Tips on caring for perennials in winter

For us, the overwintering process begins in mid-October when we start to move our plant material around the nursery into the areas where it will remain throughout the cold winter months. These areas are typically outside container areas, inside covered cold houses, and inside covered heated houses.

It is around this same time that we also begin to trade in our greenhouse shade cloth coverings for white plastic. We choose white plastic to cover these cold houses because it helps keep the temperature consistent inside the house. Perennials that stay evergreen, semi-evergreen, or perennials with a fleshy-enough root system need to overwinter in a cold house, as opposed to a heated house or outdoors. This also frees up room for plants being potted during winter.

Once the plastic is set and plants have migrated around the nursery, all plants are weeded and cut back as their foliage dies off. We do not cut back evergreen or semi-evergreen plants all the way. Instead, we trim them no more than a third; these evergreen perennials need some foliage in order to survive the cold weather.

Next, we drench and spray plants for diseases before finally, as temperatures cool (around Christmas for us here in Maryland; we are Zone 6), we cover all plants in outdoor container areas with winter blankets made of 8-ounce needle-punch fiber. These blankets help keep plant roots from freezing and thawing repeatedly as the temperature rises and falls during the over-wintering month. Additionally, we monitor the temperature underneath all blankets throughout the winter season.

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Picture of Hans Braxmeier via Pixabay 

Source: Greenhouse Grower