How Cold is Too Cold??

How Cold is Too Cold??

How cold is too cold is something we get asked ocassionally. Will this plant survive our really cold winter? Is this plant hardy for our area?

If you are some of the fortunate ones that live in areas of the country where the temperature rarely dips below freezing, you may want to ignore this post. Or should you read it closer?

If you have been growing plants for very long at all, you have heard about hardiness or cold hardiness of plants. You may have even found out what zone you’re in.

Annual vs Perennial

The terms annual and perennial are what we use to describe how certain plants will grow in different areas of our country. The United States Department of Agriculture, USDA, has studied average low temperatures all over the country.

They have divided the country into zones. In fact the latest version of this zone map is broken down into 5 degree increments. These are average cold temperatures.

If a plant is determined that it won’t survive the cold in a given area, or zone, then it is considered an annual if grown in the zone. If the cold isn’t expected to be a problem for a plant, then it is considered a perennial. It is considered hardy for that zone.

Averages are plus or minus

Remember back in your early math classes, you had to find the averages of several numbers, right? Same thing with these averages. Some years there were colder temperatures and other years were warmer. Put them together and you get the average somewhere in the middle.

Just because your zone says zero for the lowest doesn’t mean that you won’t get at least some times below zero. If you are planting plants that are only rated down to zero then they may suffer damage or even die when the temperature drops below zero.

How cold is too cold for hardy plants?

The safest way to ensure good results when growing perennial plants is to plant only ones that are at least hardy for the zone colder than your zone. Where we are is considered Zone 6a. That means lows between 5 and 10 degrees below zero. Most of our plants are rated for Zone 5 or colder.

There are several plants growing here that are rated for Zone 6 though. They generally do fine even if the temperature drops below that range. A single night with a few hours of extra cold isn’t usually a problem.

Extended times below can be an issue however. If the forecast calls for those kinds of dips, some protection may be in order. Otherwise damage or death of the plant could result.

Snow is your friend

If I had my choice, a winter with little to no snow is better. I have to drive to work in it so less is better. But, snow is your friend when the temperatures are dropping.

Snow is an excellent insulator. Several inches of snow covering a marginally hardy plant will help it handle those extra cold temperatures. If you have some snow just laying around, gently pile some around the base of those marginal plants and cover them with it as well.

Unfortunately, sometimes the lack of snow can be a problem. Some plants rely on that insulating blanket of snow for protection. Even some slightly warmer cold temperatures can cause damage or even kill plants like this.

Groundcover Sedums can be damaged like this. A couple of winters back, we lost all of our Angelina Sedum over winter because we hardly had any snow that winter. Seems hard to believe but true.

You’ll know when you know

Since these hardy plants are dormant during winter, it may be hard to know if they’re damaged or not by the cold. It is usually a waiting game to see if any damage has occurred. That means waiting until Spring.

Different plants handle extreme cold in different ways. Don’t be in a big rush to remove your plant just because it isn’t growing new leaves. That could just be a sign that the branches that were out there waving in the cold have suffered damage.

Given some time, they may start growing all new branches from the base. This is not all that uncommon. Many plants will suffer damage to their upper branches only to grow new ones down below.

Prune and trim

This is when you get out your handy dandy pruners and clean up the plant a bit. Remove any of those branches that just aren’t pushing out new growth. Even reducing a plant’s size slightly can help it recover quicker.

If it does have some new shoots growing from the base, now is the time to do some pruning for early branching. Leaving a new branch untrimmed could result in an extra tall or long branch that doesn’t fit in with the rest of the plant.

Don’t be afraid

Don’t be afraid to just flat out remove a plant if it doesn’t fare well. If it suffers lots of damage over winter, it might just be in the wrong place. I have moved several plants to better locations. Cutting back the damaged portions and digging while still early, will help with success in its new locale.

If it has suffered in several winters, it may just be time to replace it with something else. It just isn’t going to handle your winter weather. You may really like it, but it doesn’t like you. Been there, done that. There are always plants that we just want to be able to grow but just can’t. That’s gardening!