As temps drop, water plants less often

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Sprinkler systems for lawns should not be operating every day. Drip or bubblers used for irrigating trees and shrubs should not be operating daily, either. This is unhealthy for plants. Right now is an excellent time to try increasing the number of days between irrigations as long as possible.

As weather cools, our plants need water applied less often. I like to encourage people to water less often rather than turn the number of minutes back. I would encourage you to skip days and keep your minutes per application the same.

Come join us at our open house from 1 to 7 p.m. on Sept. 27 at the University of Nevada Cooperative Extension's new Lifelong Learning Center, 8050 S. Maryland Parkway. Refreshments will be served.

Enjoy a self-guided tour through the new Lifelong Learning Center facility while enjoying hands-on activities, food demonstrations and tasting, prizes and more. For more information, contact Marilyn Ming at 257-5516 or e-mail to mingm@unce.unr.edu.

Question: I had a Mimosa tree cut down and the trunk was ground down, but the smaller roots (1 to 2 inches in diameter) keep sending up a lot of new plants. What can I do to kill the roots to stop the sprouting from the roots? I have drilled holes into some the roots and put in some stump remover without any luck.

Answer: Mimosa or silk tree is considered a problem tree by many in states, such as Florida, Georgia and the Carolinas, where this tree grows with abandon. The tree sends out a few large surface roots where they can heave sidewalks, walls and foundations if planted too close to structures.

Seeds from the parent plant will sprout new daughter plants and are considered an invasive weed in wetter climates than ours. I would think if this tree were planted along waterways in the desert, it also could become invasive. Luckily, this tree is relatively short-lived here, perhaps 10 or 15 years at best, and it typically does not have much of a chance to form those large surface roots.

Silk trees usually are prone to a disease, which falls into a category called vascular wilt problems. We would see disease as branches dying back, making the tree look so ratty that it is eventually removed.

I can go on about this tree and its many problems, but it sure can add a look of the tropics in the high water use area of the landscape. I can understand why people want to plant it.

There are a couple of approaches you can use to attack your problem. First, if you are opposed to the use of traditional pesticides, you can pull the plants from the ground or use a spade and undercut them and pull them out as you see them. Over time, the new plants will become less frequent as you exhaust the roots sending up these sprouts.

It would be important to do this as soon as you see the daughter plants emerge. Probably once a week is adequate. It is important not to let these daughter plants get established, but remove them right away so the roots do not restock their food supplies.

The second approach is using a weed killer. Spot sprays with a weed and brush killer will stop them and do the same thing as manually removing them. If they are in a lawn, you can use a lawn weed killer that is effective on the tougher weeds like clovers. Fall is a great time to do this since plants are moving stored food downward into the roots at this time of year as they are preparing for winter.

If these sprouts are coming from large roots, it is going to be much more difficult and may require removing the roots from the ground.

It should take no more than three years to exhaust the roots and kill them, perhaps less. Diligence is necessary and you cannot let them get established or it will just take you longer to exhaust the roots.

Q: I have a number of 4-foot-tall pygmy date palms which I transplanted into half wine barrels. Recently, I've heard about a dreaded disease affecting these plants and I think their bigger cousins, the date palms. About two years ago, I was in Indio, Calif., and I was told that pygmy date palms were outlawed. But since then, I have seen lots of them in Vegas, including the large plants I bought. Can you explain the comeback? Moreover, how can I keep my plants safe and disease free?

A: One disease that is a problem to many palms is fusarium blight, also called fusarium wilt, which is lethal to many different palms. So far, it has not been diagnosed in our area, to my knowledge. This disease is considered a potential threat to the $40 million date industry in Southern California, where about 95 percent of the state's dates are produced in or near the Coachella valley.

In this part of Southern California, it is illegal to bring in any kind of date palm from outside the area. The disease can be brought in through the soil attached to a living date palm or an infected date palm can be planted.

The disease is thought to be transmitted on pruning shears from palm to palm. I would think it is just a matter of time before we see this disease in Las Vegas due to our heavy import of date trees from California for our landscape industry.

In Las Vegas' past, the Pygmy date palm was never considered a viable palm plant for our landscapes because it would be damaged in the low 20s and high teens. Over 15 years ago, that was a regular occurrence here in the valley.

We have seen a tremendous increase in the planting of citrus, tender palms like the Pygmy date and queen palms and other winter tender plants. Winter kill will become a problem to these trees if we return to these temperatures in the future.

Q: I am getting nursery catalogues for spring bulbs. Is the quality of mail-order bulbs worth the premium for their so-called superiority, or are local sources just as good?

A: I think you have a much greater selection of bulbs by mail order. As far as the quality is concerned, it is always nice to be able to pick through the bulbs and select for size and quality yourself rather than trust someone to do that for you and then ship them.

Always select the largest bulbs of each variety, because there is a direct relationship between bulb size and flower size. Damaged and undersized bulbs found on clearance racks are not a bargain.

A bulb should be plump, firm and heavy for its size. Avoid bulbs that show evidence of mold, scars, cuts, soft spots or blemishes, or appear withered or dried out. Two exceptions to this rule are anemone and ranunculus, which naturally look shriveled and shrunken.

Nurseries normally would buy bulbs pre-chilled and these can be planted directly into the ground. However, if you are saving bulbs from year to year, then some bulbs will have to be dug up and chilled by you before planting in the spring or they may not bloom. These include crocus, hyacinth and tulip.

To chill them, place these bulbs in the refrigerator for six to eight weeks. Don't put them in anything sealed or they will rot. But you do have to prevent them from drying out over the course of these six to eight weeks. Never put bulbs treated with a fungicide in the refrigerator.

Other bulbs, such as amaryllis, anemone, calla, daffodil, muscari, oxalis, ranunculus, spraxis (harlequin flower) and watsonia, have a low chilling requirement and do not require chilling in subsequent years, but may need to be divided periodically.

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