Spider mites can wreak havoc on rose leaves

A: You are describing spider mites. They like dusty conditions and temperatures higher than 90 degrees. Mites suck juices from leaves, resulting in a dry appearance. For positive identification, tap a branch on white paper and place it in the sunlight; watch for moving specks (mites) scampering for protection. Wash down your roses two to three times a week and it takes care of the problem.

Rosarian Lee Henan keeps mites off her roses with zinc chelates. She places one to two tablespoons of it around the drip line of each rose and waters it in. Her roses stay squeaky clean.

Q: Why are the summer blooms of my roses getting smaller than the spring and fall blooms?

A: In three words: “It’s the heat.” They will come on again this fall.

Q: What do I do with my roses through the summer?

A: Water deeply to push water even deeper into the plant. To help conserve moisture and cool the area around the bushes, mulch them.

During summer, put on only half the fertilizer you normally would apply. To improve the quality of new growth and blooms this fall, add  1/4 cup of magnesium sulfate or Epsom salts to each bush.

Q: My gardener connected our drip system to our sprinklers to water our peach tree. Is that OK?

A: I’ll say not! Emitters distribute water in gallons per hour and lawn sprinklers in gallons per minute. Look at it another way: A one-gallon-per-hour emitter running at the base of a tree for 12 minutes, delivers less than a quart of water. That won’t fill up the tree’s root ball. Expect leaf scorch, twig dieback, gummosis and borers attacking your tree. Also, the added water pressure may pop the emitters off. Separate lines are needed to water your lawn and trees.

Q: I e-mailed you in March concerned about my frozen mesquite tree. You assured me to be patient and it will come back. It is now doing fine, but I’m wondering how to water it.

A: The more you water a mesquite or any other desert tree, the more they grow. Translated: These desert trees are opportunists; they drink as much water as you put their way. And the more you water, the more you must prune.

Ponder how these natives live in the desert. Research out of Arizona found desert trees put on their top growth during rainy seasons and don’t develop much root growth. As they go into drier times, root growth accelerates.

Now consider how you water your desert trees. If you are watering every day, your trees will generate lots of top growth. Dennis Swartzell of Mountain States Wholesale Nursery was director of grounds at the University of Nevada, Las Vegas. He observed his crews pruning desert trees four times a year. After thinking about the situation, he drastically cut back the watering schedule. The outcome was UNLV using less water and pruning the trees only once a year. So cut way back irrigating your desert trees. Trees have a built-in system to protect themselves if they get too stressed out.

Q: We just moved from Michigan and I understand rhubarb won’t grow in Las Vegas?

A: Rhubarb does grow here, but it doesn’t get enough winter chilling to bring out the sweetness we all dream about in rhubarb pie. If you still want to give it a try, plant it on the northeast side of the house, but the stalks won’t be as red or as sweet as you are accustomed.

A word of caution: Never consume rhubarb leaves, because they are poisonous. And don’t expect much rhubarb until the second growing season.

Q: I’m removing the grass under my ash tree to replace it with a water-efficient landscape, but we want to keep the ash tree. How do I get rid of grass without damaging the tree?

A: Here is the right way to do it, said Joe Fortier of Mojave Water Management:

• Kill the grass with Roundup and repeat the application again in 10 days to get a thorough kill.

• Rake away the grass. Don’t remove grass with a sod cutter, because it damages tree roots.

• Now place an inline drip system under the tree’s canopy. Place the first line three feet out from the trunk and circle the tree; move out three feet and make another drip line circle around the trunk and repeat until you come to the end of the tree’s canopy.

• Cover the drip system with your choice of mulch — organic, rock or decomposed granite.

• Water the tree as you did your lawn for a month, then water longer but often — every third day — to push the roots down.

Q: Why are the leaves on my tomato plants curling or cupping up?

A: There are several factor that cause curling:

• The excess sunlight causes leaves to manufacture more carbohydrates than the plant can handle and curling or shading the leaf slows down the process.

• It depends on the origin of the plant; some varieties curl more than others.

• If a homeowner within a mile or two of your garden sprays for dandelions and wind currents are just right, fumes drift to your tomatoes, causing leaves to curl. If it is a mild dose, the plants will recover but if they get a severe dose, it causes what we call shoestring leaves.

• Now the scary one. If leaves are cupping and turning over and then become yellowish, you may have curly top virus. This virus affects one or two plants in a patch and fruit prematurely ripens. Your best control is to discard the infected plant.

Q: I see red yuccas with several flowering stalks, but mine has only one or two stalks at the most and many don’t have any stalks. The three-year-old plants look healthy, just no stalks. Is there a way to get red yuccas to grow more?

A: You don’t say how much sun they get, but red yuccas need full sun to thrive. Or you may be overfertilizing them. Notice flowering stalks next to buildings; they bend out for more sun.

IRIS SALE

The Las Vegas Valley Iris Society is having its annual rhizome plant sale from 8 a.m. to 5 p.m. Saturday and from 9 a.m. to 3 p.m. Sunday at Plant World Nursery, 5301 W. Charleston Blvd. You will be able to get irises of every color and size, including tall bearded, medium, rebloomers, Louisiana, spurea and airlbred. If you were at the show in April, remember to bring a “wish list” of those you liked to make your choices quickly. It’s amazing how well irises do in the desert. If you already have an iris garden, come and get many new introductions.

Linn Mills writes a garden column each Thursday. You can reach him at lmills@reviewjournal.com or at the Gardens at the Springs Preserve, 822-8325.