Are you under or over watering your landscape plants?

Growing plants in the desert is challenging all the way around; from the heat to cold to minimal rainfall, getting plants to thrive can be frustrating. If you are puzzled as to how to tell if you are over or under watering your landscaping in the desert southwest, here are some guidelines.

It is frustrating to try and figure out what your plants want, as by the time they show symptoms in many cases, it’s too late to save the plant. Do not wait too long, however, or you may lose most of your plants.

Under and over watering symptoms often overlap, creating even more frustration. Evaluating symptoms carefully, however, will guide you in the right direction.

Under watering symptoms include loss of plant vigor, wilting, yellow leaves, leaf curling or drop, pest attack, stem and branch dieback and eventual death. Over watering symptoms include leaves yellowing, leaves smaller than normal, chlorosis (both iron and nitrogen), slow decline, soil-borne pathogens, and eventual death.

If your home was built within the past few years, chances are pretty good your irrigation timer is set for initial planting. After the first few months, the irrigation system should have been rescheduled. In this case, almost guaranteed your plants are being over watered. If you are a minimalist and either don’t have an irrigation system or try to water by hand, chances are pretty good you are not watering enough or deep enough.

Although desert plants are drought and low water specialists, most do need some periodic irrigation to look their best. Just don’t kill them with kindness (water).

Diagnosing mysterious plant problems

Velvet mesquite, one of our best native trees

Nothing is more frustrating than putting a lot of hard work and spending tons of time caring for landscape plants, only to have them succumb to some kind of disease or pest. If your plant is looking a little sickly, here are some common symptoms to look for to help you diagnose the problem, along with fairly simple solutions.

Is your plant wilting? Obviously, the first thing that comes to mind is lack of water. If you have ruled out your plant being thirsty, there are a number of other problems that can cause wilting. The reality is over watering can also make leaves wilt, because the roots are rotting. Make sure your plant is not getting too much water. The soil needs to dry out in between waterings so the roots can obtain oxygen. Yes! Roots need to be able to breathe.

Texas Root Rot is prevalent in the southwest, and causes significant root loss in short order. By the time you see wilting, it is dead. Plant resistant species, but never in the same spot. Which plants succumb to Texas Root Rot? Here’s a sampling:

Ash

Elm

African Sumac

California Pepper

Roses

Xylosma

Silk Oak

Bottle Tree

Roses

All stone fruit trees (peaches, plums and apricots)

All nut trees

Notice not one of those is a desert native. This is one of the many reasons why I recommend planting natives.

Some insects can cause wilting as they water out of the leaves. Look on underneath leaves for sucking insects like aphids and mites. If you see them, spray off with the garden hose. No chemicals needed.

What about leaf color changes that aren’t normal for the species? Are the leaves turning yellow? In some cases, this could be nitrogen deficiency. Planting natives usually means fertilizer is rarely warranted since they are adapted to the soil. If the plant is not a desert native, and the leaves are yellow with green veins, this is a sign of iron chlorosis, caused by a deficiency of iron in the soil, or by high pH soils. Soils with high alkalinity prevent the absorption of iron. Treating is expensive and labor intensive. It is better to choose plants that grow in alkaline soils.

Also keep in mind, that early leaf coloration is often caused by drought. Stick with desert natives with low water use requirements.

Is your plant just sitting there and not growing? One of the deadliest thing that can happen to your new tree is planting too deep. If the planting hole was deeper than the root ball, chances are it sunk into the hole and dirt has gathered around the trunk. You can try removing soil that is up against the trunk base. This might work, and worth a try. Next time remember to never dig a hole deeper than the root ball.

Many times plant problems arise because the species is not suitable for our desert climate and soils. Choosing desert native plants is a smart way to avoid many problems and have greater success with minimal effort.

