Q: We live at 4,000 feet of elevation at the base of the Santa Ritas and have two “rescued” saguaros and one nursery bought.

The biggest is George (pictured). We moved George here in 2010 from a construction excavation site. We have licenses for all three of them. He did great first year then 2011, the winter from hell, arrived. A great deal of his south side froze in the wet, windy, and below-freezing temps we had for four days. He survived the damage and thrived. The side in this picture is facing north toward the Catalinas. Over the past few years, he has become a high rise apartment complex for Gila woodpeckers. This year three additional holes appeared as prior holes are now occupied by European starlings. Now he has six large holes. A month ago this splotchy patch (pictured) appeared on the north side, underneath a rather large hole taken over by the starling family. Is this some kind of fungus or could the tissue be damaged from internal carving of the hole inside and nearby? Never had the starlings before and given George’s height, no way to get rid of them. At least the Gilas return to the same homes every year but this year had to drill more!

A: The splotchy patch appears to be a symptom of bacterial necrosis caused by the bacterium Erwinia cacticida. The initial symptom is typically a small, light-colored spot with a water-soaked margin on the surface of the trunk or branches. Obviously, you are looking out for George because symptoms like that could easily go unnoticed. The tissue under the infection site appears to be showing a brown color and may eventually turn almost black. As the disease progresses, the tissue may crack and exude a dark brown liquid. If decay is slow, the tissue may not show the liquid. Although it’s tempting to blame the invasive European starlings, the bacteria could be transmitted by any number of animals, not to mention wind blowing it in from nearby plants.

If the damage was very small and reachable, I might suggest carving it out. Given the height of George and the spread of the symptoms, it might be best to either call an arborist with the proper equipment to reach that high or just let nature take its course. I can’t tell if there is any danger to people or property from the photo but it would be wise to consider the potential hazard if the problem gets a lot worse.

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.

Q: I have a royal robe potato bush that when planted last year grew beautifully! I live in Hayden so the plant is in the full sun all day.

This year, however, it is not doing well at all. I believe the reason is that it was hit hard during the winter freeze. I trimmed the branches back to about 10 inches from the roots. Even though the branches are very dry and snap off easily there are actually some green leaves growing on a few of the branches. Should I just dig it up and start over, or wait awhile to see if it comes back to the original beauty I had from the beginning?

A: The royal robe potato bush (Lycianthes rantonnetii or Solanum rantonnetii) is a tropical plant that originated in South America. It grows well in our heat with adequate water but needs a little protection in the winter if temperatures get below freezing. Because potato bushes flower on new wood, prune them in winter before they start to put out new growth. You can prune them as early as they have finished blooming for the year. The golden rule of pruning is never take off more than a third at one time to avoid stressing out the plant. Since yours has new growth showing, you could see how it grows before giving up and starting over.

Q: I would like some info about our probably dead ocotillo.

We have lived in our house for three years now. The ocotillo is in mostly shade and although it was in bloom the first year we moved in, since then there has been no green and no feathers on top. Is this ocotillo dead? I have read in your column that these plants can go dormant for a few years but have we now passed the time for regeneration? Are there any tests we can do to determine life or death? And if it is dead, what can we do about it or with it?

A: The best way to determine life in an ocotillo is to give it some water. Desert plants like this will appreciate water every two to three weeks in the summer and it should leaf out in response to irrigation. You can also lightly scrape the stems to see if there is any green tissue below the surface. That is a sure sign of life. If you decide it is dead you can leave it alone, pull it up, and/or replace it with another, your choice. Some folks buy ocotillo fencing made of these stems and they occasionally take root. So you could chop it into sections and make your own.

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