Freezing bulbs: Duration vs. low temperature

Nathan Lange
Wed, 16 Jan 2013 12:21:44 PST

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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