Citrus Tree care in Arizona

Disclaimer: Let me start by saying, I am not an expert by any means. I am simply summarizing information from people that DO know what they are talking about.

What to Trim

The short answer is don’t trim. It is not needed unless the branches are rubbing on each other. If you want to do it for aesthetic reasons this is ok, but don’t due it in the cold winter or host summer.
The most important thing to remember is that you don’t want to expose branches to the hot sun. It can damage the tree. Keep in mind that citrus tree are really a giant shrub. Mother nature intended them to have branches that nearly touch the ground to protect the bark from the sun. If you have a citrus tree that has been trimmed up to look like a tree and the trunk receives direct sun, you should cover it. I don’t recommend painting it because paint is very toxic and the tree absorbs it which is then in the fruit you will be eating.
You don’t even need to trim the dead wood says Claire Charlton. If you want to trim the dead wood, make sure to do this after the new growth in the spring has started so that you can see how much of it is actually dead. For example, if new growth is coming out of the “dead” wood, it probably only looks dead and is still alive.

When to Trim

Do it when the temperatures are mild (not too hot and not too cold). In Arizona the best time is in the spring (March to early May). You can do minimal pruning during the late fall (November to February). Try not to do the pruning around times of frost, this is what can damage the trees.

Fruit / Harvest

Fruit ripens in the late fall (November to February for most varieties). This is when you will want to harvest (pick) you citrus fruit.
In general oranges can be harvested in December through February, with the exception of Valencia oranges which are later and good through May.
Pink Grapefruits can be harvested Nov – May or Jan - April you have the Texas Star Ruby grapefruit.
Tangerine can be harvested in December and January.
Click here for a detailed document on harvest dates for the different types of citrus.

Watering

The most comprehensive guide to water citrus trees in Arizona I have found is an article called Irrigating Citrus Trees by the University of Arizona.

Tips

• Reduced fruit size – this is the first sign of water stress, but can be difficult to notice.
• Leaf curling – 1st noticeable sign of water stress. Starts by turning dull green and curling from the outer edges of the leave inwards.
• Crispy leaves – After leaves turn dull green and begin to curl water is needed. If no water is added, the leaves will become crisp and brownish. It will start at the leaf tip and progressing until the entire leaf is dead.
• Slow water – from the trunk of the tree to just beyond the drop line to a depth of two feet. Do slow watering less often, but run for many hours to allow it to get to the depth of 2 to 4 feet.
• 7 to 28 days – days between watering depending of season and soil conditions. See chart in the referenced article for specifics.
• Grapefruit and lemon trees require 20% more water than orange trees
• Allow soil to dry – Don’t water unless the soil is dry to a depth of about 6 inches to limit soil-borne disease.
• Probe for wetness - Use a rod (metal, wood, soil probe, etc) to determine how deep your water is going. The probe will move easily through wet soil (unless clay), and stop when it reaches dry soil. Regardless, you should be able to feel the difference between dry and wet soil just after watering.

Application Methods

Typically a building a basin about 1 foot beyond the canopy and about 4 to 8 inches high is the easiest for home owners. The basin can then be filled with water when it is time to water the tree. Water can safely touch the trunk of the tree if it is not damaged or planted too deeply. Do NOT pile dirt around the trunk.
You can also use bubblers, drip systems, soaker hoses, etc. The trick is to make sure that the water is distributed (at least around the drip line), not just in select areas. For more info on deep watering, click here.
If you are going to use a soaker hose, then position it under the drip line (the imaginary area just below the outer branches). If in doubt spray your trees leaves (not in the hot summer sun) and watch where the water drips. You should see a ring around the tree. Keep in mind that soaker hoses are not recommended for locations that have a lot of minerals deposits in the water because they can become clogged over time. A filter may be needed. Try to limit any particular run of soaker hose to 15 feet and 8 to 10 psi. A soaker hose will give you about 12 GPH at 10 psi, less for 8 psi. For more info on soaker hoses, click here.

