Outside of hydroponics, soil is everything when it comes to gardening. It can determine how healthy your plants are and what plants will thrive – and which will meet their demise, no matter how much you coddle them. And while it’s possible to create “ideal” soil for raised beds and planters, often there’s not much you can do to change what soil type you have in your in-ground beds. By knowing what soil type you have, you’ll be able to condition your existing soil to make it easier to work with and select the right plants for your garden.
- 0.1 What Is Soil?
- 0.2 What Makes One Soil Different From Another?
- 1 6 Different Types Of Soil
- 2 How to Determine What Soil Type You Have?
- 3 Different Types Of Soil Commonly Used in the Garden
- 4 Frequently Asked Questions
What Is Soil?
Soil is not just dirt. It’s a mix of minerals, organic materials made of dead and living organisms, air, and water. This mixture supports life by allowing plants to grow, holding and purifying water, and providing a habitat for organisms to live.
What Makes One Soil Different From Another?
Just like soil is not just dirt, there are many types of soil. Five factors cause these differences:
Precipitation breaks down minerals and salts while moving them out of the soil. Temperature determines what plants and organisms can live in the soil.
Animals and microorganisms decompose organic material into organic matter, which feeds plants and absorbs water. All three can affect the size and shape of soil particles, which affects soil structure. For example, earthworms tunnel and increase soil permeability and aeration.
Topography affects erosion, the depth of soil, and drainage. For example, soil on a slope will be more shallow, have more erosion, and not be as fertile as soil on a flat surface.
The minerals in soil come from bigger rocks, like bedrock or rocks swept up and deposited by glaciers. Different rocks will have different minerals in different amounts and in different particle sizes. The type and amount of minerals will influence color, pH, and nutrient availability.
Soil is technically a renewable resource, but it can take thousands of years to form (like bedrock breaking down into mineral particles kind of long). Younger soils will be more shallow and less fertile than older soils. Soils that have been heavily farmed without conscientiously managing soil health will be little more than dirt while soil that’s been pasture for years will have higher fertility.
6 Different Types Of Soil
1. Loam Soil
Loam soil is an even mix of sand, silt, and clay, with the ideal combination being 40% sand, 40% silt, and 20% clay. By mixing them together, each component lends the soil their advantages while lessening the impact of their disadvantages. Sand improves drainage while the clay and silt improve nutrients and water absorption. It’s easily cultivated and light enough for roots to spread easily.
Any gardener can tell you this is the most perfect soil to grow in, and if you have it, you’re very lucky indeed. While the ideal combination is 40/40/20, you can still have loam with different percentages. These different mixes will have names like clay loam, sandy clay loam, sandy loam, silt loam, or silty clay loam.
To care for your loam soil:
- Amend with compost at least once a year, or whenever you turn beds over (especially if you have a heavy production of vegetables or flowers). As time goes on, organic matter breaks down into nutrients taken up by plants, and it needs to be restored.
- Avoid tilling and use no-dig techniques when possible. Tilling disrupts the soil ecology and releases stored nitrogen, which would be better off feeding your plants.
- Use cover crops between growing seasons for annual garden beds to help enrich your soils while controlling erosion.
- Avoid plants that love sandy or heavy clay soils. While you can grow the most diverse range of plants, these plants have evolved to take advantage of those soils (for example, needing less moisture or using the clay for support) and will have a harder time growing outside these extreme conditions.
2. Clay Soil
Clay soil is soil that is made with 50% or more clay. It’s sticky when wet and rock hard when dry. Just think about it in terms of pottery – you wet the clay to make it malleable, then it dries into a hard substance. Because of clay’s tiny particle size and that it gets sticky when wet, it has smaller pores in between particles, which keeps water from draining properly. Heavy clay is great if you want to build a pond for that very reason.
Clay soil can be the hardest soil to grow in, as the more clay there is, the harder it is for anything (plant roots and water alike) to penetrate. It’s also really hard to dig in, and it’s slow to warm in the spring, so early plantings are out.
