Avocado tree may not survive winter temperatures

A: There is quite a bit of interest in growing avocados in the Las Vegas Valley. As you are probably aware, avocados are “iffy” in the Las Vegas climate — probably a little worse than citrus regarding surviving winter cold. It depends on which avocado variety you are growing.

With that said, put the container in a protected area away from extreme cold during the coldest part of this coming winter. It will be OK with temperatures approaching 32 degrees F or freezing, but protect it at temperatures below this. Around the first week of March, plant it in the ground. Make sure you amend the soil, and do not fertilize it with nitrogen fertilizer after Aug. 1.

Q: We are growing the Celebrity variety of tomatoes in our garden and decided to cover them this year with a mesh tarp for shade, because the sun has scorched them in the past. However, we noticed the vines are growing, but the tomatoes are not very big, and they are not ripening like they usually do. Are they supposed to have complete sun? What do you suggest?

A: The amount of shade provided to tomatoes is critical for continued production of fruit. The growth of leaves and stems requires less light than flowering and fruiting. If you give them too much shade, flowering and fruiting will stop, and new growth will be weak and spindly.

Shade cloth for gardens is categorized by the percent of shade it provides. For flowering plants, provide no more than 30 to 40 percent shade. Plants that do not flower can handle more shade, up to about 50 or 60 percent. Anything higher is sold to provide shade, not to make anything except mushrooms or compost.

You didn’t tell me what percent shade the tomatoes are getting, but I suspect it’s too much. Light shade, 20 to 40 percent, can be hard to find locally. Usually, this kind of shade cloth is ordered by mail order or online.

In northern climates, we would use a snow fence supported horizontally above the plants to provide shade. You can also provide shade by using a lath structure instead of shade cloth.

To get 50 percent shade, remove every other lath, or wood slat, from a solid ceiling of the lath. To get 25 percent shade, remove two and leave one. A chain-link fence with PVC slats gives you about 75 percent shade. I think you get the picture.

Q: On your list of recommended varieties for the Mojave Desert, you recommend some fruit trees with some pretty high chill hours, such as Flavor Supreme pluot, which is listed as 700 to 800 hours. Isn’t this too many chilling hours for our Las Vegas climate?

A: Chilling hours for fruit trees is an estimate of the number of hours below about 45 degrees a temperate fruit tree must experience during winter to provide a good fruit crop the next year. Most chilling hours for fruit trees are estimates and have never been scientifically verified.

Our chilling hours are somewhere between 300 to 400 per year and vary depending on the current year’s weather and climate.

You are right. I am recommending some fruit trees that have a high number of chilling hours. Most people would not buy them and plant them here for that reason. My recommendations are not from a chart of chilling hours but from observing these trees growing at the University Orchard in North Las Vegas for the past 15, going on 20 years.

If you take chilling hour recommendations literally, many of my recommended trees should not produce in this climate, yet they produce quite well. Some of the so-called “high chilling hours” fruit trees have shown no visual signs of a lack in their chilling requirement, and fruit production hasn’t slowed down either.

Tom Spellman from Dave Wilson Nursery was the first person to introduce this anomaly to me, and we decided to challenge it at the University Orchard in North Las Vegas. That orchard was developed to test varieties of temperate fruit trees in the Mojave Desert so that you might know what to plant here.

The results challenge some long-held, preconceived and published information about chilling hours. Sometimes ignorance is bliss.

Personally, I believe chilling hours are more important in some types of fruit than others and even some varieties more than others. I also believe that published chilling hours are not always accurate.

Are chilling hours important? Yes, definitely. Should we follow chilling hour recommendations literally? Perhaps not.

I believe they should be challenged. This is one reason I recommend planting things here that “do not grow in the desert.”

Q: I have two wisteria plants climbing over an arbor. I’m not the original owner, so I’m guessing they could be 10 years old. My current landscape company set my irrigation clock to water these plants three times a week, for 16 minutes, twice a day.

I think they are getting maybe 1 gallon of water, three times a week. Last year, I didn’t see any flowers, and I’m not sure if the wisteria plants are getting enough water. How much water should they be getting?

A: The amount of water they should be getting depends on their size. If they are 10 years old, they could be quite large if they have already begun to climb over the arbor. I would estimate they should receive about 10 to 15 gallons each time they are watered.

They only need to be watered once, not twice, if the water is applied slowly enough and doesn’t run all over the ground. In your situation, it does not make sense to water them twice a day.

This time of year, watering twice a week should be enough if they get enough water each time. Think of the soil as a tank of water for the plant. I would normally set it on once a week right now, soak the area well and not water again for one week. That way the plants are getting little tiny sips of water many many times, rather than one big drink.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.