Use clean, sharp knife to divide rhizomes

Q: When can I divide up my iris? When can I divide up my yucca?

A: Iris is divided in the fall, usually any time from about mid-September to mid-October. The iris is dug and the rhizomes are separated with a sharp, disinfected knife or shears. The rhizomes are allowed to air dry in the shade and out of the heat for a couple of days before replanting. You need enough nice fall weather for them to set down new roots after they have been replanted.

Some people apply a fungicide to the cut ends of the rhizomes to prevent rotting after planting. If you allow the rhizomes to air dry, use a sharp and disinfected knife and you are careful of your water management and prepare the soil for planting just like you would for bedding plants, then you should not need the fungicide.

By yuccas I am assuming you mean the "pups" or small daughter plants that pop up out of the ground a short distance from the mother plant. The daughter plant is dug and the rhizome cut in the same manner. The timing is usually different though. Usually these are cut and replanted during the summer months unless you do it in early fall and give the small plant a chance to root in the soil before it gets cold. It usually takes about four to six weeks to root.

Soil preparation should be similar in both circumstances. Use a starter fertilizer and compost when preparing the soil. Even yucca will benefit from soil improvements.

Q: We have a fan palm where the palms are turning yellow and, I'm assuming, dying. One or two would be acceptable but we are have five or six that are going bad.

A: Let's cover some ideas about why your palms could have yellow fronds. These are the main reasons: Older fronds are dying from natural causes and should be removed; fronds were damaged during winter freezes; too much water applied too often or too little water; palms planted too deeply; palms planted in heavy soil that doesn't drain well; palms planted with pure sand around the root ball; or fertilizer problems such as iron, manganese or zinc.

Palms should be planted with the soil taken from the hole plus 50 percent compost and a starter fertilizer high in phosphorus. Palms should not be planted with their root ball surrounded by pure sand in the planting hole, which is commonly done in Las Vegas. The idea of doing that is absolutely crazy.

Palms are high water users even though they tolerate high temperatures and our desert climate. Different types of palms require different amounts of water. The larger the palm, the more water it will require. One of the highest water users will be the date palm with its huge canopy spread. The amount of water will vary but most fan palms would be happy receiving about 20 gallons every time they are irrigated.

One of the common problems is irrigating palm trees with small amounts of water, like 10 or 15 minutes of drip irrigation, daily or even twice a day. Watering like this can fill the soil with water and suffocate the roots, causing them to rot, become diseased or both. So if you are irrigating your palms daily, don't do that anymore.

During the heat of the summer they can be irrigated two or three times a week, using 20 gallons each time you irrigate, but the soil must freely drain the water away from the tree. In the wintertime you might be dropping your irrigation to 20 gallons every 10 days or perhaps even as far apart as two weeks.

Sometimes the soil lacks certain types of minerals that palm trees need. Deficiencies in iron and manganese usually appear as a discoloration in the fronds at the center of the canopy, the most recent growth. This can range from light green to nearly yellow. If these inner fronds are yellowing, then we can usually narrow this to watering too often, poor drainage or a lack of minor elements such as iron.

Next February when you make your annual application of fertilizer, use a complete fertilizer such as a Miracle-Gro, Rapid Gro or Peters. You can also use fertilizer stakes. Make sure it is well balanced and try to select a fertilizer with the three numbers the same or close to the same value, like a 16-16-16 or 10-10-10. Add an iron chelate that contains the EDDHA chelate in the ingredients.

Let's see if that works along with irrigating with a large volume of water but doing it less often.

Cold damage on palms usually results in the older fronds turning a bronze color first and then browning later as they die. The general rule of thumb is if more than half of the frond has turned brown, remove it. The new fronds at the center of the palm should be healthy and green when they emerge in midspring.

If your soil is heavy and holds water a long time, then plant on a mound 2 to 3 feet high and 6 to 8 feet across so the water drains away from the roots.

Q: We have a beautiful 5-year-old Moorpark apricot tree. It has grown well and looks quite healthy. However, it seems to put out a sparse array of blossoms in spring and has a very light crop of fruit every year. The fruit is delicious. I read that the chill factor for this cultivar may be higher than our climate provides. Can I increase the chill factor by watering the branches in winter on cool days to lower the tree's temperature and thus increase the chill factor? If successful, could I get a larger crop?

A: Moorpark is a wonderful apricot variety and is used extensively in the canning and fresh-fruit industry in California. It is best if it receives about 600 chill hours during the winter. This means that the temperature should drop below 45 F for at least 600 hours for the best fruit set.

However, don't worry about the chill factor in this case. We have Moorpark at the University of Nevada Cooperative Extension Master Gardeners Orchard in North Las Vegas and it has good fruit set here, even after 18 years at our chill hours. The problem is more likely the fruiting spurs or lack of them. These will be the short branches along the major branches.

If these were pruned off, damaged or never developed, then the crop will be light due to a lack of flowers. This year was a bad year for apricots. We had good weather and then it turned very cold in March. That freeze reduced our orchard apricot production from about two tons down to about 200 pounds.

We have had no problem with Moorpark and irregular production and it has been a wonderful producer in most years. Perhaps the location of your tree in a particular microclimate of your landscape or how it has been pruned may have more to do with it than the variety itself. But a lack of chilling is not the problem.

Bob Morris is a horticulture expert living in Las Vegas. Visit his blog at xtremehorticulture.blogspot.com.