Protecting Your Garden from Frost

A:

Very timely question. I just now received it after these past two nights when temperatures hovered at 32F in and around Portland. I hope you harvested as much as possible and threw a temporary cover over the rest.

Overall, the plants most likely to be damaged at the end of the season are those that require considerable warmth, among them basil, tomatoes, cucumbers and squash. Many fall and winter vegetables will do fine through mild (minimum 28F) and/or brief frosts. Lower temperatures may kill sensitive plants even if protected.

Protecting plants against frost involves a number of factors, among them the plants’ sensitivity to cold; if grown in a pot or the ground; and the severity and duration of the frost.

Whenever you have to protect plants, these tactics are useful: 

  • Harvest everything that’s ready; tomatoes with only a slight blush of color will continue to ripen on your counter but keep them out of the sun. 
  • Drape plants with whatever breathable thing is at hand, among them large towels; old draperies, bed spreads, or blankets; cardboard box; commercial row cover; or mounded straw or evergreen boughs.
  • Don’t use plastic sheeting unless a fabric or other cover (see above) is between the plastic and the plant; leaves and stems that touch plastic will freeze. 
  • Move potted plants to a sheltered site such as adjacent to the house and under the eaves; that may be sufficient during a brief mild frost. A shed or garage will be better during colder spell.
  • Protect heavy containers where they stand with whatever materials you have on hand. 
  • To avoid cooking your plants the next day, remove all covers when temperatures rise to a reasonable level.

If a plant is frosted, you might be able to salvage most or all of it by hosing it off before sunlight strikes the leaves. (Hint: This works only when the hose isn’t frozen. Don’t bother asking how I know that!)

Thank you for your inquiry,

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