How often to water

My trees are all well over 3 years old (if yours aren’t check here), so here is the schedule I follow. Please remember, this is for Arizona only.
Jan – every 21 to 30 days
Feb – every 21 to 30 days
Mar – every 14 to 21 days
Apr – every 14 to 21 days
May – every 14 days
Jun – every 14 days
Jul – every 10 to 14 days
Aug – every 10 to 14 days
Sep – every 10 to 14 days
Oct – every 14 to 21 days
Nov – every 14 to 21 days
Dec – every 21 to 30 days

How much to water

You really have to know the diameter of the CANOPY of your tree in feet. A tape measure is the easiest way to determine that. Just measure from one side to the other and going as close to the center of the tree as possible.
If you look at the chart here for oranges (remember grapefruit take 20% more water), you will see that the number of gallons required varies greatly depending on the month and also by tree diameter.
I have four very mature citrus trees. They are tangerine, grapefruit, ornamental orange, and orange. Their canopies have the following diameters (in feet): 21, 15, 22, 17ft respectively.
That means I need the following number of gallons per day (but only water at the interval show earlier in the How often to water section of this blog).
Now that we know how much water our tree needs, we need to determine how long we need to leave the water on in order for that much water to be emitted. Ideally, you would adjust the amount of water being emitted so that it needs to run for about 6 to 7 hours. This allows for it to soak in slowly. At the very least, try for an hour or more before turning it off. In the end, you want to make sure the water makes it 2 feet deep. You can dig down to verify this if you like.
The easiest way to do this is to run your hose, sprinklers, etc in a bucket with a known measure such as 5 gallon bucket. Time how long it takes in hours to fill up the bucket. Now divide 5 by the number of hours it took to fill the bucket to get your gallons per hour (gph).

Example

Now let’s assume it is July and my ornamental orange tree with a canopy of 22 feet. In July it needs to be watered every 10 to 14 days. It is a cooler July, so let’s go to 14 days. At the end of 14 days, I need to give the tree 14 days * 72.9 gals / day = 1020.6 gals. My soaking hose emits 320 gallons per hour on HIGH, so I need to let the water run for 1020.6 / 320 =  3.2 hours. Soaker hoses typically should be run on about 1/4 of HIGH, so I estimate about 15 hours of soaking.
NOTE: If I go by the manufactures estimate of 12 GPH for a Mr. Soaker hose, then that would be 1020.6 / 12 = 85 hrs. As you can see there is a bit of discrepancy, so do your own tests on GPM.
Tangerine Tree (21 ft canopy, but round to 22 to make it easier)
Jan – 9.1 gals per day
Feb – 13.3 gals per day
Mar – 27.8 gals per day
Apr – 39.8 gals per day
May – 49.0 gals per day
Jun – 63.4 gals per day
Jul – 72.9 gals per day
Aug – 67.9 gals per day
Sep – 53.0 gals per day
Oct – 31.0 gals per day
Nov – 13.3 gals per day
Dec – 9.1 gals per day
Grapefruit Tree (15ft canopy, but round to 16 to make it easier)
NOTE: I would normally add 20% to these values, but as it turns out I am pretty close to that just by rounding up to the 16ft canopy.
Jan – 4.8 gals per day
Feb – 7.0 gals per day
Mar – 14.7 gals per day
Apr – 21.0 gals per day
May – 25.9 gals per day
Jun – 33.5 gals per day
Jul – 38.6 gals per day
Aug – 35.9 gals per day
Sep – 28.0 gals per day
Oct – 16.4 gals per day
Nov – 7.0 gals per day
Dec – 4.8 gals per day
Ornamental Orange Tree (22ft canopy)
Jan – 9.1 gals per day
Feb – 13.3 gals per day
Mar – 27.8 gals per day
Apr – 39.8 gals per day
May – 49.0 gals per day
Jun – 63.4 gals per day
Jul – 72.9 gals per day
Aug – 67.9 gals per day
Sep – 53.0 gals per day
Oct – 31.0 gals per day
Nov – 13.3 gals per day
Dec – 9.1 gals per day
Orange Tree (17ft canopy, but round to 18ft to make it easier)
Jan – 6.4 gals per day
Feb – 8.9 gals per day
Mar – 18.6 gals per day
Apr – 26.6 gals per day
May – 32.8 gals per day
Jun – 42.4 gals per day
Jul – 48.8 gals per day
Aug – 45.5 gals per day
Sep – 35.5 gals per day
Oct – 20.7 gals per day
Nov – 8.9 gals per day
Dec – 6.1 gals per day

Fertilization

If you want good fruit, you will need to fertilize your fruit.
It is possible to over fertilize your fruit also. Feeder roots are just below the surface of the soil and can be burned by over fertilization. So, be sure to not over fertilize.
Established grapefruit trees only need half the amount of fertilizer normally given to other varieties of citrus trees.
Also, you may want to test the pH of your soil. If the soil has a pH level of 7 or above then the soil is too alkaline and the fertilizer can’t be absorbed by the tree. If this is the case, add Chelated iron tablets to the soil to lower the pH.

