Have you ever used SuperThrive? It is not a fertilizer – it is a rooting hormone that helps the roots grow quicker and stronger as well as protecting the maple from transplant shock. I have been using this for 4 years and now I swear by it. It is available online through Amazon and eBay as well as many other online sources. Use a stronger solution than the recommended amount to ensure the best results.
Use a 5-gallon bucket filled to about 4 gallons with water and then add 1 oz of SuperThrive concentrate and mix thoroughly. This amount can plant two 3 gallon maples or four 1 gallon maples. Slide the rootball out of the pot and loosen the bottom roots if they are root bound. Then dunk the rootball into the solution for a couple of seconds until most of the air bubbles are gone. If the rootball is lose then dunk the entire container into the solution and turn the container on its side and gently slide out the rootball and place it in your prepared hole. Place the rootball into the hole so that the base of the trunk is level with the surrounding soil. Then back fill the hole until level and pour the remaining solution around the base of the trunk and pack down the root ball firmly and finally add more soil as needed – making sure you do not cover the root flare. Stepping around the base of the maple can pack down the soil firmly. Water newly planted maples thoroughly every two weeks. Then every couple of months use the SuperThrive solution to give them a boost the first spring and summer – again using a 5-gallon bucket.
During the winter rains you do not need to water. Then in March or April when buds forming use the SuperThrive solution to water the rootball again if it is a newly planted maple – less than 2 years old. Generally after the third growing cycle maples do not need any fertilizer or SuperThrive when planted in the ground.
Of course if a maple looks a little sick a dose of the solution can do wonders. The key is to never ever over water. Dry is better than wet for maples. Please see Caring for Japanese Maples.