Common problems with cactus and succulents

Damaged by the Agave Snout-nose weevil

Cactus and succulents are relatively problem free, as long as growing conditions, soil, drainage and sun orientation are correct for the species. Always make sure you are purchasing plants are suitable for both the heat and cold. Not all of these plants can handle the brutal low elevation summer heat, or temperatures dipping into the teens. When in doubt: Plant natives!

Cochineal scale is relatively common on prickly pear and cholla. It is evidenced by cottony-like spots on the pads and stems. This insect sucks out nutrients. If left without treatment, it will eventually kill the plant. Control is simple by using repeated hard sprays of water. It’s important to catch this early, however. If the entire plant is covered with the white substance, it’s unlikely you’ll ever be able to get rid of it. It’s been to remove and replace the plant. As a side note, the female of the insect that causes the white cottony mass is the source of a red dye known as cochineal red. The red dye is used in clothing and candy, so if you are vegetarian, think twice about eating candy dyed red!

The cactus longhorn beetle attacks some columnar cactus and prickly pears leaving chewed areas on the uppermost parts. It is identified by very long antennae, as long as the beetle itself. Hand picking is considered the best control method, so you’ll need to be vigilant. The larvae will eat the inside of the plant, so they are hard to detect and control before the plant is dead.

Sahuaro rot (bacterial necrosis), is an infection caused by a number of things. It can result from sunburn, injury (including transport to planting site), frost damage, too much water and poor drainage. Bacteria spreads inside the plant before you notice what is happening. When a black, odorous liquid oozes out of the plants epidermis, it is too late to save. If this appears on an arm, removal of the arm may save it, but it must be caught before the rotting spreads into the main stem.

And what about those holes in sahuaros made by birds? Birds and sahuaros have lived harmoniously together for centuries, so trust me, the sahuaro will be fine. Those holes, usually made by woodpeckers, will later become homes for other critters, including bats and the tiny pygmy owl.

Some agave species are attacked by the agave snout-nose weevil. You’ll know you’ve got them if the leaves of the agave are laying flat on the ground. This insect prefers stressed plants (think thirsty, overwatered, too much sun, too little sun, poor drainage, temperatures too hot or too cold) and seems to prefer the Century Plant, one of the largest of the agave species. Infestation is hard to detect, and by the time the plant wilts it is too late. Remove, dig up the weevil, and kill it before replanting.

Is your soil sick?

There are two soil born diseases that are a problem in the southwest.  Verticillium wilt and Fusarium wilt both can decimate tomato plants seemingly overnight. These diseases also affect peppers, eggplants and potatoes.

With Verticillium wilt, you will see leaves turn yellow and die without wilting, or drop prematurely with shoot tips wilting slightly during the day. As the disease progresses, the leaves may curl up at the margin but remain alive for a short time. There is no cure, so you must choose resistant varieties. I’ve had decent luck with a preventive soil treatment called “Root Guardian” available from Gardens Alive! It doesn’t always work, as I still may lose a few plants, but it must be doing something because the rest of the plants are doing fine.

Fusarium wilt starts out with leaf yellowing at the bottom of the plant working its way up.  The yellow leaves wilt before they die, followed by the entire plant.  Again there is no cure, but “Root Guardian”, as mentioned above, helps. Fusarium wilt is more common in the southwest than Verticillium.

Keep in mind that these diseases are inevitable and it is important to rotate your crops (do not plant tomatoes in the same place every year, in fact every 3 years is best) and buy varieties that are resistant.

A last resort option is to “solarize” your soil. This only works in hot, sunny climates. In late spring, cover the infected area with CLEAR 5 mil plastic. Secure the edges with weights, or bury edges with dirt. That’s it! Leave the cover there for at least 2 months. This will kill all soil diseases, insects and eggs, weeds and weed seeds; however, keep in mind it will also kill beneficial insects, soil microbes…everything. Your soil will be dead, but it will be free of diseases. After you have solarized your soil, you will need to introduce lots of compost and earthworm castings to bring it back to life.