Ron,
For GDD the Colorado site used base 50 (10C). There is a map of base 5C GDD for Canada. Unfortunately we can't extrapolate this out since it inflates the values for coastal regions and lessens it for hot inland areas...
http://atlas.nrcan.gc.ca/site/english/maps/archives/5thedition/environment/climate/mcr4034
This site also hosts a great number of other maps, which aren't really that accurate anymore! They are based on data from 1941-1970 and with urban heat island, climate change, change in precipitation patterns, etc. many of the information presented isn't accurate any longer.

There is a 'rough' way to calculate the average base 50 GDD for your area. Go to Weather underground. Look up the nearest airport (in my case Kingston, ON). Then look at the detailed weather history. Click custom period. Then select a period of a year and check out the GDD.
So for Kington:
Last 12 months: 2075
12 Months before that: 2322
12 Months before that: 2086
12 Months before that: 2567
"": 2495

Taking the average I get a value of 2309. Which tells me that it will take more then 12 full months for a defoliated T. fortunei to regrow a full crown in my climate (if we use the ~3200GDD number).

For fun, some other cities GDD for the previous 12 months, focus on areas where board members live. You can, sort of, see the trends this year. Hot west coast, cool Ontario, Interior of B.C. near average, and East Coast cooler then normal:

Vancouver (Very Hot Summer this year, lots of record heat!): 1772
Victoria: 1511
Kamloops: 2594 (I thought it would be more...)
Edmonton: 821 (Wow...)
Windsor, ON: 2891 (Thought this would be less given the cool summer this year)
Toronto: 2074 (wow. Much lower then I expected given the numbers from Windsor!)
Halifax: 1672 (Not much of a summer this year)

Paul, that's awesome and I'll check it out.

I was using the weather winner website and feeling a bit blue but your method may just make me happier.

Off to look.

Thanks for the info as always Paul! I'm going to look into it also for curiosity.

Bill

Paul,interesting info.I would have never thought the numbers would be so low in some of the areas you showed.

I think here in Fairfield Iowa we avg 3600,this formula( I believe) was developed for corn crops and runs during the "frost free" period from Aril 1-Nov 1
I think the highest I have seen in my area is 3800,lowest 3400
I was looking at the gdd for Washingtonia and it is actually 5600! according to GPICS USDA 5B
You can increase the gdd for your palms by planting in a micro climate,improving your micro climate,(like putting down black rock or mulch or by protecting from wind)my cactus bed avgs 10-15F higher then air temp on sunny days the less wind/more sun -the higher the temp gets.

I think the whole point here is to keep your palms leaves as healthy as possible over winter so they don't spend all their energy regrowing their mass,esp in areas with low GDD.

One other point is that GDD numbers once palms have stopped growing do not make any immediate difference during winter.
I have not seen any growth out of my palms during winter when soil temps drop below 50F,maybe this will change when they are well established. In the site from Co Springs they said their palms grew 1 new spear and leaf Nov-April-I have not seen this.

Here's another site to look it up. Not sure if it dose Canada.

http://climate.fizber.com/massachusetts-city-attleboro-climate.html

Bill

One other point is that GDD numbers once palms have stopped growing do not make any immediate difference during winter.
I have not seen any growth out of my palms during winter when soil temps drop below 50F,maybe this will change when they are well established. In the site from Co Springs they said their palms grew 1 new spear and leaf Nov-April-I have not seen this.

This point has been debated on the other board as well. I think it was Dr. Allen Hirsh who thought that palms (Trachycarpus in particular) could enter into a dormancy period, where most (all?) others thought that this was impossible... To my mind I think that palms can never enter a true dormancy period, rather, I think they just slow their growth rates so much that only by comparing the fall foliage and the spring foliage can we see that growth has occured at all. In terms of GDD you're probably right that we should only really count from April 1 to December 1 since even warm temps outside this period aren't likely to produce much, if any, extra growth.

5600 GDD seems awfully high for recovery to growth in Washingtonia (increase in size after defoliation).

Bill- Neat site, but no it doesn't cover Canada!

Paul-

I agree totally agree with you about GDD for Wasingtonia,I checked the site again and saw 5000 GDD,maybe next time I look it will be 4400.

I think it's important for people not familiar with the whole GDD thing to remember that the figures on this site are for regrowing mass after the palms lost ALL their leaves and replenishing stored carbs.This would not be a factor if you keep your palms leaves healthy over winter-

Washys-
We have had such cool summers the last 2 years that Washys have not done much 😥

I also think that the whole dormancy thing is a little vague,it depends on how you define it ,my palms did grow over the winter but very slowly,the spear may have grown an inch or two in 5-6 months,thats hard to see over that long of a period-especially when your as impatient as me 😯

Maybe if we have a mild winter like we did in 2006-2007 they would really grow.
I really don't see that happening here after the coldest July on record,we usually have 12 or so days 90+ in July this year we had 0! and only 2 in Aug ! Thats amazing when you consider the avg July high is 88F ! We averaged only 80F

The early summer was tough for most of us this year for sure. I'm thinking I need to atleast try to save some of the leaves on my washys this winter. I makes it tough building ten foot boxes oh well it is what it is. I might put one of those boat socks in the incloser to reduce moisture. That GDD site I found had my area at 3040 so I'm way off. The thing is though if where heating are palms the number whould change big time for the better. With a bit of luck will have a easy winter and a hot summer, it dosen't hurt to be optimistic!

Bill

I think it(heating) only effects things for the better if you are keeping temps above 50F.Then you could create some GDD during the winter-however.........
The other thing is ground temps,if it drops below 50F your palms will probably not grow anyway.

I think it's a sound idea to save some leaves,palms can deplete themselves trying to recover each year as they have to use some of their stored food to do this,you can see how a few years of this would wear them out.

I think it's important to get our own results but apply all the info thats out there for best results,you may find a loophole 😉

Jim, my washy put out one frond during the winter last year. It didn't look like it grew visually, but when I compared pictures it grew. Take a look.

Before boxing it up:

After taking protection off:

You can see the closed up frond which opened. Here it is today. I know it doesn't look like it added any fronds this year, but remember I clipped last years off in June. This year my box will have extra insulation on to help prevent contact burn with plastic. The new fronds are 36" wide now!

I kept all last years fronds until the last week of June. Then I clipped them off because it had already regrown three and last years were half brown and ugly. But I truly believe they helped jumpstart the palm in the spring! My washingtonia that I overwintered in the backyard that defoliated last year only regrew four fronds this year so far! So you are right, you NEED to keep the fronds for a jumpstart in spring.

I also keep my winter boxes between 35F and 75F. I let them get warm during the day as I believe that helps warm the ground and roots under the box.

My Fortunei did the same thing as your Washy,it had a leaf that was partially opened and it opened more over the winter,at least thats what it looked like from your pic.
You did a really nice job protecting last winter,if we had as warm of summers as we usually do,I think the Washys would have done better 🙂
One thing you could also do is add a foot of mulch around your box.I did not allow enough space nor did I mulch enough so I lost mine,I am trying another and leaving the,ahem,leaves on this time.I will use sytrofoam this time to cut down the amount of watts I need to heat it,also to protect the leaves.
If you add another layer of plastic watch the temps carefully.I tried that during an Arctic outbreak on one of my Trachys,the temp was 0F outside and went up 80F! I would hate to see what would happen on a sunny day around freezing.
Oh,the other reason I bring up the mulch is that I noticed you had a LOT of snow last winter insulating the palm enclosures,if that doesn't happen again soil temps could plummet.

wxman,
One thing you might try in spring is switching out the white rocks to something darker of you preference. I'm not saying it looks bad but I'm sure your ground temps don't warm up as fast as if you had a dark mulch. That would sure help them get going faster too. I know in Fla. they put the white rocks down to cool the soil temps. imagine if we had that problem. Nice job this year.

Bill

I also thought this would be a great idea,black mulch is a cheap way to go,I think better for helping air temps right around palm.Mulch in general lowers ground temps and should be peeled back in late winter/early spring.I think the black rock does help keep ground temps up,(IME)I had a couple pieces of slate over the ground around under my Mazari,it was warmer by a few degrees every time I checked.I hope I can get one of these through the winter one of these times!

Oops,in regard to mulch- I meant to say it slows warming in spring but it does help soil retain warmth in fall and insulates in winter
Da?

Where do you find GDD for palms?

If you want to e-mail me,I can try and send you the link to the site.
The GDD(on this site) is an estimate given for palms they tested,it also was used to approximate warmth needed during growing season April-Oct,for palms to regrow once defoliated and regain all lost mass.

jimpdelaney@yahoo.com