Freezing bulbs: Duration vs. low temperature

Max Withers
Mon, 14 Jan 2013 21:05:28 PST
Sounds like I left California just in time! In the seven years I gardened
in Oakland, I don't think we dropped below about 27 F, although I did not
have a thermometer the year I killed Deppea splendens (if killing rare
plants makes you feel guilty, try killing an extinct one). But we certainly
got cold enough for ice to form on standing water, and crystallize on bulb
leaves -- including Boophone disticta, and various (winter-rainfall)
Brunsvigias and Lachenalias, which I imagine to be the tenderest bulbs I
grew in the ground -- without adverse effect.

I know this has been discussed before, but can someone explain again
exactly what "frost cloth" is? I imagine it is like the styrofoam (spun
polystyrene, I think) sheets used for packaging, but I never saw it in
California nurseries. To judge by the number of hibiscuses I'm seeing
wrapped up this week in central Texas, it might be easier to come by here.

On Mon, Jan 14, 2013 at 7:57 PM, Michael Mace <>wrote:

> In California we're currently going through one of the nastier winter
> freezes we've had in a few years.  The overnight low last night in my part
> of San Jose was probably under 20 F (-7C) at dawn, and when I got up in the
> morning there was more than half an inch of ice on the puddle of rainwater
> in my wheelbarrow.  That probably sounds like a nice spring morning to
> those
> of you who live in places that have real winters, but for coastal
> California, it's serious cold.
> Yesterday I put a clear plastic tarp over my most exposed bulb pots, along
> with a string of Christmas lights to add a little warmth.  It looked
> festive
> when I went to bed last night, but this morning despite the tarp and the
> lights the soil on top of the bulb pots was frozen rock hard.  There was a
> fuzz of hoarfrost on many of the bulb leaves, a sight that would normally
> be
> beautiful but that made me feel a little bit sick in this context.  I
> worried that I had done serious damage to my collection.  However.
> As usual for cold snaps in California, the weather was completely clear
> today.  The sun melted the frost on everything it touched, and by afternoon
> the pots were totally defrosted.  And the bulbs look just fine.  One pot of
> Tritonia crocata shows moderate damage, and a Brunsvigia marginata growing
> in the ground has some tip burn on its leaves, but those are literally the
> only problems I can find.  Lachenalias, Oxalis, Amaryllids.even the
> first-year seedlings look fine.
> Other things in my garden are not as happy.  There's serious freeze damage
> on a coral tree, a Chorisia, and some sages.  My Bougainvillea is probably
> dead (again).  But the bulbs look happy.
> This matches a pattern that I think I've seen in other years.  Freezes that
> last only overnight don't seem to do serious damage to most of my bulbs.
> I'm sure there is some level of overnight cold that would kill them, but I
> haven't hit it.  What seems to do serious damage is sub-freezing
> temperatures that last more than a day.  Based on previous cold snaps, a
> full 24-hour period of 27 F seems to do a lot more harm than an overnight
> low of 20 F.
> I'm curious to know what other folks have seen.  Do you think a very cold
> night is less damaging than a prolonged period just below freezing?  And
> what low temperature do you start to see freeze damage at?
> Mike
> San Jose, CA
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