Should you fertilize desert landscape plants? Or is this a maintenance step you should skip? Here’s a look at the pros and cons of fertilizing, synthetic vs organic fertilizers, and the 5 times you should never fertilize your plants.
There are two schools of thought on whether desert landscape plants need fertilizing.
The first is that plants that evolved to grow in desert soil, are adept at extracting the nutrients they need, and don’t need any help.
The second is that the native soil in your yard is probably far from what it should be and so you should fertilize even native desert plants.
Let’s take a look at the reasoning behind both.
No Fertilizer Needed
Not fertilizing makes a lot of sense. Look around at wild places or even along roadsides and in median strips and you’ll see native plants like globe mallow, desert willow, cactus, agaves, and brittlebush, along with a potpourri of wildflowers thriving without fertilizer. Clearly, they are getting all the nutrients they need from the native soil, but…
How is this possible? Aren’t desert soils notoriously poor?
There’s a big misconception about desert soils. They are usually described as poor but that is not true. In fact, they are loaded with minerals, what they lack is organic matter.
And, unless you are using rainwater, you are irrigating your plants with water that is also loaded with minerals. This is evident from the white mineral deposits that accumulate on plant containers and in fixtures in your house.
According to the University of Arizona, mineral deficiencies in desert plants are rare and you should fertilize only when there are signs of deficiency. When deficiencies do occur, it’s typically nitrogen and iron that are lacking and almost always in non-native plants.
Fertilizing desert plants as a routine maintenance task is unnecessary and potentially detrimental. Too much fertilizer can stimulate plants to grow unnaturally fast. They are not only more prone to diseases and wind- damage, but will need more water and more frequent pruning, which means more cost and work for you!
Yes, You Should Fertilize
People on the other side of the discussion point out that when the land was cleared to build your home, it was stripped of its topsoil replete with microbes and organic matter. And that it will take many years to regenerate back to something approaching its original state.
Both of these schools of thought have merit. Answers to questions like these can help you decide.
- Are you living in a relatively new subdevelopment? Or are you tending an established garden that’s had years to repair the soil?
- What kind of plants do you grow? Do you have mostly natives or do you have plants that require more nutrients like roses, hibiscus, or citrus trees?
- Do you keep your yard in tip top order or do you like to leave some plant debris to return back to the soil?
Organic vs Synthetic Fertilizers
If you are going to fertilize your landscape plants, it’s best to use a fertilizer high in organic matter since our desert soil is low in organic matter.
Look for organic ingredients like kelp meal, bat guano, seed meals, worm castings, composted manure, and seaweed extract.
While there are many fine organic fertilizers, two highly recommended brands that were developed with an understanding of our native desert soil and plants are:
While Tony’s is often promoted by local plant gurus and some garden centers, I find it to be prohibitively expensive. ($60 for a 5 lb. bag). When I need fertilizer, I use Tank’s.
Organic fertilizers like these actually improve your soil, and since they don’t break down as fast as synthetic fertilizers, their effects last longer.
On the other hand, if you have reason to believe your plant has a genuine nutrient deficiency, synthetic fertilizers are more quickly absorbed and get to work on deficiencies faster. If you use a synthetic fertilizer, follow the instructions or dilute the recommended amount by half. Too much can cause fertilizer burn.
The Effects of Fertilizer on Microbes
It’s well established that organic matter provides food for beneficial microorganisms in soil and encourages their colonization.
However there’s an ongoing debate as to whether synthetic fertilizers harm the beneficial microorganisms in your soil.
Soil scientist Ashley Labrecque, B.Sc. does a deep dive on this topic in this video.
Her take is that initially, synthetic fertilizers draw water out of microbes, causing them to die. (A similar process occurs when you overfertilize your plants causing fertilizer burn.)
However, since soil is teeming with rapidly reproducing microbes, within 48 to 72 hours microbes from the surrounding soil move back in and recolonize, restoring microbe levels back to what they were.
Given the choice of using a fertilizer that supports the soil’s beneficial microbes and one that kills them, even if the effects are temporary, I prefer to support.
Amazing Fact!
A single teaspoon of soil contains millions of bacteria, hundreds of
thousands of fungi, thousands of protozoa, plus many larger organisms.
When You Should Fertilize
If you are growing citrus trees, vegetables, or non-native landscape plants, especially ones that flower abundantly like roses or hibiscus, you should fertilize for best results.
If you are growing plants in containers, you should fertilize since these plants have access to limited nutritional resources.
If you’re certain your plant has a nutritional deficiency, you can give it a boost of whatever nutrient it needs. If desert landscaping plants are deficient in any nutrients, it’s usually nitrogen or iron.
For help identifying nutritional deficiencies in plants, see the University of Arizona’s publication Guide to Symptoms of Plant Nutritional Deficiencies.
And if you get stumped, you can always reach out to Pima County Master Gardeners for help. You can use their online form, or if you live in Tucson you can stop by their office with any plant questions.
If you live elsewhere in Arizona, you can look up your county’s Master Gardener program by county here. They might offer similar services.
And if you live outside of Arizona, here’s a list of master gardener programs by state.
5 Times to Skip Fertilizing
And finally, even if you decide to fertilize your plants, there are circumstances when you definitely should take a hiatus.
Don’t fertilize newly planted plants. This stimulates new growth when the plant should be putting its energy into developing a strong root system.
And never dump fertilizer into the bottom of a hole. It won’t do your plant any good since watering moves nutrients downward, away from your new plant’s roots.
Don’t fertilize plants when they are stressed such as during a heat wave or when they’re struggling with transplant shock. I know we gardeners love to feel like we’re doing something helpful, but fertilizing can further stress your plant.
Don’t fertilize in late fall. This stimulates new growth which is easily frost-damaged.
Don’t fertilize plants when they are dormant. This means you can skip fertilizing landscape plants during the winter.
Don’t feed nitrogen to plants in the legume family (Fabaceae). Their roots contain bacteria which “fix” nitrogen, i.e., turn nitrogen in the air into a form plants can use.
The one obvious thing legumes have in common is that they all produce characteristic pods. Many desert trees and shrubs fall into this category including mesquites, palo verdes, acacias, Texas mountain laurel, ironwood, Mexican redbud, fairy dusters, and the various bird of paradise plants.
Not sure if a plant is a legume? You can use our Desert Plant Index to see if we have a “Plant Profile” in our Desert Plant Library. If a plant is a legume, we’ll mention it there.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
