Home & Garden Columns

Garden Variety: What to do When the Frost Hits, Before and After

By Ron Sullivan
Friday January 12, 2007

It has come to my attention that the hard freeze predicted (as I write this) for late this week is the first some of my fellow Berkeley denizens have experienced here. If it happened on time, you’re reading this in the Retrospectroscope, that scientific instrument that gives us 20-20 hindsight. Still, this might be useful. 

First: Don’t panic. If you have plants already hurt by frost, don’t rush out and start whacking off the damaged bits. Leave them alone until you see new growth. Some things will be OK under it all, and the dead tissue you leave on the plant can insulate the growing points against further damage. The brown stuff looks ugly but it won’t harm and it might help.  

Second: Don’t despair. If there was a freeze and you didn’t get your plants covered and there’s another night of frost on the horizon, cover them. Preventing more damage will give them a better chance to recover. 

Third: Don’t let the perfect be the enemy of the good. If you can’t quite do it right, protect your plants as well as you can. I’ll explain this more, below. 

Fourth: Get out there early the morning after and uncover those plants, especially if you’ve used plastic sheeting over them. That stuff works as a solar oven in the daytime, and your poor plants can get cooked.  

Plants typically freeze when the night is clear and the air is still. A decent breeze will decrease the peril – that’s why you see those big propeller-looking fans in Napa Valley vineyards—and cloud cover will moderate the temperatures. Your garden’s in more danger if it’s at the bottom of a hill, because cold air drops and warm air rises.  

If you have tender plants—tropicals and subtropicals, generally—in pots, bring them under the eaves, into the garage, or onto the porch. Anything overhanging them will help. Also, the thermal mass of a building, the heat it’s absorbed from the sun all day, will moderate temperatures near it.  

If you can’t move it, cover it. Blankets, old curtains, sheets – some extremists use the old down sleeping bag the dog peed in last summer. In Britain, they sell lengths of synthetic fleece for plant cozies.  

Plastic sheeting is a classic here. To best protect the plants, build a framework to hold the sheet. This can be as simple as three garden stakes around the plant, or a tipi of poles with a garbage bag pulled over it. The idea is not to let the cover touch the plant, because where it touches will be damaged.  

If you can’t avoid that, though, just throw the sheet over. Better to lose a few leaves than the whole plant.  

Experts advise watering plants before a frost, because frostbite is mostly dehydration. Maybe, but there’s one big exception: cacti and succulents. I’ve had a cactus explode—really; pieces were scattered over three feet or more—when a freeze hit it. Water expands when it freezes and turgid cells burst. Spectacular, but fatal.  




Ron Sullivan is a former professional gardener and arborist. Her “Garden Variety” column appears every Friday in the Daily Planet’s East Bay Home & Real Estate section. Her column on East Bay trees appears every other Tuesday in the Daily Planet.