Flowering dogwood lacking flowers – why (and can I fix it?)


Dogwood Cornus florida flowers

This deciduous small flowering tree (Cornus florida) is a favorite for gardeners in many parts of the world, but particularly in the eastern United States, where its known for its showy blossoms that come out before the leaves. ‘Flowering dogwood’ is actually somewhat of a misnomer – the white ‘flowers’ that attract insects are actually bracts – modified leaves – which are grouped in fours around inconspicuous green flowers at the centre that you could almost miss. So what prevents flowering dogwood from living up to its name?

Flowering dogwoods may not start blossoming for their first 2-10 years, depending on the propagation method. Blossoming can be impaired by recent transplanting, spring frosts, lack of sun, over or under irrigation, poorly-timed pruning and through the tree’s susceptibility to anthracnose infection.

This article’s really about those beautiful white bracts that look like flowers – they’re what we want to see on our dogwoods and the chief reason that the tree is so popular. But in my experience, it’s not uncommon for gardeners to ask why their flowering dogwood hasn’t blossomed yet, or others may have had trees that bloomed, but seemed to reduce their flowering capacity greatly, or stop altogether.

The brief answer given above needs to be thoroughly unpacked because there are many nuances, and I hope to bring my own experience and knowledge of flowering dogwoods to help you understand in terms that are both thorough and straightforward, why this might be the case for YOUR tree, wherever you are. And I hope you find it interesting as well.

A hint, to help you work out first of all if there’s a specific problem with your tree’s blossoming capacity. If there are any other flowering dogwoods on your property or in your area, look closely and compare them. Is there a difference?

By the way. If you’re reading from the UK and you have a native dogwood (Cornus sanguinea)… you may be disappointed. The showy white bracts (modified leaves that look like flowers) that you get on the flowering dogwood (Cornus florida) and other ornamentals such as the kousa dogwood (Cornus Kousa) don’t appear on Cornus sanguinea. You’ll have to settle for small white flowers surrounded by normal green dogwood leaves.

Before you can work out if your tree’s abnormal, we need to know what’s normal. So…

What age are flowering dogwoods when they start blooming?

Cornus Florida grown as seedlings usually start flowering are several years of growing; this can be as few as 4 years or as many as 10. The large white flower-like bracts appear around the same time as the central green flowers that the bracts surround.

So you may be doing nothing wrong – it might just be that the tree is still juvenile and not long past the seedling stage.

However, most flowering dogwoods are not sold from nurseries as seedlings. Growing trees from seeds is a slow way of getting sales, and there are other advantages in asexual propagation by methods such as planting tree cuttings, and particularly grafting.

In grafting, a small cutting (scion) from the tree is attached and fuses with the established roots (rootstock) of another dogwood tree. This cutting then gets a headstart in life, and will usually grow into a dogwood tree that will produce blooms a lot earlier (perhaps after 2 or 3 years) than seedlings, which have to spend several years maturing, expending energy in developing their roots systems.

If your dogwood has never bloomed, have a look at the base of the trunk, near the ground. A line around the trunk may be discernable, showing the ‘join’ between scion and rootstock, telling you your tree was grafted. If you bought your tree from a nursery, consider giving them a call – they may be able to tell you whether the trees were grown from seed or not, and after how many years they would normally bloom.

If you had a tree that did blossom before, but which then was moved from a container or another site, fear not – it may take two or three years for it to resume flowering. Many plants undergo transplant shock as they struggle to re-establish a root system in their new environs – a fact that’s sometimes evident in yellowing or falling leaves or a wilted appearance. Keep it well-watered during dry spells and be patient – if the leaves improve in appearance it’s likely that it’ll soon resume blossoming.

What time of year do flowering dogwoods bloom?

Flowering dogwood blossoms come out before the new leaves, first appearing as soon as early spring, and as late as early summer. They remain on the tree for several weeks. After fertilization they give way to fruit: orange-red drupes which ripen through summer and can persist until late fall.

So if you’re reading this in the northern hemisphere, we’re talking large white bracts normally appearing from mid-March or as late as the start of June – but usually in April or May.

So if you’re reading this in springtime, you still might have a late bloom in early summer.

Again it can be very useful to compare your tree to any other flowering dogwoods in your area to see if they’re way ahead or not. If they’re covered in blooms and yours isn’t, it’s a clue that you need to keep reading…

How does pruning affect flowering dogwood’s blossoms?

Considerably! If you’ve pruned your tree in the past year, read on. If not, scroll on down to the next section!

It’s a well-known general rule for tree-pruning that it should be done during dormancy – usually in late fall or early winter, the exception being dying or dead or structurally weak branches, which should usually be removed right away.

