Winter care of Citrus
1. Check foliage--if not deep green, add fertilizer. Contrary to advice given for years, well-fertilized trees are healthier and more resistant to cold weather damage. Even if new growth is produced in the fall, and then is damaged by frost, overall the tree is healthier.
2. Control pests: scale or aphids found on the trunk or foliage can be controlled with a sharp blast of plain water, insecticidal soap, neem, or a light insecticidal oil.
3. Wait until spring to do any major pruning. We prune every season but winter.
4. Fruit harvest:
Bearss limes are turning yellow in November, getting sweeter by the day.
Meyer lemons and all types of limes would be best harvested before temperatures drop below 30 degrees, or take extra measures to protect the trees.
Eureka and Lisbon lemons have thicker skins and can hang on the trees without damage to 28 degrees. If you have a bumper crop, freeze some juice in ice trays and then store cubes in freezer for later use in drinks or salad dressings.
Owari Satsuma mandarins, Dancy tangerines are beginning to ripen in late November. These fruits can tolerate dips into the upper twenties without a problem. Navel oranges are best left on the trees to sweeten until January, although you will find them appearing in stores earlier.
Minneola tangelos begin to get their gorgeous orange-red color in early winter--but they won't be sweet until March or April!
5. Potential cold damage is a combination of temperature (how cold) and time (for how long). Brief dips to the mid 20's will not damage most citrus. Prolonged temperatures in the teens caused much damage in 1990 and 1998.
Microclimates can be sought in looking for planting sites. Reflected or retained heat from warm walls or cement walks will provide additional protection. Fences or walls will prevent additional stress from cold winter winds.
Limes and lemons are the most sensitive, needing some winter protection in colder locales. Other citrus are fairly hardy once established.
6. Frost and freeze protection tips:
Make sure all plants, especially those in containers, are well watered. If dry soil freezes, it will pull moisture from the roots, causing them damage. If the soil is moist it can freeze without harming citrus roots.
Christmas lights hung in citrus have proved very successful, even with temperatures in the teens. Landscape lighting at the base of the trunk is even more sophisticated. Portable shop lights will work as well. Leave lights on all night: the coldest temperature is just before dawn!
Frost blankets (sometimes sold as seedling row covers) are very helpful. They can be draped over the plant and anchored with pins. The material is light and won't damage the foliage where there is contact. Tarps, blankets, sheets, and plastic are not as effective. If used, they are best with a frame so the material doesn't touch the foliage.
There is no need to panic with a few hours of temperatures in the high 20's. The Christmas lights and frost blankets do wonders in the low twenties, and help prevent severe damage in the rare occasions when temperatures are in the teens.
Hardiness ratings from our friends at Four Winds Growers
Citrus--listed in order of cold-hardiness, most to least cold hardy:
Kumquats*--can tolerate low 20's or even into the teens (F)
Owari Satsuma mandarin
Spring/summer ripening oranges--Trovita, Lane Late, Valencia
Spring/summer ripening mandarins--Kinnow, Kara, Murcott
Mexican lime--will drop foliage at 32 degrees.
[*Don's note: at 16 degrees in 1990, all of the fruit on my kumquat froze and dropped, but the foliage was undamaged. A Navel orange 20' away was 3/4 killed.]
Chinotto (Citrus myrtifolia), an ornamental sour orange sometimes grown as a bonsai or landscape specimen, is considered hardy to 12 degrees F.
Yuzu is considered hardy to 10 degrees F.
Trifoliate orange (Poncirus trifoliata or Citrus trifoliata), often used as a rootstock, is considered hardy to -22 degrees F.
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
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