Japanese stewartia growth rate, mature size & root issues – ultimate guide


mature Japanese stewartia pseudocamellia

Stewartia pseudocamellia is very popular in lists of ‘trees for small yards’ (or gardens) in magazines and on other websites, but I find these lists usually hugely lacking in detail. What do we even call ‘a small garden’? Believe it or not, these ‘small trees’ can completely take over some smaller spaces. It all depends on a few variables. What can you expect from this tree?

Japanese stewartia are moderately slow-growing: typically 1 foot (30cm) per year or less. Whilst they can grow beyond 40 feet (12m) tall in native habitats, they rarely do in cultivation, where 30 feet (9m) or less is expected. They have an oval habit, typically about 3/4 as wide as they are tall.

You might be considering planting a Japanese stewartia, or you might already have one – but given the arborist’s mantra is ‘the right tree must be in the right place‘… let’s consider how big these trees get, whether they’ll cause any issues, and what makes them grow faster, slower or not at all!

How fast do Japanese Stewartia grow?

Looking for examples, I’ve done deep research dive on arboretum sites and other sources. Whilst there are reports of this tree gaining 2 feet (60cm) per year, this is the exception rather than the rule. Most resources will report that these trees will grow at a slowish pace. That means 1 foot (30cm) per year or less.

Holden Arboretum in Ohio, which is in USDA hardiness zone 6 (very suitable for the species), which has several specimens, actually recorded the growth rate of their Japanese stewartia at 6-10 inches (15-25 inches) per year.

So this tree does grow more slowly than most ‘small yard’ trees, like rowan (mountain ash) and most species of cherry and crabapple, which will usually put on one to two feet per year. Japanese stewartia’s rate would be similar to that of paperbark maple, which is genuinely an excellent tree for a small space. This article describes in more detail what you can expect from that tree, with some examples.

How big do Japanese Stewartia get?

This isn’t just a question of height, but shape and spread. In fact, the horizontal spread of the tree will usually have more impact on whether it’ll fit well in on a property than the height will.

Bear in mind, these have really only been cultivated outside of their native range in Asia in the last century – so there aren’t all that many truly mature specimens.

First, height

Japanese stewartia, according to most of my trees books (and according to several extension offices) will eventually reach 30-40 feet in height (9-12m) – for reference, a 2-story house is about 20 feet tall, so that’s still rather large.

However, there are few real-world examples of trees that are this tall! Harvard University’s Arnold Arboretum, which lies in USDA hardiness zone 6 (again, ideal for stewartia), has two mature Japanese Stewartia. Those specimens originated from a 1917 seed collection – and they’re only 32 feet and 27 feet tall.

The arboretum states that while they may reach more than 40 feet in the wild (in the tree’s native range in Japan and Korea), cultivated specimens typically grow as large shrubs or small trees”. The famous tree expert F Bayard Hoya wrote that they could reach 18m (60 feet) in his seminal book of Trees of the World – but this seems unrealistic for everyday gardeners and again may reflect their natural habitat.

Holden arboretum in Ohio is also in USDA Zone 6, which suits the tree well. Its very tallest Japanese stewartia is 40 feet.

The evidence as I’ve collated it indicates that realistically a yard specimen is much more likely to reach something like 30 feet (8m) tall, which is about 3 stories.

Trees that adopt a shrubby habit may grow even shorter. NC State Extension suggested that the lower estimation of maximum height could be as little as 12 feet tall!

What about spread, and shape?

This tree has a pyramidal shape when young, progressing to an oval habit when more mature. Almost all expect sources indicate they grow outwards to around 25-30 feet (8-9m) wide – i.e. 12.5 – 15 feet out from the trunk. That’s about the width of 2 and a half to 3 parking spaces.

Japanese stewartia young autumn
Young Japanese stewartia displaying its brilliant autumn colour.

As demonstrated above, though, realistic growth for everyday hands-on gardeners may not attain this size.

As a general rule though, you can expect a tree that’s three-quarters as wide as it is tall.

Japanese stewartia are typically sold as multistem trees – rather than one main, clean trunk, it branches off right at the base. This gives you more of the striking, peeling bark on display, particularly in winter.

Multistem trees tend to spread out sooner than single-stem specimens. They aren’t trees that you typically walk underneath and shelter under. Consider whether this will suit your yard.

