No gardener wants to see the end of the season. Looking out to the flower garden on a frosty morning and seeing dead, frostbitten plants is a sad sight, indeed. Especially after a growing season of hard work and enjoying fresh bouquets throughout the house.
But not all hope is lost, as there are some steps you can take to keep the chill of the changing seasons from shutting down your cutting garden completely.
Cold fall frosts will kill many flowers that are known as tender annuals such as zinnias, sunflowers, and cosmos. Other annuals such as calendulas and sweet peas, known as hardy annuals, have a better chance of survival, especially when protective measures such as mulch and row covers are used.
What is a frost date in gardening?
A frost date refers to when temperatures drop to 32 degrees Fahrenheit, which is low enough to result in frost damage to plants. The last average frost of the year occurs in the spring and the first average frost of the year occurs in the fall. The time between those two frost dates is your growing season.
You can find out when to expect your first fall frost by using your zip code at the Farmer’s Almanac. This date will help you plan for the cooling weather.
What’s the difference between frost and freeze for the garden?
Okay, so you know what the first frost means, and you’ve looked up when to expect it for your area. But does that mean your whole garden will be flash-frozen?
When you see frost on the leaves of your flower plants, what you’re looking at is ice crystals on the surface of the leaves. It was left there from the cold water vapor in the air. Many hardy annuals can survive this level of frost because the damage is limited to the exterior of the plant.
However, a hard freeze means that the water inside the plant leaves themselves has frozen. The ice crystals will cut the cell walls of the leaves, damaging the structure of the leaves. The plant can’t support itself or photosynthesize anymore, so it dies.
If you’ve ever seen a plant with brown, mushy stems and leaves then you know it was killed by cold temperatures.
How cold does it have to be to kill flowers?
The temperature ranges for a survivable frost and a killing freeze only range about 10 degrees Fahrenheit, but it makes a big difference as to whether your flowers will survive.
Here’s how to know what to expect:
- Light freeze (frost): 32-29 degrees Fahrenheit: This is the typical frost, and won’t kill your plants if it only lasts a few hours.
- Moderate freeze: 28-25 degrees Fahrenheit: This type of freeze will put an end to even your hardy annuals.
- Severe freeze: 24 degrees or lower Fahrenheit: A severe or hard freeze will kill all annuals and damage many other plants such as perennials or shrubs.
What annuals can withstand frost?
With the right planning, you can have some of these hardy annuals still blooming in the garden during fall. These are also great spring and early summer bloomers, so you can try having fresh plants both in the early spring and the fall.
Protect them with mulch or row covers and you’ll probably get another month of blooms, depending on where you live and how severe your winter weather is.
- Calendula: A true workhorse, calendulas can even overwinter in milder climates.
- Snapdragon: Annual snapdragons can survive a winter of light freezes and may even bloom again in the spring.
- Pansies: Sweet little pansies can take a light freeze in the fall and come back to bloom in the spring if it doesn’t get too cold.
- Sweet Pea: While the tender shoots are vulnerable to a frost, the whole plant won’t be killed until a moderate freeze.
- Ornamental Kale: Just like edible kale, ornamental kale laughs at a frost, continuing to grow even through a snow fall.
- Scabiosa: A light frost won’t kill scabiosa, also known as pincushion flower, but it won’t survive a severe freeze.
How can I protect my flowers from frost?
There are a few different ways to protect your flowers. You can use materials you already have around your home, such as dried leaves or bedsheets, or you can buy row covers specifically to provide frost protection.
Using a heavy layer of mulch can add some protection to your cut flower beds. A thick layer of mulch helps insulate the soil and the air around the plants, delaying the point at which the air reaches that freezing point.
Use fluffy much such as straw, wood chips, or dried leaves that you can snuggle right up to the plant itself to trap in that warm air.
You can even cover particularly tender plants completely to limit the exposure of their leaves to the air. Just be sure to uncover them again in the morning so they can get access to the sunlight.
This is a great impromptu solution when temperatures have dropped faster than expected and you need a quick solution.
Simply drape the sheets over the plants you want to protect. Just like the mulch, it will help keep the air around the plants just a smidge higher than if it were exposed.
One note of caution: If the sheets get wet and freeze, they will transfer that cold temperature to the plants below. That doesn’t mean the whole plant will die, but any out leaves that are in direct contact with the sheet will likely show some frost damage. Just trim those back in the morning and the rest of the plant should be okay.
If you know you’ll experience a fall frost in your area and you want to plan for protection, this is the way to go.
Row covers can be made of regular sheet plastic, or polypropylene, which is like a light plastic fabric. They are placed over hoops that span the width of your garden beds, creating a little tent over your flower plants. Again, the goal here is to insulate the air around your plants to prevent the temperatures from dropping so low.
An added benefit to row covers is that they are high enough to not touch the plants, keeping all moisture off them and reducing the chance of any frost damage.
Depending on the material you use, you can extend your season by several weeks, if not more, when you use row covers. This
Try one method and see just how far you can extend your season and keep that killing frost off your summer cut flowers.