However, this tree needs treatment that’s a little different. Since the most important part of owning Cornus florida is the blossoms, you may actually want to avoid pruning during dormancy.

Why? The flowers and bracts appear on last season’s growth, so if you prune in winter once the tree has stopped growing for the year, you’re actually likely to cut off many of the buds that would have produced flowers.

Now it might be possible to tell the flower buds from the leaf buds – flower buds are usually shorter and fatter, and you can do your best to avoid cutting too many off. But if, like me, you enjoy the blossoms most of all, wait until just after the blooms have disappeared and then prune. This gives you the best chance that the tree will flower fully again next year.

Alternatively, if you’d prefer to prune in winter, you could prune selectively – one or two limbs each year. The other limbs will still produce plenty of blooms come spring and summer.

Flowering dogwoods are great at tolerating heavy pruning in general, but they do usually keep quite a good shape all on their own. If you’ve got plenty of room to grow your tree, you can minimize pruning.

Flowering dogwoods and biennial bearing

Is it possible that the lack of flowers on your dogwood is simply related to some sort of natural variation?

The answer is yes. If the tree seems to look otherwise healthy, flowered well last year and isn’t completely devoid of blossoms altogether, the cause may be the natural tendency of Cornus Florida towards biennial bearing.

Biennial bearing is a feature of many trees that set fruit and nuts, such as cherry, plum, hazel and walnut. Basically it refers to a year-on-year cycle, where the dogwood varies between a heavy crop of fruits one year, and an abundance of flowers the next, and so on.

This tendency is usually more obvious in young trees, and gradually disappears as the tree ages.

Flowering dogwood blossoms and temperature

Year-on-year temperature variations do make a difference to the number of blooms you’ll get on flowering dogwood.

The biggest impact comes from freezing temperatures that occur later than usual, in the spring, when the new flowers and bracts are just starting to appear. The flowers don’t expect frost in spring, and aren’t built to withstand it – they’re much more delicate than the woody part and a deep or sudden spring frost can kill them off entirely for that season.

Preferring moderate temperatures in general, flowering dogwoods in the US usually survive and grow best in USDA Hardiness Zones 5 to 9. Hardiness zones are defined according to how low the temperature typically drops in mid-winter: strictly speaking this means, for these zones, where the ‘average annual minimum winter temperature’ is between -20 to -15 °F (-28.9 to -26.1 °C) and 25 to 30 °F (-3.9 to -1.1°C). Here’s a link to the official USDA Hardiness Zone map. Canada has adopted the USDA system – here’s their map for reference. Australia’s hardiness zones are equivalent to USDA zone 11 in the north and zone 7b in the south, while areas in the UK range from hardiness zones from 7 to 11 according to the same US scale.

Look at where you are on these maps. You could well be living in a zone that’s either too cold or too warm for Cornus florida to thrive. Anything that affects the overall vigor of the tree can impact its ability to set flowers, given the large amount of energy the tree has to expend to produce them. This could be the cause of your lack of blossoms, particularly if the tree hasn’t blossomed before.

Do flowering dogwoods need a lot of sun to blossom?

Cornus florida dogwood edge of forest
A young flowering dogwood growing in its ideal setting – the forest edge

Yes and no. Dogwoods in general are renowned for liking partial shade: observed naturally by the fact that dogwoods are often seen growing at the edges of forests, where they only receive full sunlight for part of the day.

So a dogwood is unlikely to thrive (and subsequently bloom) if it receives too much shade, or if it’s exposed to too much sun, particularly in the hot afternoon. They’re prone to leaf scorch with too much sunlight – shriveling, brown leaf tips. An east-facing site would be ideal in the northern hemisphere, where the tree will get morning sunlight but plenty of cooling in the afternoon and evening.

The morning sun is also ideal for drying the dew from leaves early on in the day, which protects against anthracnose. Protection from anthracnose will also help your dogwood bloom. More on that later.

It’s been said that in cooler regions (such as the more northern parts of the US) flowering dogwoods will do OK in full sun, such as on south-facing sites.

Can fertilizers help?

Cornus florida will bloom better in well-drained soil that’s slightly on the acidic side – pH 6-7. If you have alkaline soil (pH >7), it may be possible to amend the pH using an ericaceous plant feed.

If your tree has never flowered despite being planted in years ago, it certainly could be worth trying some fertilizer to help flower production. The problem with fertilizers in general though is not usually the lack of them – it’s having too much of the wrong type in your soil. For example, many fertilizers (as well as lawn fertilizers, which can seep in) are high in nitrogen, may have been absorbed by the tree. This stimulates leafy growth rather than flower production, and can throw off the natural cycle of the tree’s growth phases, especially if given in spring.

