Start With The Soil

In the Southwest, one of the most critical things we can do to help our plants thrive is to create good soil for them to grow in.  I call this “Goldilocks” soil.  It has to be not to hard, and not too soft – it has to be just right.   

The Importance of Soil

First.  Soil for your plants has to hold water – but not become waterlogged.   

Second.  Soil must hold oxygen because plant roots need to breathe as they grow.   

Third.  Soil has to offer the right kind of minerals and microbes and in the right amounts.

The plant makes it’s own food by doing photosynthesis, but it needs the minerals in the soil so it can grow strong and healthy. Microbes are like “gut bacteria” in humans. The microbes need to be there in the soil to help plants absorb the minerals they need, and help with a number of other functions that scientists are just beginning to discover.

It all Starts with the Soil

When planting a plant, my Grandpa taught me, “Make a ten dollar hole for your two dollar plant.” Inflation has set in a tad, but the idea is same.    The place where you plant your plants should be lovingly prepared with time, energy, and the soil amendments your plants will need to thrive.   

That effort – including time and money spent getting the soil to where it needs to be to support healthy plant growth – will give you back by saving you time, and effort, and money from trying to fix plant growing problems later.

What You’re Starting With: Southwest Soils

Our soils in the Southwest vary widely, even within a single city, or tougher yet, within a single home lot. Without getting overly technical I do wish to point out that there are some components to the soil that your should have with best success with your plants. It is called soil texture.  We have almost every kind of soil texture in the Southwest except good loamy fertile garden soil.

Soil Texture

Soil texture is the size of the particles making up the soil.    This ranges from tiny clay particles through to coarse rocky sand.  Rocks themselves are another issue.

Clay soils are slow to drain, and dry to rock-like consistency between rains.

Sand, gravel, and rocky soils drain very quickly, gravity pulling the water deep below the reach of plant roots.

And then there is caliche. We will come back to this topic.

Soil pH

Soil pH is a measure of how alkaline (basic) or acidic the soil is.   

All living organisms have a specific pH they do their best at, and plants are no different.

Southwest soils are alkaline―they have a high pH value (above 7.0). Most garden plants prefer a slightly acidic environment―a low pH value (below 7.0). Generally our Southwest soils range around pH 8.0, while most plants would prefer 6.5 to 7.0 for growing. This is a vast, but not insurmountable, problem.

As a side note, cactus growers have noticed that growing saguaro from seed works well if they acidify the soil and water – at least a little bit. The saguaro, this mighty sentinel of the desert – icon of surviving tough conditions – and it would prefer less alkaline soil than what is out in their normal desert habitat.

Test the Soil?

I say no, save your money. Books and many articles often advocate taking soil samples to a lab for testing before you do anything else. Save your money! No matter what soil you have (unless it is a long established garden), here in the Southwest tests will show that you have alkaline soil that lacks nitrogen. 

To make alkaline soil a better place for plants and soil microbes, you will need to add organic matter―compost. If you add this after a soil test, it will change the pH and composition of the soil, nullifying your test. Tougher even is no mater how much you acidify with compost, if you water with well water, it is alkaline and will drive your soil back to alkaline over time, again nullifying your soil test.

Compost is needed in clay soils to help aerate and acidify the soil. Compost is needed in sandy and rocky soils to hold onto water and acidify the soil. Even a long established garden will need compost on an annual basis―because compost is always decaying (decomposing!), plus Southwestern water, from the city or a well, is almost always alkaline, thus pushing the soil back toward an alkaline state.

Desert Soils are Actually Rich!

Our Southwestern soils have all of the minerals a plant needs for life. But! There is an ogre under the soil, and it is called caliche.    Read on.

Plants need minerals so they can build their cells. They get everything else they need from sunlight, air, and water, but the minerals are critical to keep the whole system working.   

The minerals include:
nitrogen (N), phosphorus (P), and potassium (K). These are the big three sold in fertilizers and marked on fertilizer packages.  Nitrogen is the only one in short supply in arid soils.

Then there some other, equally critical, minerals:
calcium (Ca), sulphur (S), and magnesium (Mg).   

Also critical for plant lives are trace amounts of:
boron (B), chlorine (Cl), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and nickel (Ni).

Remember, there is generally enough minerals in most Southwestern soils. But – while there are ample minerals – there is also caliche.

Caliche blocks the uptake of all of these minerals. All of them.

