Stewartia has few or no flowers – this & other issues solved


File:Stewartia pseudocamellia (Montage).jpg

Whoever plants a stewartia, in my view, has excellent taste in trees. They’ve got stunningly unique peeling bark, striking orange-red fall color, and of course wonderful white blooms that appear much later than most other trees’ flower, and keep coming for weeks. In particular the Japanese stewartia, Stewartia pseudocamellia has grown in favor among tree lovers; while the flowers are similar across species, pseudocamellia gives the best-looking bark of all.

Or at least they should – many stewartia owners have found that their tree hasn’t produced flowers in a given year, or that there are very few – or sometimes none at all since planting. It’s a little disappointing when it happens. What explains this phenomenon?

Stewartia are usually several years old before they start flowering, depending on the propagation method. Numerous environmental factors can affect blossoming patterns, including drought, recent transplanting, late spring frosts, sunlight availability and soil issues.

I’m a huge stewartia fan, and having studied and admired these trees for some time (and spoken with some local experts) I’d love to unpack all of the above and share all that I’ve learned with you.

By the way, while most gardeners will be here to read about Japanese stewartia/stuartia (also known as Korean or deciduous stewartia), some will want to read about the US native species – Stewartia malacodendron (the silky camellia or Virginia stewartia), or Stewartia ovata (mountain camellia). Or you may be here for info on some of the other asian species, such as Stewartia monadelpha (the tall or orangebark stewartia), or Stewartia rostrata (the beaked stewartia) or Stewartia sinensis (Chinese stewartia).

Owing to its popularity, the info on this page will predominantly be written with the Japanese Stewartia in mind, but the vast majority will apply to all of the above species – read on!

When do stewartia trees usually flower?

Japanese stewartia pseudocamellia flowers blossom
Stewartia pseudocamellia in bloom in June/July

As a general rule, most stewartia species, including Japanese stewartia, flower in June and continue to blossom through July.

This is significantly later than most other flowering trees – one of the cool things is that you should have great blossoms at a time when the cherry and apple trees have long since lost their petals. Kousa dogwood would have similar flowering patterns – read about it in this article.

So for almost all stewartia species, your tree should have bloomed by the end of June and will reach its maximum blossoming potential by late July – an exception being Stewartia ovata (mountain camellia), which flowers slightly later than its cousins, sometimes not showing until July. Apologies if you’re reading in the Southern Hemisphere!!

If this is your situation, let’s ask the fundamental questions.

How old are stewartia when they first start to flower?

If this is your tree, it’s likely to be quite young. Trees don’t ‘mature’ (produce flowers and fruit) instantly – there’s a period of years before a new tree becomes a reproductive specimen.

It’s been difficult to get an exact figure on this – it’ll vary from tree to tree – but as a general rule, I’d expect stewartia grown from seeds to start making flowers within 5-10 years – at, let’s say, around 5-15 feet in height – but if they’ve been grown from cuttings from a tree that’s already mature, it will be quicker than that – perhaps as little as 2 years.

This timescale would be similar to other small-sized flowering trees such as cherry, rowan/mountain ash and flowering dogwood (the links bring you to similar in-depth articles I’ve written on these trees).

So the most likely cause here is that your stewartia hasn’t yet matured, and you simply have to keep it healthy until it has appropriately aged.

If you know which nursery your tree came from, call them up and ask how long they think it’ll take. They’ll know if the tree was grown from a cutting (shorter time to flower) or from seed (longer time to flower).

Recently planted stewartia that aren’t flowering

A phenomenon that affects many trees, including stewartia, is that of a delay or setback in flower and fruit production in the 3 years after planting, or moving from the likes of a container.

When moved from one environment to another, the roots can struggle to adapt to the change (and are often damaged in the process). They fail to take up adequate water until they get re-established.

In its most extreme form this is called ‘transplant shock’ and is marked by wilting and early brown coloration of the leaves, which sometimes drop off. It’s usually apparent in the months immediately after planting, especially in trees that are planted in summer (instead of the usual autumn or winter).

A milder form can cause slow growth and a reduced display of flowers, as the tree puts all its growth energy into forming a new root system. Many tree owners will find that trees that were flowering at the nursery fail to do so for a couple of seasons once they’ve planted them. This is normal enough, and the tree will usually survive IF you make sure you water it. Generally, this means a good root soak once a week for several weeks after planting and through the warmer months.


