My ‘Meyer' lemon tree was a casualty. I was stumped as to why it didn't survive as I had faithfully covered it every night. I have since found out that covering your plant is not the total answer to frost protection.
To minimize frost damage, try to choose plants that are not frost sensitive. If you simply must have a plant that is frost tender, at least put it in a location that gives it a fighting chance in cold weather. Identify your garden's warmest sites, perhaps an area with western or southern exposure or a spot against a western-facing wall. The wall stores the sun's heat during the day and releases it at night.
Fertilization and pruning also play a role in frost tolerance. Discontinue fertilizers and refrain from pruning after late August. The nitrogen in fertilizers promotes growth, as does pruning, and this tender new growth is sensitive to low temperatures. Citrus trees are an exception. Consult resources like Sunset's Western Garden Book to understand your plant's fertilizer requirements going into the cold months.
I was not aware of how important it is to keep plants watered during weather extremes. A thirsty plant is already stressed. Add a frost and you have a deadly combination. If nature gives us rain in winter, your plants are hydrated and less stressed. No rain? Get out there and water your landscape.
Succulents are an exception and should be somewhat dry going into a frost. I had turned off my sprinkler system and was thoughtless as to my garden's condition. When cold weather arrived, my water-deprived and stressed garden was hit hard.
Keep the soil clear under your plantings. Mulch or debris under the plant prevents the soil from absorbing daytime heat, so it remains cold. Keeping soil cleared also helps to prevent disease and discourage pests. Cleared soil warms up faster and can release that warmth back into the air. Replace mulch in the late spring or early summer to help keep the shallow roots cool and reduce water loss in hot weather.
Frost injures plants by causing ice crystals to form in plant cells. This makes water unavailable to plant tissues and disrupts the movement of fluids. Frost-damaged leaves appear burned and shriveled and turn dark brown or black.
So how does one prepare for cold weather? Many plants can survive short periods of below-freezing temperatures. You may see some blackened branch ends and dieback but nothing life threatening.
Prolonged low temperatures cause most of the problems. If frost is forecast and it hasn't rained recently, water your landscape. Citrus and other frost-sensitive plants require further protection. Cover these plants with a lightweight, breathable fabric like floating row cover. Other commonly used materials include old sheets or bed covers. Build a structure to keep the cover from touching and burning the plant.
Tomato frames can provide support for frost cloth. Remove the cover during the day so plants can enjoy the sunshine and air. Recover at dusk. Lighting under the covers will supply heat, but make sure to use only lights and extension cords rated for outdoor use.
If you didn't heed the frost warnings, you may now have damaged plants. Resist pruning the dead or damaged foliage as it will protect the plant from further damage. Force yourself to leave the plant alone until it sends out green shoots. You have been forewarned. The frost months are fast approaching so make preparations now.
Workshop: Napa County Master Gardeners will host a workshop on “Saving and Sowing Seeds to Sustain School Gardens” on Wednesday, January 21, from 3:30 p.m. to 5:30 p.m. This workshop will introduce basics of seed-saving with children, along with simple activities for seed exploration and observation. We will demonstrate the best seed sowing methods. Participants will start late spring/early summer crops, which Master Gardeners will tend until they are ready to leave the greenhouse for school gardens. Location: Connolly Ranch Education Center Greenhouse, 3141 Browns Valley Road, Napa. This workshop is free but registration is encouraged. Click here to register: http://ucanr.edu/2015schoolgardens
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.