Answer: This has been such a difficult spring for so many plants. There is not really too much you can do except wait and see how they eventually recover and leaf out. The magnolia probably lost its flowers and buds for this year. The Japanese maples probably suffered foliage damage and may have lost some tip growth on their branches and may die back partially. It can take a long time, into June sometimes, until they rebuild their strength to releaf.
When you are certain they have leafed out as much as possible, remove any dead wood. Dead wood will be off-color brown or gray and is brittle and will snap in your hand. Live wood has green inside the bark and is supple. Begin at the branch tip and prune until you reach live wood.
In the meantime, you could give them a top dressing of good quality compost for some TLC. Beyond that, it is just wait and see.
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