Tips for keeping your citrus trees happy, healthy, productive

Thrips cause lemon tree leaves to curl

Q: I am having a problem with my lemon tree. The leaves start out normally, then curl and have a whitish/grayish line on them. I am hoping that someone can help me figure out what to do.

A: An insect called thrips is feeding on your citrus leaves. These tiny insects get inside the leaf bud and feed on the new growth. Their feeding damage causes the disfigured leaves but it doesn’t do any serious damage to the tree.

The leaves are still able to photosynthesize and the tree will still produce fruit. So the nice thing is you don’t have to do anything.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to

tucsongardensage@gmail.com.

What to do about thick-rind grapefruit

Q: My red grapefruits this year have thick rinds. Is there a way to avoid this in next year’s crop?

A: Thick rinds on citrus may indicate too much nitrogen and a lack of potassium or potash in your fertilizer. Make sure you are using a complete fertilizer that contains some of each of nitrogen, phosphorus and potassium. Since it is the time of year to put down your first fertilizer dose, you can hopefully get this problem fixed before your next crop.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to

tucsongardensage@gmail.com

Splitting oranges

Q: I have an orange tree that is 9 years old. The oranges look OK and are being watered by a sprinkling system. I also had the tree pruned this year and am getting more growth. They are starting to turn orange in color, but I noticed some oranges had already changed to the color orange or partially orange. Those are the ones I had to pick off the tree because they were all split in the middle with an orange on either side, except for one that was black (inside) on one side. I want to know what is causing the oranges to split in half. I do occasionally give them some extra water (especially in the summer) with a hose for about 20 minutes or so. Is there anything I can do to keep from losing all my oranges?

A: Split fruit can be caused by a variety of stressful conditions for an orange tree, including extreme fluctuations in temperature, humidity, soil moisture and fertilization. The rind splits when water and sugars are transported from the roots to the fruit and the rind is unable to expand quickly enough. If you are watering and fertilizing properly and otherwise taking good care of the tree, it is less likely you will have problems. The factors we have the most control over are fertilization and soil moisture so it is important to provide fertilizer at the right time of year and deep irrigation rather than just watering on the surface. I am afraid your sprinkler and hose method is not enough for your tree. I recommend you check to make sure your irrigation schedule is providing water down to 36 inches below ground. You can check this with a soil probe. It is best to install a drip irrigation system around the outside of the tree canopy and operating on a schedule that provides water 36 inches deep every seven to 10 days in the summer, every 10 to 21 days in the spring and fall, and every 14 to 21 days in the winter.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email: plwarren@cals. arizona.edu

Why won't my navel orange tree bear fruit?

Q: I have a green and healthy navel orange that is about 5 feet tall and that was planted about 4 1/2 years ago. But I have never had any fruit that matures. I get some blossoms, but I never get any oranges. What should I do about it?

A: First of all, your tree is not that old. Generally, it takes two or three years before a young citrus matures and bears fruit, and your tree is just a little bit older than that. But the other problem is that navel oranges generally don’t like a hot, dry climate like we have in Southern Arizona. If you get a hot, dry, windy day in June, all those orange blossoms can get knocked off and no fruit gets started.

For more do-it-yourself tips, go to rosieonthehouse.com. An Arizona home building and remodeling industry expert for 25 years, Rosie Romero is the host of the syndicated Saturday morning Rosie on the House radio program, heard locally from 8-11 a.m. on KNST-AM (790) in Tucson and KGVY-AM (1080) and -FM (100.7) in Green Valley. Call 888-767-4348.

You can try to trick those navel oranges by planting other trees around them to protect them from heat and wind.

You may also not be doing enough fertilizing. August-September is a good time of year to fertilize; so try to do it as soon as possible. Then fertilize again in January-February and again in April-May.

Check charts online for how much and what type of fertilizer to use, depending on the size and age of your plant.

When to pick tangelos, tangerines

Q: How long can tangelos be left on the tree and still be good? After picking, how long should the tangelos last? Should tangelos be stored on the counter or in the refrigerator?

