A little knowledge is a dangerous thing
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1.What is the best fertilizer regime for japanese maples in containers? Have been using a j. maple balanced fertilizer at half strength for a few years, plus slow release blood and bone meal twice a year for the last few years with good results but everything you read seems to contradict itself so advice is welcome.
2. Could this be damage from over watering or aphid treating and not just the aphids?
3. Aside from not over watering, over feeding, under watering, letting them dry out, and providing some afternoon sun protection on hot days for the next few weeks is there anything else I can or should be doing to help in their recovery?
If I had to guess, your leaf problems stem from using a soap treatment on the aphids — especially if it was a home-made soap spray, and even more especially if you gave them repetitive treatments. Many maples react badly to soap sprays. Commercial soap sprays like Safers are a bit better, but the sodium or potassium salts of fatty acids, with strong alkali component found in soaps can raise hell on maple leaves. Worst affected are trident maples, but Japanese maples (and others) are susceptible, too.
As for fertilizers, you trees will not care and there is NO SUCH THING as a maple fertilizer (except perhaps in the fertile imagination of fertilizer marketers). Anything with NPK and especially trace elements will work just fine….More at Re: Japanese maple care and recovery … – Internet Bonsai Club
So remember if you have a problem or an issue with your tree do a little research to make sure that you are taking the right action. It would be a shame to loose another fine young or established bonsai tree. A little TLC can work wonders for bonsai.