Plants grow in soil. This is a fact that we learn early in life and rarely – if ever – see contradicted by our experiences in the world. There are many things that plants get from soil, including nutrients, water, and stability.
Today, let’s explore the question: why do plants need soil?
Soil serves as a substrate for plants to grow in. It provides the plants with support for their roots, anchorage in the ground, and a web of air and water that they can tap into. Most nutrients are also in the soil, and a plant must take nutrients through its roots. Therefore, it seems like plants need soil to grow.
However, you may have come across the idea that plants don’t always need soil to grow, which we’re going to look at in more detail now.
Plants don’t necessarily need soil to grow, amazingly, but soil meets pretty much all of a plant’s needs, and a plant that isn’t grown in soil will die quickly unless certain conditions are met. It is often easier to grow plants in soil, and both the plant and the soil will usually benefit.
So, first of all, what does soil provide a plant with?
- Root space that allows oxygen to reach the roots: pockets in the soil help to keep the roots aerated so the plant can access the oxygen.
- Support that keeps them upright so that they don’t just fall over: the soil and root system keep plants upright.
- Water: water permeates the soil, easy for the roots to access.
- Nutrients: nutrients are usually dissolved in the water inside the soil, again easy for the roots to access.
- Temperature protection: the soil protects the roots from direct sunlight or heavy frosts, and will keep the roots at a relatively stable temperature.
All of these needs are met by soil, and aren’t met if you remove the plant from the soil.
Remember that soil benefits from the plants too. Although plants take nutrients from soil, they return these nutrients in the form of dead leaves (or the full plant when it dies), and in the droppings of animals that come to browse on the plants.
However, soil is not always the best medium for plants to grow in, despite its multitude of advantages.
Soil may sometimes hinder a plant as well as helping it. We’re going to explore this next.
How Does Soil Affect Plant Growth?
Soil quality is very important to consider when it comes to plant growth. Soil varies enormously in how dense it is, and this makes a big difference to what grows in it and how well it grows.
Very light, soft soils tend to be easy for plants to root into, but these often do not contain such concentrations of nutrients, so the plant may not grow as well because it lacks access to some of the things it needs. Water will drain away quickly, leaving the plant deprived.
Heavy, clay-like soils are better at trapping water and holding onto the nutrients dissolved in it, but they come at a price; the plant’s roots have a much harder time working their way down into it.
Plants that grow in heavy soil often grow slowly. Their roots will grow in clumps, taking advantage of any pockets in the soil – but suffering from not being as widely spread.
Clumped roots obviously don’t form a wide network that can efficiently feed on anything within the plant’s reach. Many plants slow their growth in heavy soil even if nutrients are available.
Find out more about when it’s time to change soil in your houseplants in my article here, or on the contrast, if you want to stunt the growth of your plants, learn here how you can keep them small.
Plants that grow in soft soil, by contrast, may grow faster.
Their roots can spread easily and they can create a network spread out beneath the ground to grab any water and nutrients that are available. Unfortunately, the soil tends to be of much poorer quality, and is more prone to drying out than the clay soils.
Obviously, there is a happy medium between these two soils, but it can take a lot of effort to get to it. That might bring you back to one of our earlier suggestions: what if we grow plants without soil?
Do All Plants Need Soil?
No, not all plants need soil.
In fact, it could be argued that no plants need soil – they just need the structure and system that soil provides.
If the needs that were listed earlier (oxygen, support, water, nutrients, temperature stability) can all be met, then soil is not necessary. It is usually just convenient.
The most challenging part of growing plants without soil is often how to get enough oxygen to their roots if you submerge the roots in water.
You can provide the other things relatively easily, using a man-made item for support, providing water with nutrients dissolved in it, and protecting the plant from temperature fluctuations.
Some plants have the ability to extract oxygen from water, and these can be grown directly in water, without the need for oxygenating. For others, you may be able to provide an alternation between water and air – a process often called aeroponics.
Growing plants in the air and spraying on a solution of water and nutrients sounds very sci-fi, but it can be done with some plants and some careful setup.
Let’s look at some plants that you can grow in water and air.
5 Plants That Don’t Need Soil To Grow
This plant will happily grow in just water. You can simply take some cuttings from the plant, put them in water, and leave them to grow. Change the water from time to time to prevent it from stagnating.
It has attractive, large leaves with graceful tips, and would look lovely sprouting directly from a vase.
If you’re looking to buy, this is my recommendation for Philodendron on Amazon.
A houseplant (not a bamboo!!) that is famous for being very hard to kill, lucky bamboo will grow hydroponically. You will need a deep glass with some gravel at the bottom to keep the “bamboo” upright and give it support.
Lucky bamboo looks a lot like true bamboo, and has juicy green leaves crowning its slender stem.
Lucky Bamboo is an amazing plant. If you’d like to have it in your house, I recommend this Lucky Bamboo on Amazon.
You may have noticed that orchids don’t come in ordinary soil, but you may not realize you can grow them out of their growing medium – and actually just on a piece of bark, which is their natural habitat.
You will need to gently tie the roots to the bark until they take, but once they have, the orchid will happily grow in the air, with just an occasional drink of nutrient-rich water. Orchids have splendid blooms and are very beautiful, exotic plants.
Here’s my favorite orchid on Amazon. It’s a beautiful pink orchid, comes in bloom and in a beige ceramic container.
These amazing trailing tendrils look like something from a fairy tale, and you can grow them indoors – usually – by providing a humid environment and plenty of phosphorus-rich liquid fertilizer every two weeks. This isn’t the easiest plant to grow indoors, but it can be done!
If you love these glossy, dark, angular leaves, you will be pleased to learn you can grow ivy indoors in water. Take a cutting with plenty of nodes, and allow it to root in water. Change the water every so often, and top it up with nutrients once in a while.
You can certainly grow plants without soil as long as you make sure that their basic requirements are met.
With plenty of technology, carefully developed nutrient solutions, and a bit of study, growing plants without soil has become very possible in today’s world. Plants may even grow better without soil!