Protecting Plants in Cold Weather

Gardeners with the preparedness gene are always ready for the coming winter rainstorm.  Sandbags line the driveway, tools are in the shed, drains and rain gutters are debris-free.

The wolf at the deep freezer door?  Low overnight temps like those we've seen this weekend could mean potential leaf, stem tip, bud and flower damage await tender perennials.

In northern climates, bulbs, succulents, even tropical trees in pots, come indoors until nighttime soil temperatures are in the 50s.  In Southern California, most home don’t have l’orangeries, atriums, sunrooms or greenhouses to shelter plants during colder months because, frankly, we rarely need such a thing.  And when we are in need, long workdays disallow weekend gardeners the luxury of rolling numerous pots into the den for a night or two. 

So, how do we cut our losses when unusual weather strikes?

Nobody’s saying, “I told you so,” but here’s another reason to mulch.  Mulched plants in the ground will not be exposed to extreme temperature swings from day to night, retaining more of the daytime soil heat with a 4 to 6” layer of mulch on top.  An increase of two or three degrees in soil temperature could be the difference between frost-tipped damage and complete loss of a plant. 

If you haven’t mulched, but have time to drape your plants in a waterproof tarp, a drop cloth doubled or tripled will provide greater insulation than a single layer. In between the folds are small pockets of air, which insulates.  Same idea as dressing in layers.  Loosely drape the entire plant, if possible, in flexible tarp.  If the plant is large or the tarp small, snug it around the base or trunk, faux mulch-style. 

Or, use two wooden stakes to affix a Christo-like moat or tent around your plant.  Use a large clear plastic trash bag to fashion this floating, mini-cold frame, but don’t allow the plastic to rest on the plant.  And don’t leave this in place for more than a day at a time.  Secure the bag to the ground, but leave an opening so the plant doesn’t suffocate.  The carbon dioxide and oxygen being exchanged shouldn’t be trapped inside the bag.

Some gardeners use bed sheets for a delicate drape around their most prized pots.  In the rain, protect that fabric covering with a plastic trash bag or dry cleaner’s bag.  A thin layer of waterproof material will prevent the bed sheet from turning into an icicle.  Remove plastic during daylight hours.  Water can collect in the folds, creating weighted pockets, which may damage limbs or leaves.  And even on a rainy day, air circulation is important to the continued health of the plant. 

Where possible, relocate potted succulents to a covered or protected area.  A south facing wall is ideal, even on a gray day.  A dense tree canopy can offer temporary protection to containers.  If no house wall or tree shroud is available, group pots together. Those on the outer edges will shield the interior pots.  Not a perfect solution, but one that will control losses.

Don’t store plants in the garage if you park your car there.  The ethylene gasses released by the car engine, even as it cools, stimulate faster aging of plant tissue, leaf drop and ripening of fruit. 

In a worst-case scenario, stay inside during the rains, gazing fondly at your bare, untended plants.  When the sun’s out again, note those plants that did not fare so well. Water-filled leaves, such as those on succulents, or papery-thin leaves and flowers, such as those on bougainvilleas, will suffer more damage.  Shrubs or trees previously stressed by heat, drought, or pests are likely to sustain winter injury.  Unless these ornamentals are part of your daily devotional, consider other varieties of your unfazed greenery as the way to “hedge” against future losses.