Monday, December 9, 2013

Calculated craziness...

Yucca faxoniana (left) Yucca thompsoniana (right)
I have recounted elsewhere (on several occasions) the tale of the giant yuccas that are found here and there throughout Denver Botanic Gardens...and of these the one on the left (Yucca faxoniana) always elicits the most amazement due to its enormous size and subtropical feel. We are on the verge of fulfilling an entire week where the temperature has been well above freezing in the daytime, dropping well below zero Farenheit at night: deep freeze, in other words. The cold snap that's got Denver in its grip has stretched from coast to coast, bringing extreme temperatures much earlier than usual. Of course, there are casualties every year--but years like this makes one wonder--why would sane people try growing treeform yuccas that only grow natively hundreds of miles away to the south--at much lower altitudes to boot? The answer is that this was a calculated craziness--Mountain States Nursery in Arizona gave us these plants to test--and they had observed enough of their plants in enough places that they knew it would work...

Same spot two months later
Last spring we had an unseasonably cold snap to 7F above zero in early April that devastated plants throughout Denver--I was worried about the giant yuccas, but realized later that they are warm season plants--it takes a lot to rouse their meristem into active growth in spring or fall for that matter--these are less likely to suffer from unseasonable cold snaps in the cooler seasons...

Ebracteola wilmaniae
I had grown a little cocky about growing this wonderful ice plant I'd gotten from David Salman. Of course, looking at the map below at where it comes from, I should have been a tad more circumspect: most of the hardy ice plants we grow come from the high Drakensberg--far to the east and south of where this grows in nature. And this was one of many South Africans that succumbed to the nasty cold snap last April..fortunately, nurserymen had backup stock in I have it in the garden again. Will it survive our current arctic blast?  Stay tuned.....

Echinocactus texensis
Looking at the range of Horse Crippler, you would expect it to be much tougher than the giant Faxon's Yucca I started up with: after all--it grows at much higher altitudes, over a hundred miles to the north. Moreover, it is a low plant that would theoretically be somewhat protected at ground level, as supposed to a monster Yucca that's exposed to the elements--and yet this cactus is by no means ironclad. I have known specimens to persist a decade or more, but eventually a strange winter comes along--I suspect if we were to grow enough from seed and select, reliably hardy strains might emerge--but meanwhile we should enjoy those we can persuade to stay with us for a while...don't ask me about the year I killed a dozen gathered from my ex-wife's land in Texas, or how the tenant who rented the land pulled the rest out lest they "cripple their horses"...


Echinocereus knippelianus

This unlikely candidate for Colorado gardens actually performed far better for us for far longer than any Echinocactus...Coming as it does from hundreds of miles further south in Nuevo Leon than even Yucca faxoniana, I would have never thought it would do. I'm glad I got lots of pictures of it when it was at its peak a few years ago--this was another casualty of our April misery this year...But we must try it again!

Amorphophallus konjac
With so many plants dying in our April freeze, I was sad that I had planted my Amorphophallus the fall before--why did I pick this year to try and overwinter this? I dug a very deep hole, put in lots of rich compost and sited it in what I thought was the perfect spot. June arrived, and day after day, week after week passed by with no sign of this. Obviously dead. I returned from Scotland at the END of June, and only then did I see the huge spathe emerge...hurray! But will it come back a second year--and eventually bloom? What hubris, to plant this fey (if massive) bulb that comes from Southeast Asia, basically, on the windy cold plains of Colorado? But isn't that what we gardeners do? Everything we're not supposed to that is?

Magnolia grandiflora

The last and final case of craziness is the struggle to grow southern Magnolias, here the last place we should be growing them. Elsewhere I describe the largest specimen (I know of anyway) in the Denver Metro area--and this picture shows one of several specimens planted at Denver Botanic Gardens--which bloomed wonderfully this year as you can see despite our despicable cold...

So is there a calculation to our risks, or is it just horticultural craziness that we plant these things and expect them to grow--you can be the judge!


  1. Amazing at what you are able to get through your winters, but I would draw the line at the Magnolia grandiflora. Even if it can survive the cold, they make no sense being planted where heavy snows or ice will snap branches, which is the reason many otherwise hardy broadleaf evergreen trees aren't reliable in the PNW either. Sometimes it's better not to tempt fate, or get too attached to things.

  2. That may be a concern, but I've seen them do well in Rochester, NY and there's plenty of snow and ice there. Drying out during our winters might be more of a problem. There are in fact several excellent cvrs of Magnolias and of Hamamelis from Rochester that would be great candidates here.
    And even though latitude and elevation count for something when searching for hardy plants, it seems obvious that their gene pools hold vast reserves of adaptability that can and does override those criteria.

  3. There is a magnificent Magnolia grandiflora here in Pittsburgh. It's probably 50' tall. I worry every year the owners will cut it down because it's too big! They do that here.

  4. Hi Panayoti, I have been thinking about which plants I grow that are out of place. I think the Penstemons must be the plants from warm climates that are most surprisingly hardy in my northern Illinois garden. As you already know, I have over wintered Penstemon cardinalis, Penstemon clueti, Penstemon murrayanus, and Penstemon utahensis outside for a number of years without issue. I also have Anemone coronaria and Aesculus pavia, which are both a stretch. I have many more plants from the opposite extreme. The plants I grow that hail from colder areas include Aster alpigenus, Oxytropis podocarpus, Eritrichium aeritoides, Erigeron pinnatisectus, Physaria alpina, various Phlox, among others.


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