I was lucky enough to acquire a large beautiful Japanese themed, painted ceramic pot, from a lovely gentleman whose wife had passed away and who had loved this pot. I want to take good care of it. My idea, when I acquired it, was to plant a Japanese Maple in it and keep it outside on my flagstone patio in Toronto. However, it was used indoors by its previous owner. I am nervous about keeping the ceramic container outside with a tree in it in case it freezes and cracks. I have been brainstorming with myself on how to make this work because I think it will be a very beautiful element in my back yard. It just occurred to me that, perhaps I could grow the J. Maple in a plastic pot, inserted into the ceramic pot, so that no frozen soil actually comes in contact with the ceramic during the winter months. My question for you is, will the J. Maple survive, or better yet, thrive in a plastic pot? If you have any advice to give in this regard, I would be grateful to hear it!
Dear Gardener, thank you for asking your interesting question on growing a Japanese Maple in a container.
Growing a Japanese Maple (Acer japonicum, or Acer palmatum) in a container is a great idea. The chance to show off your gifted beautiful pot by using it as the container for an exquisite tree sounds perfect. Protecting the ceramic pot by having a plastic pot inside the direct container of the tree will work well. Try and find a plastic container that is nearly the size of the ceramic pot, but not a tight fit. This is in case you need to lift the tree out to drain water out of the ceramic pot.
The Japanese Maple is so beautiful in all its sizes, varieties, and its magnificent leaf colour, that I suggest you plant the container close to a window where you can admire it from late spring to very late fall where it will reward you with its best show of fall colour.
My suggestion is to grow one of the dwarf varieties, but it seems that even the medium-sized Japanese maples can be grown in containers. Ideas on which varieties to select for containers can be found here: https://www.gardenia.net/guide/great-japanese-maples-for-containers
Kind and size of containers
The size of pot should be appropriate for the size of the tree. The container should be about twice the size of the tree’s root ball. Your plastic inner pot, and hopefully your ceramic pot, should have many drainage holes. This is important. Japanese maples like lots of water, especially during the growing season (water them every second day during the drought days of August). However, you do not want the soil to get waterlogged, which can kill your tree. When you are planting the tree in the container, use a light potting soil that will facilitate drainage.
The roots of a Japanese maple grown in a container are more vulnerable than if the tree was growing in the soil. Keep the container well watered through several heavy frosts. The tree should be completely dormant at this point.
Overwinter your tree in a protected spot after the tree has dropped its leaves. Ideally, and only if it is not too heavy for your back, move the tree to an unheated garage or basement or very protected corner of the garden where temperatures remain above freezing. No light is needed when the tree is dormant.
The next step is to mulch the pot to insulate the tree with at least three to four inches of mulch. I have seen pots surrounded by bales of hay which looked like a good way to ensure that the tree is well insulated. This step will moderate the freeze/thaw cycle we often experience over the winter. A container will thaw more quickly than the ground, and cause your trees to break dormancy, and then be killed by the next freeze. The pots should not be allowed to completely dry out over the winter, so check them occasionally and water sparingly to keep them just slightly moist. Bring your pots back out in the spring once you see signs of new growth on the trees.
Japanese maple trees can grow 12 to 24 inches (30 to 60 cm) per year, reaching 10 to 25 feet (3 to 7.6 metres) after 15 years — but you can keep them to a smaller, manageable size with yearly pruning. The best time to prune Japanese maples is during winter when the trees are dormant.
Finally (although this is a topic that could easily be a book), you may enjoy this article that was published in the Toronto Botanical Garden’s magazine on Japanese Maples in Fall 2020: article by The Tattooed Gardener