ivies /Hedera

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Alisdair

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Re: ivies /Hedera
« Reply #30 on: December 13, 2012, 09:58:42 AM »
Trevor Nottle (aka Trevor Australis) has a very appealing effect, mixing different ivy cultivars, which we saw on the October MGS South Australia trip in his garden in the Adelaide Hills:
« Last Edit: December 13, 2012, 10:00:50 AM by Alisdair »
Alisdair Aird
Gardens in SE England (Sussex); also coastal Southern Greece, and (in a very small way) South West France; MGS member (and former president); vice chairman RHS Lily Group, past chairman Cyclamen Society

David Bracey

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Re: ivies /Hedera
« Reply #31 on: December 13, 2012, 11:26:04 AM »
Trevor what is your Blacberry Killer mix?  It used to be 2.4.5.T but I suppose that`s banned.  Interesting that blackberry was one of the first reported plants to be resistant to a herbicide.
MGS member.

 I have gardened in sub-tropical Florida, maritime UK, continental Europe and the Mediterranean basin, France. Of the 4 I have found that the most difficult climate for gardening is the latter.

Trevor Australis

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Re: ivies /Hedera
« Reply #32 on: February 02, 2013, 11:09:53 PM »
Some of you may know that we had the highest temp heatwave ever recorded here a few weeks ago. It reached just over 450C here in the Adelaide Hills and over 470C down in the city. None of our ivies showed any signs of leaf burn despite being fully exposed to the sun but for 'Buttercup' which grows in dappled shade. H. colchica Variegata which has large golden yellow marginal variegations had no damage at all. A bush (adult) form of H. helix with pleasing spatulate leaves also fully exposed did not burn at all even though it gets no irrigation: it grows around and over our letter box on the road verge. tn

M Land. Arch., B. Sp. Ed. Teacher, traveller and usually climate compatible.

Joanna Savage

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Re: ivies /Hedera
« Reply #33 on: November 21, 2017, 06:33:54 AM »
Returning to Ivy, I have some questions, but first the background to them. In this area of steeply sloping ground there are mulberries to be found in areas of abandoned forest. These trees are relics or descendents of relics of a silk industry in Lucca. For six years or so I watched one of these trees being overpowered by Clematis flammula. Finally I could not look at it any more so  in February I cut my way through the undergrowth to the base of the mulberry. I soon found the source of the Clematis, cut it at its base and a couple of weeks later I was pleased to see the Clematis in the mulberry had died off. I will need to check again this winter to be sure it is not trying again.
However I also found a great clump of ivy growing lower down on the mulberry. I sawed into the trunk of the ivy so that it no longer had contact with the soil. Since then, with binoculars I have noted the tallest growth of the ivy has stopped and even wilted, yet it remained green. Now in November it has flowered prolifically and produced black berries.
So the questions are, does ivy actually parasitise the host plant, or does it use it only as a support until it can smother the host? And then there is the vigorous flowering on what appears to be a dying plant. Is it the case that plants have a final fling at setting seed when they are in their death throes?

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MikeHardman

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Re: ivies /Hedera
« Reply #34 on: November 21, 2017, 07:45:28 AM »
Methinks, Joanna, you're going to get various degrees of 'informed opinion' rather than straight fact. Here's mine, FWIW...

It used to be said that ivy kills host trees by strangling them, but then that was made out to be unsubstantiated lore. At the same time it was stated that death occurred by the ivy overpowering its host by weight (especially when wet), perhaps helping bring it down in a storm. But I don't know of any substantiating evidence for that.

AFAIK, ivy is an epiphyte, not a parasite as such, though it obviously competes for nutrients, water and light, and it could harbour harmful pests (or beneficial ones). As such, it may weaken its host through competition.
I suspect most of us have seen tree trunks growing over a constriction or obstruction of one sort or another, eg.  fence wires and rails. Yet I have never seen such overgrowth happening where a tree is encircled with ivy - not even where the ivy forms a complex interlocking mesh of branches. That leads me to presume that ivy does not strangle its host, though exactly how the ivy adjusts to the increasing girth of its host's trunk, I can only hypothesize.

I am not entirely surprised by the panic flowering post-severing of the ivy's trunk.
The ivy may have continued to obtain some moisture from its numerous aerial roots attached to its host's trunk. It may even have put out proper (feeding) roots into litter in bark crevices. And the loss of circulation from the roots may have altered the chemical/hormonal balance, resulting in a promotion of flowering activity. That's similar to how, if one has an apple tree that's producing too much vegetative growth, one can stimulate flowering by partially 'ringing' its bark. ...And slightly less similar to how nipping-out the growing tip of a shoot can promote the development of side-shoots (that happens because the tip contains meristem tissue, which produces auxin and strigolactone hormones, which ordinarily suppress the growth of lateral buds).

Let's see what other folks have to say...

Mike
Mike
Geologist by Uni training, IT consultant, Referee for Viola for Botanical Society of the British Isles, commissioned author and photographer on Viola for RHS (Enc. of Perennials, The Garden, The Plantsman).
I garden near Polis, Cyprus, 100m alt., on marl, but have gardened mainly in S.England

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JTh

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Re: ivies /Hedera
« Reply #35 on: November 21, 2017, 01:48:34 PM »
You ask what other people say, Mike, here is what I found:
From http://herbaria.plants.ox.ac.uk/bol/plants400/Profiles/GH/Hedera:
'Despite popular belief and superficial appearances, Hedera helix is not a parasite. It produces its own food resources via photosynthesis but attaches itself to the stems of trees by adventitious roots. Only when ivy gets very large, making the tree to which it is attached top heavy, is it likely to become a problem.
Ivy flowers during autumn and early winter, and produces fruits into late winter. Consequently, ivy is a very important source of nectar and pollen for late-season insects. It is also an important source of winter food for birds, and a nesting site during the spring.'

and from http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:90723-1

'Ivy is not a parasite, does not normally damage sound buildings or walls, and is rarely a threat to healthy trees. Regular trimming can prevent ivy becoming too heavy, a problem that can be exacerbated by the additional weight of rain and snow.'

Problems due to heavy snow is not normally such a big problem in the Mediterranen region, I suppose. It's wonderful to see the flowering ivy in the autumn when it's full of bees, you can actually smell the honey from far away
Veterinary surgeon by training with a phD in parasitology, worked as virologist since 1992.
Member of the MGS and Branch website editor. Gardening in Oslo and to a limited extent in Halkidiki, Greece.

Joanna Savage

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Re: ivies /Hedera
« Reply #36 on: November 24, 2017, 06:25:12 AM »
Many many thanks to Mike and JTh for their ivy comments. In the particular case here, the ivy has been without roots into the ground for ten months, two of the summer months being the hottest and driest on record. As JTh cites reports that ivy is not parasitic, Mike's idea of ivy being in an epiphytic relation to its host is a good one as the plant is still vigorous and green but not expanding in size.
This winter, when a couple of weeks of frost have tamed the undergrowth I will return to the tree to see if I can find ivy feeding roots on the bark of the tree.
With regard to ivy and snow bringing trees down, there are numerous cases around here in abandoned olive groves where the olives have fallen to the ground but the ivy thrives.