Overwintering Shrub Cuttings

(Question)

Hello There,

I have several rooted cuttings of Daphne, Fothergilla, Korean Spice Viburnum, Summersweet and Hydrangea, which I took from plants in my garden this spring/summer.

They are in my cold frame at the moment, but I am wondering if this is the only solution for overwintering them. Similar cuttings overwintered in the cold frame died last winter (although last winter as you know, was particularly harsh). I have read that ideally, 2-4 degrees C would be best to ensure winter survival, but it will get much colder than that, even in the cold frame.

Any tips or suggestions? If the cold frame is best, should I also cover with straw? I am in zone 5, just east of Aurora.

Thanks and best regards

(Answer)

You certainly are on the right track. Temperature plays a very important role in the survival of root cuttings over winter. A constant temperature of around 5C is ideal but we know our winters can be much colder than that. Cuttings should not be allowed to freeze. It’s going to be difficult to maintain a temperature of 5C in a cold frame in Ontario.  A green house would be a better option because you could rig up some form of heat. It is an expensive option though. If your cuttings are actually in pots then placing them in the garage, a cool part of a basement or a cold cellar is an option.  If your cuttings are in the ground and have actually rooted try putting a deep layer of mulch around them. Covering the cold frame with straw will further help with insulating and keeping the cuttings from freezing.  Hopefully your cold frame is in either a sheltered or partially sunny part of your garden.  And maybe our winter will not be as bad as last year!