Q.  I have three questions. How often should I water? Do I need to put mulch around the plants and then cover them with rocks or keep the mulch exposed? Do I need to fertilize plants with a desert-type fertilizer or can I use the same stuff I use on my regular plants and how often?   A. How often to water. Winter; once every ten to 14 days. Spring until May 1st; once a week. May 1 through the summer; twice a week. September 15 to December 1; once a week. These are approximate dates. Adjust with the weather. Purple leaf plum mulched with wood mulch in a desert landscape of rock mulch. Wood mulch adds organic matter back to the soil as it decomposes and is needed in soils around some plants like purple leaf plum.             Wood mulch is a substitute for rock mulch. Rock mulch will cause problems with some plants. If you want all rock mulch, then make sure the plants used can tolerate rock mulch. Wood mulch is used without rock mulch and should be three to four inches deep around plants. Ammonium sulfate is a high nitrogen fertilizer containing 21% nitrogen (21-0-0)             Fertilizers are the same for all plants. If you want growth, use high nitrogen fertilizers. If you want flowers and root growth, use a fertilizer with high phosphorus. Good fertilizers are more expensive than ordinary fertilizers and are frequently worth the money. Sprint 138 iron contains iron in the chelate EDDHA form which works very well in our highly alkaline soils             If you can’t afford good fertilizers then make sure you use a good fertilizer at least once a year and use less expensive fertilizers the remainder. Use them when you can and the first application of the season is usually the best time to use them.             One application per year is enough for most plants except lawns and plants that you appreciate for their flowers. In those cases four applications are best; Labor Day, Fourth of July, Memorial Day and Thanksgiving. If the plants are tender to winter cold, skip the last two fertilizers of the season.             Plants that turn yellow are usually iron deficient and will need a GOOD iron fertilizer. Not all iron fertilizers work in our soils.