Salts in Southern Nevada's soils can be very dangerous to plants

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Landscape watering is a challenge in Southern Nevada. Our landscape watering situation may be a little bit different than many people might imagine after moving here, even if they have moved here from another arid or desert environment.

The principal difference is in our soils. Our native soils contain a lot more salts, some of them potentially very damaging to plants and building materials, and a lot less organic material than some other native soils in other arid climates. I have about 800 records of soil tests done in our valley by our soil testing laboratory before it closed about 15 years ago. In nearly all of these records, soil salts were a big problem.

Some of my recommendations regarding irrigating new plant material may seem excessive to some. And they might be excessive if our soils did not have all of these salt problems and had some organic material already. The salt levels in our soils can range up to 25 times higher than what is considered a safe level.

One particular salt common to our soils is boron. This particular salt is extremely nasty to plants. This salt can sometimes range as high as 40 times safe levels and can be very difficult to manage. These high levels of salts are not consistent throughout soils in our valley, but appear in pockets that are hard to predict.

The textbook way of determining if your soil has high levels of salt is to send a soil sample to a qualified agricultural soil-testing laboratory. This will cost somewhere between perhaps $35 and $70 for a complete soil analysis.

The only way to remove accumulated salts in soils is to percolate quality water through it, making sure the soil drains. This process is called leaching, which dissolves soil salts and moves them to the perimeter of the wetted area. This is why you see white rings develop around irrigated areas in the landscape. Leaching will not work if the soil does not drain easily.

Another way to handle this problem is to assume that salts in the soil are high to begin with and leach the soil prior to planting. This would mean digging the holes for plants, and while leaving these holes open, filling them with water several times and allowing them to drain before planting. If you intend to use amended soil from the hole and for backfilling around the plants (which is what I recommend), you also should leach salts from this soil, as well.

Another quick-and-dirty way of handling this problem is to assume salts are a problem and address it at the time of planting. You can do this by flooding the landscape plants as you are planting and for a few weeks after planting. I might mention that this is not the textbook way of handling this problem, however, it usually works.

Even though many landscapers do not understand the reason why they are doing it, most of them will set the irrigation clock to come on daily, sometimes two or three times a day, and turn it over to the homeowner. This addresses the potential salt problem and pushes the salts outside of the root zone, where they accumulate.

What the homeowner does not understand is that they are then given a landscape that is being irrigated much more frequently than it needs to be. Without any reason to believe otherwise, they think this is the way the landscape should be irrigated. It is not. It is up to the homeowner to reschedule the irrigation clock for a more appropriate watering schedule. Homeowners usually do not realize this, and even if they did, most would not know what an appropriate schedule might be.

But there is help. Some of you have asked to be notified when a new class was beginning on desert landscape design. Now is the time to enroll in this class if you have been waiting for it. You can do that by calling the Master Gardener help line at 257-5555. This class will teach you how to put your personal needs and wants onto paper and into your finished design concept.

The classes will be held weekly on Tuesday evenings starting in September. There is a required fee for the class.

Question: I have a 4-year-old date palm that has three very large offshoots. When is the best time to remove these shoots and how can they be propagated?

Answer: Date palms, if you want to keep them true to the mother plant, have to be propagated from offshoots. If you don't care about getting a plant exactly like the mother plant, you can start the plants from seed.

Even though your plant is not old enough to begin fruiting, you can still collect fruit from more mature trees. In commercial plantations, only offshoots are used because they want to maintain the identity of the fruit. For landscaping purposes, this may not be important.

Generally speaking, the success in propagating from offshoots depends on the variety of date palm (some offshoots root better from some varieties than others), the size of the offshoot, and the time of year. Again, generally speaking, the smaller the offshoot down to about 4 inches in diameter, the more success you will have.

The best way to express the size of the offshoot is talk about its diameter. The diameter is the widest point at the base of the offshoot, and this is typically underground. If a date palm has offshoots above ground along the trunk, these are reported to root poorly compared to those that originate below ground. The smallest successful offshoots are 4 inches in diameter at the widest point. As these offshoots get bigger, the chances of success decrease after about 10 inches in diameter.

The best times of the year to separate an offshoot from the mother plant for propagation are fall and spring, the fall being the best if you can give it some winter protection. The next best time is spring, but it is best to give these separated offshoots some shade, or at least some sort of relief, from the hot summer sun while they are getting established.

Q: I need to know what sort of little green inch worms get onto my potted lantanas every single spring and summer. They sometimes nearly eat up my plant's leaves, as well as some petunias. I used an insect spray on the plants from time to time, and it seems to keep them at bay. Can I do anything else to keep these darn little pests from trying to eat my lantana plants every single year?

A: I am guessing this is the tobacco budworm, which is common this time of year and fits your description. They are a general feeder and can be particularly troublesome on geraniums, petunias and ornamentals related to tobacco. They will damage other plants, as well. They hit different plants in different parts of the valley and may not be consistent throughout the area. It depends on their food supply.

Unfortunately, the only control is to plant things they don't like or protect the plants with an insecticide spray. I would recommend some organic pesticides, such as formulations of Bt (Dipel or Thuricide), or use spinosad, which I think will give you better control than Bt in some cases. Make sure you check the label and make sure what you are buying is approved for your situation.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension.