Winter Exposure of Troughs

[cohan]

This topic was spit from the Alpine Shows and Events 2012.  It deserves its own thread.
--- Moderator

Trond, there is cold winter weather, and then there is cold winter weather In the middle of our coldest weather (mine is a little worse than Lori's, on average) its hard to believe that any plant or animal can survive!  But I think the question here is not about cold alone, but about exposure-- for example, plants that are hardy here can still not usually be left in pots on the surface of the soil over winter, though okay if sunk.. so, does a trough with plantings that extend high above the soil behave like a rock garden (connected to the soil, and so hopefully safe..) or would it be too small and isolated like a pot?
I wouldn't try anything valuable in that sort of planting unless I had extras  

[Hoy]

Cohan, I know you winters are more sever than mine! However, in the mountains the winters can be rather harsh!
We often divide the plants in two groups - the "snowbed plants" that prefere to grow in depressions usually covered by more or less snow during the winter; and "ridge plants" that prefere to grow on ridges etc fully exposed to the weather! I believe that plants from the latter group should tolerate planting in a "minimountain"  Many Saxes belong to this group, and if you like Lori, grow your plants from seed you should have some in surplus to experiment with!

[Tim Ingram]

I wonder how gardeners in places like Denver get on with many of these plants? It sounds as though snow cover can be erratic over winter and temperatures very much lower than we get. As a gardener I foolishly try to grow a huge range of plants and get away with it to an extent because of our relatively equable climate. But it is a salutary lesson when I hear of gardens elsewhere dropping to -40°C in winter! On the whole though plants are much tougher than we probably give them credit, and its good to experiment like Trond says. We actually have the opposite problem of being too mild and so all the best alpine gardens tend to be up north.

[RickR]

On the whole though plants are much tougher than we probably give them credit,

So true!  Even the root hardiness has exceeded well beyond my expectations.  Every year, my potted materials sit in the garage for a period just before they get put to bed outside for the winter.  This is the time while I wait for the ground to get sufficiently frozen to hold my materials frozen through the winter without multiple freeze/thaw cycles.  During this time, there is always at least a few nights down to 0F (-18C) outside, often even less. The garage affords a 10F (5C) moderation in temperature.  Even so, with the few winter potted plant deaths (perhaps 1%) I observe in the spring, I can't be sure that those cold temperatures were the cause.

What I can be sure of is that plants in general (and even their roots) are a lot more cold hardy then normally reported!  (Obviously, many of us have already figured that out.)

This winter, it has been so ridiculously warm that the ground never got cold enough (in my opinion) until mid January.  By then I thought, what would be the point of outside storage.  So they have been in the garage all winter for the first time, and have dried out way more than a usual winter, but with more freeze/thaw cycles.  It will be interesting to compare with my normal overwintering procedure, and see how this affects ensuing growth and survival.

This past weekend for a three day inside event at our arboretum, I brought some relatively good looking alpine plants from my overwintering collection to show.   The lewisia, antennaria, echinocereus, sempervivum, draba, orostachys, iris, saxifrage, sedum, penstemon and pulsatilla all show perky signs of growth and unscathed health.

[cohan]

Trond and Rick- I agree many different factors to hardiness depending on the kind of plant, where it comes from and what it has adapted to in the past..
I remember Lori mentioning to me, for example, that she usually does not mulch, and found when she had done so she sometimes ended up with rotted plants.. While there are presumably some other kinds of plants will survive cold better if they are covered by snow or mulch (eg, marginally hardy woodies that routinely freeze back to snow or mulch level)..
I expect, in my generally snowier winter than Lori's, that some dryland plants will have an issue here with wet conditions under the snow in spring (now, there is a foot to several feet of snow around, which will take many weeks to melt, during which time I expect the soil surface in many areas will be wet and icy)-- time will tell! I am thinking that one strategy I will use is strongly sloped plantings to let moisture run away to a greater extent; draining soil is of little advantage during the many months that the ground is frozen and no moisture can penetrate!

[Spiegel]

Cohan, I think the general rule is that troughs that spend the winter outside should be considered at least 1 zone colder.  Unless you have a trough with tremendously thick walls the roots are exposed far more than when planted and when they have the protection of a lot of soil.  I've lost plants in troughs that sail through winters when planted in the garden.  Since my troughs are integrated throughout the garden, it stand to reason that it's the trough environment itself that's suspect.  I've thought of wrapping them in insulation but haven't tried it yet.  As it is the garden looks awful in the winter, draped as it is with chicken wire over everything to stop the antlered rats from browsing.

