One of the 5 "C's" of Arizona, citrus is one of the easiest edible plants to grow in the Phoenix. Not only is the fruit delicious and healthy, the blossoms are gorgeous and they smell wonderful this time of year. Citrus is well adapted to our desert climate, and hundreds of varieties are available to us, from standard oranges, lemons and grapefruit, to exotic pomelo and kumquats. Did you know that Clementines are now available to grow at home?
Even if you live outside the Valley of the Sun, read on to learn some tips and techniques for growing and enjoying citrus.
When, Where and How to Plant a Citrus Tree
A proper citrus planting site should have the best soil possible, with good drainage. If there a white, hard layer of calcium called 'caliche' in the soil, remove it with a pick axe. If you want to grow a large tree, make sure that the tree is spaced no less than 10 feet from other trees or obstructions, and that the roots will not be restricted. However, some people prefer to grow dwarf varieties or to prune trees to keep them small, in which case they can be planted much closer together.
For more information about intensive tree planting and dwarfing, click here.
If possible, protect the tree from wind and cold. For growers in colder climates, P. Allen Smith has very good information about growing citrus in containers. Read all about it here.
The recommended time to plant in Phoenix is March through June, or September and October. I prefer to plant in the spring, just after the danger of frost is passed. This gives the tree time to grow and put on foliage that will help to protect it from the summer sun, and to grow large enough to withstand a frost the following winter.
Proper planting starts with digging a hole that is slightly wider, and slightly shallower than the rootball. Fill the hole with water to ensure proper drainage and to moisten the surrounding soil. Remove the tree from the nursery pot and tease the roots apart. If roots are circling or girdled (strangling each other,) score the rootball or cut out the circling roots. Immediately place the tree in the hole and backfill with soil.
Fertilizer is not recommended at this time. Tamp down, water thoroughly, and check for settling. Do not plant too deeply or bank soil against the trunk. Wet soil against the tree trunk can contribute to disease.
1. Light pruning can be done any time of year. Keep in mind that if you expose previously shaded parts of the tree to the sun, you will need to protect those parts from sunburn usirng brown or white tree paint (or any water-based paint.)
2. Severe pruning should be done in late winter.
3. When pruning, keep in mind that flower bud induction begins when vegetative growth stops during the winter months. Budding occurs on new growth. Overzealous pruning of new vegetation will diminish bloom on your tree.
4. Thin citrus by selectively removing limbs at their base (where they connect to the tree trunk) to allow light to penetrate the canopy. Do not shear or “head” your tree, as this practice will encourage the growth of offshoots that will create a dense canopy that will prevent light from penetrating.
5. For ease of harvest, control the height of your tree by cutting the apical meristem (uppermost growth tip) when the tree has reached the desired height. Unless you want to “skirt” or trim up the canopy for esthetic reasons, allow the lower branches to grow to the ground. The best fruit tends to be on these lower branches that are protected from the sun.
6. Trim root suckers and branches growing below the graft while they are young and easy to cut.
To learn about dwarf pruning methods, click here.
1. Purchase trees from a reputable, local nursery. Check with your local university extension office or Master Gardeners program to find out which varieties are best for your climate. Locate yours here.
2. Do not purchase by mail or bring in from out of state. In most cases, transferring trees across state lines is illegal without a license. Transport restrictions serve to prevent the spread of citrus diseases.
3. Know your tree’s true age. Though often sold in the same size pot for the same price, a 1 year old tree will be about 2 feet tall. Add about a foot per year. Most citrus trees will not produce much fruit for 3 years, so it may be tempting to buy a taller tree. However, if it has been in the same small pot for too long, the roots may be circling or girdled.Trees in this condition are called root bound, and they tend not to thrive after planting.
If you see any roots coming out of the pot, or if you can gently remove the rootball from the pot and notice that the roots are circling, leave the tree at the nursery and select one that is in the appropriate size pot for the size of the tree.
4. On the other hand, a small tree sold in a larger pot for a higher price is not a good buy, either. As trees grow, nurseries need to move them into larger pots. This is necessary, but if you purchase a tree that has recently been repotted, you will pay a higher price even though the tree may not be any bigger or older than similar trees that remain in smaller pots.
