Not all growing media is the same, and all plants have preferred soil types. For example, while most plants thrive in loamy soil, some prefer rocky substrates. Therefore, gardeners can benefit from studying the differences between soil and rock when planning their garden.
The difference between soil and rock is that soil consists of organic matter, including degraded rock particles, that form over hundreds of years of wind and rain erosion. Rock consists of cooled lava or deep soil layers that endure high pressures. Both are options for growing media for plants.
Are you wondering which material would work best for your plants? This article will examine the differences between these substances, helping you select the best option for your garden.
Soil vs. Rock: Are They the Same?
Soil and rock are not the same as their composition differs significantly. For example, rock and stone tend to be far richer in minerals than soil, and they’re also far denser than most soils. So you can effortlessly crumble a clump of dirt in your hand but may struggle to do the same with rocks.
Learning more about how these materials form is a fantastic way to understand their differences and similarities.
How Soil Is Created
Believe it or not, there was once a time when the Earth was a soilless planet. Soil is a mixture of decayed plants, eroded stone, and decomposed animal matter. But the first terrestrial plants didn’t arrive until about 500 million years ago!
As such, Earth’s earliest soil formed beneath its massive oceans. It was a combination of eroded stone particles and decomposing aquatic creatures and vegetation. The first terrestrial plants likely clung to this silty substance, exposed to air by receding oceans.
Then, as terrestrial vegetation proliferated, it created a new layer of decaying vegetation that would eventually become the soil we know today. Notably, this process of soil creation continues today, forming new layers of dirt and rock that change our planet’s landscape.
Modern soils typically consist of four primary elements—sand, silt, clay, and humus. The percentages of these components determine a soil’s type.
Sand is formed when wind and water erode rocks into tiny grains. Sandy beaches tend to form in places where the ocean meets land due to this process of weathering. Silt is similar to sand but consists of far smaller particles, often due to prolonged exposure to water.
When this silt begins to form thick layers (typically over hundreds, thousands, or even millions of years), the upper layers press down on the lower layers, turning the bottommost silt into sticky clay.
Humus is one of the few soil elements that isn’t reliant on erosion or pressure. Instead, it forms when plants and animals die, collecting at the top of the earth’s surface.
After fully decomposing, this organic matter becomes a nutrient-rich substance that provides a fertile surface for future plants to grow.
Generally, you may classify dirt into four standard groups based on these elements:
- Sandy soil
- Silty soil
- Clay soil
- Loamy soil.
The most desirable soil for most gardeners is loamy soil, as this soil is rich in decayed organic matter (humus) and nutrient-rich topsoil.
How Rock Is Created
Several processes produce rocks, and each determines the type of rock created. Still, all rocks fall into one of three groupings:
Some types of rock form when volcanoes erupt, blasting red-hot magma into the sky or across the land. When this lava cools, it forms a dark substance called igneous rock.
But other rocks are made of compressed soil. These rocks form when layers of soil develop and build atop one another.
Over time, the uppermost soil layers put enough pressure on underlying layers to turn the soft soil into a hardened material called sedimentary rock. Sandstone and limestone are two common types of sedimentary rock, and they’re far more malleable than igneous rock.
The densest and most durable type of rock tends to be metamorphic rock. This material forms deep underground, typically on or near fault lines. As tectonic plates shift and converge, the earth’s crust experiences immense pressure.
This pressure causes the crust to metamorphose from igneous or sedimentary rock to a more dense substance—metamorphic rock! Marble and soapstone are two examples of this highly pressurized stone.
Plants That Thrive in Soil
Most plants need soil to grow. After all, dirt is soft enough to allow roots to spread and grip, allowing plants to anchor themselves to the ground and grow upward. Fertile soil is also rich in nutrients that help plants form healthy leaves, strong stems, flowers, and fruits.
Still, every plant has a preferred soil type. So let’s quickly examine which plants prefer specific soil types to understand which plants thrive in soil.
Plants That Prefer Sandy Soil
If you’ve ever strolled along a sandy beachside dune, you’ve likely noticed groups of plants growing in the sandy soil. Though sand doesn’t contain the same diverse range of nutrients found in loamy soil, it’s an excellent growing media for:
- Bearded iris (Iris germanica)
- American Beachgrass (Ammophila breviligulata)
- Searockets (Cakile edentula)
- Salvia (Salvia nemorosa).
