I planted 3 black tulip magnolias. They seem to have wintered well and also seem to have many buds. I wrapped them with burlap over the winter. When do I unwrap them? They are in a sunny, south facing, sheltered location. I live just south of Thornbury and we seem to have a nice micro-climate here. It’s very warm now but also early. I don’t want to leave the winter protection on too late, nor to take it off too early. Help?
Thanks for contacting Toronto Master Gardeners with your question about caring for your magnolia trees. In order to answer this question, it’s a good idea to review the growth conditions required by this beautiful cultivar.
Magnolia Black Tulip is what is known as an an “interspecific hybrid.” Its showy blooms are rich pink in colour and emerge in spring before the dark green leaves. A vigorous variety, this hybrid makes a fine ornamental landscape tree that grows to an eventual height of 20 feet, a spread of 10 feet, with a low canopy of about 3 feet from the ground. Preferring full sun to part-shade conditions, it is hardy to zone 5a. It requires an evenly moist well-drained soil for optimal growth, but will die in standing water. It is not particular as to soil type but has a definite preference for acidic soils. Since you are already protecting it with burlap wrap over winter, you are probably also aware of the advantage in applying a thick mulch around the root zone to protect it in exposed locations or colder microclimates. A relatively low maintenance tree, the Black Tulip magnolia should only be pruned after flowering to avoid removing any of the current season’s flowers. It grows at a fast rate, and under ideal conditions can be expected to live for fifty years or more.
According to Natural Resources Canada, Thornbury is in hardiness zone 5a. Here is that link.
http://planthardiness.gc.ca/?m=22&lang=en&prov=Ontario&val=T
Hardiness zone maps vary especially in recent years with the effects of climate change. This source shows Thornbury in zone 6a.
https://www.plantmaps.com/interactive-ontario-plant-zone-hardiness-map.php
Since you are located just within the hardiness zone for the Black Tulip magnolia, it is wise to protect them from harsh winter conditions just as you have been doing.
As for when to unwrap them, you can use the gardener’s rule of thumb dictated by the last frost date. Frost dates are calculated based on data from the National Centers for Environmental Information (NOAA) based in North Carolina. https://www.ncdc.noaa.gov
Frost is predicted when air temperatures reach 0°C, but because it is colder closer to the ground, a frost may occur even when air temperatures are just above freezing. Always keep an eye on your local weather forecast and plan to protect tender plants accordingly. Weather, topography, and microclimates may also cause considerable variations in the occurrence of frost in your garden. Remember that since frost dates are an estimate based on historical climate data, they are probabilities only. There is a 30% chance of a frost occurring before or after the given dates.
This site shows a last frost date of May 11–May 20 for Thornbury.
https://www.plantmaps.com/interactive-ontario-last-frost-date-map.php
The data at Farmer’s Almanac is consistent with that source. It shows a last frost date of May 14 for Thornbury.
https://www.almanac.com/gardening/frostdates/postalcode/N0H%202P0#
Mid-May may seem like a long time to wait to uncover your magnolias. I certainly understand the temptation to do it a little earlier if the weather forecast continues to indicate a warmer than average spring.
For more information, click here.
Mar. 22, 2021