On the plus side, clay soils are also heavy with nutrients, which, once accessed, can grow vigorous plants.
To make the most out of clay soil:
- Add two to four inches of compost twice a year (or anytime you turn over a garden bed) to improve drainage and soil structure. Done consistently over years, you’ll see the soil structure become more easily gardenable.
- Choose plants that love clay soil like hostas, irises, Black Eyed Susan, lilacs, coneflower, lantana, dogwood, elderberry, brussel sprouts, kale, daikon, peas, beans, and potatoes. While deep-rooted plants find clay difficult to penetrate, shallow-rooted plants don’t have that problem and they can benefit from clay’s stability. But that’s not to say that no deep-rooted plants can grow in clay. Some root crops like daikons can help break up heavy clay soil.
3. Sandy Soil
Sandy soil is mostly sand particles. It feels gritty to the touch. Because sand particles don’t absorb water but create a lot of space in between for water to move, sandy soil drains quickly and nutrients wash away. On the plus side, sandy soil doesn’t suffer much from compaction and is very good for plants that like loose soil (like carrots).
Sandy soil can be challenging to grow in, with its low levels of nutrients and poor moisture retention, but it is easier to cultivate than clay soils.
To make the most out of sandy soil:
- Add amendments like compost, glacial rock dust, kelp meal, or other organic amendments to improve the amount of nutrients available and moisture retention whenever you turn over a garden bed. Compost teas can give quick nutrient-boosts in between compost applications.
- Mulch to help keep moisture from evaporating. Organic mulches like bark will also absorb water from rain and hold it for longer.
- Water shallowly and more frequently. While growing guides often advise watering deeply and less frequently to encourage deep roots, that advice isn’t for you. The water will drain away much more quickly than clay or loam soils.
- Choose plants that love sandy soils and/or frequently drying out, like lavender, sedum, salvia, sage, tulip trees, butterfly bush, carrots, and parsnips.
4. Silty Soil
Silt is between sand and clay in terms of particle size, and it’s mostly composed of quartz. Silty soil is comprised of at least 80% silt. When dry, silty soil feels like flour. When wet, it’s loose like sand, making it prone to erosion. Silty soil can be the most fertile soil in the world, but without roots and other components to hold it down, it’s likely to wash away. It can get compacted easily.
Silty soil is the most nutrient-dense soil in the entire world, and pure silt soil is incredibly rare.
To make the most out of silty soil:
- Improve drainage and soil structure by adding compost every time you turn over the bed. Compost will ease compaction, help keep silt in place, and provide more pores for water to drain out of.
- Use cover crops, mulching, and terraces on slopes to curb erosion. Cover crops will hold your soil in place in between growing seasons. While it’s best to garden on flat ground (especially when growing annuals), if you only have a slope available, use terraces.
- Avoid tilling silty soil and use no-dig gardening techniques when possible. Every time you disturb the soil with tilling or pulling up roots, your soil will erode.
- Choose moisture-loving plants like willow, birch, dogwood, cypress, lettuce, and brassicas. If you can provide adequate drainage, most plants will happily grow in silty soil (and prefer it to straight clay or sandy soil.) Any plants that can thrive in clay will also thrive in silty soil.
5. Chalk Soil
Chalk soil contains – you guessed it – chalk and limestone. It’s larger grained and stonier than other soils. Because the particles are bigger, it drains really well but doesn’t keep any moisture. It’s basically like sandy soil. Chalk soil also breaks down organic matter much faster, meaning you’ll find it challenging keeping your soil fertile. Mixing in compost will help add nutrients and keep moisture.
Like clay, chalk soils become sticky and unworkable when wet, but you can start cultivating them without causing serious compaction earlier than you can with clay soil.
Chalk soil is alkaline (pH 7.1 or above), so this isn’t your ideal soil for acid-loving plants like rhododendron and blueberries. pH levels restrict which nutrients are absorbed easily (especially iron and manganese), so it’s best to pair alkaline soils with alkaline-loving plants who use those restricted nutrients more efficiently. Because it’s much harder to acidify soil than it is to alkalize it, changing the pH is not practical as it’ll take a ton of sulfur.
