When I talk to gardeners who are new to Arizona, they’re often most excited about finally getting to grow citrus trees. For years, they’ve been dreaming of plucking lemons—and oranges and kumquats—from their own backyards. Arizona is one of only four states in the United States growing citrus commercially—indeed, one of the first things that we learn about Arizona history is that this tangy fruit is one of the five C’s that played a crucial role in our state’s early development, along with copper, cattle, cotton, and climate.
Around 1970, at our state’s production peak, Arizona had 80,000 acres of commercial citrus orchards across low-lying, frost-free areas of Yuma, Pinal, and Maricopa counties. Many of the groves in the Phoenix area were lost to urban development, and Yuma is the center of our state’s citrus industry today. California, Florida, and Texas produce the bulk of most types of citrus, with Arizona making moderate contributions here and there, mostly of lemons and tangerines. We come in second place (of two contestants) with our lemon production. California still tops us there by around 20 million boxes a year.
Arizona’s commercial production may be relatively modest, but judging by the number of citrus trees in our landscapes and the boxes of free fruit that begin showing up in breakrooms every November, home production in Arizona is doing just fine. Some say it’s our amiable winter, with its hint of cold weather, that makes our citrus taste sweeter than the rest. But in some parts of Baja Arizona, the winter can bring more than just a hint of cold weather. It’s easy to be caught unprepared for that first cold snap because it often comes without much warning. Our plants can get sideswiped, too.
Since we don’t always get clues from Mother Nature that things are about to get chilly, you may need to coax your citrus trees into dormancy by slowly reducing how often you water in the months leading up to your area’s first winter freeze. In Douglas and Bisbee this happens around Nov. 3, in Tucson around Nov. 25, and in Ajo around Dec. 25.
We want our citrus trees to be dormant when it freezes because fresh, new growth is more sensitive to cold temperatures. Older growth, older trees, and dormant trees are hardier, but younger trees and trees with lots of new growth can take quite a hit. Each frozen branch becomes a wound, and the tree must use stored energy to seal off lots of these little wounds at once while fighting off bacterial and fungal opportunists. Older trees are likely to have enough stored energy to produce more foliage and recover, but young trees may not have enough “storage space” to be so well prepared.
Those of us in areas prone to freezing may want to read the University of Arizona publication “Protecting a Citrus Tree From Cold” for detailed information about frost protection, or Tony Sarah’s article “Winterizing Citrus” at EdibleBajaArizona.com for the short and sweet version. A couple of points that both articles make are worth repeating here. The first is that the various types of citrus have different cold tolerances. Kumquats are the hardiest, down into the high teens. Mandarins (tangerines), sweet oranges, limequats, and Meyer lemons are hardy to 24-26 degrees, while tangelos and grapefruits prefer 26-28 degree lows. Lemons and limes are the least hardy, and will suffer damage when exposed to temperatures below 30 and 32 degrees, respectively.
The other point is that a well-hydrated tree will tolerate cold temperatures better than a thirsty one. Watering recommendations often seem counterintuitive, and this is one of those cases, but you should water your plants a day or two before a freeze. If leaves are curling and the branches are limp it’s likely to take more significant damage.
There’s an important distinction to be made here between water amount and water frequency. Watering frequency changes regularly with the seasons and other environmental conditions, while watering amount changes slowly (increases) as the tree ages.
To promote deep rooting, the experts at the University of Arizona recommend watering to a depth of two to three feet every time you water an established citrus tree. Soils with high amounts of clay must be watered slowly to get water down to this depth, but they dry out slowly, too. Water moves more freely through sandy or gravelly soils, requiring less time to water to the proper depth, but more frequent water and fertilizer applications. Getting to know your soil is one of the first steps to determining the watering needs of your tree.
A soil probe is a great tool for figuring out how deep the water is going and where the soil is dry. It’s a long, smooth rod with a pointed end that moves easily through damp soil and stops where the soil is dry. Once you’ve determined how long it takes for water to get to the proper depth in your soil with your watering method of choice, you can determine how frequently to water by allowing the top six inches of soil to dry out between water applications.
