I have a 9th floor balcony garden of flowers and shrubs. How can I protect them over the winter? They are growing in fixed, wooden planters. Mulching isn’t possible for me. Would wrapping in burlap help?
Burlap is a good choice for protecting plants from cold drying winds during the winter. You can use it to wrap the actual plants and/or create a wind break screen to block the wind. As you are on the 9th floor, I would suggest you could try to do both.
Also in your case, you need to try to prevent the freeze/thaw cycle, so need to provide some kind of insulation around the planters. Two suggestions that may help with this problem, is to wrap your planters in bubble wrap or, cut styrofoam to snugly fit around the outside of the planters and tape in place. As it is already November, water the planters once more so the soil contains lots of moisture when it freezes. This will enable plant roots to continue taking up as much moisture as possible. Wait until after there has been some frost before wrapping the planters to ensure your plants are dormant. If you have any annuals in the planters, now would be a good time to remove and discard them.
I hope this works for you. Success in overwintering balcony plants depends a great deal on the species you are growing, the direction the balcony faces and of course, the type of winter we experience. If you need to replace some of your plants next spring, consider selecting plants that are 2 full hardiness zones colder than your region.