A: The recommendation is to pick citrus when it is ripe, since they don’t ripen any more once off the tree. Since we all have different tastes, it is best for you to pick one or two and try them. If they taste as good as you hoped, then pick them all. You can also experiment to see how the taste changes over time and just pick enough to eat each week. If you have a lot, storing them in the refrigerator is recommended since they will spoil more quickly if left at room temperature.

Tangelos and tangerines have some of the shorter harvest times of all the citrus fruit, and each variety is ripe for about two months. Depending on which variety you are growing, harvest is recommended between mid-November and mid-February.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to

tucsongardensage@gmail.com

Orange dog caterpillars

Q: I am finding orange dog caterpillars on my citrus now. Some are very small and some are almost two inches long. Why are they different sizes? Wouldn’t they all hatch at the same time?

A: The giant swallowtail butterflies (Papilio cresphontes) that lay the eggs from which the orange dog caterpillars emerge are active throughout the citrus growing season so the caterpillars you are seeing are likely from more than one egg laying event and did hatch at different times.

These caterpillars, which famously look like bird poop, molt through five instars or phenophases before they form a chrysalis or pupa, from thence into beauty. The rate at which they grow is related to the availability of food and the air temperature. Since your caterpillars are all on the same plants with the same conditions, it is safe to say they are all growing at the same rate.

If you’re curious like me, you can monitor their growth as a science experiment to see how long it takes for them to pupate. If the idea of sharing your observations with others in the interest of science gives you a thrill (also like me), there is a program on the Internet and an app for your smartphone called Nature’s Notebook.

There is a workshop on how use this application at Brandi Fenton Memorial Park from 9 a.m. to noon Friday, Sept. 25. Register at the Pima County website, ow.ly/Sd21w.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to plwarren@ cals.arizona.edu

Will 'suckers' grow and produce fruit?

Q: My Tangerine tree is quite large and has “suckers” growing up from ground. Can I dig these up with a root ball? Will these produce fruit if grown? Folks and common sense tells me that coming from below “Graft” area that they will grow trees but, NOT bear fruit. Also, I live a mile south of the old Desert Treasures orange groves. So what happened to the “Thermal Belt” that used to be in this area? Because now we freeze like the rest of town!

A: Any suckers growing from below the graft union on the tree will be from the rootstock. You are correct in saying that the growth from below the graft will grow and it may even produce fruit but it will not be edible. The rootstock is chosen based on its hardiness rather than its fruit quality.

Since these suckers take energy to produce, it is best to prune them off whenever you see them so the tree can put its energy into something you might find tasty. I checked with our University of Arizona Climate Scientist, Mike Crimmins, and there is no thermal belt we are aware of having been in your area. This has been a colder year than normal with 10 days having freezing events so far. The average is 16 for the whole season and there is plenty of winter left. So it’s possible you are noticing it more this year.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

Spring time is time to fertilize

Question: I understand that the first fertilizing of the season for citrus trees is Valentine’s Day. However, given our warm weather, projected to continue for at least the next week, would it be advisable to move the date up?

Answer: Yes. Valentine’s Day is really just a day that is easy to remember that is based on the expected growth stage of citrus at this time of year. Since we seem to be jumping into spring on Groundhog Day, despite the advice from Punxsutawney Phil, it makes sense that the plants will respond accordingly and having the fertilizer available for their early growth is a good idea.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

Citrus tree leaves dropping after freeze - what can I do?

Question: What should I expect of my citrus trees after the recent cold weather. They’re losing every leaf. Is there anything special I should do to give them a fighting chance to survive?

Answer: The important thing to do now is wait and see how they respond once the warm weather begins. Since the foliage has been reduced, you should cut back your watering by half. Without leaves, trees will take up less water and you do not want excess water around the roots. Also hold off on any fertilization until March 15. Once they start growing again you will see where the dead parts are, and then you can prune them off. It is best to wait to prune until after the last frost date (March 15) in case we have another freeze. The dead parts will protect underlying live parts. In the event of another freeze, it would be good to cover your citrus with frost cloth or a reasonable facsimile thereof if they are small enough to do so.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

Do I need to paint my citrus tree?

