What’s the difference between sand and soil?


I always though vegetation can’t grow on sand, but then there was this news about a mini forest pop up after the monsoon rain in Saudi Arabia.

In: 4

Sand are particles of Silicon Dioxide. Soil is a mixture of minerals (which might include some sand), organic matter, water, and air.

Plants can’t grow in pure sand, sure, but sand only goes so far down and if enough water and organic matter gets mixed in with the sand, then it has essentially become a kind of soil.

Organic material

Straight sand is just minerals and tiny rocks and contains no nutrients or the like.

Soil is a mix of sand and silt and clay and organic material (Humus) which provides nutrients to plants. Its this organic matter that gives soil its blacker color. It comes from dead and decayed plants and can bring carbon and nitrogen down into the soil for future plants.

What you see on the surface as sand may actually have a layer of soil underneath it. This is one of the tricks with mulch, you need a thick enough layer that anything trying to grow upwards through it dies before it breaches the surface. If the layer of sand over the soil isn’t super thick then you’ll end up with plants that seem to be growing in normal sand.

All these are true. Plants can’t grow in sterile sand but many plants can grow in living sand(a lot of the ocean floor is sand). Many plants we want to grow are not suited to sand.

In living sand, like you would find at the edge of a beach, there is decomposing plant matter and a lot of bacteria and fungi that are eating that plant matter. There’s also small organisms like snails eating the bacterial goo and pooping plus bacteria to eat that poop. This living sand provides all the benefits of what most people call soil. It’s just more freely draining than the soil you’d find in your garden.

If the sand is completely clean and sterile, there is no bacteria or fungi trading minerals to the plant. It also means there’s no bio-goo to hold some of the water for later.

The shifting and loose nature of sand also makes it difficult for many plants to stay rooted. The ones that do well don’t mind if some roots are exposed and use those roots to make a net trapping as much moist living sand under them as possible.

[Here is a pic of natural beach grass thriving in sand.](https://images.app.goo.gl/nbPYeRmxrvJHBAgd7)

As others have mentioned, soil is the combination of mineral (i.e., ground up rocks) and organic content under your feet – i.e., sand, silt, clay, decaying plants and animals, their wastes, etc.

When people talk about sand, they can mean one of two things: (1) the mineral portion of the soil with particles whose diameters fall into a specific range (e.g., 0.075 cm to 4.75 cm in the Unified Soil Classification System, aka USCS); or (2) a soil whose predominant constituent is sand particles (e.g., under USCS a soil classified as a sand consists of more sand than gravel, and >5% silt + clay).

So in the context of your question, plants can grow in a soil that is classified as a sand, which is classified as such because it is mostly sand-sized particles. Most plants can’t grow well in sandy soils for various reasons, but some have evolved ways to do it.