It’s definitely been cold at night lately. A couple of weeks ago Lindbergh Field experienced record lows down to 38F, and Ramona had night temperatures in the high teens. Yikes! How do our plants in San Diego respond to such “extreme” cold? Are they going to suffer?
First off, whether a plant suffers from cold damage, depends on the plant. Many plants in San Diego garden can actually tolerate some snow (e.g. Azalea, Buddleia, Camellia, Ligustrum, etc.)
Second, the extent or severity of cold damage depends on how cold it actually gets. As long as temperatures stay above 40F, very few types of plants in our San Diego gardens will suffer from one or two nights of severe cold.
However, Phalaenopsis orchids are one such plant that can suffer greatly when temperatures drop below even 50F.
Here dark, soft, mushy, brown/black spots show where cells ruptured from receiving more cold than the plant could handle. Let this leaf remain for as long as the plant decides to keep it. This leaf will eventually turn yellow and fall off.
This leaf is almost entirely black and mushy. Remove this leaf with sterile clippers right away.
Most San Diego garden plants will tolerate temperatures below 40F, but frosts (temps under 32F) will definitely harm many of our plants. Colder than usual winter nights can damage early plantings (January thru March) of cold-sensitive, summer veggie crops like Beans, Cucumbers, and Basil. It is always best to simply replace cold damaged veggie plants once temperatures warm up a bit.
In San Diego cold damage to plants is worse when potted plants sit in standing water. Plants roots lack air and are more susceptible to cold damage. “Cold tender” succulents (whose roots require LOTS of air) are way more likely to suffer when soils are excessively wet.
I state many times that the ability to differentiate between the youngest and oldest leaves on your plants, gives you a powerful tool to assess the health of your plants.
For almost all plants, it is common for the oldest leaf to turn yellow and fall off once in awhile. However if the youngest leaves or stem tips look damaged, discolored, or disfigured in any way, something is definitely wrong with your plant. Cold damage could affect any part of a plant but is most likely to affect the leaf tips (the most tender tissue) of the youngest leaves.
Plants closer to your home and closer to other plants are less likely to suffer from cold than those plants out in the open in exposed areas. Therefore, during cold spells, move your potted plants closer to your house or group them together. Alternatively, cover cold sensitive plants with frost blanket or a light sheet.
Spring is on the way!