I am starting to winterize some potted plants around my home and would like to wrap some with Rockwool insulation. There is one piece around two Rosemary plants (see photo). This piece (R14 insulation) was left over from a renovation job and the contractor gave it to me. I bought a length of poly and heat-sealed it over the insulation to make it air- and water-proof. Now I'm looking for one or two more pieces. The reason I like Rockwool is that it sheds water rather than absorb it--unlike the more popular pink or white insulation. And it is fire resistant, and stronger. None of the local retailers (Home Depot, RONA, Canadian Tire, Dick's Lumber, etc.) sell Rockwool by the piece; they only sell whole bags. That is WAY too much for my purpose. So I am here asking if anybody in these forums knows a contractor who might be using this product on a job and would have one or two pieces left over they don't need. I am willing to pay. As long as I don't have to buy a whole bag--just one or two pieces.
It is a good idea to provide some insulation to borderline hardy plants like rosemary overwinter. Many options are available such as a makeshift cover of branches and leaves or a structure that contains leaves around them. Burlap and perhaps rockwool do provide insulation from the cold. Adding plastic is problematic though and can lead to disease because it prevents air circulation around the plants.
I fear the advantage in this: is negated by this: Also, cold air will just get through to the plants round the outside of the poly container . . .
I don't quite understand this . . . is it because of the plastic that cold air would just get through to the plants round the outside of the container? Otherwise, what's the point of trying to insulate vulnerable plants with insulating materials like burlap, leaves, rockwool, etc.
Yes, because the plastic circled round the plant and abutted against itself won't form a good seal, it'll be very draughty. Rockwool on its own pushed against itself will filter the air through slowly and be much better insulation.
Make friends with friends with Southern exposure And Greenhouses yes I am being cheeky i have tried to save Perlagoniums Rosemary Dahlias Chrysanthemums Etc It just does not work for me - I’ve tried for 20 yr in pocket cold zone near West Vcvr with outflow climate let us know how your plants are - always interesting to learn on this forum
Also - I’d be concerned about the safety of some materials near what you might use in food prep (Rosemary) if you’re really keen - go and ask the shipping delivery at your smaller build supply often there are damaged / broken bales and pieces they will give you (to save disposal $)
I fully recognize that Coquitlam sees colder temperatures in winter than what I see in Steveston, BUT, I've been growing rosemary outdoors for well over 20 years. They're in a sheltered area in the lee of a north facing fence in a raised planter. While frost can be an issue, my biggest concern is drainage: rosemary HATES wet feet and the raised planter drains very well. Here it is to the right in the picture during this past January's snowfall. For the first time ever we saw rosemary seedlings pop-up in some pots I had under the shrubs in 2023 and transplanted those into 3 inch containers in potting mix with some extra perlite for drainage and they overwintered outdoors in a sheltered area and survived the January deep-freeze just fine without any special frost protection (went down to -14C). I'll go out on a limb and say that your biggest problem will be the pots you have them in, there likely isn't adequate drainage in those to properly deal with the winter rains. Keep them out of the rain as much as possible, you may even go as far as to dig the pots into the ground close to the house. Good luck!
