end up perking back up, but I highly recommend using some sort of hoops to provide a low tunnel to those plants.
Cool Flowers in Unheated Greenhouse
I had a variety of cool season flowers in my unheated greenhouse. On those cool nights, they had an extra layer of protection with the plastic or frost cloths. Flowers and fillers included Ammi, carnation, dianthus, loads and loads of snapdragons- large and small.
On cooler days with those cooler nights, I would keep the clear plastic on top. It kept the plants much warmer than just the greenhouse alone.
Although they all love cooler temperatures, these flowers took off on the warm spring days with warm sun, high humidity, and warmer summer-like temperatures. On these days, windows would be opened; sometimes I would leave the door opened. Everything would be watered, once or twice a day. All the frost cloths and the clear plastic were removed.
Warm Season Flowers in Unheated Greenhouse
I’ve also kept some warm season annuals when it warmed above 32 degrees Fahrenheit outside in the greenhouse. They can withstand some cooler temperatures. These includes my balcony mix heirloom petunias- the hundreds that I started, as well as some geraniums that I started from seed. There’s not much growth on the cooler days, but they stay vibrantly alive. On some of the cool nights, these flowers took priority for covering. On the warm spring days with either high humidity, high temperatures, or lots of sunlight, these warm annuals took off.
Covering with Frost Cloth Outdoors
Frost Cloth
I had a frost cloth on hand from a year previous from Gardener’s Supply. It protects to temperatures of 28 degrees Fahrenheit. I have the 6’ x 20’ size, but it is also in larger sizes of 6’ x 50’ and 12’ x 20’. The 20’ size is more for raised beds, while the 50’ size would be best for in the field.
My beds out in the garden was about 24’ to 28’. I ended up using blankets for covering of the other cool flowers. Oops. But the biggest mistake with this was not securing the covering on both sides. Ehh, the newly planted Sweet William were not covered when we had a hard frost. They survived. Sweet William can handle cooler weather than below 28 degrees. But it was not my intent to other them unprotected.
Row Cover Garden Hoops
My original plan was to buy pre-arched plant support wire hoops to support my row covers, but I didn’t want to pay the extra shipping. I only needed one set for my one row cover.
Searching on Amazon, I found rust-proof fiberglass hoop frames. They are adjustable, making different sizes. I was nervous about them being made out of fiberglass, with strands of glass creating the polls, but they have a smooth finish to where you don’t get cut.
The kit also comes with clips to clip the frost cloth to the garden hoops. I didn’t use sandbags to hold down the cloth, and with our wind on the ridge, the cloth stayed in place.
At the ends, I did use gallon jugs with the fabric bunched up to close off the low tunnel.
I do want to plant to buy more frost cloths and more garden hoops for next season. I really loved using these adjustable garden hoops with the clips. It makes me debate whether to try the pre-arched wire hoops since they don’t come with the clips to secure the fabric.
https://www.amazon.com/dp/B09MCVD8ZC?psc=1&ref=ppx_yo2ov_dt_b_product_details
How to Install Garden Hoops and Row Cover?
1 Gather Materials. The kit with the link above includes 30 pieces of fiberglass rods, small green plastic clips, and plenty of metal connectors.
2 Build Hoops. Attach five fiberglass rods together, connected by four metal connectors. It is easy for them to fall apart. To avoid frustrations, be careful when moving them.
3 Insert into Ground. Take one end of the pole and insert about 6 inches deep, 2 to 3 inches on the outside of the flower bed. Insert the other end of the pole.
4 Continue Adding Hoops. Continue building and inserting the garden hoops. After inserting one at the top end, insert one in the bottom. Then divide up the other ones across the flower bed. Mine were about 5’ to 6’ apart from each other.
5 Add Row Cover. Spread the frost cloth the whole length of the flower bed, leaving enough fabric on both the top and bottom ends to secure with milks jugs, or another heavy object. The row cover should extend the whole way to the bottom on both right and left sides.
6 Insert Clips. Attach the clips to the row cover near the bottom of the garden hoop. Do this on both sides. Stretch the fabric to the next garden hoop, and repeat attaching the clips.
7 Secure Ends. Bunch the extra fabric on the end. Lay a milk jug or other heavy object on top of the fabric. This needs to be done on both ends to ensure that the cold air is not blown into the hooped row cover.
8 Not Enough Row Cover. If you miscalculated how much row cover you have versus how much garden space needs covered, use blankets or sheets overnight to cover anything that is left. I know this is not ideal, but this was a miscalculation I made and this worked by putting blankets on top.
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