(and other Citrus in the event of a frost*)
Although uncommon, local winter temperatures do occasionally drop below freezing, so before any such big chill hits, it’s good to spend a little time contemplating how to protect your navel oranges and other citrus from frost damage.
Should a frosty dip in temperature be forecast, do water all your citrus (and the rest of the garden, especially frost-tender plants.) The roots of thirsty plants suffer much more from icy-cold soil than do hydrated ones. Shelter potted plants in a warm spot inside, if possible, or under an overhang. If that’s impractical, cover the foliage with a frost blanket/row cover such as Harvest Guard (120 square feet @$18.00). Citrus in the ground should also be protected with frost blankets, which can remain on the plants during the day. [Other fabrics may be used for this purpose, but should not touch the foliage, and should be removed during the day.]
Another interesting, optional practice is to spray fertilizer monthly on your citrus through the winter. Don Dillon, co-founder of Four Winds Citrus Growers, has said that winter foliar feeding can be helpful for a couple of reasons: plant roots can’t take up nutrients very well from the soil when temperatures are low, but the trees are able to take in nutrients through their leaves. Also, even if tender new growth produced by this feeding is hit by frost, those damaged leaves will still act as a protective frost shield for the rest of the plant (providing you don’t prune them away too soon.) This liquid fertilizer could be Citrus Grower Blend (from Grow More, 10 oz. @ $6.99), or an all-organic alternative like fish emulsion and kelp (EBS Fish Emulsion with Kelp, 32 oz. @$12.99). Be sure the plants are well watered before applying the fertilizer.
Finally, don’t fret too much if a freeze “prunes” your pommelo or glacées your grapefruit. With nurturing, many damaged citrus recover quickly after a cold snap.