Plants need time to adjust to colder temperatures
Normally we enjoy very nice fall weather in Las Vegas until about the first week of December and oftentimes without frost. This would be pretty normal. To have freezing weather before this, or unusually cold weather, would be a bit odd. As long as the temperatures continue to drop slowly to our winter minimum lows, our perennial plants that can withstand some light freezing weather will survive the winter.
If November temperatures drop suddenly, or we have snow before trees drop their leaves, then we can have problems. If we are enjoying, for instance, nighttime temperatures falling just below 50 F and then it suddenly drops to 30 F the next night, then we might see major freezing damage in plants that normally might tolerate temperatures to 20 F.
To survive the winter minimums, winter-tender plants need time to acclimate to these low temperatures so that they can create their "antifreeze."
Decreasing fall and winter temperatures helps leaves drop. One good cold snap in the fall can cause tree leaves to drop prematurely. One day the leaves are there and, in just three or four days after the freeze, they are on the ground .
There is a good side to this early leaf drop. If we have one of our "every five year" snow events, and it comes after early leaf drop, we miss all the damage snow can cause . If snow comes early and these trees have not dropped their leaves, then we can have massive limb breakage due to the snow load on limbs.
How we manage winter-tender plants going into the fall months can make the difference between their survival and death from winter freezes. It is important to withhold fertilizers, particularly nitrogen, during and after the month of August. It is also important to change your irrigation clock so water is delivered less frequently.
If winter-tender plants are still pushing new growth or are still succulent at this time of year, there may not be enough time for them to begin their adjustment for winter cold. This adjustment takes a couple of months of decreasing temperatures and longer nights.
Q: I have a dwarf lemon tree that is about 14 years old. It produces plenty of fruit, and I keep it relatively small. I trim it in the winter but have never professionally pruned it. Could you recommend a source on how to properly prune this tree?
A: I don't know of a source to help guide you in pruning your citrus tree. I will try to give you some basic directions.
Light pruning can be done anytime, but heavier pruning should be done right after harvest.
Light pruning would include removing small branches that are interfering with growth or causing too much shade inside the canopy. You can judge if there is too much shade in the canopy by looking at the ground. There is enough light if you can see speckles of light throughout the shadow of the canopy on the ground.
First, remove branches that are crossing or any branches growing back toward the center of the tree. Next, remove branches that are growing straight up or straight down. Once you have done this, stand back and look at the shadow of the canopy on the ground. Is light passing through the canopy and causing speckles to form throughout its shadow on the ground? If this is now happening, perhaps you should stop pruning until after harvest.
Citrus does not require much pruning, but getting rid of problem branches would be recommended.
Q: I am having trouble with purple lantana. They are dying out. The gold lantana is still doing well. I am watering three days a week at 20 minutes and four days a week at 7 minutes. I have noticed that my neighbors are having the same type of trouble. I hope you have a solution.
A: Lantanas, in general, flower on new wood. As they get older, the flowers will get further from the center of the plant, provided it does not freeze back. This tends to make the center kind of bare, with most of the foliage and flowers at the ends.
If it freezes back and does not die out because of very low temperatures, then the plant will stay more compact and will need to be trimmed back to a few inches in early spring. But this plant, if it is in a place where it stays warm and does not freeze back, will tend to get leggy and not have much foliage on the inside.
Make sure you cut it back to keep renewing new growth close to the center of the plant. You can do that now to some degree. Cut back one third of the stems to a couple of inches in length. Stagger the cuts so that they are random on older wood through the canopy.
It will require watering fairly often if the soil drains water easily. Fertilize lightly in the spring and fall. To maintain bushiness, irrigate frequently like any normal shrub. If you decide at some time to replace it, add compost to the soil at the time of planting.
Q: We love your advice. Please explain and tell us any information about our trees. We sent you some pictures. I removed the dried area and flushed them with water. We lost large cottonwoods years ago that had the same condition.
A: The pictures show a liquid coming directly from the trunk of the tree. This may be a disease called wetwood or slime flux, which can infect many different types of trees.
The liquid coming from this disease will have a putrefied, yeasty smell, which quite often attracts flies. In many cases, the liquid does not seem to be coming from any cut or damage to the tree. It seems to come directly from the limb or trunk.
This particular disease is normally not lethal. It is considered more of a nuisance than anything else.
There are no fungicides or other pesticides that will make any changes. Hopefully the tree will have a long life living with this problem.
Bob Morris is a horticulture expert living in Las Vegas; he is on special assignment in the Balkh Province, Afghanistan, for the University of California, Davis. Visit his blog at xtremehorticulture.blogspot.com.
