January
21, 2008
My
roofdeck plants have been lucky this year. I left some marginally hardy plants (Helleborus
argutifolius, leadwort, and ton of
bulbs) on the roofdeck. Usually I
would pull them in and crowd the stairway, but I want to see if I can keep them
alive.
They
would be hardy planted in the ground.
But on the roofdeck the constant thawing and freezing is tough. Last year that killed everything not
hardy to zone3.
My
objective for this experiment is to keep them cold and frozen, but above 100F. I gathered the containers close
together, and prepared some old sheets, thin blankets, and mess bags stuffed
with various materials for insulation.
The
overwintering containers were placed in a southeast corner, where conductive
heat from the two walls and roof can help moderate temps. Extremely hardy containers
(basket-of-gold & sedum ÔAutumn JoyÕ, serviceberry & Asiatic lily,
sedum & hen-and-chicks) are on the exterior to provide a windbreak. The larger wooden barrels of
bulbs/perennials, the tray of St. John worts/Colchicum byzantium, and the herb half barrel make up the next
layer. The Kentucky coffee tree
and oak barrel 2 are against the north wall. And in the most protected spot along the west wall near the
door are the small pots with Corsican hellebores, leadwort, Crocus speciosus, daffodils from Heath at OKC, etc.
Every
time low temps were forecast, the plants were saved by snowfall. Snow is the best insulation
possible. Its fluffy nature allows
for many air pockets, which buffer against extreme temps. After the snow I shoveled more on top
of the pots to really insulate the containers. The goal is to eliminate gaps and passages where cold winds
can enter or warmer air can escape.
Unfortunately,
I piled up too much before Christmas vacation. When I returned mild temps had melted most of the snow. Shoveled snow is always harder and
heavier than fallen snow. As the
shoveled snow melted it formed a hard ice crust that broke off one of the two
branches on the Kentucky coffee tree.
Lesson learned: donÕt pile snow on delicate branches or plants.
Since
my plants were saved from the cold temps the last two times we experienced
single digits, I was expecting salvation from the recent negative dips. Skiling and others forecasted 2Ó of
snow, which is enough to cover the containers the pots and have plenty to
shovel into gaps. I removed the
blankets, pots, bags of pine needles, and bags of shredded paper that I was
using to insulate the plants in place of snow after the mid January thaw.
Snow
was falling light but steady. I
checked back 2 hours later before dark.
The snow had stopped! There
were only trace amounts, barely enough to dust the ground. Plus the temp had dropped into the
teens! The blankets were frozen
like cardboard. How was I going to
insulate the plants before dark?
I
placed an old sheet (the blue one from Grandma Coot) over the least hardy pots,
then added the insulating bags of pine needles and shredded paper. The frozen blankets were fitted around
the containers and finally empty pots were placed on top of the frozen
blankets. Nylon mesh bags with
empty water bottles were pushed into open spaces. But even with all that, there were lots of gaps and shafts
for air to escape or penetrate.
Without snow, it is impossible to completely insulate them and retain
all the conductive heat.
It
is currently -50F. That
is officially zone 6 which all my plants can survive. But hardiness zones are based on the air temperature not the
soil. If the soil temps are
currently -50F too, then once again I have probably loss a ton of
bulbs (Crocus speciosus, Crocus
tomassinianus, Narcissus, Muscari azureum, Tulipa ÔCasa grandeÕ, etc.) and the Corsican hellebores.
It
is supposed to moderate into the 20s and snow Monday (MLK day). This time, IÕll only remove the
blankets (I added an old comforter from Tahir) once IÕm sure the snow is
falling.
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Snow shoveled on top of containers for insulation |
EPILOGUE
January
25, 2008
They
seemed to have survived the negative temps and are now resting comfortably
under about a foot of fallen and shoveled snow. But the roller coaster continues. Negatives now, 40 is predicted in a few days, then it is
back to cold temps.
I
have a lot more insulating and shoveling to do this winter. I think IÕll build a cold frame next
year.