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February 05, 2025 13 min read 0 Comments
Soil amendments are substances growers add to the soil to adjust pH, increase water retention, and improve drainage so they are healthy and yields are abundant. Amendments do not provide high levels of nutrients like fertilizers but enhance the soil so plants can access available nutrients.
Think of soil as the blank slate for gardening and each amendment you add as the building blocks for healthy crops. Some people start a garden without testing the soil or adding amendments, and for a little while, it might perform just fine. However, yields will increase, drainage will improve, and plants will be healthier once you get the right balance of these vital building blocks.
Stop wasting money on expensive amendments you’re unsure of or being overwhelmed by complicated formulas. Let us help you determine what your soil needs to take your garden to the next level. In this article, we’ll break down the five top amendments to start using this season to help improve your soil for maximum yields or to scale up your production.
You’ve likely heard about soil testing, and maybe you’ve even seen a write-up of the results but have been confused by them. Let’s discuss how to test your soil and identify what will best serve your garden.
Different soil types react differently to irrigation, extreme weather, compost, and roots, so knowing how to treat it will enhance your gardening results.
Our article, How to Determine the Texture of Soil | Textural Determination with the Soil Texture Pyramid, breaks down the four soil textures (sandy, silt, clay, and loamy) and explains how knowing this will help you grow more efficiently. Your soil’s composition depends on where you live, so while you can’t completely change the type, you can improve it by adding amendments and watering correctly to get you closer to the much-desired loamy soil.
While DIY soil kits may give you a baseline of what’s happening, we highly suggest annual professional lab testing for the most accurate results and recommended action steps. Contact your local extension office or university to inquire about soil testing. Ensure results include pH, organic matter percentage, nutrient levels (we’ll discuss vital nutrients later), and drainage capabilities.
Monitoring your garden’s performance is crucial, as it helps you recognize deficiencies or overapplications. Plants tell us when something is “off,” and paying attention is up to us. Symptoms could be a sign of stress, too much nitrogen, or roots that can’t breathe. Here are a few things to watch out for:
Yellowing leaves
Discoloration
Failure to thrive/stunted growth
Few or no flowers may indicate excess nitrogen, especially when growing ornamentals.
Dried-out or soggy soil
Plant death
Take application recommendations with a grain of salt, and remember that your garden’s soil is unique. Take notes from past seasons and consider your soil's specific needs. For example, organic matter will drastically improve clayey and sandy soil by feeding beneficial bacteria and fungi, increasing drainage, reducing compaction, and promoting healthy root growth.
Amendments can be organic, mineral-based, synthetic, or natural, each serving its purpose. Which you choose is a personal preference. Let’s discuss common amendments of each type.
Compost is the gold standard and one of the most common amendments because it benefits all soil types. It will improve your soil over time, help reduce erosion, improve water drainage and retention, reduce pest pressure and disease, stop runoff, boost nutrient availability by increasing the cation exchange capacity, decrease the need for synthetic additives, and boost crop yields!
Compost, which is decomposed organic matter, can be plant or animal-based, and not all composts are created equal. When bringing compost to your garden, ensure the product is high-quality, not overly high in salt, and safe to apply at the time of purchase. Unfortunately, when not appropriately made, compost can pass along weed seeds, jumping worms, and soil-borne diseases. Do your research and be prepared to pay a little more for a better product.
Manure is a mix of animal poop and their bedding, which may contain hay, straw, and wood chips.
Composted manure has been heated above 145° and turned often, killing weeds and stabilizing organic matter. Avoid applying it heavily as it can be high in nitrogen, which can cause healthy plants with lots of lush foliage but no flowers.
Source fresh manure from a trusted local farmer, but be aware it may contain pathogens, weed seeds, and high salts, which are dangerous for fruit and vegetable production. Let it age for at least four months before applying directly to crops. You can speed this process by turning the pile frequently, keeping it moist, and allowing aerobic bacteria to raise the temperature above 145°.
If you must apply fresh manure, do so in the fall. By spring, it will be safe to mix and plant into. Do not use fresh manure for edible plantings.