Overview of Fertilization Process

1. Water the tree before applying the fertilizer. Best if do this a day before you fertilize.
2. Apply fertilizer evenly beneath the tree’s canopy as instructed by the fertilizer.
3. Water the tree after fertilizer is applied to wash nutrients into soil. Be sure to wash all areas that have fertilizer so that it will be washed into the soil where the feeder roots can access it.

Fertilization Schedule

In general the tree needs the most fertilizer from the time they bloom until they have firmly set fruit. It is very unlikely that a tree will starve to death. Trees can survive years without fertilizer. I take that to mean when in doubt do less.
This seems to depend on who you ask, the soil, where you live, etc. General advice seems to be that you can do it as often as every 4 to 8 weeks in the Spring and Summer (the growing season) which is from February through August. Then in the fall and winter do it every 2 to 3 months.
The direction above don’t appear to be specific to Arizona. In Arizona, the advice seems to be three times a year. The recommended times are March, late May, and September or better yet, use the holidays as a reminder: Valentines Day, Memorial Day, and Labor Day.

Is all citrus fertilizer the same?

The short answer is no. You get what you pay for. Just like vitamins for humans it is all about the fillers and how they can interfere with the absorption of the nutrients. The general rule of thumb is that you get what you pay for. The cheaper products bulk up the quantities with fillers and the more expensive products generally have less fillers. With that said, don’t try to compare the costs of name brand to less known brands. Be aware when you are paying for the name, not the product. You want to read the back label and look for products that have as many minor elements as possible (at least 6 elements, but 8,10, or 12 is better).

Fertilizer / salt burn or sun burn?

Sun burn is most severe on parts of the tree that get the most sunshine and will occur on any part of a leaf. Fertilizer/salt burn starts at the tips of the leaves and will be more severe on the side of the tree that gets more sun, but will also be present on parts of the tree that receive less exposure.

How much Fertilizer

Click here for a chart on recommendations for Arizona. You should really use what the fertilizer bag says, but you can use the chart to make sure you are not over fertilizing and at least pretty close. Remember, mature grapefruit trees only need half the shown amounts.

Example

Calculating the diameter of the trunk of your tree
It seems that all fertilizers want to know the diameter of your trunk. So, let’s figure it out.
You could eye ball it, but I prefer using a little math to figure it out. How ever you do it, measure about 4 to 6 inches above the ground to get an accurate measure.
I measured the trunks of each tree with a tape measure you would use to measure your waste line so that I could get an accurate measure of the circumference (the distance around the trunk). The reason I did this is so that I can calculate the diameter of the trunk (assuming that is is mostly circular).
I have four very mature citrus trees. They are tangerine, grapefruit, ornamental orange, and orange. The circumferences are 46, 25, 34, 23 inches respectively. To calculate the the diameter I just divide these number by 3.14 (pie). This gives me 14.6, 8.0, 10.8, and 7.3 inches respectively for the diameters.
From this just follow the instructions on your favorite Citrus fertilizer. Yes, there is special fertilizer that is specially made for Citrus and that is what you should use. Palm fertilizer is an ok substitute if Citrus fertilizer is not available.
If you use the chart described above and assume large fully grown untrimmed trees and a 5-10-5 fertilizer that would mean a 30 lb bag is needed for the entire year. Meaning, for each fertilization, 10 lbs is needed. For me, the chart and the fertilizer bad didn’t match. The chart indicated a bit more for more and less for others depending on the trunk size. When in doubt, I would say follow the instructions on the bag of fertilizer.

 

Certified Arborist

I think it is important to take advise from certified arborists such as Arizona Tree. I have not used them yet, but plan to if/when the time comes.

Sources

When & How to Trim Citrus Trees in Arizona
Irrigating Citrus Trees
How to select the right fertilizers for all your tropical plants
Drought – Watering Trees
Mr Soaker Hose
How to Deep Water Plants
How to Water Citrus Trees
How to Fertilize Citrus Trees
Fertilizing Citrus Trees – Best Practices for Citrus Fertilizing
Citrus Care: How to Fertilize Citrus Trees
Growing Citrus in Phoenix Arizona
Annual Fertilizer Requirements for Citrus (by City of Gilbert, AZ and UofA)
Low Desert Citrus Varieties (by UofA)