What’s the best way to overwinter plants I’m propagating?
I would like to know the proper way to overwinter plants I’m propagating. I have one pot with five Cardinal Flowers (to divide for a Spring plant sale), two pots with ornamental shrubs (from cuttings made last Spring), and three pots with apple rootstock (less than a pencil width that were pulled and potted last Spring.) Do I sink them in the ground (please say no) or can they pass the winter in our cellar (40 to 50 degrees) with occasional waterings?
Lynne M. Holland, Horticulture and Social Media Professional
Those sound like some great plants to be adding to your yard in the spring but how they spend the winter will depend a bit on the plant.
Let’s start with the cardinal flower since it is a native plant and sounds like it is small. This article about urban balcony gardens has a nugget in there just for that question. “Planters in exposed locations may need to be protected in the winter with an insulating tarp, depending on what you are growing in them.” Putting that type of plant in a protected spot and tarping it AFTER the ground has frozen will eliminate heaving and other issues that temperature fluctuations bring.
When it comes to ornamental shrubs and the apple rootstock I recommend you dig them into the ground (pot and all) in a protected area (away from north and west winds and preferably not in a direct southern exposure either.) Once the ground is frozen then cover that area with an insulating layer of leaves or evergreen boughs. The idea here is to get them into a similar microclimate to which they will eventually be planted and then cover the frozen ground to eliminate temperature fluctuations in a way that still allows for some airflow.
If it is too difficult to dig the hardy plants in this year, then do what I do for my hardy potted plants. In my yard, we have a space between the garage and a fence where we put the pots of those things that are winter hardy. It is pretty well shaded and protected from the wind. We put them close together and bookend them with a big paper bag of leaves on each end. After Christmas, we put the cut-up Christmas tree boughs over the tops of the pots loosely. Once the days and nights moderate (usually in mid-March) we take the boughs off. Then a month or so later, we move the bags away and move the pots out into the open.