The Effect of Weather: Winter weather can be erratic. In 1990/91, many of our living areas reported 0° with a week or more below 17° day and night. In 1991/92, there was essentially no frost at all. Almost all of the common landscape plants here are adapted to a reasonable amount of cold, although they can be hurt in an especially hard winter.
Observations after the last bitterly cold year showed that in many cases, the cold hardiness of individual plants varied in relation to that plant's overall health. Proper plant choice and placement, combined with suitable watering, regular fertilization and appropriate pruning can produce a landscape better able to handle the rigors of an extremely cold winter. Cool weather requires that you dramatically reduce the frequency of your automatic watering. This will help preserve the health of plants through the winter. The first frost can come in early November; the last frost is usually in early March.
Keeping Your Lawn Green: If you wish to keep your fescue lawn green through the winter, the most important things are the timing and type of fertilizer applied. Without adequate nitrogen, lawns will go dormant after the first hard frost and will be difficult to green up again until spring. In order to make sure your fertilizer and water get to the root zone of your lawn, it's a good idea to de-thatch and rake thoroughly prior to the coldest weather.
Dr. Q's WinterGem™ (21-3-7) and Best Nitra King® (19-4-4) are popular commercial fertilizers, formulated for winter application. Apply in early November and again in mid-December and mid-January, to help keep your lawn from going dormant. Bermuda lawns will remain dormant until spring and require no fertilizer unless they have been over seeded with annual rye.
Hardening Shrubs, Vines & Trees: It's important to give soft, green summer growth the chance to harden up. Soft growth is easily damaged by frost. You can speed up hardening in two ways-- by withholding water and by fertilizing with low nitrogen, high phosphorus and potassium fertilizer. When you fertilize, check the condition of tree stakes and trellises, since cold weather is often accompanied by strong winds.
Application of surface mulches over the root zone of plants keeps the ground from freezing and allows root growth to continue all winter. The only plants that should be pruned in the winter are deciduous trees and shrubs. These should be pruned around New Year's, when solid dormancy is likely to have occurred. Do not prune evergreens or desert plants until early spring.
Protecting Irrigation Systems: Because the ground seldom freezes here, irrigation systems are often sloppily installed. In a proper installation, all pipes should be buried six to eight inches deep or permanently covered, with a drain valve installed at the low end of each line. Pressure Vacuum Breaker (PVB) valves exposed to the elements need to be protected to avoid messy and expensive repairs. You can use a product like Frostbite's PVB Protector or Insulated Foam Pipe Wrap to protect exposed pipes. Because it is self-adhesive, it's easy to install (also good for reducing heat loss on exposed hot water and water softener pipes).
Exposed lengths of PVC pipe can be protected by prefabricated Tube Pipe Insulation. Other products are available for covering spigots. If a hard freeze is expected, close the valve to your system. Then drain your drip system by removing the end cap. This will prevent damage to soft pipes by the expansion of frozen water.
Special Care for Desert Yards: Desert plants grow whenever water is available to them. Since new growth is tender, it is very important to limit the water given to desert plants, especially cactus, during the winter. Most desert-adapted species can survive a cold winter well with one good soaking at the end of October or mid-November, then no more water until late February. This is particularly true for cacti, which may look shriveled, but will survive severe cold much better. Often we experience a rather warm winter, and your watering schedule will need to reflect this. Warm winter watering can be as often as two to four times per month. Spring watering will resurrect them quite nicely! Do not prune desert plants in winter. It induces soft new growth that can be damaged by cold weather. In early spring, apply a specialty fertilizer like Dr. Q's® Desert Plant and Cactus Food to get showy blossoms.
Container Plants: Plants in containers are subject to an even greater set of extremes, since they are not surrounded by a mass of insulating earth. All subtropical and tropical patio plants should be moved inside or to a windowed garage for the winter, where they can be protected from freezing temperatures. Some plants may show symptoms of shock when moved indoors but should recover. When you put them back out in the spring, expose them gradually to the sun, or they will burn. If you want to have colorful flowers in containers through the winter, choose hardy types like Snapdragons, English primrose, Kale, Stock, and Pansies. All benefit from full sun, but primroses can be grown in shade.
Subtropicals: Citrus, bougainvillea, evergreen hibiscus and other sub-tropicals are very tender to frost. If you have them planted in the ground, protect with a heavy layer of mulch over their roots, and be prepared to use physical cold barriers, like burlap, thermal plant blankets or in the case of a vine like bougainvillea try using an inverted nursery pot filled with mulch to keep the base of the plant warm. Protection should be used if the temperature is expected to drop below 35° on any night. It is preferable that the blanket or burlap not be put directly on the plant, but be used as a 'heat tent', supported by sticks or lumber. In a very cold winter, even extreme measures may not be enough to save tender sub-tropicals. Most should not be allowed to dry out during the cold weather. That will damage them as much as cold temperatures will.
Annual Flowers and Vegetables: Tomatoes, eggplant, corn and other summer vegetables will blacken after first frost. Replace them with suitable winter vegetables, including broccoli, cabbage, carrots, radishes and lettuce. Most of these can withstand our normal winter weather, although extreme cold can completely stop their growth until spring.
Re-plant summer flowerbeds with hardy winter varieties like pansies, stock, kale, and primroses. Freshen up the soil with some Pay Dirt™ and use Gold Dust® Starter Fertilizer to help them get a good start.
Emergency Measures: Severely cold weather (below 20°) is often preceded by 24 hours or more of steady, strong wind from the north. If you observe this or hear that cold weather is expected, move quickly to protect your plants. Soak the ground around non-desert evergreens and sub-tropicals. Use blankets and burlap for protection. Remove these coverings during the day unless the wind is blowing or the temperature re-mains below 30°. Do not walk on lawns covered with frost, since footprints will be visible after the thaw.
Source: ©2009, Star Nursery, Inc.