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. 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.
Soil texture and type matter
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, 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. Few or no flowers may indicate excess nitrogen, especially when growing ornamentals. 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.
Types of soil amendments
Amendments can be organic, mineral-based, synthetic, or natural, each serving its purpose. Which you choose is a personal preference. 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.
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. 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.
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. 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. Only Class A biosolids, which have undergone rigorous treatment to reduce pathogens and metals to safe levels, are recommended for use in home gardens.
When growing acid-loving plants like blueberries, azaleas, and rhododendrons, consider using elemental sulfur to lower the pH and create the acidic conditions these plants need. Other mineral-based options, such as iron sulfate, can also help maintain an optimal soil environment. Regular soil testing ensures you achieve the right balance for healthy growth and nutrient availability. 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. Vermiculite improves aeration and drainage and acts like a sponge when placed in the soil, making it a beneficial additive for seed-starting.
Synthetic vs organic vs mineral-based approaches
Synthetic Fertilizers vs. 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.
Soil by texture: what to do
What are your goals? What are your garden’s nitrogen needs? Is there a concern for too much salt? 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, 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. Over time it can become depleted of mineral nutrients so occasional additions of rock phosphate and greensand will add back micro nutrients. 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. 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. Mulch trees and perennials with compost or mulch before the first frost.
Best practices for applying soil amendments
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 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. 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.
Practical references
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, flagging growth, and stunted development as clues to the soil’s needs. The soil is a storehouse for all the elements plants need to grow: nutrients, organic matter, air, and water. Soil also provides support for plant roots. When properly prepared and cared for, soil can be improved each year and will continue to grow plants forever.
Texas gardeners must work with many different soils. Sandy soils do not hold enough water; in windy areas, blowing sand can injure vegetables. Figure 1. Vegetables need a deep and well drained soil with adequate organic matter. Good garden soil with proper moisture will not form a hard ball when squeezed in the hand. It should crumble easily when forced between the fingers. It should not crack or crust over when dry. Almost all garden soils can be improved by adding organic matter to make soil more workable. Plant materials include leaves, straw, and grass clippings. Work material into the soil several months before planting to allow it time to decompose. Manure: Use composted manure and incorporate it into the soil well ahead of planting. Do not use fresh manure, as it can damage plants and introduce diseases. Compost: Compost consists of decayed plant materials. Sawdust: Compost this before adding it to the garden. Green manure: Plant rye or oats in the fall and plow or spade it under in the spring. Most heavy clay soils benefit from the addition of gypsum. It adds some nutrients but, more importantly, it loosens clay soils and makes it more workable. Spread about 3 to 4 pounds of gypsum per 100 square feet over garden soil after it has been dug in the winter. Add sand and organic matter to clay soil to make it more workable. Figure 2. The soil should be tilled as deeply as possible, at least 8 to 10 inches. Deep tilling loosens soil and lets vegetable roots go deeper. Turn each shovelful of soil completely over. Till soil when it is moist but not wet. Working soil when it is too wet can cause it to become rough. Spade the soil in the winter to prepare for spring planting. Winter temperatures and moisture help mellow soil. Add organic matter each year during soil preparation to build and maintain the soil. Be sure all plant material is turned under the soil. Before planting, rake the soil clean and level it. Figure 3. In most Texas areas vegetables should be planted on raised beds. If the garden is large enough, make rows 36 inches apart. Straight beds are nice but not necessary. Figure 4. Use a shovel or rake to pull the soil up into beds 8 to 10 inches high. Pack beds or allow them to settle before planting. Also level the tops of the beds and widen them to about 6 to 8 inches before planting. Plant on top of the beds.
Q: Amending my soil feels daunting. A: A soil amendment is any material added to the soil to improve its composition and fertility. The soil in much of the Colorado Front Range is clay and alkaline. The best garden soils are about 50% solids (sand, silt, clay, plus organic material), 25% water, and 25% air. Much of Colorado’s soil is clay; it also tends to be slightly alkaline and low in organic matter which makes it less porous. Fertile soil is the foundation of a good garden. Soil and the biological life that lives there provide storage for plant nutrients. Soils change as plants utilize the available nutrients and rains deplete them. Water holding capacity - ideally well-drained but holding adequate water. Nutrient holding capacity - ability to retain needed minerals. Amending soil aims to address the above aspects of soil fertility. The first time you’ll amend your soil is before planting your garden by mixing material in to the first few inches of existing soil. A soil test will include recommendations for correcting problematic properties including nutrients, texture, water retention, pH. There are two types of soil amendments: organic and inorganic. Organic amendments come from something that was once alive; they include sphagnum peat, grass clippings, dead leaves, compost, manure, biosolids, and sawdust. Organic amendments create larger pore space by forming larger chunks of aggregates of the small clay soil particles. Inorganic are either mined or man-made; they include vermiculite, perlite, small gravel or rocks (aka squeegee). Adding squeegee as a soil amendment is a great way to increase drainage in our clay soil for native and other low-water plants, without adding additional organic material. Many of the plants found our Garden In A Box kits are native to the Front Range, and others are non-native adapted meaning they prefer soil similar to our Colorado clay-like soil and climate. Because of this, adding a lot of organic material is not necessary for these plants and in some cases they can be harmed by too much organic matter. - Manure, while it is readily available, use it with caution. It’s often high in salts, which can build up in soil and become toxic to plants. Unaged manure can be harmful to plants - so always seek aged manure which will have little to no foul smell. Sphagnum Peat vs. - Compost Tea - Biologically active compost steeped in water. All of the benefits of compost plus it can be sprayed on the leaves to suppress foliar diseases.
tags: #soil #for #landscaping