I recently planted lily of the valley and gooseneck loosestrife in oblong metal containers to prevent them from becoming invasive. Each container has multiple drainage holes poked in the bottom and, during growing season, will sit on cement pavers.
I am in zone 6b. I has seen us go as low as -20° wind chill, but that is rare. Because the plants are in metal, should I put them in the garage over the winter and lightly water them once a month or should I just let them sit out in the weather? I haven't grown either plant before and would appreciate guidance and suggestions.
The garage does have a west facing window and they could get some light. If they don't need or want light, I could tuck them back on the other side of the garage where it's pretty dark. Please help. Thanks!
Over wintering plants in metal ccontainers
Rules of thumb for over-wintering:
A plant in a pot that is on the ground and mulched or buried in gardens/beds should be safe if its hardy to 1 zone lower than yours. Plants unprotected on the ground, slab, deck ...... should survive unprotected if it's rated hardy to 2 zones lower than yours. Plants buried in the ground against the N side of a heated building are usually hardy to 1 zone higher than yours, and a plant in an attached but unheated garage should be hardy to 2 zones warmer than yours ....... as long as your SO doesn't forget to close the garage door when (s)he comes home on one of those -12* nights. If that's a concern, you can cover your plant with an over-turned cardboard box, which will trap geo heat rising through the slab floor and allow it to tolerate extremes it otherwise couldn't.
Don't forget to occasionally water (toss some snow on) plants you're over-wintering. If their roots dry out completely, it's not a good thing.
Al
Thank you Tapla. Cindy is correct; I will not be burying the containers. That is great information and makes me feel more secure in thinking that my plants really will make it through this winter. I was actually thinking about wrapping the containers – the outside of the metal – with bubble wrap, but it doesn't sound like that will be necessary.
Thanks to you both!
Most growers think that wrapping a pot somehow keeps its contents warmer, but let's think about that. If you put a Dixie cup full of water in a 0* freezer, within a couple of hrs maximum, the cup and water are 0*. If you put the cup inside of a high quality cooler, it might take 24 hours for the cup & water to reach 0*, but reach 0* it does. In order for insulation to help keep containers warm, it has to be utilized to trap heat from an extraneous source. The box I suggested above works because it traps heat rising through the garage floor. The box would also work if the opening was on the side and the box was pressed against the wall of a heated building. If you wrap a pot, leave the bottom unwrapped and wrap sides and top to trap heat rising from the ground.
It's not freeze/thaw cycles that kill temperate plants. Plants can tolerate hundreds of freeze/thaw cycles that that actually freeze the soil solid before they thaw. There are 3 kinds of water in plants that need to be considered when talking about cold-hardiness. Water in the soil, water in plant tissues that occupies space between plant cells (inter-cellular water), and water within plant cells (intra-cellular water). Soil water and intercellular water (between cells) can freeze solid and not kill a plant. This can occur over and over again, unless a killing low temperature is reached at which water INSIDE of cells freezes. This is the type of cold that kills temperate plants.
In many plants, water moves out of plant cells in winter, leaving behind a concentration of salts, sugars, and other solutes in the remaining water that actually serve as anti-freeze, which is why plants temperate plants can tolerate temps WELL below freezing.
Al
I verified that both plants are good to zone eight so they should be fine in the garage without protection. Thank you for your post. It was very informative and yes, it did make me think.