I would like to know how long the ornamental cabbages and mums stay in the garden. I would like to transplant them from the urns to the ground. We live in the Don Mills and Finch area of Toronto.
These two plants are quite different despite both being fairly frost tolerant. They are used extensively at this time of year in a lot of gardens to give colour and interest when many other plants are past their best.
The Ornamental Cabbage belongs in the Brassica family along with such plants as Broccoli, Brussels Sprouts, Collard, Kale, Cauliflower, Turnip, Edible Cabbage and Kohlrabi. These are all cool weather plants that can withstand quite a bit of frost but as annuals, will not survive through our severe cold winter. If you are cleaning out your urns you can plant the cabbages in the soil while it is still workable, in order to prolong the season and maintain colour and interest in your garden for the next few weeks. These plants will give you better colour pigmentation if they are planted in a slightly acidic soil, in full sun and are allowed to dry out slightly between waterings. Over the winter they may become food for animals such as rabbits or deer but more than likely, they will be a slimy mess when spring comes around. If you do not have the appropiate place in your garden, it is probably best to discard the Cabbages now into your compost pile or place out with your garden waste for city collection.
Chrysanthemums are herbaceous perennials which means they die back during the winter but regrow again the following spring. These plants belong in the Aster family and there are over 140 known varieties worldwide. Assuming you have cultivars that will survive in your hardiness Zone, which is not always the case with potted chrysanthemums, they should be taken out of the urns and planted into the soil as far in advance of the first frost as possible. For optimal growth and flowering they need at least 5 hours of sunlight during the growing season, good air circulation so should be planted 15-30 inches apart and adequate watering in well draining soil as they don’t like having their roots wet, so choose your site carefully with these conditions in mind. After planting, it is crucial to water the plants well until freeze up in order to lessen transplant shock to the root system. Cut down the foliage only after it has been killed back by a hard frost or prolonged cold weather, if you like a clean tidy winter garden. In the spring when you see new growth, cut back any dead material and add a layer of compost or well rotted sheep manure which will give the plants some nutrients. You can also feed with a 20-20-20 fertilizer solution every couple of weeks while the plant is vegetatively growing, switching to a 10-20-20 strength when the plant begins to flower.
Another option for the Chrysanthemums is overwintering in a cool, dark place while ensuring damp roots throughout their hibernation, which should keep the plants alive for spring ground planting. This can be done in the current urns or you can re-pot each chrysanthemum plant into something smaller for storage. Beware of freeze and thaw cycles with your pots and urns as it may cause cracking, splitting or breakage of the containers.
For more detailed information about overwintering chrysanthemums, please have a look at this answer to a previous question posed to us by another gardener.