Freezing bulbs: Duration vs. low temperature - experience

James Waddick
Mon, 14 Jan 2013 21:08:41 PST
Dear Mike ( and all), 

	You are experiencing a rare event that tends to mimic our annual long term situation. Perhaps a couple of comments might be helpful.

	Our primary protection for tender bulbs is growing them in pots and bringing them indoors. Period.

	For temporary protection - when you haven't moved all those tender plants indoors, the best protection is a cloth covering - NOT plastic. Plastic seems to transmit the freezing temps at every spot it touches the plant. I cover plants preferably with thick piece of non-woven mulching cloth. In a pinch an old sheet will do. Never plastic. Even non-woven weed barrier can be used. Not only does it wick moisture away, but seems to offer true insulation which plastic does not.

	Some growers in cold climates use some equivalent of bell jars - glass or plastic covers that do not touch the foliage. Glass like plastic can transmit the cold directly to foliage and result in damage if touching the foliage. I generous cover, that does not touch the plant can work to insluate the plant by taking advantage of the usually warmer soil temp and temper the immediate conditions under the cover. These have to be removed as soon as temps warm up or they can easily over heat   even 'cook' plants under them.

	We can also by experience tell what plants can take a minor drop below freezing say to about 27 or 28 degrees F, rather than a drop to 25 or less. It is surprising how many tender plants can take it to 27 covered by just a thin cotton sheet.

	These overnight drops rarely do serious bulb damage because they do not penetrate the soil in the pot. Only long duration, below freezing can penetrate the soil. 
	Of course our hardy bulbs in the ground like tulips, narcissus and such will freeze solid when temps reach well below 0 F and stay below freezing for extended periods. Frost can penetrate the ground from a few inches to feet below the surface and everything freezes. Amazingly they survive.  For example, last night got to about 10 or 11 F and today did not get up to freezing. Tomorrow is forecast for just above freezing, but by the end of the week we may be near 50 degrees and the Galanthus that have closed their buds tightly, will pop open and be in full undamaged bloom.

	I suppose the message is to grow climate appropriate plants, but you can always get caught unawares by the vagaries of real world weather variation. 

	Lycoris radiata survives here even during the coldest weather, but the foliage is not as hardy as the bulb. During really cold winters the foliage is frozen and frosted away totally and the bulb takes the entire growing season just recovering and will not bloom or poorly. During milder winters the foliage has little or no damage and might bloom heavily. I suspect you'll find out which of your bulbs are this marginal. I also suspect you'll loose foliage and bloom much more than you will loose the bulb. 

	Gardeners have to be patient. 		Good luck and hope things recover fully in a year or so, but this might be a poor spring and summer for bulb flowers there. Hope this adds a bit of perspective. 		Best of luck		Jim W.

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