Earthworm castings, or worm debris, are a less aggressive manure. They contain trace elements and water-soluble nutrients that seep slowly into the soil, making themselves available to plants. Castings aerate the soil and provide nutrients for beneficial microorganisms like bacteria, fungi, and worms. Reapply castings quarterly, mixed into potting mixes, or at the time of transplant.
The method and amount of application will depend on what you’re growing, the type and fertility of your soil, and your garden needs.
Peat moss improves soil aeration, increases acidity, loosens thick, clayey soils, and helps retain moisture. However, it’s a non-renewable resource from peat bogs, covering less than 3% of Earth’s land. Earth’s peat bogs are the largest store of natural carbon that helps improve our water quality.
Consider using coco coir instead, which does not have the same acidity but does have many of the same soil improvement benefits. The living layer atop peat bogs is sphagnum peat moss, which sometimes lines outdoor hanging baskets. However, you can also use coco coir to line baskets and your garden, which has similar benefits and will lower your gardening carbon footprint. You can use eco-friendly coconut coir, worm castings, and pine bark(which adds acidity) as an alternative to peat moss.
Mulches include green manure, grass clippings, pine wood chips, leaf mold, plant roots left after harvest, and cover crop debris. Consider how long each will take to break down and how that affects the soil. For example, wood chips can lock up the availability of nitrogen needed to break down the wood chips’ high carbon content. Know the wood source to ensure no disease or weed seeds are present. Aging them for at least a year creates a better amendment than when they’re fresh, as decomposition requires a lot of energy. Alternatively, mix them with a high nitrogen amendment like alfalfa pellets(often sold as animal feed).
Use cover crops like clover, oats, and buckwheat to naturally build your garden’s fertility, protect soil from runoff and erosion, suppress weeds, and boost organic matter. They provide the added benefit of providing a safe space for beneficial insects, birds, and critters to lay eggs and raise brood, as well as food for local pollinators like butterflies, bees, and hummingbirds. Our article, Top 5 Benefits of Using Cover Crops in Home Gardens, will provide tips on how to get started and how your garden will benefit.
Green manures are crops like mustards grown to plow under to fumigate root nematodes, pests, and diseases, increase organic matter, and improve soil structure. They also break pest cycles, prevent erosion, and protect fallow fields between cash crops.
Biochar is a carbon-rich by-product of burning organic waste. It can improve water retention and access to soil nutrients and provides an excellent habitat for beneficial soil microbes.
Biosolids are the by-product of wastewater treatment centers. The National Academy of Sciences deems it safe to use on crops intended for human consumption as long as the farmer follows other federal guidelines. Michigan Department of Environmental Quality
Related: Beginners Guide to Soil, Media, Amendment, and Fertility
When growing acid-loving plants like blueberries, azaleas, and rhododendrons, use lime to adjust pH. Note that adding too much can prevent plants from absorbing other vital nutrients. The effects of excess lime can take up to three years to fully manifest.
Gypsum, made of calcium and sulfate, reduces sodium levels, making it easier for plants to uptake water and oxygen and form healthy roots. Air pockets benefit compacted clay soils, where roots may otherwise have trouble accessing the oxygen they require.
Side dress with rock phosphate during flower and fruit production to boost yields and encourage continued healthy root formation.
Greensand helps improve the texture of clay soil and adds potassium, iron, and magnesium.
Perlite is a lightweight volcanic glass material that growers use to improve aeration by adding air pockets to the soil.
While often lumped in with perlite, vermiculite has a consistency similar to mica. It improves aeration and drainage but acts like a sponge when placed in the soil, making it a beneficial additive for seed-starting.
Related: How to Test Soil pH Before Planting — and Why You Should
Synthetic fertilizers offer immediate nutrients to plants, whereas organic amendments feed the soil. Eventually, organic matter breaks down, feeding microorganisms that turn that food into plant-available nutrients; the process just takes much longer.
