Washingtonia robusta hardiness from seedling to mature

[Dave Brown]

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 followed by a hasty rewrite

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 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 thay are not much good if the palm has been killed

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

mature trunk diameter greater than 25cm
Leaves above -3C
Leaves -3C to-5C
Leaves below -5C
Palm above -5C
Palm -5C to -8C
Palm below -8C

Juvenile trunk diameter 15 - 25cm
Leaves above -3C
Leaves -3C to-5C
Leaves below -5C
Palm above -3C
Palm -3C to -6C
Palm below -6C

Large seedling - trunk diameter 10 -15cm
Leaves above -2C
Leaves -2C to-4C
Leaves below -4C
Palm above -2C
Palm -2C to -5C
Palm below -5C

Seedling - trunk diameter 5 - 10cm
Leaves above -0C
Leaves -0C to -3C
Leaves below -3C
Palm above -0C
Palm -0C to -3C
Palm below -3C

Small Seedling - trunk diameter Under 5cm
Leaves above +2C
Leaves +2C to -1C
Leaves below -1C
Palm above +2C
Palm +2C to -1C
Palm below -1C

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

[Yorkshire Kris]

Only thing I disagree with is wrapped. As I think they can survive perfectly well if wrapped up with horticultural fleece even when small. I know that there is a chance or rot setting in but this is limited if kept dry. I kept a small B&Q multi trunked in a tub wrapped in fleece for two years outside. Last winter it stayed in the garage rather than outside which is just as well. Even if fleeced it wouldn't have survived last December.

[Dave Brown]

That is not the experience of most experienced palm growers, including me, and the most common form of protection given is open sided rain shelters to keep as dry as possible. Cold and damp which is what fleece gets, is a real killer of palms that like plenty of airflow.

[Yorkshire Kris]

I was going to experiment with treating a washy like musa basjoo and wrap up in winter with straw and keep the rain off. I'm guessing this would be a bad idea as it would restrict airflow and would inevitably get a bit damp.

[MikeC]

Better to provide top cover only to reduce radiation frosts and keep the palm dry in winter.

I'm thinking of one of those builders bulk bags with four wooden poles in the ground over the top of the plam during winter?




Or make a sort of free standing roof with this and some wooden frame.

http://www.wickes.co.uk/twin-wall-polyc ... urce=123_4

Then is spring, take it apart and store it all in shed.

[The Codfather]

Good idea.....and it can slide over the top of the frame....

[Yorkshire Kris]

OR...

put four fence post metal base things in the ground. When it comes to winter put the four fence posts in the bases and attach a polycarbonate sheet on the top? In spring remove the posts and the bases and be hidden with foliage etc

[MikeC]

OR...

put four fence post metal base things in the ground. When it comes to winter put the four fence posts in the bases and attach a polycarbonate sheet on the top? In spring remove the posts and the bases and be hidden with foliage etc

That's the sort of thing.

As the palm gets bigger it all gets a bit more difficult mind.

Looking online I can see 3m long wooden fence posts, so there's a fair bit of scope there!

http://www.buyfencingdirect.co.uk/post- ... 0-x-3000mm

I'd probably leave the post mounts in the ground



And plant four small groups of ground cover bushes next to them, like hebe or something.

[Mr List]

are you trying to keep the ground dry aswell as the palm or just the actual palm above ground?

[Yorkshire Kris]

Yes leave the mounts in the ground and cover with plants or up-turned plant pots maybe?

[MikeC]

I've got this cunning plan now for a raised bed for each large palm (extra free draining soil in the raised bed), and a fence post holder at each corner. Then a polycarbonate "roof" than sits on top that can be taken apart with clips or bolts.

Put this over the palm from later October through to end of March should see the worst of the weather off.

[Yorkshire Kris]

This is what I've been intending to do with my palms WHEN they get planted in the ground. I've come up with many ideas that I have yet to put in action yet because I've been able to stick stuff in my garage but when I get plants in the ground I'll put my plans into action.

[eddie]

I've made a sort of greenhouse around it. Four wooden poles in the ground with some crossmembers and cover the structure with plastic stapled to the wood. A light string around the palm to provide frost protection. The leaves I strap together with a soft string. This method worked for me the last three years.

It's kind off stormproof, I only need to staple the plastic back to the wood from time to time in winter.

Looks like my Washi's have an internal alarm clock, growth starts the first week of march regardless the temperature. Last year it was still cold and yet growth started the first week of march

I've got minimal frost damage this year

[Dave Brown]

mmm.... sort of gone badly off topic here.

Person 1 - "Washingtonia, is it hardy"

Person 2 - "Well stick for posts in the ground........."

Person 1 - "but is it hardy"

[Palmpje]

Thank you Dave, this is really good usable information.