Notes from the Field: People and Plants Braving Cold Temperatures in the Bay

winter planting
Last week was cold! Our plants were dormant, but our volunteers braved the weather.

Brrrrrrrrrrrr. Has anyone out there in the Bay Area been feeling a bit chilly? The temperatures are starting to rise, but last week was cold! While my friends on the East Coast may laugh at the West Coast’s weakness to cold weather, temperatures in the Bay Area have been chillier than they have in years. San Jose broke a record low set 82 years ago when it recently dipped to 30 degrees, while cities such as Oakland, Mountain View, and Napa also reached lower temperatures than they have in almost a decade.

But while we blast our heaters, bundle up, and drink hot chocolate what are our plants doing?

At many of our restoration sites, our plants are going through a dormant phase to resist injury from freezing night time temperatures. When plants are exposed to low temperatures their cells can freeze, limiting water and nutrient exchange. This causes the plant’s leaves and shoots to become limp and blackened. Soils may also freeze, limiting the uptake of water through the roots. When the morning sun begins to defrost plants, the sudden change in temperature causes more damage as the cell walls rupture.

But rest assured volunteers — your efforts planting our native California plants are not lost because our native plants are very hardy and adapted to surviving cold conditions. Some native perennial plants will go dormant in colder temperatures to reduce metabolic activity and therefore save energy.

There are two types of dormancy — predictive and consequential. Predictive dormancy is when the plant prepares for the cold as temperatures drop or water is limited. The plant will shed its leaves and halt active growth to store energy until conditions are more optimal. Consequential dormancy is when the plant reacts to cold temperatures after they have been reached. This is more common with unpredictable weather patterns that can vary at a rapid rate.

Our vegetable gardens at home are at greater risk than the shoreline plants. The first frosts have damaged my hopes of overwintering my bell peppers and eggplants in south Berkeley. Normally California is lucky to have great growing conditions throughout the year, allowing even some summer crops to survive the winter and blossom again the following year. However, unexpected temperatures this year may mean I’ll have to stick to my usual winter leafy greens.

If one is prepared, there are several measures you can take to prevent the cold weather from damaging your plants:

  • In the fall, position plants more susceptible to low temperatures close to walls of you house, under trees, or near large rocks to protect the plant
  • Mulch with a thick layer of straw around the plant to protect and warm the soil
  • Continue to feed plants compost or a balanced organic fertilizer to give plants a boost through the winter months
  • Before frosts, water the soil thoroughly. Wet soils will heat up better than dry soil, which will protect the plants roots and warm air near the soil surface.
  • Use a permeable cloth such as bed sheets or drop cloths to cover the plants at night for insulation. Avoid the cloth being in contact with the plant by propping it up with stakes. Remove the cloths during the day, once the sun has warmed temperatures for some time.
  • Cluster potted plants close together or near a wall for protection and warmth
  • Leave wilted/damaged vegetation until the spring time. Removing leaves or dying stems adds stress to the plant in an already susceptible state. In the spring time cut back the frosted growth to allow new shoots and buds to emerge.
  • Near the end of dormancy is the best time to prune trees and shrubs. The plant already contains stored energy from its dormancy which will reduce shock and help wounds caused by pruning to heal faster as it enters active growth.

Unfortunately us humans can’t afford to go dormant for the winter (though it sounds great to lay in bed nice and warm all day) and the restoration department at Save The Bay isn’t slowing down. Big thanks to all our volunteers for braving the cold and helping to restore the Bay’s shoreline. We’ve successfully installed over 11,000 plants at our sites so far, and have a lot more to go. So bundle up and come plant with us this planting season!

Our full schedule of restoration programs can be found at savesfbay.org/volunteer.