Soil Amendments 101: What They Are & What They Do

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Soil amendments are products, usually meaning organic matter, added to the soil to improve the soil condition. You can add amendments to improve the soil’s texture and structure, build up nutrient content, improve drainage or water retention, and adjust the pH level. 

Most plants prefer to grow in soil with a neutral pH, between 6.5-7.5. 

How Do I Know if I Need Soil Amendments?

If your garden isn’t growing particularly well or is really difficult to work in, or is too wet or dries out too fast, it’s probably time to consider adding some soil amendments.

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The best way to figure out what amendments your soil needs is to get a soil test done. You can pick up a home test kit that allows you to test pH and check the different essential nutrients like nitrogen, phosphorus, and potassium. If your soil feels nice and drains well, this might be all you need to do. At the very least, do a pH test because that’s the best place to start before you worry about other nutrients.

If you think there are more significant problems with your soil than lack of nutrients, you might want to get a full lab analysis done. In partnership with county extension offices, Iowa State University offers soil testing, analysis, and recommendations for amendments for all Iowans, meaning home gardeners to large producers. You can pick up forms and soil sample bags and then send your samples to the lab for testing.

How Do Different Soil Amendments Improve the Soil?

It’s essential to check your soil pH first because if your pH is highly acidic, it won’t matter how many nutrient amendments you add, your plants still won’t be happy. Agricultural lime is one of the most common soil amendments for pH; it will neutralize acidity and bring your soil into balance. 

If your soil is highly alkaline, the best way to bring it back towards neutral is to add well-composted organic matter every year. This process will take a few years to get it back into balance. Either way, adding compost to your soil every year is a great way to improve it consistently.

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Organic matter, usually meaning compost, improves every aspect of soil. It helps with texture, drainage, water retention, nutrient levels, beneficial microbes, and bacteria. Besides compost, you can also use cover crops as amendments.

Glacial rock dust can also help to neutralize soil acidity, though it’s less effective than lime. It also helps to improve mineral balance and encourages healthy bacteria, which are essential to healthy soil.

Alfalfa meal is a byproduct of growing alfalfa; it’s a great addition to your compost pile or bin as it accelerates the breakdown process. It’s also beneficial to add right to the soil.

Kelp, or seaweed, is another popular garden soil amendment. Kelp contains lots of nutrients and micronutrients, but it should be used sparingly to avoid sodium buildup. 

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Well-composted manure from cows, horses, goats, chickens, or other ruminants helps improve nitrogen levels and soil texture and structure. It must be well-rotted, meaning it should have little to no smell before being added to your garden soil. It’s one of the most common soil amendments that people are familiar with. 

Mushroom compost is a byproduct of the mushroom growing industry, and it’s also excellent soil amendments that improve nutrients, structure, and beneficial microorganisms.

Sand, gravel, or horticultural grit are soil amendments that can be added to soil to improve drainage and aeration. 

Fertilizers are also technically soil amendments, although most of them only improve the soil over the short term. Even slow-release fertilizers still only last until they are fully dissolved. While fertilizers are a quick and relatively easy way to get the nutrients to your plants as quickly as possible, they won’t improve your soil over time. Overuse of fertilizers can harm the environment around us. 

mix of soil amendments


If you find you need to add a lot of fertilizer to your garden every year, it’s definitely time to get your soil tested, as it probably has several deficiencies. It’s not that fertilizers are bad, but if you can’t grow anything without fertilizer, your soil might be dead. Dead soil is devoid of living microorganisms or nutrients, so almost nothing can grow or survive in it, and that’s when we call it dirt. If your soil is dead, throwing more fertilizer at it will only cause more damage; you’ll need to build it up to bring it back to life! 

How Do I Apply Soil Amendments?

Packaged soil amendments usually have instructions included with or on their packaging. If you’re going to purchase soil amendments in bulk, it’s essential to discuss what you need and add it to your soil with an expert. You can contact the Warren County Extension office or have a chat with our team at Ted Lare.


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