GARDENING: Protect sensitive plants that were nipped by cold

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There were some pockets of cold air in town recently that may have had a freezing effect. If you experienced this, then you are probably in a low spot or some sort of collection for cold temperatures.

Most likely, cold-sensitive plants like bougainvillea, some citrus, natal plum and cape honeysuckle were affected. If they were nipped, protect them at their base with compost piled around their trunk. If it is a tree, then wrap a blanket or any type of insulation around them during the coldest part of the night -- typically from about midnight until sunrise.

Nights will be most damaging if there is an alert given that freezing temperatures are coming that night, there are clear skies and a wind. Anything you can do to keep the wind off of the plants will help down to about 25 degrees Fahrenheit or so. Clear plastic will help keep the wind off, but will not help keep the plant warm.

Question: I have a pink chitalpa tree in my front yard. I was wondering if I can cut this tree back and shape it. If so, is this the best time to do it? Also, I wanted to know if I should fertilize this tree and what kind to use. I have drip system watering.

Answer: Chitalpa needs very little shaping since it is a tree with a rather open canopy. There are some "corrective" pruning jobs that can be done that will improve the tree such as removing crossed branches, branches growing straight down or up, cutting back excessively lone branches, removing dead branches or disease.

If you are going to shape it, remember that when you begin shaping a plant away from its natural form, you are starting a maintenance project that will require future shaping of the tree. The more shaping you do that is out of character with its normal shape, the more often you will have to do shaping to keep it looking like that. If you are prepared to continue this maintenance project, then by all means, shape it.

We generally prune plants with pretty flowers, like chitalpa, right after the flowering season is over. The tree appears to flower on what we call current season wood, which means that the flowers are formed on new growth.

General rule of thumb -- you prune flowering plants that are valued for their flowers only, after they finish flowering, regardless of the time of year. The right time would be any time the tree is dormant, so you could begin now and into the very early spring. If you want to keep the flowers for awhile longer, then delay until just before new growth in the spring or after a hard frost.

Q: On one of my Robertsonian orange shrubs, two of the good size oranges have split. They aren't quite orange, but are more green. The rest of the oranges on that shrub are beautiful but not yet orange. Why did they split?

A: I don't know what a Robertson orange is but I can only guess that it is some type of mutant from an orange of a known variety. The term Robertson usually refers to some genetic abnormality.

However, splitting of orange fruit can be quite common, usually on green fruit. The exact reasons are not known, but it is thought that the rind sets up early and becomes less flexible. The tree then takes on more water and nutrients sending it to the fruit. The fruit becomes engorged with all this water and nutrients and splits, usually from the bottom of the fruit toward the top. Sometimes it's a minor split and other times it can be right down into the flesh.

My suggestion would be to make sure your oranges are mulched to help eliminate fluctuations in soil moisture conditions that trigger the rind to set up early. Manage your irrigations so that the soil never becomes droughty while the fruit is enlarging.

By the way, green fruit are quite common when temperatures are warm. In the tropics, citrus has to be degreened and forced to turn orange with ethylene gas after harvest. Otherwise you can buy citrus fruit from markets there fully mature and ready to eat that are quite green. Having orange oranges is a consumer necessity and growers are forced to turn them orange if they expect them to be sold.

Q: I have a mature Bears lime shrub that has fruited well this year for the first time. How can you tell when limes are ripe?

A: Limes are ripe when the fruit skin or rind is no longer dark green but beginning to become yellowish. Limes commercially are picked too early because we are accustomed to seeing dark green limes.

Another indicator is when they begin to drop from the tree. They will probably not all be ready at once, but trickle in maturity over a period of weeks. A good citrus to have that follows limes in harvesting are mandarin oranges, which are fairly cold-hardy for a citrus.

By the way, if you want to grow citrus from seed, most of the sweet oranges -- key lime, grapefruit, tangerine and tangelo -- will grow true from seed. Tangelo is more cold-hardy than grapefruit, but not as cold-hardy as mandarin orange. Key lime is very tender toward cold temperatures, as are most sweet oranges. Buying any citrus tree grafted onto sour orange rootstocks will be more cold-hardy than on its own rootstock.

Q: We bought a chaste tree when it was in bloom. The leaves are now turning very yellow, which may be what is supposed to happen, but our neighbor has a large tree, and his has not turned yellow. Are we doing something wrong?

A: This is about the right time of year for the leaves to turn yellow and drop. The tree will be leafless this winter.

It is hard to say if you are doing something wrong, but it sounds normal. Your neighbor may have fertilized it quite a bit, which can cause the leaves to stay on longer or it just could be genetically different from yours, and yours could just be one that loses leaves earlier. About the only mistake I could think you might do is to over water it, that is watering it too often and rotting the roots. Water this tree deeply and infrequently after it is established.

Q: I have a tree called calamondin. The main trunk got dried where some branches came out. It's now 5 feet tall. Do you think it has a chance to bear fruit? Somebody told me I am just wasting my time. The tree is so healthy. Do I need to keep it or throw it away? Please tell me what to do.

A: Calamondin is a citrus that produces fruit resembling an orange, but smaller, and peels more like a small tangerine. It is one of the cold hardiest of the citrus, right behind kumquat, Satsuma orange and Meyer's lemon.

It is grown mostly as a tree, but if you want to keep it for the fruit you would use the fruit in place of lemons or limes for flavorings and cooking. You could juice them, but it is very tart and would take lots of sugar to make it sweet. It's up to you whether you want to keep it. The tree is nice looking and makes a very good patio tree or container plant around patios.

Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.