5. For Arizona homeowners, the label on your tree should include a CDA (California Dept of Agriculture) or and ADA (Arizona Dept of Agriculture) number, such as CDA # 1002376. Buy a locally grown tree, if possible, as the will be best adapted to our unique growing conditions.
An over-watered or under-watered citrus tree is a stressed tree!
Drought-stressed trees initially show signs of leaf curl. The leaves will be limp in the afternoon and rolled up like a taco. Add water. (Note: if the leaves are contorted, but still standing upright and not limp during the afternoon, the problem may be thrips damage, not water stress.) Continued stress caused a decrease in fruit size, and the tree may drop flowers or fruit. The good news is that citrus can recover from mild drought stress easily, and will usually flower again within a month of receiving adequate water.
Proper irrigation requires that the soil be saturated to a depth of two feet from the tree’s trunk to its dripline (edge of the canopy.) Click here for a chart that shows approximately how much water citrus trees of different sizes require.
Keep in mind that the chart gives a daily amount of water, but that does not mean that trees out to be watered every day. Instead,every time that you water, saturate the soil to a depth of 2-3 feet, and then allow the top 6 inches of soil to dry out before watering again to the same depth. Use a soil probe or long screw driver to test your soil. Always water to at least a 2 foot depth to avoid salt accumulation and ensure that all of the roots are receiving water. Obviously, you will need to water more frequently in the summer (every 7-10 days) than in the winter (every14-30 days.)
To water properly, create a basin around your tree that extends past the canopy. Drip emitters or sprinklers should also extend beyond the canopy. Provide at least 3 emitters per tree, preferably on their own water line or zone. If possible, remove grass from around your tree (it absorbs nutrients and water that your tree needs.) Avoid watering foliage. Tree basins, or wells, need to be expanded as a tree grows to mirror the size of the canopy (the upper part of the tree, including branches and leaves.) Move emitters to the edge of the well.
Signs of over-watering include leaf yellowing and defoliation. Soil should be allowed to dry out somewhat between watering. Do not allow the trunk to remain wet after watering (this invites disease.)
Citrus trees need the following elements:
N (nitrogen) is the most important. Lack of N leads to yellow leaves, leaf drop and small fruit. Older leaves tend to turn yellow first, then younger leaves. Do not confuse this with winter yellows, which occur due to cooling of the soil and does not cause leaf drop. Over fertilization leads to dark green leaves and dry, puffy fruit with thick peels. How much N does your tree need? Roughly ¼ lb of N for every year of life ( ¼ lb in year 1, 1 lb in year 4.) When the tree is 5 years an older, it needs 1.5 lbs of N per year. (Grapefruits need about ¼ lb less, lemons about ¼ lb more.)
P (phosphorous) is necessary to root growth and bloom. It is found in most complete citrus foods. Trees require roughly 1/10-1/2 pound per year, but too much P is not really a problem.
In Maricopa County, applications of Iron and Zinc are usually necessary. Lack of these nutrients can mimic N deficiency, but younger leaves will yellow and will remain small. Leaves may display interveinal chlorosis, yellowing of the leaf while leaf veins remain green. Ironite is a good source of iron and zinc. Use chelated iron or lignosulfonates instead of iron sulfate, which is not effective in high pH soils.
Two options for fertilizing are "all in one" citrus fertilizers or single-element fertilizers. Whatever you choose, apply according to the instructions on the bag. Water in granular fertilizers. Avoid fertilizer spikes, which tend to dissipate too quickly on our alkaline soils.
How to read the fertilizer bag...
Fertilizer labels display a “guaranteed analysis” of how much nitrogen (N,) phosphorous (P,) and potassium(K) are in the bag, in the order N-P-K. For example, a fertilizer with analysis 15-30-15 contains 15% N, 30% P, and 15% K. If the bag is 10 lbs total, multiply 10 x .15 to calculate how much N is in the bag (1.5 lbs in this case.) If your tree needs 5 lbs of N per year, then you will need to apply 3-4 bags per year.
So, if you will fertilize 4 times per year, apply one bag at each application to total 4 bags for the year.
Fertilizer should be applied in multiple small applications as opposed to one large application, before July 1 to prevent fruit dryness due to over application of N. Choose one of the following fertilization schedules.
