I purchased shrub protection “tents” for my hydrangeas. These tents allow air, light and rain to penetrate while protecting the plants from freezing rain, harsh winds, and snow accumulation. My question is whether it is too soon to cover them now. I am in Lindsey, ON, zone 5a.
First of all, we assume that the Hydrangeas that you are protecting belong to the species H. macrophylla or bigleaf/mophead hydrangea, which blooms on old wood and is vulnerable to winter injury in Ontario. Providing winter protection would help ensure flowering next year.
Plants receive winter protection once they are fully dormant and the ground has mostly frozen. The protection serves a two-fold purpose: to mitigate the damaging effects from wind, sun and ice, and to minimize fluctuation in soil and ambient temperature. The protective tents look like a great way to deflect the elements. What it does not provide, however, is sufficient insulation. May we suggest a thick layer of dry mulch (e.g. dry leaves or wood chip) around the base of the shrub to help keep the soil temperature stable around the root ball. The protective tent can then be set on top of the mulch, around the shrub.
Bigleaf hydrangea is also prone to another type of injury, when its buds break too early in late winter/early spring which are then damaged by a cold snap later; shrubs planted in very sunny locations are especially at risk. If this situation applies to your hydrangeas, you may want to consider mounding the dry mulch higher to give additional protection to the buds.
We wish you the best of luck with your hydrangeas.