If you’re trying to stimulate blossoming rather than growth, I’d go for one that’s proportionally higher in potassium. These are often marketed specifically for flower production. If possible, use an organic fertilizer designed for flower production. You’ll usually be applying this to the roots no more than twice per year.

Tomato fertilizer is a good example of a high-potassium fertilizer that’s easy to come by.

It’s quite easy to test your pH and your levels of nitrogen, phosphorus and potassium using a soil test kit – I like to use the Rapitest soil testing kit to check my soil. It’s available on Amazon.

Could a lack of water (or too much) prevent flowering?

Have you been through a recent dry spell? Lack of water is actually a common enough reason for flowering dogwood to produce a poor display of bracts.

Flowering dogwoods aren’t great at tolerating dry roots and will soon wither in prolonged dry periods, particularly if the tree is young. When the weather’s dry, it needs a 20-30 minute root-soak once a week.

Could you use a sprinkler? Yes, but I’d recommend a hose. This is because getting the leaves wet can make it more likely to get anthracnose infection – see below.

You can check manually whether the ground’s too dry by pushing your finger about an inch into the soil near the base of the tree. If the soil feels moist and sticks to your finger, you’re good. It it’s dry, give the roots some water.

If your dogwood’s been planted in a marshy spot, it’s not likely to flower well, or to grow well, period. Dogwoods are quite prone to root rot and don’t do well in waterlogged soil. If it’s not too late to move it to a spot that’s a bit dryer in general, do so. Remember, you can always water a tree if the soil’s too dry, but you can’t do the opposite!

Diseases that affect the flowering dogwood

Unfortunately, the flowering dogwood has become well known for its susceptibility to diseases – especially the fungal diseases of dogwood anthracnose and infestation by dogwood borer larvae. This susceptibility (shared also by the Pacific dogwood Cornus nuttallii that grows on the US west coast) has led to a large decline in numbers of flowering dogwoods since the 1970s and led to the popularity of the anthracnose-resistant Kousa dogwood, which has similar flowers.

Have a look at your flowering dogwood. The first thing to check for is brown or tan spots on the leaves. If these can be seen, check for any clusters of leaves that appear to have died off or shriveled. Then look for any round or patchy defects in the bark of the trunk or limbs, which may represent cankers – infected damaged spots.

Anthracnose infections in dogwood trees are caused by the threateningly-named fungus Discula destructiva. They can lead to the demise of the plant if the infected parts aren’t removed as soon as they’re identified. They don’t specifically inhibit flowering, so much as kill individual branches and affect the growth and vigor of the tree.

Here’s a video from Clemson Extension Home & Garden Information Center where James Blake’s showing us a flowering dogwood with the very similar ‘spot’ anthracnose – worth watching, so you’ll know how to spot the disease early.

You’d want to distinguish leaf spots from leaf scorch, which is a browning only at the leaf tips and around their edges due to excessive sun – this will be more prominent on the sun-facing half of the tree.

If you’re seeing leaf spots or dying limbs, I’d recommend consulting a trained arborist for advice on specific spraying recommendations (fungicides for anthracnose, and permethrin insecticide for dogwood borer). You can (and should) prune off infected areas, but you’ve got to disinfect your secateurs between cuts and dispose carefully (by burning or in the trash) of anything that’s removed.

But you can reduce the risk of developing these infections in the first place. If it’s too late to plant a disease-resistant cultivar, try to avoid getting the leaves wet when you’re watering your tree (the infection favours constantly moist foliage), and make sure you don’t damage the bark of the lower trunk with a lawnmower or weed trimmer, which gives an entry point to pathogens.

Summary

I hope you’ve found this article helpful. To summarise the flowering dogwood’s flowering issues:

  1. If you’re reading this in April or May, give it time – it can start as late as June (in the northern hemisphere!)
  2. If your dogwood is young, recently planted and has never blossomed, it might not have matured yet, or may be adjusting to the transplanting, re-establishing its roots
  3. If you pruned it during winter, you may have cut off lots of buds – hopefully better luck next year
  4. If blooms were good last year, it might be taking a year off – due to biennial bearing tendencies
  5. If it’s spending the majority of the time in the shade, or in waterlogged soil, it may never produce many flowers – consider moving it or starting again. Go for a partially-shaded area next time.
  6. If it’s been dry lately, the tree may be parched, which often affects flowering – water weekly through summer
  7. If you see any leaf spots, unfortunately there’s a high risk of anthracnose

If this post was helpful to you, please check out some of my most recent articles!

Image attributions

Plant Image Library from Boston, USA, CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0, via Wikimedia Commons

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

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

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