Cacti can adapt to waterless periods

Q: How often do my cactus plants need to be watered? We have several different varieties and have been told to water them various ways such as at night time and every day. Also, I noticed one is looking a little yellow.

A: The time of day is not so critical. Much more important is the frequency and the amount.

I wish there was a simple answer. Certainly, daily would be hard to support even under the most unusual conditions. The two major considerations are where the plant originated and the soil type where it is currently growing.

If they originate from dry deserts like the Mojave, then once every two weeks probably would be adequate. Watering this often would give them good growth, if that is what you want.

This is provided you do not have sandy or clay soils. In soils with a high amount of sand you will want to water more often, perhaps once every seven to 10 days using less water. In clay soils you would be watering much less often but applying more. If you want to slow the growth of your cacti, then water less often.

Some cacti will give you indicators that it is time to water. On cacti with pads like the beavertail or prickly pear, growth will slow on new pads and older pads will show signs of shriveling.

Many cacti have shallow roots to take advantage of light rains like we had recently. The water did not go very deep in the soil so roots close to the surface took up the water quickly. Deeper roots would have never gotten that water.

Some of the taller cacti have extensive root systems that spread long distances to hold them up when they get top heavy. For larger cacti, it would be best to have some water available a distance away from the plant to encourage a more extensive, supportive root system.

In a very general sense, try watering half as frequently as noncacti in the landscape. If these plants are growing too rapidly for you, then reduce your frequency even more. But remember, they have mechanisms to help them cope with long periods without water.

Q: I was surprised to learn in your recent column that amaryllis is cold tender and should be brought into the house each winter. I have several amaryllis plants in the ground close to my house. Some of these have been in the ground for several years. I simply plant my winter amaryllis bulb each spring after it has finished blooming and the temperatures have warmed up. In successive years, they start blooming in late April through mid-May — usually in early May. Other members of the Sunset Garden Club also have them growing in the ground.

A: I really appreciate you gardeners at the garden clubs keeping an eye on me. It helps keep me on the level. It also brings up a point that needs some discussion. The major point I am trying to make is this: Even though this column is directed primarily at horticulture in the Las Vegas Valley, there is tremendous variation in the weather throughout the valley due to microclimates.

Microclimates are the variations in weather that occur due to things such as buildings, pavement, walls, vegetation and elevation changes. People who live in the older sections of the valley will have different weather experiences in their yards than people in newly constructed parts of the valley.

During the winter, people living closer to the Las Vegas Wash are going to experience harder freezes than people in downtown Las Vegas. People living in the north or northwest part of the valley are going to experience cold weather coming in from the north and northwest during the winter. Generally speaking, people living in the extreme east of the valley have warmer temperatures than those living in the extreme west. And then there are the tiny microclimates that vary from yard to yard and even from different parts of the same yard.

At the University of Nevada Cooperative Extension Master Gardener Orchard, which is located in the northwest part of the valley and not protected at all from buildings, walls and other urban features, citrus will not survive — not even the most cold-hardy types. Last winter our low hit 17 F. The year before it reached 11 F. Yet in downtown Las Vegas we have people growing the most cold-sensitive citrus, such as limes, and they are doing well. In fact, some gardeners living in the downtown area told me they experienced no freezing temperatures last winter.

For just about all varieties of amaryllis, the bulbs will freeze at temperatures between 20-25 F. If your microclimate provides this type of protection, then the bulbs will survive the winter. If your microclimate doesn’t, then it would be best to bring them indoors. Sometimes it is very difficult to give recommendations that work in all of these microclimates.

So let me modify my original recommendation on amaryllis. If you have a warm-winter microclimate in your yard, one that is protected from wind and has radiant heat from surrounding walls and buildings, amaryllis may be safely left outside for the winter. Otherwise, if you are in parts of the valley that offer little winter protection, it will be risky. But whatever you decide, do not overwater the amaryllis bulb during the winter months or it will rot.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.