Tuesday, 22 December 2015

A plantsman's plant

Peter Williams tells how he learned to grow Cornus canadensis - Dwarf dogwood

I first tried to grow this plant about 25 years ago when I ran a small, part-time nursery specialising in acid loving plants. I bought stock of Cornus canadensis on a number of occasions and each time I potted about three-quarters for sale and planted out the remainder. None ever seemed to do well. The potted plants sulked in the compost I used for rhododendrons and other acid lovers, and those planted out into what I thought were ideal soil conditions, all disappeared.  I gave up on the species.
About 10 years after my last attempted introduction, I was lying flat on my stomach trying to get at the base of a weed that was growing through a large and very dense rhododendron, when I saw a tiny rosette of Cornus canadensis.  It was so shaded under the rhododendron that it was almost dark and the soil was very dry. I eased the tiny specimen out of the soil and planted it in a very shady spot at the edge of north-facing woodland bed. I had little expectation of it doing well but the plant had clearly ‘learned its lesson’ and grew away rapidly.  In the first full growing season in its new location shoots appeared all around the plant and a few flowers were produced. Eight or nine years later, it now covers about 20 square metres and flowers profusely in June and July.  It is even invading the edge of the lawn! I now dig out ‘chunks’ in early spring for friends and sell vigorous potted specimens at our charity open-garden days. I do not know why this plant was so temperamental for so long and then flourished. 
As its name indicates, this species’ home is North America, Canada, Siberia and southern Greenland where conditions are cool and wet and soils are base-poor and acid, very similar to my own soil. Its’ natural habitat is usually montane dwarf shrub communities but it is also known to invade montane grassland and is obviously quite a vigorous spreader when ‘playing at home’ because it is a weed of lowland blueberry crops where the fields are recently cleared woodland.  

Interestingly, it has a close relative that occurs in similar locations to C.canadensis but which extend to Europe and even moorland areas of the UK.  This is C. suecica the Dwarf Cornel and it is of very similar appearance to C. canadensis.  North Yorkshire marks the southern edge of its distribution in England and I have seen it growing in Hole of Horcum on the North York Moors.  Where the two species grow together hybridization is possible and the resultant hybrids are said to have intermediate characteristics.
The common name for this species in North America is the Bunchberry because of the bright red fruits produced each autumn that are used for pies and jellies. My clone has never produced fruit suggesting that it is not self pollinating, but it does have good autumn colours before it is totally covered by leaf fall in autumn.
The flowers of this Dogwood are typical of the family – the true flowers are surrounded by coloured bracts that look petal-like.  Incidentally, the common name Dogwood comes from a corruption of the French word dague meaning dagger because the stems of the larger Dogwoods were used for skewers.
The flowers have one very special feature – they open explosively to release their pollen when touched by a large insect.  This can be seen in a fascinating video sequence recorded at 10,000 frames per second.
A picture is as good as a thousand words. This video when taken had ten thousand pictures – and is very quick

The advantage of having such explosive release is that it reduces pollen predation and increases the chances of the pollen becoming attached to the hairs of pollinating insects.  It also helps in wind pollination of adjacent female flowers.
So why did this species fail for so many years in my garden and by report, those of many other shady gardeners?  Some studies in North America suggest that it cannot tolerate mean summer temperatures higher than about 18 0C, so perhaps it needed fairly dense shade to prevent thermal damage. Another possible suggestion is that it was attacked by vine weevil – but I was not aware of this happening in the areas of my garden where it failed, and I never found vine weevil larvae in the compost of the potted plants. My planting advice would therefore be to get the plant established in a very shady area where it gets no direct sunlight. If it becomes established it may well be able to spread out of the shade and become far more light tolerant.


Described as an herbaceous sub-shrub even at Christmas it is still a beautiful ground cover
The lush growth of this species in my garden might now become its downfall.  In North America it is eaten by deer and moose and we are having increasing trouble with Roe deer grazing!  
Peter’s deer lemma according to Roger
Peter swears this was taken before he constructed his fence

When I first met Pete he was spending a long time and a small fortune rabbit-proofing his garden in the hope that his only problem would then be the moles. It sounds from the above that he probably laid on his tummy! He has previously told the story of how some years later he found a rabbit highway marked in the snow under his entrance gate! Now it is the turn of the deer who can easily jump over.
Just like in my post last Christmas Po Simpson with his photographic magic comes into the story. Last summer some of Peter’s prize rhododendrons were eaten. It was almost certainly deer. Po set up his night camera. 
Here is the evidence

There is no hope for this girdled stem
You will now understand Peter’s feelings when he recently learned that deer love to graze on Cornus canadensis.
By the way it has never grown for me either. Peter, if you can forgive my mirth at the thought of you lying horizontally pulling out weeds will you give me some pieces?
Is there any hope?

Three years ago this  sorbus in my garden was severely damaged by a deer just as badly as the above picture

Peter's Christmas pictures I asked Pete to go out into his garden to take seasonal pictures on 20th December





Prosthechea vitelina orchid growing in the heated greenhouse



Growing through a natural leaf mulch

8 comments:

  1. We are fortunate not to have deer or rabbits in the garden,only badgers and cats!
    Merry Christmas.

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    1. I think I would settle for the rabbits!
      Merry Christmas to you and all readers

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  2. C. canadensis is a lovely plant but I don't even try to grow it because of our alkaline soil. When we were hiking in Quebec back in September it was very common in the woods and along trails. In this part of the world we call it "bunchberry".

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    Replies
    1. Very sensible Jason. Even with a highly suitable acid soil it took Peter years to discover the secret - to grow in a cool shaded place

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  3. Although I have been aware of it I have never tried Cornus canadensis maybe one for me, I will have to try it. I have to admire a man who weeds under shrubs on his stomach, that's what I call dedication, I would have trouble getting back up again! The fact that the Cornus was found under a Rhododendron raises further questions on the allelopathy of Rhododendrons or is the Cornus resistant? As a Meconopsis lover my favourite picture is of the over-wintering rosette, just one of the excellent attributes many of the species display.

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  4. I think it is further evidence that Rhododendron is not allelopathic Rick. I remember you made a helpful comment on our previous discussion on that specific post.

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  5. The squirrels are the bane of my life, I keep telling myself that what they eat and destroy is just a fraction of what I have in my garden and I just have to accept it – but I still get upset when I come out and see pots of crocuses and fritillaria, totally raided! I am glad I don’t have to battle deer and rabbits, but I have some experience with moose from Norway, they used to come into my garden and eat the new shoots on bushes and trees in the spring and my strawberries in the summer. Scandinavian moose are even bigger than police horses….not an animal you go and shoo away!

    Loved the exploding Bunchberry video, I wish I had equipment to make something similar – spectacular!

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    Replies
    1. I won't tell Peter about the moose, it would give him nightmares.
      I am afraid the bunchberry film is not mine, I would credit the author if I knew the videos provenance
      The deer is Po's work of course! It's a brilliant picture of the Christmas moon done on his digiscope on the next post up

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