Garden Planning: Why you should test your soil!

It’s garden planning season! Seed magazines have begun to arrive in the mail and the weather is…encouraging us to curl up on the couch and dream about summer. Spring is always a busy season, so if you’re hoping for a great garden this year, we think it’s great to spend some time now planning for success.

To that end, we’ll be sharing some of our favorite garden planning tips over the course of the next few weeks so you can have the best garden you’ve ever grown. Growing in the high desert isn’t easy, but we’ve picked up a ton of tips and tricks to help achieve success in a very challenging growing environment.

In this first chapter, we’ll be discussing what we think is the single most important thing you can do to help achieve success whether gardening or farming: Soil Testing. Sending a sample of your garden soil to a lab for analysis on the nutrient contents and other properties of your soils gives you a wealth of information that you can use to help your plants grow better, manage your garden for sustained success, and potentially even save money.

WHY TEST YOUR SOIL?

Plants evolved to work with the microbes in the soil to extract all the nutrients they need from their environment. That means there are 2 parts to soil health: the properties of the soil itself, and the ability of the soil to sustain a complex web of microscopic life. By some estimates, there are over 4 tons of microbe life in an acre of topsoil – you’re feeding an entire elephant’s worth of bacteria and fungi in the top 6 inches of soil. They’re using the same resources that the plants are, and in the process creating byproducts and releasing those nutrients in forms easier for plants to take advantage of.

Is your soil up to the job?

Experienced gardeners tend to be very good at managing their soil health, but the truth is that without actually testing your soil, you’re still just guessing. Soil testing gives you the actual numbers that inform the best way to manage your soil for great plant growth, healthy microbial life, and long-term success in your garden.

HIDDEN HUNGER

The other major benefit of soil testing is to reveal any major deficiencies or excesses in your garden soil. The nature of our desert environment is that dry conditions mean less activity in the soil. Plants and microbes spend parts of the year dormant and water can’t work all year long to break down minerals to release their nutrients. This means that it’s highly likely our soils are missing something.

Plant nutrient deficiencies aren’t always apparent. You can find pictures of extreme nutrient deficiencies from a lot of sources on the internet, but a milder deficiency isn’t always easy to figure out. If you feel like you’re doing everything right but your plants simply aren’t performing, it’s possible that nutrient deficiencies are the problem.

For any yield goal (the amount that you want the crop to produce), a plant will need a minimum level of each essential nutrient. If it’s short on any one, then that nutrient will limit the plant. Ever had a healthy-looking tomato plant that just didn’t give you any tomatoes? It’s possible that a hidden hunger – one or two missing nutrients – was the cause.

BALANCED NUTRIENTS

Soil is an extremely dynamic environment where all kinds of nutrients, acids, bases, and microorganisms are interacting constantly. Some of these interactions are positive for the gardener or farmer, and some work against us. One of the things we need to understand is that plants can struggle just as much if there is too much of a nutrient as if there is too little. One of the best tools ever made to help visualize this is “Mulder’s Chart,” a complex-looking circle that does a great job showing how nutrients interact with each other:

Mulder’s chart: Not just the scribblings of a maniac! To learn more about how to read Mulder’s chart, check this out from Michigan State University.

 If that looks like nonsense, here’s an example of what it’s telling us: The more Nitrogen you have, the harder it is for plants to take up and use Potassium (Potash, K). On the other hand, Nitrogen helps the plant take up and use Magnesium more effectively, and vice-versa.

The basic problem with soil nutrients is that you can’t make a fertilizer that has all the right nutrients for every soil. Even if you found a fertilizer with perfect nutrient balance, it would interact with the nutrients already in your soil. As we said before, if you don’t know what’s already in your soil, you’re left guessing what your plants need, and how much.

HOW TO TEST YOUR SOIL

Hopefully we’ve sold you on the need to test your garden soil for nutrients. So next: how do you go about doing it? Here’s our best take on How To Test Your Soil In Three Easy Steps:

1.      Take a soil sample. Using an aluminum or stainless steel shovel (or a soil probe if you want to go all-out) dig 4 or 5 holes in a square pattern in your garden space, at least 6 inches deep. Make sure one side of the hole is flat and straight up and down and take as even a slice of the soil from the surface to 6 inches in depth as you can. Place the soil samples in a bag or bucket and mix them together.

2.      Find a lab. There are many reputable soil testing laboratories across the country. Look for one that offers complete soil tests. The test should include at a minimum CEC, pH, organic matter, Nitrogen, Phosphorus, Potassium, Sulfur, Calcium, Magnesium, Iron, Manganese, Copper, Zinc, and Boron. And since results will vary from lab to lab, I would also strongly encourage finding a lab that offers recommendations based on your results. Our favorites are A&L Laboratories in California, Midwest Laboratories in Nebraska, or Kinsey Agricultural Services in Missouri. Follow the lab’s instructions for sending in the samples. Typical soil test cost (in 2024) should be about $60-$65.

3.      Interpret the results. Ok, this is admittedly the hard part. It takes a some effort to learn how to read soil test results and make recommendations based on them, but it is well worth the effort. For starters, labs tend to make very good recommendations based on your individual results, and we are also available and happy to help read soil test results with you if you get them.

INTERPRET YOUR RESULTS

This step requires a lifetime of learning to perfect, but learning the basics gives you a huge leg up in improving your soil health. Here are some of the things you’ll learn from the soil test:

-Cation Exchange Capacity (CEC): This number tells you a lot about how well your soil holds on to nutrients. Sandy, light soils have a low CEC and can’t hold a lot of nutrients. Heavy clay soils have a high CEC and can hold a lot of nutrients.

-pH: pH is a diagnostic number – you’re shooting for 5.5 to 6.5 generally, and having a higher or lower number can often indicate that your nutrient balance is a bit off in the soil, or if you have too much or not enough of something. Adjusting pH often requires adding lime to raise the pH or sulfur to lower it.

-Organic Matter: Generally speaking, more organic matter is better. Humus (mature organic matter in the soil) helps almost everything involved with gardening, from loosening the soil to providing nutrients to retaining water. You’re shooting for 3%-5%.

-Nutrient Levels: I would need a few hundred pages to even begin to cover all the nutrients, but there are a few things that even a beginner can pick out. Look for any numbers that are at or near zero first. If a nutrient is missing entirely, address that first. After that, start with macronutrients (Nitrogen, Phosphorus, Potassium or N-P-K), then the secondary nutrients (sulfur, calcium, magnesium), then the micronutrients (iron, zinc, manganese, copper, boron), and trace nutrients after that. I’d recommend downloading the Ag PhD Crop Removal app, a free app that tells you how much of each nutrient a crop needs in the same units that your soil test report will include. Make sure you have enough for crop removal, and build levels from there. Finally, check for excess amounts of anything (your lab should comment on these) and if you’re still looking for improvements after that, look into nutrient ratios. The soil nutrient rabbit hole goes as deep as you want to go, so there’s always more to learn!

Hopefully we’ve encouraged you to start testing your garden soil for nutrients. It might sound expensive, but when you consider that $60 is the cost of 6 or 7 pounds of salad greens, soil testing is an investment that can pay off very quickly even in a home garden.

Next time we’ll be taking a look at the actual plants. Where should you be buying your seeds? Is buying plants worth it? What are our favorite seed providers? All that and more next week in our Garden Planning series!