[cohan]

Sorry Tim-- this whole conversation should have been somewhere else!
I think I've seen that guideline before, Anne- of course here, there are only so many zones lower you can find plants
I have a large pot- 14x14 inches which I had several Sempervivums (hardy here) and a couple of other things in.. I thought that size might be safe enough, but lost all but one Semp, even though the whole thing was buried in snow for almost the whole winter; since then, I've made sure the pot was in contact with the soil directly (it was on boards at first, and soil contact is supposed to be important) and piled sod around it for winter, and new plantings in it have been fine for a couple of years.. I may try it exposed again once I have the S ciliosum, which survived the first year, backed up elsewhere...

All other pots I have outside are sunk to the rims in soil for winter....

[RickR]

We have a member here that has more than a dozen troughs of hypertufa and of styrofoam.  He says he has better winter survival in the styrofoam ones.  That's not surprising, given the insulating qualities inherent with the styro troughs.

[Spiegel]

Some of my troughs are half-buried in the garden and that has provided a lot of insulation.  I go to great lengths to insure that nothing
can get into the troughs through the drainage holes.  Even the ones sitting on stone or blocks are close enough to the ground that it's possible to heap gravel around the base of the trough.  We get a lot of wind here and it keeps the wind from lowering the temperature of the base of the trough even more.

[Hoy]

We have a member here that has more than a dozen troughs of hypertufa and of styrofoam.  He says he has better winter survival in the styrofoam ones.  That's not surprising, given the insulating qualities inherent with the styro troughs.

But don't they freeze from the top? And take longer time to thaw?

[Spiegel]

I have open-ended trough covers on the ones that need it or can't stand winter wet.

[RickR]

But don't they freeze from the top? And take longer time to thaw?

I would imagine, yes.  But that would be a good thing.  In this climate we can only grow things that like a deep freeze.  The point is that the styrofoam moderates the temperature swings, compare to hypertufa: less freeze/thaw cycles and slower warm ups and cool downs.

[Spiegel]

I've found that hypertufa troughs start breaking up in my climate after a few years.  I have a couple of troughs that are pure cement and they're fine.  They've been finished in a way that's aesthetic.  The styrofoam troughs are marvelous in this garden and any future troughs will certainly be styrofoam.  They are also moveable, at least the ones of small and medium size.
Rick, I agree with you about deep freeze.  The worst damage seems to be extreme fluctuations in temperatures (such as recently here).
We are setting records for high temperatures and the plants are not happy.

[Todd Boland]

I have about a dozen troughs...all hypertufa...so far not a hitch in regards to breakage (and they are over 10 years old now).  I get far less heaving of plants in the troughs than in the open garden.  Generally I have little die off in the troughs and some plants do far better in the troughs like Kabschia saxifrages, while other do far better in the open garden like gentians.  Normally I get enough snow to insulate them but two have been exposed much of the winter and I will admit the material does not look great.

It has been an unsual winter here too...fluctuating temps in the extreme, but we are not experiencing the current heat that most of North America is currently having.  Still lots of snow in the garden and currently everything is covered in 15 mm of freezing rain.  But parts of the garden have been open most of the winter (in particular my crevice garden) and a couple of weeks ago we dropped to -14 C with 65 Km wind...MAJOR devastation.  The frost in those open areas is the deepest I've ever seen in my area, where normally, we have little frost in the ground.  My two Cremanthodiums are located in this open area...I hope they are root hardy! Worse, the cold wind dessicated all the evergreen alpines and erica in a single day.  The Delosperma, which looked fine up to that point, are now mush.  Veronica, Ramonda, Erica (except carnea) and other evergreen types are brown.  There is not a single green leaf left on my Fargesia. I hope there is some life left in the root to regenerate but with the frost so deep now, I hold out little hope.  I am thankful that parts of the garden are still under snow but my crevice garden will likely have lots of spots to fill this spring.

On the bright side, I will have space for all my new seedlings coming along!

[cohan]

Our soil always freezes solid, and presumably to some depth, and for many months- I doubt any plant except some tree roots is able to grow below the frost line.. the frost in the ground typically begins before any notable snowfall--in wet and shady spots the surface can stay frozen in mid fall when days are still well above freezing.. dry soil, of course doesn't freeze so early, and dry sunny spots (mostly against some buildings or under spruce trees) probably thaw a lot sooner; shady damp spots are probably frozen for 5 to 6 months...
The ground will also remain frozen in most places until some time after all the snow has melted- we can have a lot of surface water for a short time as the water cannot soak in until the ground thaws!
So I don't believe (I wont say I know, because I can't claim to have the exact science!) the problem with pots/small troughs sitting on the surface is because the soil freezes--- all the soil here freezes-- but must be, as others say, the ups and downs of exposure, or quite possibly smaller units of soil reach lower temperatures than the main body of soil, even if they are all frozen...