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Last updated 14/05/20 10:00.
Cold weather damage to evergreen plants
What do with cold weather damage
The extraordinary cold weather and windchill from prolonged East winds in March 2018 has caused devastation to some of the more tender evergreen trees and shrubs especially from the southern hemisphere. The Garden Diary has much photographic evidence of leaves being stripped from laurel hedges and other evergreen camellias, michelias and some rhododendrons here. The more lasting damage to evergreen plants will, sadly, only become apparent in the coming weeks.
Certain evergreens are already looking pretty sad. Daphne bholua varieties had blackened and dropping leaves well before the snows melted. Euphorbia mellifera has complete leaf drop and the echiums have been reduced to blackened stems. All over Cornwall Drimys winteri already has drooping and scorched leaves.
What is far worse however is the lasting damage to other evergreen trees and shrubs which appeared to have survived the cold intact. Two to three weeks after the first cold spell all the New Zealand Hoherias have dropped all their leaves here and the variegated forms of Hoheria are now only just starting their own full leaf drop. Those evergreens which had rising sap in the stems and twigs which were putting on early spring growth are especially vulnerable to delayed action leaf drop and dieback from the top of their branches.
So the first rule is to WAIT for 4-6 weeks from after the snow has gone before taking any remedial action on damaged plants. Gardeners need to remember that most evergreens shed their old leaves anyway in May or June which is not that far away.
THEN the guidelines to adopt are as follows:
1. Those evergreens which have been totally or partially defoliated BUT which show new leaf shoots from the tips of the twigs need no pruning or cutting back. After 2 or 3 weeks of fine and mild weather what is left of spring will see apparently stricken plants bursting into new growth.
In this category here I expect to include all the Escallonia varieties and especially Escallonia iveyi which currently hasn’t a dingle old leaf left here. The same will apply to other tough evergreen hedging plants such as all forms of privet (ligustrum), hollies (ilex) and hedging lonicera which may have blackened leaves after snow.
Also in this category SO FAR I would put all the defoliated or partially defoliated (perhaps on only one side of the tree) Michelias, Manglietias and Crinodendrons. We know from experience that they are tough and resilient enough to withstand heavy defoliation and still produce good new growth without any die back
2. Those evergreen shrubs which already had more serious leaf drop or completely browned leaves WILL need a degree of pruning. You will however not be able to tell how far back the dieback goes for 4-6 weeks. Scratch the stem or trunk of the plant then to see how far down you have to go to find green rather than brown stems below the bark. Often you may see a new side shoot from the stem 3 – 4 or even 6 feet down from the top of the plant. Cut the branches or twigs back to just below where the steam turns from brown to live green preferably where a new vigorous side shoot is appearing.
In this category here I would put many hydrangeas which had already come into full bud and leaf rather too early this year. Photinia ‘Red Robin’ and other Photinia species have what looks at present to be 2-3 feet of die back but it may well turn out to be more than this.
Fuchsias, especially the hedging varieties and those not already cut back last autumn, will have substantial die back. Some were in leaf before the cold. Serious pruning, probably to near ground level, may well be the only option. The same applies to Romneya coulteri.
Daphne bholua varieties may very well be dead or dead at least down to the level of snow cover. This won’t be clear for a while yet either.
3. The position with regard to taller growing evergreen trees which have defoliated AFTER the cold has passed is more difficult to determine yet. The leaf fall well after their severe shock may not preclude new leaves appearing in due course on some or all of the branches or twigs. If this does not occur in 6-8 weeks then, again look for side shoots of new growth starting to appear then you will need to ‘hatstand’ your tree down to say 6-10 feet on all its main branches. Given a few years and more milder winters it may recover and grow away again perfectly well.
4. Many more tender herbaceous plants which are currently both blackened and dispirited may well indeed be dead. The Salvias which have survived our recent mild winters are a case in point and you will have to start again. In the West Country we have become used to Argyranthemums and Osteospermums surviving from year to year. Not this year! However black your Echiums may look today those biennials which have had a year’s growth, and which were due to flower this year, may well still be capable of doing so if they still have a few green leaves on the crown. The flowers may not be huge. First year Echium seedlings will be dead but plenty more will germinate this summer where the seedlings have died. So don’t rip out any Echium which has an green on it just yet.
As with every gardening disaster the precise nature of any casualties is never quite the same after seriously cold spells. Some pleasant surprises may accompany some unexpected losses. Plant location and shelter from the wind can make a huge difference to plants which are only a few feet apart.
Every damaged species needs to be reviewed over the coming weeks and perhaps treated differently. Don’t rush in too soon to prune with undue pessimism because plants can be more resilient then one often thinks. Conversely die back and pruning do need to take place in a timely manner or living plants may subsequently die.
If you are in any doubt about how to deal with a potential cold casualty please do send us some pictures and we will try to help and advise you on how to tackle the problem. In the meantime I will try to photograph how we tackle our problems here in my Garden Diary as the weeks progress.
It is never as bad as it first seems!