Organic amendments contain lower NPK levels, which makes adjusting soil a long game. However, they typically contain micronutrients plants need and continue feeding the soil for much longer. Alternatively, synthetic fertilizers give you the boost you need in a pinch, which is worth it for some growers. In general, you can use synthetic feeds when you’re starting new gardens or your plants need a jolt of something right away, but once your soil is healthy, rely on organic options to keep it that way.
Organic options are more sustainable, healthier for the planet, and won’t cause concern for run-off or chemical leaching concerns. It’s easy to grab synthetics when you want immediate results, but organics are the way to go if you’re in it for the long haul.
Compost or aged manure
Worm castings
Vermiculite and perlite
Mulches
Agricultural lime or elemental sulfur
Before choosing amendments, ask yourself:
What are your goals?
What are your garden’s nitrogen needs?
Is there a concern for too much salt?
What are the local regulations?
How often do I need to apply the amendments?
What is the cost?
Sandy soils can be challenging to work with due to their small particle size and inability to hold much moisture. Typically found in coastal regions, near forests and deserts, and along riverbanks, sandy soil has a gritty texture and has a hard time holding onto small plant roots. Incorporating compost, grass clippings, or aged manure will help it retain moisture, increase the percentage of organic matter, and release nutrients to your plants as they break down.
Till in cover crop debris to add organic matter to sandy soils. Perform soil tests often, as sandy soil tends not to hold onto nutrients, and amend as needed. Grow vegetables like carrots, beets, radishes, and Mediterranean herbs that prefer sandy soil.
Large particles in clay soils tend to stick together, making it hard for roots to breathe. Before adding plants, improve the soil tilth by adding greensand and compost. Otherwise, moisture can build up and cause issues. In addition, planting cover crops in off seasons can significantly improve the tilth of clay soils by adding organic matter deep under ground in the form of decomposing roots.
Loamy soils require much less maintenance and only the occasional compost application. This soil type features the perfect balance of clay, sand, and humus, allowing plants to develop, grow, and produce properly. Overtime it can become depleted of mineral nutrients so occasional additions of rock phosphate and greensand will add back micro nutrients.
For further information about improving your soil’s tilth, feeding beneficial organisms, and treating various soil types for excellent garden results, refer to the Colorado State University Extension's comprehensive resource about soils, fertilizers, and soil amendments.
Related: Top 10 Best Fruit Trees For Clay Soil
Consider the time of year before adding amendments.
During seed starting:
Mix compost into your seed-starting mix.
Vermiculite can prevent root rot, overwatering, and damping off. For seeds that require sunlight to germinate, lightly sprinkle vermiculite atop the seeds and bottom water to ensure they stay in place.
Worm castings or casting tea will give transplants a boost in root development.
Alternatively, use a professional-grade seed-starting mix that contains all the nutrients seedlings require.
Midseason soil amending:
To boost production as long-season crops like tomatoes and peppers set fruit, add rock phosphate every few weeks around them.
Side dress perennials with compost to continue feeding underground microorganisms.
Preparing for winter:
Mulch trees and perennials with compost or mulch before the first frost.
For plants that like acidic or alkaline soil, adjust the pH with lime or sulfur in the fall to prepare for the next season. Alternatively, add a slow-release general fertilizer to the garden; it will be incorporated by spring.
Now, let’s discuss best practices for applying soil amendments for best results.
Most experts advise applying amendments at the end of the growing season after removing crops and debris. Doing so allows the amendments to incorporate into the soil, become part of the ecosystem, and be ready for planting next season. Amend sandy soils in the spring and apply side or top dressing as needed throughout the growing season.
Always follow application amounts and instructions on the packaging for best results and to avoid overapplication. Err on the side of less is more before adding more, and disturb the soil structure as little as possible when applying amendments. Work organic matter into the top six to eight inches of soil, and always water the soil after adding amendments.
If you rely on hand tools, hard tine rakes, digging forks, and broad forks work well for incorporating amendments. Extensive home gardens or small market gardens can use a battery-operated tilther to help mix the top of each garden bed. Large operations often rely on mechanical tools like tractors and compost spreaders.
