Freezing bulbs: Duration vs. low temperature

Wed, 16 Jan 2013 12:40:17 PST
I have a few two year old Alstromeria seedlings. Two of the A. magnifica
suffered leaf damage and perhaps more. The single A. ligtu was fine. My
temperatures did not get below 36 degrees F but there was significant
radiational cooling due to the open sky and lack of wind. 
Richard in Vista, CA

-----Original Message-----
From: []
On Behalf Of Nathan Lange
Sent: Wednesday, January 16, 2013 12:22 PM
To: Pacific Bulb Society
Subject: Re: [pbs] Freezing bulbs: Duration vs. low temperature

I would like to hear about people's experiences with Alstroemeria cold
tolerance. I had many plants left outside unprotected since last night's
forecasted low of 33F by the National Weather Service was a full 6 degrees
off from reality (it was actually 27F). Well, that's not entirely true; I
was curious to see what would happen. 
Undoubtedly, the plants can survive down into the 20's and this will vary by
species but I wonder how cold most species/cultivars of Alstroemeria can go
before damage becomes apparent.

I routinely use inverted black plastic pots for cold protection with great
success on a number of species. The trick is to use a second pot over the
first. It should go without saying that all pot covers must be removed the
next morning. Covering the foliage may not be the only concern. If you are
growing plants in plastic pots that are out in the open, all the roots at
the edge of the root ball are in contact with the plastic pot and highly
susceptible to night time temperatures.

Floating row covers are widely available here in Northern California. 
When it becomes to cumbersome to elevate the material off the plants, I just
throw a second and sometimes a third layer over whatever I'm covering. The
key is to create as many layers of insulating air as possible. That being
said, positioning is everything and blocking a plant's view of the overhead
sky could easily save it. Just moving an uncovered potted plant under the
eave of a building or canopy of a tree could easily prevent damage depending
on the circumstances.

Don't forget to water your plants. Plants are generally more susceptible to
cold damage if they are also water stressed. Cold weather arrives with dry
air and this has certainly been the case this past week in California. I
watered a lot of dry plants yesterday. Remember to water early in the day
and keep all water off the foliage at night. Any water left on leaves at
night can freeze and do significant damage. The alternative is to pretend
that you are growing citrus and run the water overhead all night long to
keep the temperature of the ice from going too far below freezing. Of
course, controlled water stress *prior* to cold can generate some beneficial
tolerance to cold temperatures in some species but this should not be
confused with water stress *during* the cold period.

Bright sunny mornings are not at all helpful. They just make you feel
better. Freeze and chilling injury damage can be greatly exasperated by
bright sunny mornings accompanied with rapidly rising temperatures. This has
been the case here in Northern California for almost a week. If I had to
choose, I would move an uncovered potted plant under the west or north eave
of a building and completely avoid the east and south exposures. If I had a
marginally cold tolerant specimen planted in the ground shrouded in floating
row covers, I would still definitely block the morning sun from hitting it
with cardboard or some other barrier.  In some instances, this is almost as
important as covering the plant.

But it all depends on the weather and everyone should have at least one
min/max thermometer to know what's going on outside. I can't imagine growing
anything without them.


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