Caliche

Caliche is a close cousin to the plaster and wallboard (Sheetrock is a registered trademark) in the walls of your home.   

According to rock people (Geologists) caliche is technically a form of sedimentary rock. Caliche is a hardened deposit of calcium carbonate naturally formed in the soil.  Nice in your walls, not so nice in your garden. In the soil this calcium carbonate “plasters” the soil and rocks together, forming a tough, generally impenetrable layer a few inches to a few feet deep.    Tough for plants to grow in.

The word “caliche” is a Spanish word that is based on the Latin word calx, meaning lime. Not the lime you eat, the lime that is a form of plaster or cement.

Side note. You may also have some calcium carbonate in your medicine chest. Antacids are calcium carbonate too. But I digress.

 

Caliche Formation

Caliche forms when that calcium that is present in our soil along with other minerals gets dissolved in rain water and carried down into the soil. In wet climates, this calcium rich water just keeps going downward and wanders away from the land into rivers and into the sea. In arid areas, the sun sucks the water right back up out of the soil, and the calcium is left below the soil. Do this over and over again, and it forms into layers of calcium.  Because of it’s chemical nature, this calcium carbonate is able to knit together rocks and soil. We call these accumulated layers caliche “beds.”

Plants are not without blame in the formation of caliche! It is not just sun evaporating the water. Plant roots take up water, but they only need a tiny bit of calcium so they leave most of it behind, helping build the caliche layers.

Caliche is generally light colored, from white to light pink to reddish-brown, and found in layers anywhere from a few inches to a few feet thick.    To make this more fun, multiple layers can exist in a single location. Also called hardpan or calcrete.

Caliche and Gardening

Caliche causes many problems when trying to grow plants. First, a caliche layer does not allow water through.    This leads to waterlogged soil.    Roots will drown and rot if the soil is waterlogged.    Also, harmful salts can build up in the soil due to the lack of drainage, stressing plants.

Second, caliche beds prevent plant roots from growing deeply into the soil, which means the roots have a limited supply of nutrients, water, and space, thus the roots can’t develop normally. Trees may not grow strong anchoring roots, and will be easily toppled by a heavy wind.

Third, caliche beds, even 10 feet down, cause the soil above them to be alkaline. Alkaline soil, along with the calcium carbonate from the caliche, can block roots from taking up minerals in the soil, especially iron. An iron deficiency will cause the plant’s youngest leaves to become yellow.

What is perhaps most frustrating is that plants do need calcium. Our soil (unless an old sandy river bottom) is rich in the essential minerals, including calcium, but these are blocked by the alkalinity of caliche. Acidifying the soil with compost and other soil additives helps dissolve the caliche and free the essential minerals.

Soil Acidifiers

There are a number of soil additives but easiest of all is compost. 

Compost is rich in a natural acid called humeric acid. Remember that we are trying to acidify our soil for the plants. You can buy compost in bags at any plant nursery. You can make it at home. I have posted “How to Make Compost in the Desert” and also a separate discussion about composting when you have an HOA.

Peat moss is another excellent and renewable (in North America anyway) source of soil acid. If you see an article knocking peat moss it might be written in Europe, or by a writer that has not visited the Canadian peat harvesting operations like I have. The peat recovery system is amazing and helps maintain a rich and healthy bog ecosystem.

Coffee grounds. You can acidify your landscape soil with used coffee grounds. Most coffee shops give them away. Avoid using coffee grounds where you want to grow plants from seeds. Coffee grounds contain inhibitors that keep seeds from germinating. If you want to grow seeds, simply compost the grounds first.

Vinegar. I recommend this to treat spot areas. Use 1 cup white vinegar in 4 gallons of water. Pour this around your citrus and roses as a fast way to acidify the soil around a single alkaline-stressed plant.

Now that you know how to nurture it – Consider a fruit tree!

May I recommend my book?  The Southwest Fruit & Vegetable Guide offers not just growing guides but some of the latest varieties – including ones specifically for raised bed and container growing. Price is what you would pay on Amazon – only when you buy from me you get a signed copy!

From the review:

“In this updated 2nd edition of Southwest Fruit & Vegetable Gardening, you’ll find much-needed advice and practical tips on growing an edible garden, no matter which part of the southwestern US you call home.

Profits from the sale of this book go to the Arizona-based Horticulture Therapy non-profit Tierra del Sol Institute.

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