Are Knockout Roses Cold Hardy – How Much Cold Will Knockouts Take?

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The Knockout family of roses come in a variety of colors and are some of the most popular flowering plants on the planet.

Knockouts are highly popular for their repeat flowing and extended blooming season, making them an excellent choice for backyard decorations and aesthetic gardening. 

Knockout roses are very cold hardy

The flowers are compact and grow rapidly into deciduous shrubs, which can be double or single petals. Since knockout roses have an exceptional disease resistance when compared to their traditional counterpart, they’re very well known for their easy care and hardiness.

In other words, these flowers are low maintenance and hardy disease plants. But how cold hardy are knockout roses?

In this article, we’ll walk you through a complete guide about knockout roses’ ability to withstand the cold, as well as a brief guide on how to care for them in the winter. So without further ado, let’s dive in!

Are Knockout Roses Cold Hardy?

Knockout roses are known to be disease resistant. When it comes to cold resistance, Knock out roses are bred to be extremely cold hardy. Knock rose are recommended for USDA growing zones 5 and all the way to zone 9 or 10. 

However, rest assured that Knockouts will survive extremely cold temperatures as low as 10° degrees Farhenheit.

Despite the extremely cold hardiness, they might still require some winter protection if you want the plant to stay in top condition. Also, they’re still prone to frost damage when temperatures fall below the maximum tolerable level.

How to Care for and Protect Knockout Roses in the Winter

As you now know, knockout roses resist weather changes nicely. They can survive through extremely cold as well as relatively long drought periods. In other words, they’re more of a “plant them and forget them” flower.

As a rule of thumb, your Knockouts do not need any special measures to care for the plant in winter. However, if the temperature in your area falls below the maximum tolerable level for knockout roses, you’ll need to give them some winter protection. Here’s what you need to do:

Cover Your Knockouts!

Although knockout roses can survive the cold weather itself, it’s always the strong and cold wind that accompanies the winter that does the damage by either plucking them off the soil or drying them out to death.

One of the best ways to protect knockout roses from the harsh winter is by covering them. Since they’re originally hardy and can withstand the weather, simple covering such as burlap, sheets, or any insulating material would be enough to protect them from the elements.

For in-ground knockout roses, you can also add two or three inches of mulch, fir boughs, leaves, or pine around the base of your plant to keep the root ball protected.

If you cover the plant during the winter, make sure that you remove any extra mulch that’s still covering the plant deeply. Also, inspect the roses for signs of damage and trim them.

If you plant the roses in containers, you won’t need to cover them for the winter because they’re already protected from the weather. Instead, you’ll only need to keep them outside through the start of the season to retain their winter hardiness. 

After the first few threads of frost in the season, take the container inside and keep them in a suitable area, such as your garage. Remember to water them if they start to dry out.

Provide Knockouts With Plenty of Water

Make sure that you deeply water the plants before the winter to help them stay hydrated through the winter. 

However, you should avoid over-watering the plant and creating pools around it, as this can suffocate the plant and cause winter rot.

Protect Knock Outs from Breakage

Besides drying the plant up, cold wind can also break and damage the plant canes. A good tip here is to tie them upright or make a 5 to 8 inches deep mound under the base of the roses.

Details on: Preparing Knockout Roses for Winter

What Are the Effects of Frost Damage on Knockout Roses?

Despite being cold, hardy, very harsh winters can cause frost damage on the knockout roses and even kill them, especially if they’re unprotected.

If temperatures fall below 10° degrees Fahrenheit and the plant is unprotected, signs of damage such as dead blooms, stem discoloration, breakage, and other obvious signs of damage will show.

In fact, you might not notice it, but the knockout rose bushes might continue suffering from the winter damage throughout spring and summer.

This will show in the noticeable decrease in foliage, stunted growth, fewer blooms, and more struggling signs.

How to Treat the Damage Caused by Extreme Cold on Knockout Roses

Of course, the best way to avoid the frost damage caused by extremely harsh winters is to prevent them from being damaged in the first place.

However, if the damage already occurred, the first thing you need to do is remove and trim all the signs of damage that the plant has developed over the winter.

An important thing to note here is that the treatment should only be done after the winter and not during the cold. 

If you trim or prune the plant early, it’ll trigger new growth in the winter, which will come out severely damaged and won’t survive through the following winter.

Related: Tips on How to Trim Knockout Roses

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