Q. I wrote to you before about my plants and you said to move them to a cooler location. You also said that if they were healthy, they can take a hotter location. I don’t want to move these plants so can I improve their health and not move them? What about a different irrigation strategy? Add compost to the native soil so that it has more organics in it  This raises the organic content of desert soils. When you are done adding compost  to the soil to raise its organics, lay organic mulch on top of the soil surface to continue to “feed” the soil organics over time. A. The relationship between plant health and how much heat stress it can take is tricky. The most common reasons for poor plant health is its location in the landscape, soil improvement or lack of it and irrigation. It’s very helpful to know where a plant originates. The plants origin tells you it’s best location in the landscape, how much soil improvement is needed and its irrigation requirement. This prior attention to details reduces your involvement in the landscape. If the plant originates from cooler climates but can handle the heat, it performs best if it’s planted in the cooler parts of a landscape. It performs best planted on the east side of the landscape so it gets shade from the hotter late afternoon sun. Add Organics to the Soil Like Compost All plants benefit from some amount of structural amendment (think compost) added to the soil at planting time. The amount of amendment should vary from 10 to 30% (one in ten shovels full vs. one in three). Desert plants from the Southwest benefit from the 10% soil improvement but plants that originate from non-desert countries benefit from 30%. Throw in a couple handfuls of high phosphorus fertilizer as well. More Water? As far as irrigation goes, what size was the container at planting time? Plants bought in 5-gallon containers should receive five or 6 gallons of water at each irrigation. Plants growing in 15-gallon containers should receive 15 or 16 gallons of water. When irrigating new plants larger than this at least half of the volume of its container should be used to judge how much water to apply when first planted. How often to apply this water depends on the time of year or season. This is what is changed seasonally on the irrigation clock.

Q. If I use compost around plants and trees, do I still place wood mulch over the compost? Is it needed, or redundant? When the using compost as a fertilizer and soil amendment the compost should be a rich compost full of nutrients. Compost can be a soil amendment, making the soil “fluffier”, but if it’s rich as well then it will add fertilizer or nutrients to the soil. A. Regarding fruit trees, wood chips applied 3 to 4 inches deep on the surface of desert soils is always a good idea. It is also a good idea for many traditional landscape plants, like photinia, mock orange and roses, to have wood mulch or wood chips on top of the soil rather than rock. All these plants are healthiest if rich compost is applied as a fertilizer in the spring. In this demonstration at the University Orchard, compost was added to the soil, the backfill, surrounding the tree roots. The trees were planted the bare root. The woodchip mulch was added to the soil surface in combination with the compost added to the soil. But if compost is added to the top of the soil every year, the woodchip mulch is not necessary for soil improvement. It does a great job however of controlling weeds and conserving moisture around the roots.             Under some circumstances, some plants get by without wood chip mulch or compost applied as fertilizer. Trees and shrubs that are truly “desert adapted”, or suitable for desert landscapes, can get by without wood chip mulch or compost. All they need is a little bit of fertilizer in early spring every year. These are plants such as mesquite, acacia, Texas ranger and palo verde.             In desert landscapes, with the surface of the soil covered with small rocks suitable for walking, your only alternative may be feeding plants with fertilizers applied from bags, a.k.a. mineral fertilizers. These can be applied directly to the surface of the soil near drip emitters and watered in.             Would desert adapted plants be healthier with compost and wood chip mulch? Definitely. But they can tolerate our desert soils without compost and wood chips better than traditional landscape plants.