I have a pretty small Japanese Maple, and I’d like to grow it a bit and get the base built up. Typically the advice seems consistently “put it in the ground”, but I’m in Minneapolis and I don’t think it’d tolerate the winter outside (currently all my trees are in a cold frame I slapped together). Is it possible for me to get the fast growing you get from the ground without killing the thing over the next winter?
Was thinking grow bags and pulling them at the end of the year and then replanting the next spring after it warms up a bit, but I’m making this up as I go so any advice would be appreciated!
So let’s step through the exercise.
This spring’s growth is going to be dictated by the resources already in the trees root system. Then, foliage hardens off and the tree is in energy positive. This fall, the tree will begin to expand its vascular system and really grow those roots into the larger space provided by the ground.
It’s going to be in the second and subsequent years that the growth will really take off due to the now larger supply of resources in the roots.
So, I think if you put it directly in ground and lift in the fall you may not get the desired result of accelerated growth. However, if you have it in a grow bag and don’t do any damage to the root system when lifting it you may still get most of the benefit.
Given your constraints, a grow box may be a suitable solution.
Another option is an Anderson Flat or grow box with a very open bottom. Plant it in the box and then leave the box on the ground. That way the fine roots can escape into the ground but it’ll still be mobile to move into a protected area. The fine roots don’t store much, so they should be able to be safely removed year after year.
Quite a few Japanese maples are hardy to USDA zone 5 and most of Minneapolis is zone 4b which is only slightly colder. Can you provide some winter protection for the trees in the ground? Putting a wind screen around them, mulching bases (I like pine needles since critters don’t like the sharp points), and then dumping snow on top of them would probably work.