3 applications: February 1, April 1, and June 1
4 applications: February 1, March 15, May 1, and June 15
6 applications: monthly, from February 1 through July 1
Note: lemons and limes can be fertilized through October 1. Apply the majority of fertilizer in the spring, only applying about 1/3-1/4 in the fall. Lemons and limes do not granulate (dry out) due to over application of N, and they tend to need more nutrients than other citrus.
Citrus planted in a lawn will also need a little bit extra fertilizer, as it has to complete with grass for the nutrients.
Citrus varieties are classified as ‘Early,’ ‘Mid,’ or ‘Late’ season varieties. This system provides a general guideline to understand when to harvest.
However, the only ‘sure-fire’ rule of thumb is to harvest when the fruit tastes good. Fruit that does not look ripe may be ready to harvest despite its appearance. Taste test your fruit to determine when to harvest.
Fruit that is picked from a tree will not continue to ripen. Fruit left on the tree will continue to ripen and sweeten as the season progresses.
The University of Arizona Cooperative Extension publishes a detailed harvest calender for the low desert. It can be accessed online here.
Citrus trees are sensitive to the sun. To avoid sunburn lesions on the tree trunk, paint the tree and exposed limbs with water based paint (it does not have to be white.) Sunburned leaves turn brown or yellow, usually only on one side of the tree.
However, if the entire tree has leaves with brown tips, the problem is more likely salt damage than sunburn. Water less often and more deeply to alleviate salt damage. Gypsum and liquid sulfur can also aid with salt abatement and help the tree absorb necessary nutrients.
In the winter, cover small trees with frost cloth when there is a freeze warning, or string Christmas lights (not LED) and turn them on to help keep your tree warm. Wrap the trunk in burlap, or shine a shop lamp on the tree. Irrigate the tree the evening before a frost warning. Plant in a warm area of your yard. Generally, southern exposures and the slope peaks tend to be warmer than low areas. Weedy areas are also cooler than weed-free areas.
If your tree suffers frost damage, generally newly-grown twigs will turn brown. Wait to prune until late spring. Then cut back to undamaged wood. New growth will be slow and you may not get any fruit for a season, but the tree should recover and bear fruit the next season.
Protect your tree from subsequent sunburn due to depletion of the canopy. Cut back water and N due to depletion of the canopy. Increase water slowly to prevent root rot, and fertilize in the fall to encourage leaf growth. Don't worry about the late application of fertilizer granulating fruit, since production will be low or non-existent due to the frost damage.
Frost damaged fruit should be immediately harvested and juiced! Freeze the juice, if there is an abundance. Damaged fruit will make itself obvious as it will soon begin to fall off of the tree.
Sooty Canker (Hendersonula:) A fungal infection that invades bark that has been damaged by frost, sunburn, or pruning wounds. Treatment is not necessary as the fungus does not spread to uninjured tissue.
Asian Citrus Psyllid: No reported cases yet in AZ. Check with your local university extension office to find out if it has spread into your area. The psyllid carries a microbe that causes citrus greening, stunting fruit growth and eventually killing the tree.
California Red Scale: Causes red spots on fruit rinds. Report it to the Dept of Agriculture in your state.
Thrips: Causes a brown ring around the stem-end of the fruit. Damage is cosmetic only and fruit can be eaten.
Citrus Peel Miner: Causes brown “trails” on fruit rinds. Damage is cosmetic only and fruit can be eaten.
Mites: Cause “stippling” on fruit. Mites look similar to tiny spiders. Spray with soapy water to control.
Black Rot: Decays the inside of fruit. Bag and throw infected fruit away.
Fruit splitting: Caused by N deficiency, uneven watering, sunburn, genetics (some varieties are more prone to splitting than others)
Chimeras: Segmented coloration on fruit or leaves. No treatment is necessary. It is just a natural mutation.
Sheepnose: Due to heat and over application of N. Tends to dissipate as tree ages.
Sunburn: Brown or yellow fruit discoloration. Usually occurs on one side of the tree. Provide sun protection, if possible. If the tree is generally healthy, a small amount of sunburn on a few fruits should not be a problem.
Information concerning citrus diseases, complete with photos, is located online here.