Each year, thousands of Arizona residents email or call Rosie Romero’s radio show with questions about everything from preventing fires in their chimneys to getting rid of tree roots invading their sewer system. His goal is to provide answers that suit the specific lifestyle wherever someone lives in Arizona.

Q: I have a peach tree and a couple of citrus trees in the middle of my lawn. They’re doing OK, and they are well watered by my sprinkler system, but every summer I think maybe I should paint the trunks with tree paint to protect them. Are the trees getting enough water with this irrigation system?

A: If the trees are healthy and doing well, and they dry out between waterings, I don’t think you have to worry about the sprinklers. The paint is generally used when the trees are younger and the bark is tender. But you can paint them if you want to.

A good product to use is natural-style bark-colored paint instead of white. You also do not have to paint citrus trees if you let them grow into a bush shape – their natural formation – because the foliage will protect the trunk.

Q: A few weeks ago, I noticed water coming into my kitchen from a leaky pipe behind the microwave. It damaged the wall and my cabinets. It turned out that the problem was a nail that had been driven into a pipe 19 years ago, and there had been a slow leak for a long time. I had a recovery firm come in and everything was thoroughly cleaned up. But when I filed a claim with my insurance company for the clean-up costs, they said that the water had to have been visible some time ago, and we did not react quickly enough to mitigate the damage. So they’re going to deny my claim.

A: After you get a written statement from the insurance company denying your claim, you can take it to the state Department of Insurance and make an appeal. Unless you had seen a big stain on the wall or a pool of water on the floor, I’m not sure that you could have known about the situation before the real flood took place in your home.

Q: A couple of weeks ago, I had a six- to eight-inch diameter tree that blew over. I straightened the tree out and set it upright again, but I’m wondering if there’s anything I can do to make the tree do better and recover from this event.

A: You’ll know in a couple of weeks if there’s any permanent damage to the tree. The situation may work out OK, but it might not. You can give a tree vitamins and hormones to help it recover from a shock like this, but that’s about it. If the tree does well and recovers, you should be sure to stake it properly so this kind of damage doesn’t happen again.

Buy two or three stakes at a nursery. Then you fasten the trunk to the stakes by using soft webbing ties.

To prevent a tree from blowing down, it’s also important to water the tree in an area out farther than just near the root ball around the trunk. That type of irrigation will encourage the roots to grow outward more and more as they seek water; those expanding roots provide better base support for the tree when it’s windy.

Right time to trim citrus

Q: I have a question about trimming our two dwarf grapefruit trees. We just removed all the fruit from them. We would like to trim up the bottoms (they both touch the ground, and when the fruit comes on and grows larger, they are very weighed down). There are some dead limbs in the middle also. Can we trim the citrus trees now before they start to bloom for the next batch of fruit?

A: Yes, you can prune your trees now. Dead limbs and sprouts (aka watersprouts or suckers) can be removed any time. Between February and April is best for pruning live branches. This allows the tree to leaf out and protect any limbs that may be exposed to sun. What is commonly called skirting or limbing up from the bottom should be done carefully to avoid taking off too much. The natural shape of these trees helps protect the bark from too much sun and resulting scalding damage that could occur. Removal of the low-hanging branches should only be to improve access to the soil surface, the irrigation system, or to the interior of the tree. Citrus wood is naturally strong and is not as likely to break under the stress of a large fruit load. Furthermore, citrus trees can produce fruit in all but the most shaded part of the tree, and need not be regularly pruned to allow light into the interior of the canopy. Even when the crop load is heavy, individual fruit size is large, so pruning to reduce the crop load and improve fruit size is not necessary except occasionally with tangerines. Finally, citrus fruit quality is typically just as good or better from a minimally pruned tree as compared with one that is heavily pruned. Lower canopy fruit often is of the best quality because it is not often affected by sunburn, scarring by windblown soil particles and by the movement of adjacent branches and twigs, or by bird predation.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

How to handle a big freeze

Q: Several years ago when we had the big freeze my grapefruit had to be pruned quite a bit. Then last year I had about 75 or 80 fruit. I am a snowbird and when I came back this winter I did not have any fruit. The tree is not large, about five or six feet, but right now it has some very nice blossoms that are wonderfully fragrant. My son fertilized the tree several weeks ago.

