What is a Growing Medium for Plants?

Growing media, also known as a growing medium, is the material in which plants grow. What is growing medium used for? A growing medium serves three primary functions. It:

Provides physical support for the plant.
Facilitates root growth.
Delivers nutrients, water, and air to the plant through its roots.

While soil is the most traditional growing medium, it’s far from the only option. It’s typically best to amend soil with one or more additional growing media for optimal results in your gardening endeavors. Each medium has its own distinct characteristics which may enhance your plant growth. The key traits of a growing medium are:

Bulk density: The weight of the medium.
Water holding capacity: The percentage of water a medium can retain when saturated.
Air porosity: The volume of pore space that contains air after a medium drains.
pH level: The determination of how acidic or alkaline a substance is.
Electrical conductivity (EC): The soil’s ability to carry an electrical current, which indicates the nutrient amount that’s made available to crops.

Different Uses for Growing Mediums

A growing medium is necessary in any type of gardening endeavor. The manner in which you’re gardening will determine how the media are used and what options are best for your needs. Some common gardening options include:

Container gardening: Potting soil is typically used for container gardening. This is often a blend of several types of growing media, including perlite, vermiculite, and peat.
Outdoor gardening: Additional growing media are less critical in outdoor gardening, but some amendments may improve the soil that’s in your yard. It’s often best to addÂ 2 or 3 inches of topsoil to your garden plot and mix this in with the existing soil. Topsoil may contain many types of growing media, such as sand, compost, and wood fiber.
Hydroponic gardening: Hydroponic gardening is a soilless endeavor, yet it still requires a growing medium to help secure the plant’s roots. Some popular hydroponic growing media include coco coir, expanded clay pellets, and rice hulls. These soilless media are often mixed with perlite or vermiculite.

Types of Growing Mediums

There are many different growing media that you can choose from for your garden. The best option is nearly always a blend of two or more media that complement each other well.

Soil

Soil is the most traditional and readily available option. This makes a great base in an outdoor garden or starter for some container gardening projects, though it is susceptible to pests and diseases. Soil is:

Affordable.
Sustainable.
Rich in nutrients.

Compost

The product of organic decomposition, compost is a nutrient-rich growing medium that makes an excellent base for outdoor gardening. It is:

Weed-free when prepared at the right temperatures.
Rich in all major nutrients.
Natural and sustainable.

Peat Moss

Peat moss is the result of long periods of decomposition in peat bogs. Greenhouse gases are released as a result of the mining process for peat moss, so some shy away from the environmental implications of using this medium. Peat moss is:

Sterile.
Excellent at water retention.
Acidic.

Bark

Tree bark that’s finely milled is a popular growing medium in outdoor container nursery mixes. Pine bark is preferable. Hardwood bark should be composted before use. Pine bark is:

Able to resist decomposition.
Beneficial for aeration and drainage.
Effective at storing carbon.

Coco Coir

Coco coir comes from the fibers on the outer husk of the coconut. It typically comes in pressed blocks that you can rehydrate into a soft, soil-like medium. Coco coir is:

Fungus-free.
Excellent at retaining water.
Good at increasing aeration.

Rice Hulls

A byproduct of the rice industry, rice hulls are a natural growing medium similar to peat moss and coco coir. Rice hulls are:

Lightweight.
Good for a year before they break down.
Good for improving drainage and aeration.

Perlite

Perlite is made from crushed volcanic rock. This soilless substance is:

Ideal for oxygen retention.
Very lightweight.
Best when mixed in a 50/50 blend with another medium.

Vermiculite

Vermiculite is comprised of hydrated laminar minerals. It works well in a 50/50 mix with other soil media. Vermiculite is:

pH neutral.
Lightweight.
Good for water and nutrient retention.

Pumice

Pumice is a foam made from whipped volcanic glass. It is a soilless growing medium that is:

Porous.
Lightweight yet stable.
Effective at retaining water and nutrients.

Expanded Clay Pellets

Expanded clay pellets come in round balls that are lightweight and porous. This is a hydroponic growing medium that secures roots but does not retain water. These pellets are:

Reusable.
pH neutral.
Effective for increasing air holding capacity.

Sand

The particle size of sand plays a big role in its usefulness. Sand with a larger particle size is best for gardening. A medium or coarse sand is:

Inexpensive.
Effective for increasing drainage.
Heavy.

How to Select a Growing Medium

Every gardening project is unique, so it’s important to select a growing medium that will serve the distinct needs of your plants and growing system. Some factors that you should consider include:

Drainage: Some plants, such as palms, prefer a sandy, well-draining soil while others, like hosta, grow well in a heavier clay soil. The irrigation and drainage system available to your plants plays a big role as well.Â
pH level: Each plant has its own preferences for pH level. For example, magnolias and gardenias like acidic soil, while lavender and honeysuckle like an alkaline soil.
Nutrients: All plants need nutrients, and your growing medium will help deliver them. Do you need a hydroponic medium that will deliver nutrients through the water efficiently, or a medium such as compost that already contains the nutrients you need?

Selecting the right growing medium for your garden will help it thrive by delivering the proper moisture, air, and nutrients to every plant.