Western Colorado’s soil leaves plenty to be desired, and here’s how to help

Clay and sand reign supreme in our native soil, so amending it is neccesary for vegetable gardens.

When you amended the soil, you transform it physically to help it retain or drain water and hold nutrients for plant roots.



Adding different amendments to native soils can improve growing conditions for plants, especially vegetable gardens. The goal is to change the structure of the clay or sand-dominated soils we have in western Colorado.

Here are just a few different types of amendments commonly used by gardeners.

■ Manure: All manure is not created equal in the world of gardening. Some are very high in salts (cow manure) and most need to be aged before application due to their high ammonia levels (piled for at least six months). Alpaca and horse manure are valued for their high amount of organic matter and lower salt levels.

■ Compost: Decomposed organic matter, which is not legally regulated, could be any type of material in any state of decomposition. This includes plant-based compost, manure-based compost, or agricultural byproducts such as chicken feathers. Compost can vary in contents and salt levels, even from bag to bag from the same company, as shown in tests conducted by soil scientist Jean Reeder for the Colorado Master Gardener program.

■ Vermicompost: This is another word for worm manure, which has relatively low salt levels compared to animal manures.

■ Cover crops: This “green manure” is one you grow with the idea of turning the plant matter back into the soil. Options include buckwheat or nitrogen-fixing legumes such as clover or hairy vetch.

Amend, amend, amend.

That was the mantra we learned in Colorado State University’s Master Gardener class when I took the course five years ago.

We have cruddy soil here in western Colorado, maybe some of the worst in the state, and that’s saying something in a state with rocky, challenging soil everywhere you look.

A geologist’s heaven is a gardener’s nightmare, and often, people who move here from other places where you can just stick something in the ground and it flourishes are often disappointed and wonder if their green thumbs have turned brown.

Why can’t we have nice, fertile soil like Iowa? Because this valley used to be under a prehistoric lake and there is plenty of evidence left behind in the Mancos shale and other geologic wonders.

It’s just the way it is here. Clay and sand reign supreme as far as native soil is concerned in the Grand Valley, and those two things aren’t much help when you’re trying to grow non-native plants, including vegetable gardens and many of the plants you can find at local nurseries.

So what do you do about it? Amend the soil. That means adding other things to the soil to transform it physically, to aerate the soil and help it retain or drain water and hold nutrients for plant roots. We want what gardeners call soil tilth, meaning that it’s able to support plant growth and it’s a healthy, living soil that is a nurturing environment for anything you would like to grow. Without tilth, healthy plants are difficult or impossible to grow.

But here’s the problem.

If you look at your options for soil amendments, there are so many choices available at the garden centers. And guess what? In Colorado, the industry isn’t regulated. If you buy “compost” it could be anything. If you buy a bag of “composted manure” it can pretty much be anything. Unlike fertilizer, which legally requires three numbers on the bags that indicate the percentage of nitrogen, phosphorous and potassium, you don’t really have a guarantee of what you’re buying with compost, how long it was aged or what its chemical makeup involves.

I had no idea about any of this until I took a class two years ago with Jean Reeder, a soil scientist who worked for the U.S. Forest Service until she retired.

Reeder has conducted her own research on soil amendments and found that even bags of the same product, sold at the same store, can vary in contents and quality.

In an analysis of 60 different products in the categories of composted manure, plant and manure compost, plant compost, biosolids (composted human waste), vermicompost (worm castings), and homemade plant-based compost, she found widely varying results.

In her tests, she found that three of the composted manure products had incredibly high salts levels that would not be desirable for growing any kind of vegetable. Some products labeled “topsoil” for raised-bed gardening had toxic levels of manganese as well. Topsoil is not legally defined, and can include manures that typically have high salt contents, including cow manure.

Managing soils is a complicated business with a constantly moving target — from year to year, your goals might change given the soil texture, nutrients available to plants, aeration and organic matter in the soil. Professionals such as Reeder spend their whole careers studying soils and their chemistry, biology and structure, yet home gardeners buy bags of amendments willy-nilly and dump it on their gardens, thinking they’re somehow improving the soil. Truthfully, if you blindly buy bags of “compost” or “topsoil” and mix it into your garden, you could be doing more harm than good. So what do you do?

The good news is that over time you can create a living soil, using methods such as mulching, adding compost and even growing cover crops and turning them back into the soil to decompose.

The bad news is, there is no quick fix for soil building. I started amending hard-packed clay and sand soils more than a decade ago at my house, and now that garden patch is full of worms and boasts rich, dark soil full of organic matter.

Reeder is a big fan of using cover crops to improve soil health and using grass clippings as a slow-release mulch to slowly provide nitrogen to your plants. She suggested using 1/4 inch of clippings per week in the garden around plants and on bare soil, where they will decompose over time. This is an easy and free way to fertilize your soil and contribute organic matter. If you use herbicides on your lawn, wait at least four weeks to use any clippings from that grass (including weed-and-feed kinds of fertilizer) to avoid damaging the plants you’re mulching.

Your goal is to have soil that has about 5 percent organic matter, but that’s hard to gauge without official scientific data (but you should know that most Colorado soils have less than 3 percent organic matter, and I’m pretty sure I have some that’s less than 1 percent).

First things first, you should get a soil test. Instead of spending money on a problem you haven’t yet diagnosed, why not figure out what you have and start from there? A soil test is affordable and easy to do, and experts can analyze the results for you and make specific recommendations on what to do in your garden considering what you want to grow. If you want to grow native, salt-tolerant xeriscape plants, the recommendations will be different than if you want to grow tomatoes or vegetables that require more nutrients.

Colorado State University’s soil testing lab is open year-round, and the soil-test kits cost $35 per sample. The test includes a pH analysis of the soil, as well as analysis of salt and nutrient levels. But most importantly, the tests come with a professional interpretation of the results and recommendations on what to do next.

Kits are available at CSU Extension’s office at the Mesa County Fairgrounds or by emailing .(JavaScript must be enabled to view this email address).

Erin McIntyre is an advanced master gardener and journalist. Email her at .(JavaScript must be enabled to view this email address) with story ideas or feedback.


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