Ever notice how the perennials that you have in the ground work just fine, they come back every year, but when you try to over winter a
perennial in a container, oftentimes it will die. Well the ground acts as an insulating factor protecting those roots. But when the perennial is just sitting
in a container like this it’s subject to the air temperature around it. Research from Oklahoma says that the container itself and the root ball actually
reaches the same temperature as the surrounding air. So if it’s ten below, the root ball is ten below.
One of the best ways is to dig a hole in the ground and then sink the container right in the ground and bring the soil back up to the level
of the top of the container. That way the ground does act as an insulating factor. If you don’t have to access to the soil to be able to sink your containers into the ground then the best thing to do is insulate your container.
You can insulate it with bubble rap or two or more inches of this styrofoam that’s
readily available in the hardwares. If you have the bottom of the container in
contact with the ground that’s even better, because air movement around the base of the container will pull heat out of it. In addition, you wanna group the containers
into a corner and perhaps cover them with straw or leaves — whatever you can do to insulate those roots just like they would as if they were in the
ground and moderate the temperature because roots are much more susceptible to freezing temperatures than are the chutes. They’re just not as winter hardy. So you want to protect those roots and you’ll have much more success each year with over wintering
your perennials in containers.