Hello, Susan Magnolia, Spring 2020 experienced a freeze after blooming began, many branches still have buds, but no further growth/leaves. Any recommendations to start growth on the bare branches, now June 25th. Applied 1 spike fertilizer June 14th. Planted 2018. With thanks
Thank-you for contacting Toronto Master Gardeners with your question.
‘Susan’ magnolia, one of the “Little Girls” series of hybrid magnolias, is a lovely garden tree. Because it blooms a little later than the star magnolia and the saucer magnolias (Magnolia stellata and M. x soulangiana), it is not usually affected by spring frosts. Unfortunately, this year in Toronto, we experienced a very late, hard frost which affected many woody plants and perennials.
Now that your tree has produced considerable new growth, you will be able to see where the frost may have caused some die-back. You should prune out this dead wood (including the unopened buds), because it could otherwise attract disease. Using clean, sharp secateurs, prune back to where leaves have begun to grow. Prune as little as possible this year so that the tree will have as much photosynthetic energy as possible for its recovery. You may need to prune lightly next spring (after flowering) in order to restore the shape of your tree.
The other recommendations are to fertilize (which you have already done), and to ensure that your tree has a plentiful supply of water this season so that it can regain its strength following this damaging event.
Below, I have included a link to some information about pruning out the frost-damaged branches:
https://homeguides.sfgate.com/freeze-damage-magnolias-66623.html
Here is a resource with general information about Magnolia ‘Susan’:
http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c328