What the Heck is a ‘Soil Amendment’?

It’s the hidden ingredient in a beautiful, productive garden.

To amend something means to add to or create a change, generally beneficial.

When we’re talking about gardening, that is precisely what we are doing — adding to our soil so that plants will grow better.

Have you ever noticed how seed packets often instruct you to plant in average well-worked garden soil?

What the heck does that mean, anyway? Read this previous article to get an idea of what to look for in that ethereal ideal garden bed.

Most of us are working with soil that is less than perfect. It may have too much clay or be exceptionally sandy. It may be packed so hard you need a pick to make a dent in it, or perhaps it becomes a swamp after a hard rain.

We want to add soil conditioners that can:

• improve the tilth of the soil.
• add to its water holding capacity.
• allow the soil to hold on to nutrients better.
• reduce compaction, which allows air and water to penetrate.

An amendment is anything we add to the soil, but it will fall into two broad categories, organic and non-organic.

Inorganic amendments are either mined or human-made.

To improve drainage or aeration, a gardener can add vermiculite, perlite, pea gravel, and sand. Trace minerals, as well as, greensand, bentonite, humates, rock phosphates, langbeinite, can increase the mineral content of the soil.

An organic soil conditioner is anything that was once alive.

These substances may include sphagnum peat, wood chips, grass clippings, straw, compost, manure, biosolids, sawdust, wood ash, bone meal, and many more.

Organic matter gradually improves soil aeration and the soil’s ability to hold moisture. Many organic amendments contain plant nutrients and act as natural fertilizers, as well.

Organic matter is food for the microbes — critical bacteria and fungi, along with earthworms and other essential elements of the soil web.

Ideal garden and landscape soil would have 4% to 5% organic content.

The original prairies in the central United States contained 5.5 to 6.5 percent organic matter before they were tilled up for farmland. This has now declined to 2 to 3 percent. Soil scientists estimate that a one percent increase in organic matter can result in a 12% improvement in crop yield.

At the 5% level, the mineralization (release) of nitrogen from the organic matter will be adequate for most plants without additional fertilizers. We will need to add more compost if we are removing produce, grass, or other crops from the land.

Which soil amendments should you add?

I can only answer that question with “It depends.”

Once you’ve done a basic, hands-on check of your garden as described in the ‘Is My Soil Sick?’ article, you’ll have a starting point. The appropriate amendments will depend on the needs of your soil.

If you want more detailed information, I suggest finding your County Extension Office using this directory. The Extension office is a free resource to help with questions about your garden, lawn, farm, and much more. They can also suggest a site to get an in-depth soil analysis. The test results will help you determine any macro and micro-nutrients that will be beneficial additions to your soil.

Well-rotted plant-based compost is the best organic material.

No, not because microbial life is vegan. Animal manure may add too much salt to the soil, and if it is not well-rotted, it can potentially contain pathogens. You are less likely to have problems with compost made of decomposed plants.

There is not a uniform label or even description for compost, so you have to investigate it, whether it comes in a bag or you pick it up in bulk.

Finished compost should be dark, reasonably fine, and not have chunks of identifiable components. If you can still see sticks and large pieces of bark, vegetable peels, and other items — it has not finished decomposing. Just like healthy soil, good compost should be dark and smell like fertile soil.

For a new garden, you should add at least three inches of compost over the entire bed. Each year add three more inches in addition to any inorganic materials recommended by your soil test.

You will see your soil become more vibrant and productive as you add these amendments — ingredients for healthy soil and delicious, nutritious vegetables.

Our most important job as vegetable gardeners is to feed and sustain soil life, often called the soil food web, beginning with the microbes. If we do this, our plants will thrive, we’ll grow nutritious, healthy food, and our soil conditions will get better each year.

This is what is meant by the adage ”Feed the soil, not the plants.

― Jane Shellenberger, Organic Gardener’s Companion: Growing Vegetables in the West