Plants That Prefer Clay Soil
Clay soil can be too dense and moist for some types of plants, but it’s the preferred soil type for plants like:
- Daylily (Hemerocallis)
- Castor bean (Ricinus communis)
- Bee Balm (Monarda)
- Silvergrass (Miscanthus).
Naturally, you’ll also want to ensure that the plants you choose for your garden are appropriate for your hardiness zone. If you’re unsure what hardiness zone level you live in, you can use a helpful reference chart to find out.
Plants That Prefer Silty Soil
Dried river beds and streams tend to be rich in silty soil. This material is ideal for growing most trees, shrubs, and flowering plants. Because silt is often rich in minerals and nutrients, it’s also an excellent choice for vegetable gardens.
If you’re planning on planting in silty soil, you might want to choose plants like:
- Lenten rose (Helleborus orientalis)
- Flowering dogwood (Cornus florida)
- Bigroot geranium (Geranium macrorrhizum)
- Japanese barberry (Berberis thunbergii).
Plants That Prefer Loamy Soil
Loamy soil is the ideal growing media for most fruits, vegetables, and flowering plants. It’s a fantastic choice for gardeners looking to grow homegrown produce and is readily available from most garden nurseries and home improvement garden centers.
The best loamy soil for your garden depends on the kind of garden you’re designing. For example, those with plenty of yard space may prefer to till a part of their property and mix the native soil with in-ground gardening soil.
Alternatively, those looking to start a container garden may want to choose potting soil instead of all-purpose gardening soil.
Plants That Thrive in Rock
Vegetables, fruit-bearing plants, and most types of trees thrive in soil. But some plants prefer to grow on rocks. Typically, these plants fall into one of three categories:
However, some flowering perennials, herbs, and grasses grow on rocky surfaces:
- Yellow Alpine Alyssum (Alyssum serpyllifolium)
- Coral Bells (Heuchera)
- Thyme (Thymus vulgaris).
Still, these plants are exceptions, as most plants that thrive in rock gardens and rocky environments are mosses, cacti, and succulents.
Mosses That Grow on Rock Surfaces
Many types of moss flourish on rocky surfaces, especially those found in wet or humid environments. So if you’re planning on starting a rock garden, you may want to install some moss to bring your garden to life.
Some of the best rock-loving mosses for gardeners include:
- Rock cap moss (Dicranum)
- Swan’s-neck thyme moss (Mnium hornum)
- Common haircap (Polytrichum commune)
- Spoon-leaved moss (Bryoandersonia illecebra).
Cacti That Grow on Rock Surfaces
Cacti are native to arid environments with little rainfall. This quality makes them top-notch choices for outdoor gardens in dry regions.
Additionally, cacti can thrive in nutrient-poor sandy soils and often grow on rocks. Some of the hardiest cacti that grow on rocky surfaces include:
- Mammillaria fraileana
- Blue flame cactus (Myrtillocactus geometrizans)
- Peanut cactus (Chamaecereus silvestrii).
Succulents That Grow on Rock Surfaces
Succulents are similar to cacti, but they typically don’t have spines. Still, one finds cacti and succulents in the same environments (deserts, arid environments).
As such, both are capable of growing in rocky, sandy substrates. Examples of succulents that grow on rock include:
- Stonecrop (Sedum)
- Hen and Chicks (Sempervivum tectorum)
- Aloe vera (Aloe barbadensis miller).
Which Is the Best Option for Gardening, Soil or Rock?
The best option for gardening with rock is when you plant succulents, cacti, and mosses. Soil is the best option when you choose vegetables, shrubs, and fruiting plants which prefer loamy soil substrates. You’ll need to consider each plant’s unique requirements when choosing between soil and rock.
Soil and rock are both formed by natural processes. Additionally, both can create each other.
For example, dirt consists of eroded rock particles and decomposed organic matter. But soil can turn back into rock when exposed to prolonged periods of high pressure.
Both substances are rich in minerals, but soil tends to be the better choice for most fruit-bearing and flowering plants. Loamy soil contains humus, a complex mixture of organic material that makes it a particularly fertile substance ideal for most (but not all) plants.