Japanese maple are sensitive to the soil they are planted in. I planted one recently and purchased some "azalea/camellia" planting mix. My nursery suggested that I use one part azalea planting mix to 3 parts regular potting soil (I used Miracle Grow potting soil that keeps the plant from being over watered or under watered. Japanese maple like an acidic soil and many soils are more alkaline. You might want to replant your tree adding an acidic soil amendment.
Thank you Karen I will make it more acidic :)
They also like some shade.
One of the issues faced by Japanese Maples in pots is the temperature of the root zone, not just the direct sunlight. It looks like it could be that or a water issue. Any plant in a pot will require much closer supervision with watering, than one in the ground. You don't mention where you are so I am not sure what your ambient air temps are. One thing you can do to help out is actually plant pot in pot. Place the tree in a comfortable sized pot for the roots, then get a larger decorative pot to set it in. Place enough mulch at the bottom to bring the inner pot up to level and place the potted plant in the center, and insulate the sides with more mulch, add a light layer over the top as well, but not on the trunk. This will help keep the roots a bit cooler. If you are in a really h ot climate, you can put ice cubes on top to keep the temperatures lower on the roots as well as adding moisture to the soil during really brutally hot days. (did you know this is how they control bloom time on the Azaleas during the Masters Golf tournament if it looks like they are going to bloom to early?)
looks like it might have got too dry. It only takes one time being dry to look like that. It also can be fertilizer burn, but Im going with too dry. :)
I'm thinking that it's too dry also. I've got a Japanese maple that I've kept in a pot for 6 years now and it has had this look when it doesn't get enough water. Mine faces west (but in Canada) and gets afternoon sun and seems to be doing fine. I usually keep it in the unheated garage in the winter with a thermal blanket wrapped around the pot.
Also check for reflected heat. I have a problem with my patio because the bricks reflect heat up and my house also reflects heat. I have to water everything twice as much as anywhere else, even in big pots.
@LInda I am no expert on this, I have one Japanese maple planted in sandy soil and another in regular garden soil. They are both in shady areas and thriving well and I live in zone 5. It may not like being potted, but perhaps the best source of info might be from your local nursery - bring a leaf sample in with you sealed in a baggie. Just curious, you have such a beautiful pond so I am wondering if you have considered planting in that area. Japanese maples look awsome next to ponds. Thanks for posing the question.
My first thought was "not enough water"....try mulching heavily & water regularly. Also there are water retaining granules you can buy that soak up water, swelling to many times their size & release it slowly into the soil. My friend has a red Japanese Maple that is thriving in full sun in his front yard (zone 7). It would probably be happier if you could just plant it in the yard.
I have found my Japanese maples do not like to be overwatered OR underwatered. to me this looks like an overwatering. I have one in a very very large pot, and I set the hose on it for quite awhile...about once a week when its cooler and 2 times a week when hotter. It does get a little watering from a sprinkler but the plant leaves keep most of the water from hitting the soil.