Growing Japanese Maples in Pots
I have been growing Japanese Maples in plastic pots for 3 years as part of a hobby with plans to give more developed plants as gifts. They sit on my lawn. I decided to repot the oldest. I noticed 2 things which may or may not be related. First, there seemed to be little root development. The roots looked the same as when Iplaced them in pots 3 years ago. Second, many of the holes that I had drilled in the bottom of the pots were clogged with mud. Should I drill holes on in the side of the pots near the bottom? Place the pots on plastic film? Other suggestions to help me grow my Japanese Maples?
Here is some information. The root growth can be affected by winter temperatures, container size, poor drainage (if the roots were too wet this can affect root growth), and type of medium used in the container. Also, you did not mention if if lack of root growth affected the above growth of the trees.
If the drainage is poor in the container, you may need to drill more holes, and make sure the soil drains well underneath the container too. Plants in containers may need protection from the winter elements especially if the containers are small. Containers may need added insulation, or relocation to more protected areas, during severe winter conditions.
Take a look at the publication regarding Tree for Landscape Containers for more information and our blog post http://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/430/430-023/430-023_pdf.pdf