To make the most out of chalk soil:
- Add compost and other organic amendments regularly (once or twice a season, or any time you turn over a garden bed) to improve nutrients for longer periods and to increase moisture retention. Compost teas can give quick nutrient-boosts in between compost applications.
- Mulch plants to keep water from evaporating. Organic mulches like bark will also absorb water from rain and hold it for longer.
- Choose alkaline-loving plants that are drought tolerant, like those from the Mediterranean and prairies. Avoid planting acid-loving plants in-ground and instead grow them in containers).
6. Peat Soil
Peat soil is the opposite of chalk soil, where it’s so acidic that organic matter has difficulty breaking down, and so creates peat. It will feel spongy because of all the organic matter. The high amount of organic matter increases aeration, but because the organic matter is very slow in breaking down, not a lot of nutrients are being released for plants to absorb.
The high amount of organic matter also soaks up moisture like a sponge and keeps it for long periods of time. Since peat soil is most common in places that get a lot of rainfall, this can spell trouble as the flooding drowns plant roots. Its high acidity also makes it challenging to grow anything but acid-loving plants like heather, witch hazel, and rhododendron. Peat soils vary in acidity, going even so acid as pH 3 or 4.
To make the most out of peat soil:
- Add more drainage, whether by digging drainage channels or blending with lime, sand, or glacial rock dust.
- Take advantage of your peat soil by creating a rain garden or using marsh plants. Choose acid-loving plants like heather, witch hazel, and rhododendron.
- Use containers and raised beds instead of in-ground gardening to grow a wider variety of plants without having to break up the peaty soil.
How to Determine What Soil Type You Have?
Depending on your soil and struggles, you might have already had flashbacks when reading the descriptions. If not, it can be as easy as picking up a handful of soil and rolling it in your hand.
If it feels fine-textured and slightly damp, and when squeezed holds its shade for a short time, then it could be loam soil.
If it’s sticky when wet, easy to smear, and you can roll into a long thin sausage, then it’s likely clay.
If it feels gritty, it falls through your finger, and you can’t roll it into a sausage, it’s likely sandy.
If it has a slightly soapy, slippery texture that doesn’t clump easily, it’s likely silt.
If it’s stony with larger grains, then try putting it in a jar of vinegar. If it froths, then it’s chalk soil.
If it feels spongy when squeezed, looks dark, and has lots of organic matter fibres in it, it’s likely peat.
If you can’t tell based on a squeeze (soils are complicated and don’t neatly fall into the 6 types), then try a settle test. Sift a handful of soil to remove any debris, then add it to a transparent jar of water with dish detergent (mason jars work great!), shake well, then leave to settle in 12 hours. Because the different particles settle at different rates, it’ll naturally sort out the different types of soil.
Loam Soil: The particles will settle into distinct layers, with the finest particles at the top and the biggest at the bottom (clay is the smallest particle, silt the next smallest, and sand the largest). The water should be clear.
Clay Soil: Both clay and silty soil will have cloudy water with a layer of particles at the bottom. If it holds its shape when you squeeze it and you can roll it into a sausage, then it’s clay.
Sandy Soil: Sand will settle at the bottom of the container, leaving the water mostly clear.
Silty Soil: Both silty and clay soils will have cloudy water with a layer of particles at the bottom. It’s silt if you squeeze it, it holds its shape briefly but you cannot roll it into a sausage.
Chalk Soil: Chalk will have a pale gray color and leave gray or white grit-like particles at the bottom of the jar.
Peat Soil: Peats soil will have slightly cloudy water with particles floating along the surface.
Most soils won’t fall directly into these 6 types. Rather, they’ll be combinations of sand, clay, and silt. If you measure the layers of sediment, you can determine how much of these are in your soil. You may find that while your soil is predominantly clay, it also has a lot of sand. These combinations will give you a better idea of what your soil texture and structure are like.
