I live in Toronto in a condo/ terrace facing south. I have high winds around 5-30 miles. The sun is strong for about 6 hours in the summer months.
I have two cedar trees recently repotted into larger round pots along the east glass partition. No insulation. I used premium potting soil and 3 way mixture.
On the west glass partition of the terrace are blue point juniper trees planted in the summer in a two 2X2 insulated containers with the same soil combination previously mentioned.
In November, I placed a plastic cover over the trees only when conditions reach below freezing then I remove it once temperatures are above freezing. I don’t have the ability to secure wooden steaks into the terrace floor to wrap the cover around to avoid the plastic cover from touching the branches.
I would appreciate your opinion.
Thank you for your timely question. Protecting plants from severe weather conditions is on the mind of many gardeners this week.
In terms of protecting your evergreens from the windy conditions on your condo terrace, we would advise against using plastic. Using plastic as a winter cover can cause damage to the plants. The plastic will act like a blanket which will not allow the plant to breathe freely; the plant heats up and sweats and can start to mold with no air movement. If you want to use a screen to protect from wind and sun you can build a burlap screen on the windward side of your plants. Or simply place your containers in the most protected area on your terrace.
Once the soil freezes the foliage can no longer transpire and when evergreens go dormant their need for light decreases. Plants will likely suffer more damage if exposed to wind and sun, so keeping the plants out of the sun and wind will be beneficial.
Choosing the container:
It sounds like your container choices will serve you for this year. The larger the container the better to protect the plant from fluctuations in temperature as the soil in the root zone will experience less frequent freeze and thaw. Junipers and cedars require well drained soils, so make sure your pots have drainage holes.
Your “Blue Point” Junipers and cedars will benefit from the addition of 1-3 inches of leaf or bark mulch. Mulching the soil will not prevent the soil from freezing but will regulate the fluctuations in temperature and slow the loss of water. Be careful not to allow the mulch to touch or cover the trunk of the tree.
The most effective way to have healthy plants that survive severe climactic conditions is to ensure that we are planting the right plant in the right place.
This article describes how, when planting evergreens in containers, the selected plant should be a zone more cold tolerant than those grown in the ground.
Other Toronto Master Gardener answers that you may find helpful are: