Freezing bulbs: Duration vs. low temperature

Joseph Kraatz
Wed, 16 Jan 2013 12:49:11 PST
It would be interesting to know what type of thermometers are being used to record the temperatures.   It has to be a professional max/min thermometer located at the location of the plants.  I have been recording temps for the weather service for years and I know how important it is to record temperatures for accurate reports.  When I hear reports of damage above 32 degrees I am very suspect of where this thermometer is located.  Any entries on this should actually included thermometer locations and their accuracy.  Joe, Oceanside, CA

On Jan 16, 2013, at 12:40 PM, "richard" <> wrote:

> 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.
> Nathan
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