At 10:38 AM 4/12/03 -0400, Steve Wolfinger wrote:
I had bought a japanese hornbeam from the philadelphia flower show in early
march... it was already budding out.. so i kept it inside... since the
nighttime temps around here wiere still dipping into the low 30's and 20's.
It leafed out inside and was doing fine by the window. I put it outside
when the daytime temperatures would get into the 50's and 60's. and would
bring it inside at night. but lately we've had a cold snap.. and i brought
it back inside. The leaves are starting to look unhealthy... some of them
wilting slightly.. and gettting some brown/black edges. for the next
week... the nighttime temperatures are supposed to be in the high 30's and
40's.... hopefully they will stay that this time and i can leave it out.
my question.. should i have left it out from the beginning? has moving the
tree in and out ... put too much stress on the foliage... and will the tree
put out a new set of leaves if these die??
Steve
Boy, that's always a tough one to call.
For the future, the solution is to keep it deeply dormant as long as
possible. I realize in this case, it was not possible. The answer here
depends on the species. First, your probably have Carpinus japonica.
Although not as hardy a C. coreana, my experience is that it is pretty
tough when it comes to frosty spring weather.
Most temperate woody trees do not immediately lose all their acquired cold
hardiness as soon as the buds swell in the spring. The loss of hardiness is
a slow process that proceeds at a rate determined by both the soil and air
temperature. As the buds begin to swell, there is a rapid loss of deep
dormancy. This means that a dormant tree that could tolerate -10F in late
January, may not be able to tolerate a hard freeze of 20F after two weeks
of warm weather.
However, the cold damage threshold after this point can rise more slowly
after bud swell if temperatures return to freezing (28+), but not hard
freezing conditions (28F-). I must tread carefully at this point, because
in this area of bud swell to leaf opening, the species and often even the
cultivar, will determine the level of freezing that the plant can tolerate.
For C. japonica, I have observed that bud swell to early leaf opening, a
nightime temperature of 26F was tolerated. As the leaves begin to really
expand and turn green, a temperature of 28F for a few hours will probably
be ok or only cause minor damage. Even at full leaf unfurling, this and
most woody temperate species, will tolerate freezing temperatures of about
30F with only minor damage.
Two years ago we had a horrible freeze in April after a very warm spring.
Nearly all my trees were in full leaf when the temperature overnight
plunged to 20F. That year all the foliage was burned off C. japoncia and
just about everything else. While the Acer palmatum cultivars were severely
damaged and many died, the C. japonica completely recovered, although some
of the other Carpinus species suffered severe dieback.
I don't know if I really answered your question, but I hope I have given
you enough information for future decisions. As for moving plants in and
out, I will sometimes do it if there is no alternative, but I don't, as a
rule, recommend it as a routine. Moving plants in this fashion can make
them more vulnerable to soil fungal diseases, and I think is what you may
be seeing. It is always better the leave the plants outside if they can
tolerate it.
Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14
http://www.EvergreenGardenworks.com
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