My question is should I be giving the tree extra watering now? I would certainly like to have fruit next winter. Also, I have a very small Meyer lemon tree. I have only had two small lemons in three years.

Could you please give me some suggestions for watering so I can look forward to fruit next winter?

A: Caring for citrus does require regular fertilization and irrigation. Fertilizing should be done three times per year if they are in the ground and more often if they are in containers.

We recommend fertilizing in February, July and September for ground planted trees and monthly if you are growing citrus in containers since more frequent watering of containers flushes the fertilizer through the soil.

Watering your plants should be done every 10 to 14 days at this time of year to depth of 24 to 36 inches. Your citrus will need water more frequently, every seven to 10 days, as the weather gets warmer.

Smaller and younger trees need more care than older established ones so your lemon tree may need more irrigation than your grapefruit. Look for signs of wilting such as curled leaves to determine its condition.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

How you might save a citrus tree

Q: I saw your newspaper column and wondered if you could help me. A year ago I lost a grapefruit tree. It started with one branch rotting and continued to the trunk of the tree. Now the back branches on my two citrus trees are rotting away. First the bark starts to peel away and then the branches become rotten underneath. Several nurseries have said that I either watered the trees too much or the frost is killing the branches. I’d appreciate any information.

A: The most common trunk disease we see is Phytophthora gummosis. Symptoms are often first recognized when the bark dries, cracks and falls off. The disease comes from the soil, starts in the rootstock and can spread to the crown. The decline of the tree can happen within a year or take several years. Sap oozes from cracks in the trunk and can create a gummy blob on the trunk if it is not washed off by rain.

There are other causes for gumming and some are minor problems so it is good to get it diagnosed. The way to do this is to dig in the soil near the crown of the tree to expose the small absorbing roots. Healthy roots are firm where rotten roots have a soft outer tissue that slides off easily. If this is the case, you can collect some of these roots and the surrounding soil and have it analyzed by a plant pathologist.

As the nursery folks told you, excessive watering is the environmental key to this disease. As you may already know, with any disease you have to have three things: a susceptible host, the presence of the pathogen, and the environmental factors that allow the disease to thrive. With an established tree in soil with the pathogen the only thing you can control is the environment.

Schedule irrigation to prevent standing water around the root zone. In the winter we recommend watering every two to three weeks to a depth of 36 inches. In the spring and fall water every 10 to 14 days and in the summer every 7 to 10 days. Make sure the water is getting to the absorbing roots near the edge of the crown of the tree and keep the emitters away from the trunk.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to

tucsongardensage@gmail.com.

Six years is a long time without an orange

Q: I have a 6-year-old miniature orange tree. It has lush green foliage but to date I have yet to see the first orange. It is on an irrigation system and is fertilized by our landscaper. Do these trees take this long to bear fruit or could there be something else going on?

A: Usually a tree is producing fruit before it is 6 years old. If your tree is producing flowers but no fruit, it could be a pollination problem. If the tree isn’t producing flowers, there a few potential problems. The most common are a fertilization or water problem, so it would be good to know what kind of fertilizer and irrigation schedule your landscaper is using.

Typically, citrus fertilizer requirements are based on the type and size of the tree. For example, a small orange tree, 2 to 3 feet tall, requires 0.25 to 0.50 pounds of nitrogen per year. This amount is applied in thirds, each third being applied in January/February, March/April, and May/June. If you don’t want to do the fertilizer math, we have a handy chart to help based on the percentage of nitrogen in your bag of fertilizer. Search for az1671-2015.pdf on the Internet.

