· John Heider's Answer
· Hi Ronda-I just noticed Brooks answered your question also. He is very knowlegable regarding Japanese maples. I'll give you my answer also as it recaps some of what he has already said.
It sounds as if your japanese maple is going throught some shock first from the frost damage and now the unseasonably hot summer. Japanese maples will tend to slow their growth in extreme hot weather.
Although the Mikawa yatsubusa is a fairly hardy variety that takes more heat than others it does need protection from direct sunlight especially when the weather is above the high eighties low nineties. Protection from hot winds is extremely important also.
At this time I would prune off any dead stems and remove any completely damaged leaves. The Japanese Maples have a second set of leaves that will probably start appearing in a couple of weeks. Move the tree into filtered light where it is protected from direct hot sunlight and drying winds. Potted trees will have a tendency to dry out faster in this warm weather. First make sure the trees potting soil is well draining. Soil that holds to much water can be as damaging as too little water. You can dig down 6 to 8 inches and check the soil water content. The soil should feel cool and moist, not dry or wet. Even in the shade I water my potted maples twice a week in this warmer weather. Of course this depends on how well draining your soil is. It is also important to make sure at least once a week your pots are watered well enough to drain freely from the bottom to make sure the soil is moist evenly throughout the pot. I keep a layer of bark over the potted soil to help hold moisture in and keep the soil and surface roots cooler. At this time I would also hold up on any fertilization as forcing a tree that is already stressed could harm it even more. If your tree showes no signs of spotting or discoloration of leaves and stems, swelling areas of stems, or signs of insects I think removing it from hot direct sunlight and monitoring its moisture will help to pull your tree from the stress it is experiencing.
You mentioned you had moved your tree in the garage for the winter. It is wise to protect a potted tree in the winter from freezing winds that can damage the tree and its surface roots. It is also important that your tree gets as much cold weather as possible so that it goes into a completely dormant state to stay healthy and produce nice growth the following year. Your tree is hardy to zone 5 so it should survive the winter in a protected location. The garage could possibly be to warm for a good dormancy. Here in zone 9b many of our Japanese maples tend to deteriate slowly over the years and don't develop each year or have the longevity they should have because of our warmer winters.
Hope this helps. Let me know what happens after it has been protected from the afternoon sunlight and keep moist, not to wet, for awhile.