You might think all danger of frost is long gone, but in years past, our county has experienced freezing temperatures well into late April and even early May.  It's better to be prepared and know the dangers, so the following information may be helpful.
 
Freezing can occur when air temperature is lower or higher than 32˚ F, with plant tissue temperatures measuring lower than 32˚.  It is this low plant tissue temperature that is significant because plant surfaces radiate heat into the atmosphere.

Plants are most susceptible when there is a sudden rather than gradual drop in temperature to freezing.  The most susceptible types of plants to a freeze are broadleaf evergreens and plants not in dormancy, especially young or weakened plants.  Buds, flowers, younger leaves and shoots are especially vulnerable to freezing temperatures.

Freezing temperatures severely dehydrate plant tissues.  Water in the plant tissue or on the plant's surface freezes and when this happens, it expands the plant's interior cells, causing irreparable damage to the pistil of the flower.  It is only when the temperature rises that the damage to your plant becomes apparent.  A "burned" appearance may start at the top of the plant on the highest leaves (or the leaves most exposed to the freezing temperature), working its way down the stem and on through to the lower leaves.  Flowers may look translucent brown and then will wither and turn black.  Buds and shoots may curl, turn brown or black and then die.  The worst scenario?  A freeze can kill whole branches as well as entire plants.

A fruit tree's damage is different from a plant's, and the damage will vary depending on the time of the freeze.  It may lose its leaves, but this won't damage the tree as it will refoliate. More significant damage would be flower buds either failing to develop or if they have developed, they will drop off the tree.  Furthermore, a freeze after fruit has developed could severely damage the fruit.  Depending on the time of the freeze with respect to the cycle of the tree, the buds or fruit may appear normal after temperatures rise, but if the internal female organs are damaged, the tree will bear little or no fruit; in fact, the tree may shed its frost-damaged fruit for the overall well-being of the tree.  Furthermore, a freeze lower than 27˚ F will kill any open blossoms which developed during unseasonably warm temperatures that spurred buds to open prematurely.  As if all this isn't enough to adversely affect fruit production, decreased or non-existent bee activity could result from damaged blossoms due to a freeze. 

A freeze could also damage your tree's bark, causing it to peel, crack or split open which then puts it at risk for canker development and boring insects.  In addition, your tree could start to show earlier fall color than others of the same species that didn't suffer frost damage.

Most likely, the soil will protect the roots of your plant or tree if there is a freeze.  However, keep in mind that a young tree's roots or the roots of herbaceous plants could be vulnerable.  If this is the case, mulching the soil in the root zone will help protect them. 

After damage is apparent and the last frost date has passed, remove the damaged or dead sections of your plant or tree by cutting out those parts just into healthy tissue; this will help prevent further damage.  Watch your weakened plant or tree for disease and/or insect infestation while it slowly rebounds and replenishes its energy.  You may also lightly treat your plant or tree with a 5-10-10 fertilizer after it exhibits some regrowth. 
           
The Master Gardeners are offering a free class tomorrow, April 1, on how to use native plants in your landscape.  It begins at 9 a.m. and is located in the Ag Extension Office at 311 Fair Lane in Placerville.  The instructor will tell you which ones are especially suited to our area and how to care for them, which is especially useful information since many of these natives aren't susceptible to frost damage.  An added benefit to attending the class will be a discussion of what to plant to attract birds, bees and butterflies to your garden.

If you can't attend or have a question about this or some other home gardening topic, call our office at 621-5512 Monday through Friday, 9 a.m. to noon.  You can also come in to talk to us; we're located at the above address.