Hardiness ratings for plants are based on the minimum temperature the top of a plant can stand before it starts to display damage. What happens underground is a whole different story. For plants in our landscapes the soil temperatures rarely go below freezing except for maybe the top 2-3 inches and even then it is usually just for a few days. But when plants are in containers or raised planters, the soil mass is much more exposed and often as not can freeze solid, resulting in root damage. This is where many container plants bite it. Once the roots are frozen, the plant will usually die a slow death even though the tops may look just fine. What can we do to minimize damage to our container or landscape plants when it gets so cold?
Well, being prepared by watching the weather forecast is the first thing. Moving containers close to the house or even into an unheated garage is helpful. Wrapping the pots and plants with an insulation blanket is very helpful. We sell a mesh material that insulates but also breathes which is important. One material I really like is a quarter inch thick bubble wrap that is lined on both sides with foil. I will wrap pots and trunks and leave it on all winter as long as the top of the plants are exposed. You can also buy frost blankets that are sewn together into little tents which are handy to place over a plant, again for the entire winter if necessary. Avoid plastic garbage bags either clear or black. They do not breathe and if the sun comes out they will cook anything inside the bag.
The other step in frost protection is to make sure our plants are well watered. We might not normally think of this in the dead of the winter but conifers and broadleaf evergreens use a lot of water -- even in the winter. If the soil is dry (perhaps because a plant or pot is under the eves or the canopy of the plant sheds water so it doesn't get into the pot) then we really need to watch the moisture in the soil. Most freeze damage is the result of desiccation. You can also spray the foliage of plants with a product called Wilt Proof that will minimize moisture loss.
Finally, when plants are frozen, it is best not to handle them too much. In the case of lawns, simply stay off of them. With bushes, try not to rough them up any more than you have to when installing a frost cover or watering. Frozen tissue breaks easily rather than bending.
I am sure we will have a few more very cold nights and days before spring arrives so be ready for action. Water ahead of cold weather and have your frost blankets ready to install. And then don't forget to take them off once it warms up!
Steve Smith is owner of Sunnyside Nursery in Marysville and can be reached online at email@example.com.
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