Hello – Thank you for reading my question. I recently planted a young Stewartia, it is only 2m high at this time, but has a nice low branching system off the main trunk. I then planted a Dwarf Blue Spruce and a Snow Queen Oakleaf hydrangea on either side. They are each about 8ft away from the tree and 4ft forward from the tree centre. My husband thinks it’s funny they’re so far out, but I was planning for the tree’s and shrubs’ full sizes, with the idea I could fill in gaps with perennials which I have started to do. I would much rather just have the tree and shrubs and not have the additional work of the perennials in this spot, but I don’t want to be moving the shrubs away from the tree in 10-20 years or be forced to limb up the tree. I want to measure twice and plant once. (I planted a goldmound spirea halway between the tree and the hydrangea, but even four feet from the tree seems crazy to me!) Am I overthinking this? Thank you for your time.
Thank-you for contacting Toronto Master Gardeners with your question. It’s great that you are trying to plan for the ultimate size of your shrubs and tree. So often people neglect to do this and space their plants based on their current appearance (personal experience comes to mind here!) and within a few years discover that they have crowded their garden plot.
The Stewartia (Stewartia pseudocamillia) is a beautiful garden tree that will ultimately reach a height of 20 to 40 feet and a width of 15 to 30 feet, depending on your garden conditions and whether it is a single or multi-trunk specimen. Your spacing plan sounds reasonable considering that its shape tends to be pyramidal and the tree generally has a low canopy of about 3 feet from the ground. Having said that, both the Stewartia and the Blue Spruce (there are many cultivars, Picea pungens ‘Globosa’ is very common) are slow growers so you may have a fair bit of empty space to deal with for a considerable time. (I planted a Stewartia myself 3 years ago and it has shown very little growth to date.) The hydrangea (Hydrangea quercifolia ‘Snow Queen’) and the Goldmound Spirea (Spiraea japonica ‘Goldmound’) will reach mature size more quickly. The spirea will have a maximum height of 3 feet and be pruned to keep it small. It can be moved fairly easily if you notice things becoming too crowded. You could consider using some other small-medium shrubs in the area in the early years, with the plan to move them later when the stewartia is larger. Shrubs require less maintenance effort than perennials, as a general rule.
The link below takes you to some good general information about growing Japanese stewartia, including size at maturity.
http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=m440
Here is some additional information on Hydrangea quercifolia ‘Snow Queen’:
Finally, a link to more on Dwarf Blue Spruce:
https://www.extension.iastate.edu/news/2005/apr/apr05112.htm
Best of luck with your planting!