For irrigation, make sure you are providing drip emitters in a circle around the root zone at the drip line of the tree. The amount of water delivered should allow the water to reach 36 inches deep in the soil. You can check the depth with a soil probe. Timing for the irrigation is once every seven to 10 days in the summer, 10 to 14 days in the spring/fall, and every 14 to 21 days in the winter.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com

Caring for lime tree

Q: I planted a Bearss Lime tree about five years ago. When we had the bad freeze a few years ago it froze. Since then it has come back and has grown very well. However it never produces. I fertilized this year. It had blossoms but no limes. Can you suggest a remedy? I also water it regularly.

A: It seems you have the basic care strategy down but maybe it could be tweaked to be more effective. To start, we recommend fertilizing citrus three times per year: January/February, April/May and August/September. The amount of fertilizer you use should be based on the type, age and size of the tree. We have a chart you can use by searching for “University Arizona citrus fertilizer” on the Internet.

Watering should be done every seven to 10 days to a depth of 36 inches in the summer. In the spring and fall you can back off to watering every 10 to 14 days and in the winter, water every 14 to 21 days. This is for citrus planted in the ground. If your tree is in a container, you will have to water more often and base that frequency on how fast the soil dries out.

Bees and the wind will accomplish most of the pollination of citrus flowers. If you are not seeing any bees on your citrus flowers that could be a problem. Making sure you have an attractive habitat for bees by planting other flowering plants nearby is helpful as is providing a water source. Also keep in mind that citrus produce more blossoms than fruit.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to plwarren@cals.arizona.edu.

Transplanting stressful on plants

Q: I have two dwarf Hamlin orange trees that are dying. They have been in large pots since I got them about seven years ago. They are both losing all their leaves and the branches are dying (dried out). I thought maybe they were getting root bound so I transplanted them in the ground but they weren't root bound. In fact I didn't see any good size roots just a lot of little ones. I admit I'm not good at feeding them. I've put Best citrus food 13-10-4 on them but not every often. Up until this year they were pretty good at bearing fruit but the fruit this year was scarce and not eatable. Do you have any idea what I might try to do to save them? They are in pretty bad shape. This started about a year ago.

A: The transplanting process is stressful on plants so it might take a while for them to come back to good health.  To make sure they have the best chance, you need to make sure they receive sufficient water and fertilizer.  Your water is best delivered through drip irrigation.  In the summer they should receive water every seven to 10 days to a depth of 36 inches. In the spring and fall, you can back that off to watering every 10 to 14 days.  In the winter every 14 to 21 days is sufficient.  Fertilizer for citrus should be provided three times each year. The first dose should be in the January/February time frame.  The second does should be in April/May and the third dose should be in August/September.  If you need information on how much to use, check our handy publication chart in our publication AZ1671-2015 using your favorite search engine.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona.  Questions may be emailed to tucsongardensage@gmail.com.

Blood orange may need more time to bloom

Q: I have a 4.5-year-old blood orange tree in my yard. It’s the healthiest (by leaf color, height, breadth) of all my citrus trees.

However it’s my only tree that won’t bloom. I tried a bit of water stress this year but instead of blooming, when all my other citrus bloom, it just leafs out more. It is 10 feet tall, and 6 or more feet wide. Any advice on what I can do to encourage blooming? I had heard cutting off the tips of leafing branches would help, so tried that on some of the tree this year, but still not a single bud. The tree is on the east side of my house, planted about 6 feet from my wall, and so is well protected from freezing as well.

A: Some citrus trees take longer to start blooming than others. It could be that you need to wait another season or two before it begins to flower. Other than age, the three main factors allowing trees to bloom are sufficient water, fertilizer, and light. Assuming your tree is in full sun or nearly so, I recommend taking a look at how much fertilizer the tree is receiving. Based on the size of your tree, you would need to supply between 1.25 and 1.50 pounds of nitrogen per year. This amount should be divided into thirds and applied during the following time frames; the first application in January/February, the second in March/April, and the third in August/September. The last factor is water and based on your description this is not an issue. Just in case, the recommended irrigation schedule calls for water every seven to 10 days in the summer, every 10 to 14 days in the spring and fall, and every 14 to 21 days in the winter. Each time the water should reach a depth of 36 inches. This depth can be measured with a soil probe.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com