If after more than 10 years you’ve still got no flowers, consider whether something’s fundamentally affecting your tree’s health. Consider this much sooner if your stewartia isn’t looking healthy – by that I mean it doesn’t seem to be putting on height, or the leaves are wilted or have scorched brown tips. The following sections may help to narrow it down – this is all about your tree’s immediate environment.

Stewartia flowering and sunlight

Stewartia grows properly in either full sun or partial shade (partial shade probably being the best). But it doesn’t do well in the shade. If it isn’t on a south-facing spot where it’ll see the sun at least part of the day (I’m talking in the Northern Hemisphere here of course!) it may be difficult to establish a tree that’ll survive in the long-term.

Stewartias that are stressed by lack of sunlight will struggle to mount the energy to display a full show of flowers (a sure sign of health).

HOWEVER, in hotter regions of the US (the southern states) the sun can be too strong – and stewartia need a bit of shade here or they struggle. It’s probably ideal for a west-facing site.

Stewartia flowering and irrigation

Stewartia are drought-intolerant trees, but the effects of drought sometimes aren’t seen instantly. A drought-stressed tree won’t have the energy to produce many flowers.

Often homeowners plant trees with joy, but then the busyness of life makes them forget to water their trees frequently! It’s probably the most common cause of young stewartia that die in their first year – which is a shame. Remember you’ve put thought, time and money into your stewartia (and they aren’t the cheapest tree either, because they’re tricky to propagate). Protect your investment!

And here’s one cheap, easy and fuss-free way to keep your tree free to access water – mulch, such as organic bark chippings, should be spread over the roots of your tree (a circle of at least 4 feet across) after planting and then replenished yearly thereafter. Some don’t bother, but then they’ve got a trunk surrounded by grass – which soaks up the vast majority of the available rainwater.

Why put down mulch around your stewartia?

  • It suppresses growth of grass and weeds, which compete for water
  • It slowly and constantly decomposes, adding nutrients to the soil
  • It insulates the roots against temperature change
  • It helps rainwater penetrate easily into the ground
  • You won’t have to mow right up to the trunk – reducing the risk of damage from e.g. trimmers
  • It provides a pleasant-looking border for your tree

Essentially, it mimics the forest floor in these trees’ natural habitat.

tree mulch
The mulch around one of my trees right now!

(By the way, if you’d like to know more about what happens to trees when they get damaged by the likes of lawnmowers and weed trimmers, I’ve explained in this article).

On the other hands, if you try planting one in a marshy part of your property where the soil is poorly drained, it likely won’t thrive or flower properly – stewartia don’t like having ‘wet feet’. Rainwater ideally go through the roots – they aren’t meant to sit in it. Roots need oxygen, too! Is the ground marshy around your tree? It might explain your lack of flowers.

Stewartia flowering and soil conditions

Most arborists know that stewartia like acidic soil, and indeed there’s some authoritative literature confirming this. Michael A Dirr’s seminal book Manual of Woody Landscape Plants reports that Japanese stewartia fare best in mildly acidic soil, ideally 5.5-6.5.

Do you know your soil’s pH? If it’s neutral or alkaline, your stewartia may not thrive and may never flower well.

As a clue, stewartia grown in alkaline soil sometimes get chlorosis – yellowing of leaves indicating a lack of the green leaf pigment chlorophyll. Chlorosis can also be a sign of iron deficiency or drought stress, though.

Often these are planted in front yards the soil has been heavily compacted by machinery during the building of the house. This can prove a struggle for stewartia, particularly when the soil’s of a clay consistency.

In general though, if it’s been well aerated, stewartia will be happy on sand, clay or loam soil.

Can weather affect stewartia flowers?

Stewartia are hardy trees and can survive in a range of temperatures – in the US they grow best in the most temperate parts, struggling in the far north due to persistent freezing, and the deep south where the sun can subject them to browning leaf tips (leaf scorch). This equates to Zone 5a to 8b in the US (according to NC Extension. Here’s a link to a USDA hardiness zone map, so you can check if you live in the right region to grow stewartia).

In the UK, they tend to withstand winters just fine.

However, just because they survive doesn’t mean untimely cold weather can’t stop a stewartia from flowering. In fact, if there’s a sudden temperature drop to below freezing in the spring time, the first part to be killed off is the delicate new flower buds at that crucial stage of bud development when the tree exits its dormant period.

