Washingtonia robusta hardiness rating (Unprotected)

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Dave Brown
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Washingtonia robusta hardiness rating (Unprotected)

Post by Dave Brown » Sun Jul 10, 2011 10:18 am

As this is one of the most common questions due DIY Sheds selling them, and sometimes labelled as 'Hardy', I have put this information in a dedicated topic. The info below has been written in reply to previous topics but is not easy to find.

Obviously each person's experience will be different, but at the time of writing in early 2009, the consensus of experienced palms growers was that the figures were about right. Also this was written before the run of harsh winters started, and where as some of us had Washingtonia growing unprotected, in recent winters some form of protection IS required to get even mature palms through. There are exceptions ie Southsea on Portsea Island, but but these are rare, and we have to regards Washingtonia robusta as Half Hardy. Washingtonia filifera, on paper, can take colder conditions than robusta, but it requires a dry climate, which we find difficult to provide.


Washingtonia robusta hardiness rating in UK - Spring 2009
Exotic gardening for many plants is still in it's infancy, so what we all did 10 years ago is probably different to what we would do now. It is amazing how new information can totally supercede what we were doing before. The basjoo protection in that page I learned from Angus White of Architectural Plants back in the early 1990s and was based around the -19C temps they got at the Nuthurst Nursery in Feb 1991.

I have edited my webpages a couple of times in the 5 years since the information was written, as it does change. You look at a page for the first time in a couple of years, and think OMG did I write that :shock: followed by a hasty rewrite :roll:

Ok I've been growing Washingtonia from seed since the late 1970s, and lost my first batch of 5/6 year old palms, that were planted out, in the winter of 1984, so since then have grown them as a pot/tub plants until they got too big to house. Only then did I try them outside again.

My experience is noted as a 'plant label tags' is below. This is my attempt to show that hardiness improves with trunk size, and will hopefully deter people planting out seedlings that stand no chance of withstanding even a mild UK winter. There are numerous variables that can affect hardiness, the biggest being the duration of the cold. I do not expect even mature trunk size Washies to survive more than 2 or 3 days of freeze. Palm health will also play a big part. Damaged or unhealthy palms are less likely to take cold. Some may dispute the small seedling leaf hardiness figures and indeed the leaves can be tough, but even if they do not show frost damage they are not much good if the palm has been killed :roll:

I expect some debate over these figures, they are just my interpretation of Washingtonia robusta hardiness. :wink:

mature trunk diameter greater than 25cm
Leaves above -3C icon_thumleft
Leaves -3C to-5C :|
Leaves below -5C icon_thumbdown
Palm above -5C icon_thumright
Palm -5C to -8C :|
Palm below -8C icon_thumbdown

Juvenile trunk diameter 15 - 25cm
Leaves above -3C icon_thumleft
Leaves -3C to-5C :|
Leaves below -5C icon_thumbdown
Palm above -3C icon_thumright
Palm -3C to -6C :|
Palm below -6C icon_thumbdown

Large seedling - trunk diameter 10 -15cm
Leaves above -2C icon_thumleft
Leaves -2C to-4C :(
Leaves below -4C icon_thumbdown
Palm above -2C icon_thumright
Palm -2C to -5C :(
Palm below -5C icon_thumbdown

Seedling - trunk diameter 5 - 10cm
Leaves above -0C icon_thumleft
Leaves -0C to -3C :(
Leaves below -3C icon_thumbdown
Palm above -0C icon_thumright
Palm -0C to -3C :(
Palm below -3C icon_thumbdown

Small Seedling - trunk diameter Under 5cm
Leaves above +2C icon_thumleft
Leaves +2C to -1C :(
Leaves below -1C icon_thumbdown
Palm above +2C icon_thumright
Palm +2C to -1C :(
Palm below -1C icon_thumbdown

All trunk sizes
Winter Dry icon_thumright
Winter Wet icon_thumbdown
Shelter icon_thumleft
Exposed icon_thumbdown
Good air flow icon_thumleft
Wapped icon_thumbdown

As said in the forewood, in recent winters have been more harsh, so for most of us som form of protection will be required. For me in winter 20010/11 (December) I had -10C and with 33cm of snow. The protection I gave was a plastic covered parasol to keep snow and radiation frost out of the crown, together with 200w of rope lights when temps dipped below freezing.

PLEASE NOTE this is a mature trunk palm and seedling/juvenile would need supstantially more protection, but they hate being wrapped as this allows fungal infection and rot :roll:


Please only reply to this on the hardiness discussion, and start other topics on protection
Attachments
2010-12-01 08-39-28 Washie in the snow.jpg
Best regards
Dave
icon_thumright
_________________________________________________
Roll on summer.....
http://www.hardytropicals.co.uk

patrykgiel

Re: Washingtonia robusta hardiness rating (Unprotected)

Post by patrykgiel » Mon Oct 17, 2011 4:21 pm

Hi Dave Brown, I'm from Poland. Can I use your photos of Washingtonia in our Polish palm forum ??
Please

Alexander

Re: Washingtonia robusta hardiness rating (Unprotected)

Post by Alexander » Mon Feb 13, 2012 12:09 am

Dave,

How is that Washingtonia doing now by the way? I hope it did not suffer to much from last winter!

Alexander

jimhardy

Re: Washingtonia robusta hardiness rating (Unprotected)

Post by jimhardy » Sat Mar 03, 2012 5:43 pm

Those numbers look famailiar Dave.


:D


Totally agree about leaf hardiness......

Once it gets below 23F here they are in danger,
19F pretty much wasted them last year
,it was only supposed to get down to 25F :(


This is well applied on days that warm right back up in
full sunshine,don't even want to think about what would
happen to the plant if it didn't warm up!


Although last year we had a very dry summer/fall and I saw
temps down to 25F with no frost because the air was so dry.
Amazing what can survive when frost does not act as catalyst....
speeding freezing of the leaves.

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Dave Brown
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Joined: Sun Jul 09, 2006 10:17 am
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Re: Washingtonia robusta hardiness rating (Unprotected)

Post by Dave Brown » Sat Mar 03, 2012 9:03 pm

Some interesting things to consider there Jim icon_scratch icon_scratch I know musa basjoo leaves survive -4C (27F) without damage under cover where frost did not form, so super dry, freezing air, may not cause damage in the way damp freezing air might.
Best regards
Dave
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_________________________________________________
Roll on summer.....
http://www.hardytropicals.co.uk

Andy P

Re: Washingtonia robusta hardiness rating (Unprotected)

Post by Andy P » Sat Mar 03, 2012 10:57 pm

Would be very interesting to see an equally and accurate list of Washingtonia survival temps only with a simple rain cover in the equation. Seems to make a great difference.

derrick

Re: Washingtonia robusta hardiness rating (Unprotected)

Post by derrick » Sun Nov 04, 2012 5:08 pm

Im thinking how to protect mine this year i have a timber frame some tarapaulin some sand bags they dont like being water logged and need ventilation some type of shelter i can remove

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