Much of Baja Arizona sticks to feeding citrus trees around Valentine’s Day, Memorial Day, and Labor Day. There are fertilizers that are specifically formulated for citrus trees, and the standard balanced fertilizers (like a 10-10-10 formula) can be used as well. Avoid using a slow-release fertilizer in September if you live in a frost-prone area, as it may encourage new growth through winter. New trees don’t need any fertilizer until they’re established, and only limited amounts, if any, for the first year after planting.
If a properly planted citrus tree is being watered and fertilized correctly, it should require minimal maintenance otherwise. Except for occasional removal of suckers that sprout up from the roots (or anywhere else below the graft point) very little pruning is necessary. Lower branches are left alone to help protect the trunk from sunburn, and the canopy maintains a naturally rounded form on its own.
There aren’t many pests to worry about, either. The most common citrus pests that I see in Tucson (thrips and leafminers) cause mostly ornamental damage. There are a few caterpillars that may eat up a small branch or two, most notably the orange dog caterpillar, which fools potential predators by disguising itself as bird poop. I’ll usually leave them alone if it’s a large tree that won’t miss a few leaves. If the tree is young or taking too much damage then you can knock caterpillars back by hand-picking them or spraying them with an organic pesticide that is safe to use on edibles.
The No. 1 pest to watch out for right now is the Asian citrus psyllid. This tiny insect can spread a disease called citrus greening, which would wreak havoc on our citrus industry as it already has in Florida, Texas, and California. The Arizona Department of Agriculture is asking those of us with citrus trees at home to learn the signs and symptoms of the pest and the disease, and refrain from bringing citrus into Arizona from any other state.
The Asian citrus psyllid adult is tiny, about the size of an aphid, with mottled brown wings. The nymph stage of the insect is probably easier to notice because it produces white, waxy tubules that begin to build up on tender new leaves and branches where the insects are gathered. Insects shouldn’t be taken to a nursery for identification. Instead, call your county extension office or the Arizona Department of Agriculture for help. Citrus greening, the bacterial disease known as Huanglongbing, hasn’t been spotted yet in Arizona, but it can take a tree up to two years to show symptoms of the disease. If you’ve identified the Asian citrus psyllid on your citrus tree then you should watch for asymmetrical yellow splotching on leaves, and lopsided fruit that tastes salty and bitter. The symptoms of citrus greening can be confused with other more common problems, such as nutrient deficiency, but these symptoms are often the same on each side of the leaf, while the mottled yellow spots caused by citrus greening are completely different on the left side of the leaf than they are on the right. Infected trees will decline over five years, and there is no known cure, so it’s important that we stay vigilant to protect Arizona’s citrus.
Another good reason to buy citrus locally is for the rootstock. Like most fruit trees, citrus trees must be grown from cuttings to get reliable results. You can plant a Meyer lemon seed, but it won’t grow into a Meyer lemon (it will likely have entirely different traits). Unfortunately, a parent tree might not like the soil that we want to grow it in. Our soil has a high pH, which makes many plants unhappy. We get around this problem by grafting cuttings (called scions) onto the roots (called rootstocks) of plants that tolerate our problematic soil conditions.
John Babiarz, co-owner of Greenfield Citrus Nursery in Mesa, sees a big difference in the performance of trees grown on anything other than the Seville sour rootstock, which tolerates the soil of the Salt River Valley. The trees out of Yuma are more often on a Carrizo C35 rootstock, a trifoliate hybrid that tolerates sandy, rocky soils, but doesn’t do well in the Salt River Valley. Citrus trees purchased at big box stores are likely to have come from a nursery growing trees for an entirely different market, and Babiarz suspects this is often the culprit when homeowners have major problems getting their nonlocally purchased trees to grow. He recommends purchasing from a reputable nursery that purchases or grows trees for the local market.
Greenfield Citrus Nursery will host an annual Master Gardener Citrus Clinic on Jan. 20. It’s worth a day trip to Mesa for the experts, speakers, beekeepers, plant sales, and tasting table. The University of Arizona also has detailed publications on growing citrus available online, and our county extension agents and master gardeners are extremely helpful and knowledgable. ✜
Amy Belk is a garden writer and photographer, a certified arborist, and a certified nursery professional who has been learning from her garden for 16 years. She and her husband homestead on a little piece of the desert in the heart of Tucson.