It will be obvious when buying them in the nursery whether they’re multi- or single-stem specimens.

multistem Japanese stewartia pseudocamellia
A ‘multistem’ Japanese stewartia

Japanese stewartia growth table – what you can expect

Age of Japanese stewartiaExpected height (lower estimation, feet)Expected height (higher estimation, feet)Expected spread (feet)
5362 – 4.5
105124 – 9
157.5186 – 14
2010238 – 17
2512.5309 – 23
Based on a lower estimate of 6 inches per year and upper estimate of 14 inches per year. Spread based on ratio to height of 3:4.

Once they get to 25 years of age, it’s unlikely that you’ll see your Japanese Stewartia getting any taller – though the branches may spread out a little more.

How long do Japanese stewartia live?

There’s very little data on how long these trees live. There are only two ways to accurately conclude this – either using growth rings from dead or felled specimens in their native forests of Asia (which there doesn’t seem to be any literature on) or by knowing the exact date at which specimens were planted.

The oldest known living trees I can find are those Harvard University’s Arnold Arboretum. There were planted more than 100 years ago.

However, it’s unlikely that a Japanese stewartia planted today will live that long. In Holden Arboretum, Ohio, even with their expert care, only 30% of trees of this species that were planted in the 1980s have survived to date.

Why? It begs the question:

Are Japanese stewartia easy to grow?

Not particularly. But it comes down to the conditions it’s in in the first place – availability of water, drainage and the corresponding soil type. In Holden arboretum where only 30% of the trees survived since the 80s, they said “mortality has been high on heavy soils that get waterlogged or are prone to drought, but very low on moist acidic well-drained sandy loam”.

Japanese stewartia are fairly drought-intolerant. If you’ve got one of these trees you’re likely to have to commit to watering it regularly. This typically means a good soak weekly during the warm months, and monthly during dry spells in the cooler months.

A Japanese stewartia on boggy or waterlogged soil will grow more slowly than expected, or not survive.

They’re prone to leaf scorch (particularly if you try to grow one in the southern states of the US). In such a region, it’ll need partial shade and very frequent watering.

You can reduce the risk of the roots drying out by mulching the base of the tree well (a circle of mulch 3-4 inches thick and about 4 feet in diameter will help water permeate into the ground much more effectively, and reduce competition for water by suppressing the growth of grass and weeds).

Do Japanese stewartia have invasive roots?

Whilst there’s little available data, the roots of this tree are not known to cause problems with sidewalks, driveways, septic tanks, foundations or drains.

Trawling many forums where this tree is discussed, I couldn’t find any Japanese stewartia owner who has had problems. The Florida Extension office has said that surface roots are ‘not a problem’.

How to make Japanese Stewartia grow faster, and healthier

You might want to refer to my other article on preventing Japanese stewartia problems. But here we go!

  1. Plant them on a site that gets full sun, or partial shade (I’d suggest partial shade if you’re in warmer climes e.g. USDA zone 8, and full sun if you’re up in Zone 5). Here’s a USDA map so you can see where you are.
  2. Plant them on a well-drained site with deep soil. They don’t do well on boggy, marshy land. The presence of clay soils compounds this issue – consider loosening a wide area around the planting hole when you’re putting it in, and mixing in some grit to improve drainage. They don’t do well in alkaline soils – it needs to be acidic. You can test the pH of your soil using a Rapitest test kit (the best one in my opinion).
  3. But that doesn’t mean it doesn’t like water – of course it does, in fact, on the other hand they don’t tolerate drought. Water the tree weekly in the summer months, and don’t forget. Dying stewartia trees are usually dying as a result of drought.
  4. Consider the use of some fertilizer! A slow-release ‘complete’ fertilizer containing nitrogen, phosphorus and potassium is your buddy here. Follow the manufacturer’s instructions and don’t overdo it. I like Jobes Fertilizer Spikes or Miracle-Gro Shake ‘N’ Feed.
  5. Make sure you mulch around the base of the tree! 3-4 inches thick, 2 feet out from the trunk. This helps water permeate into the roots and insulates them from temperature extremes and freezing, as well as mimicking the forest floor and preventing competing growth of weeds and grass.

I hope you’ve found this article helpful! While there are a couple of disadvantages, I really this this is an incredibly rewarding tree – not often seen, but not easily forgotten.

Image Attributions:

Photo by and (c)2007 Derek Ramsey (Ram-Man), GFDL 1.2 http://www.gnu.org/licenses/old-licenses/fdl-1.2.html, via Wikimedia Commons

Alpsdake, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

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