Different Types Of Soil Commonly Used in the Garden
Topsoil is the top layer of soil that usually runs 5 to 6 inches deep but can also go 12 inches. This is where plant roots grow, organic matter breaks down, and beneficial microbes live. Topsoil is what we’re talking about when we talk about the 6 types of soil and what fills your in-ground garden beds.
You can also buy topsoil for garden projects (like building a raised bed or recovering areas affected by soil erosion), and you can choose different types to improve the topsoil you already have, like buying a sandy topsoil to improve drainage. Not all topsoil is equal, though, with some topsoil just about as useful as dust (used mostly for building projects) but others blended for quality garden soil. The better the topsoil, the higher the price.
Garden soil is topsoil that’s been blended with compost or other ingredients to better support plant growth. You only use it for in-ground or raised bed gardening, as it doesn’t have enough drainage for container gardening.
Raised Bed Soil
Raised bed soil is a mixture that’s been developed specifically for raised beds, and usually includes ingredients to provide nutrients and improve drainage. You don’t specifically need raised bed soil – a mix of topsoil and compost (like garden soil) will do just as well and possibly save you money. You can even fill the bottom layer with kitchen scraps that will compost in place. Just make sure you completely cover the kitchen scraps with a generous layer of topsoil and finished compost to avoid unwanted visitors.
Potting mix is used for container gardening, growing plants in pots. There is no actual topsoil in it. It’s formulated with other ingredients to absorb water and increase drainage, as well as provide nutrients, so that plants don’t either dry out too quickly or drown. It’s made using a recipe of composted wood, peat moss, coconut, sand, compost, worm castings, and/or kelp meal.
Gravel is small, irregular pieces of rock that are bigger than sand but smaller than stones. While gravel occurs in nature because of natural erosion (this is a stage in the process that takes bedrock to fine minerals), gravel is also produced commercially by crushing large rocks. In the garden, gravel is used for drainage, foundations, and walkways. You might build your shed on gravel, which provides a stable base while redirecting water away to prevent flooding, or you might use it in a drainage ditch to help prevent flooding. Or you might use gravel to create a pathway.
Compost is a mixture of decomposing organic material that’s used to feed plants and improve the soil. You might have a compost bin in your garden to decompose leaves and kitchen scraps or a vermicompost for worm castings. The process is essentially the same – breaking down organic matter until it’s a rich brown, soil-like substance. Adding compost can not only feed your plants, but it can also improve drainage and water retention – which can really help with everything but peaty soil.
Mulch is any kind of material that’s used to cover the soil. Mulching is usually done to keep soil damp longer (preventing the sun from whisking moisture away) and to prevent weeds from popping up. You can use natural materials like shredded bark, pine needles, straw, or even compost as mulch, or you can use synthetic materials like weed barriers and landscape fabric (never use shredded tires!).
Frequently Asked Questions
What Are Soil Amendments?
Soil amendments are any kind of material that you use to improve a soil’s physical properties, like water infiltration, drainage, water retention, permeability, aeration, and structure. It’s also used to reference organic materials you’d add to improve nutrients, like adding alfalfa meal to increase nitrogen.
What’s The Best Soil For Gardening?
The best soil for gardening is loam, as it balances out drainage with water retention, has excellent aeration, and provides plenty of nutrients. Most gardeners will never have the pleasure of loam soil, so it’s best to learn how to garden with your particular soil type. The more you work with your soil, like choosing plants that thrive in your soil type, the easier time you’ll have.
What Does Soil pH Mean?
Soil pH is how acidic or alkaline your soil is. The pH level affects how easily a certain nutrient can be absorbed by a plant (or how “available” a nutrient is). Plants have adapted to grow at different pH levels by making the most of the low levels of nutrients. This is why it’s difficult to grow acidic-loving plants in alkaline soils and vice versa – they get too much of nutrients they need little of and too little nutrients they need more of.