Create new beds before adding amendments, then flatten them out with a rake so they stay in the bed instead of falling into the pathways. Add straw or seedless hay to the paths to ensure the beds stay put and amendments don’t leach after being watered or receiving rainfall.
When you’re ready to expand to market gardening, focus on soil health for long-term success and reliable garden health. If you grow too quickly, you may unintentionally neglect soil health.
Money-saving ideas:
If you need large quantities of amendments, contact your local nursery to inquire about bulk pricing. Often, at the end of the season, they offer savings before prices increase in the new year.
Order with other local growers so shipping fees are split.
Local agricultural or gardening groups may offer a group sale with a central pick-up location, allowing everyone to benefit from bulk pricing.
Utilize cover crop debris and leaf mulch for easy, inexpensive, and effective organic matter.
Once your garden reaches a specific size, consider feeding through irrigation lines to save time and energy and ensure consistency. This process is called fertigation, and it directs liquid fertilizer to the plant's roots, reducing the risk of evaporation.
Explore machinery and tools that offer automation and are easier on your body when applying amendments to large amounts of land, such as compost spreaders, cultivators, plows, and harrows.
Adding too much nitrogen-rich material
Ignoring soil pH levels when choosing amendments
Misidentifying soil problems and wasting resources on the wrong fix
Working in heavy soil when it’s wet exacerbating compaction
Soil amendments are additives gardeners mix into their soil to help boost yields, improve soil health, prevent disease, and increase water retention and drainage.
Test your soil annually through a professional lab and follow application recommendations. Pay close attention to your plants and note things like leaf yellowing, flower drops, and poor performance, as these can be signs of nutrient deficiency. Contact your local extension office for more detailed information and assistance.
Soil testing and improving soil quality are crucial if you want significant results in a small garden. Regardless of the garden size, plants are set up for failure if nutrients are unavailable.
Organic soil amendments are best for long-term success, enhancing microbial activity, environmental safety, and maintaining soil structure. Use synthetic amendments sparingly and only when you need a quick boost, but note that over-use of synthetic amendments can have the opposite effect when used too much and deplete your soil or burn plants. Some gardeners successfully combine synthetic and organic, depending on their garden’s needs.
When starting a new garden, add amendments after receiving soil test results from your newly built garden beds or containers. Add compost and manure in the fall so they have time to age and settle into the garden.
Compost, worm castings, and leaf mold are the safest and easiest amendments to make at home. Starting a compost pile is an effective way to repurpose garden and kitchen scraps and continue the food cycle while mowing and composting leaves, which is an easy way to use fallen leaves each fall.
Follow Penn State Extension’s recipes for homemade potting media for a fun DIY project.
Related: Reusing Spent Trays of Cut Microgreens
Select amendments based on your soil test results and soil type for best results. Leaf mold, compost, worm castings, compost tea, manure, and biochar are easy to start with and have long-lasting positive effects on soil and microbial activity. Greensand and gypsum improve clay soil tilth, which is beneficial when growing vegetables.
Apply amendments like lime, sulfur, and compost in the fall to incorporate them into the soil and adjust the pH levels by spring. Apply worm castings at seed-starting and transplant times, or use them as a side-dress.
Typically, yes, but consider any adverse interactions when using chemical amendments. One method involves addressing the most pressing concern in the garden and allowing that to take effect before proceeding to the next. This will limit stress on your plants. Organic amendments like compost and vermiculite or sawdust and compost are perfectly fine to mix, but take caution when combining more than two, especially synthetics, to avoid adverse side effects.
Water drainage is essential when container gardening. Add vermiculite, compost, and pine bark to improve water retention and drainage while ensuring plant roots can breathe. Avoid adding topsoil, and blend amendments before planting by hand or hand tool.
Add topsoil to new garden areas or before sowing seeds in the spring for a fluffy, silty working material. Use it to alter the soil’s composition, not to add nutrients. Mix this into potting soil in containers, metal or wooden raised beds, and grow bags to fill the space and save money. Remember, when growing in containers, your plant’s roots can’t reach down in search of water and nutrients, so it’s up to you to provide them.
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