Japanese stewartia flower buds pseudocamellia
The flower buds of Japanese stewartia are susceptible to frost, which can kill them off before they get the chance to open.

If your tree hasn’t bloomed this year, consider whether there were any sudden cold snaps in the spring time. Hopefully next year, the problem will have rectified itself. If the tree’s young and isn’t too big yet, you can actually loosely wrap it up in plastic or horticultural fleece if you know a spring frost’s coming, which will help the buds survive. It’ll be worth the effort come June!

Stewartia and biennial bearing

Biennial bearing refers to a pattern common in many flowering and fruit trees which naturally causes an abundance of flowers one year, and then an abundance instead of fruit the next year.

Essentially, trees (including stewartia) can just have ‘off’ years! If the tree’s otherwise looking healthy to you and has leafed out, if it has been kept watered through dry spells, and has no wilting or discoloration, consider giving it to the following year to see if it picks up again – especially if last year was particularly good for flowers.

Could it be caused by pests, or an infection?

Stewartia are genuinely free of serious diseases and pests. It’s really unlikely that such a problem is to blame if it isn’t blooming well.

However, look out for tiny insects and beetles on the leaves and trunk, brown or black spots on the leaves and/or petals and any fungal growth around the trunk. If you think there might be a problem, I’d call in a local arborist to have a good look.

Stewartia that are already stressed, such as those sitting on wet soil or which have scorched leaf tips, are much more likely to develop a pest problem.

Could it be down to a problem with the bark?

Just have a quick look at the base of your tree to check if the bark is damaged. Most of the stewartia species, including the Japanese stewartia, have thin bark – it’s one of the things that makes it so attractive, but it means it’s quite easily damaged by lawnmowers, weed trimmers or nibbling animals.

If the cambium (directly under the bark) is damaged, there’ll be a serious issue with the flow of water and nutrients. If you’d like to know more about whether a tree with damaged bark can survive (and how to help it), read my article here.

Can fertilizer help a stewartia tree blossom?

Yes, it might. It’s important to choose the right fertilizer here. Potassium-rich ones stimulate fruit and flowers. Those rich in nitrogen tend to stimulate leafy growth, sometimes at the expense of other parts, including flowers.

Possibly. Sometimes it’s the wrong fertilizer, so much as the lack of it. Nitrogen-rich fertilizers tend to stimulate leafy growth at the expense of flowers. Potassium-rich ones stimulate flowers and fruit.

Fertilizers are usually labeled with an N-P-K ratio, corresponding to nitrogen (N), potassium (K) and potash (P). A ’10-10-10′ fertilizer, for example, has equal ratios of all three. ‘Bloom booster’ commercial fertilizers are available that typically are higher in ‘K’.

Just be sure to follow the manufacturer’s instructions and apply them only as frequently as directed. Trees that are fertilized too often can suffer as a result.

For a natural high-potash alternative to commercial fertilizer, consider wood ash.

You can actually find out whether your soil is low in N, P or K at home with a home soil test kit. I always use the Rapitest soil kit – it’s accurate and pretty easy. You can get it on Amazon.

I hope you enjoyed this article! Check out my home page to see what else I’ve been writing.

References

Spongberg, S.A. Studying the Stunning Stewartia. Living Collections. Available from: https://www.pollyhillarboretum.org/wp-content/uploads/2015/12/Studying_the_stunning_Stewartia_Spongberg.pdf

Dirr, M.A., 1990. Manual of woody landscape plants: their identification, ornamental characteristics, culture, propagation and uses (No. Ed. 4). Stipes Publishing Co.

Nair, A., Zhang, D., Smagula, J. and Hu, D., 2008. Rooting and overwintering stem cuttings of Stewartia pseudocamellia Maxim. relevant to hormone, media, and temperature. HortScience43(7), pp.2124-2128.

Nair, A. and Zhang, D., 2010. Propagation of stewartia: Past research endeavors and current status. HortTechnology20(2), pp.277-282.

Hsu, E., Boland, T. and Camelbeke, K., 2008. Stewartia in cultivation: The cultivated species are reviewed and new cultivars are highlighted. PLANTSMAN-LONDON-7(2), p.78

Image Attributions

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

Photo (c)2006 Derek Ramsey (Ram-Man), CC BY-SA 2.5 https://creativecommons.org/licenses/by-sa/2.5, via Wikimedia Commons

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