What Makes Good Soil Media

Good soil media meet all of a plant’s needs, from hydration and nutrient delivery to drainage, aeration, and support. An effective soil media should:

• Retain moisture well.
• Be weed-, pest-, and disease-free.
• Drain and aerate well.
• Have consistent quality.
• Be dense enough to support seeds and seedlings, yet light enough for roots to grow easily.
• Have low salinity.
• Have good cation exchange capacity, which allows the soil to retain nutrients.
• Have good value and be easy to obtain.

Soil alone can be heavy, inconsistent, and low quality. This is why plants benefit from having soil media mixed into their pots or growing spaces.

Types of Soil Media

Soil media often contain a blend of soil, soilless growing mediums, and fertilizer, as each of these components brings its own benefits to the mix. Types of media you might add to your soil or find in a mixture include:

• Bark: Various types of ground or composted bark drain and aerate well. Pine bark, in particular, has a high cation exchange capacity. While fresh bark is nice and moist, it tends to dry quickly and can be challenging to wet again.
• Clay pebbles: Also known as hydroton, expanded clay pebbles are popular media for hydroponic and aquaponic growing systems. They’re sterile, lightweight, and easy to work with.
• Coco coir: Made from the fibers of coconut husks, coir is popular among gardeners because it can absorb up to tenfold its weight in water yet still drains and aerates well. It’s also quite pest- and disease-resistant and can be reused. Coir’s neutral pH level makes it ideal for growing many types of plants and vegetables.
• Compost: Compost can be made from a variety of decomposed organic materials, including livestock manure, leaves, grass clippings, and wood byproducts. The result is a dark, nutrient-rich growing medium that has a neutral pH and retains water well. High-quality compost also contains beneficial organisms that help protect plant roots and seeds from disease.
• Perlite: This white medium is a sterile form of volcanic glass. It drains and aerates well but is so lightweight that it must be combined with other media so it doesn’t float to the top of the container. 
• Pumice: Another volcanic byproduct, pumice also has draining and aerating properties due to its light weight. It can retain water better than perlite but is not sterile.
• Rockwool: This material can be used to maintain healthy root systems in both traditional and hydroponic gardens. The sterile rockwool cubes or plugs provide an oxygen- and nutrient-rich buffer around the roots.
• Sand: Coarse sand such as quartz sand improves a soil’s aeration and drainage but doesn’t hold water well. Because it’s so heavy, some gardeners prefer it for top-heavy plants or those in windy areas that are prone to tipping over. Too much sand, however, can make a container plant too heavy to move. This is one of the least expensive and easiest-to-find soil media. Look for washed or horticultural grade sand.
• Sphagnum peat moss: This lightweight and sterile organic material has good water retention, boasts antifungal properties, and helps aerate soil. Many gardeners like using this medium to germinate seeds, and it’s fairly inexpensive. Due to its low pH level, peat moss is ideal for acid-loving plants. Because too much peat can prevent soil from draining well, this material is often mixed with another soil medium such as coco coir.
• Styrofoam: Some gardeners substitute Styrofoam for perlite because it provides similar porosity and aeration but costs much less. 
• Vermiculite: This sterile mineral often gets blended with perlite because it retains water and fertilizer better but does not aerate as well. It also contains vital nutrients such as calcium, magnesium, and potassium.
• Water retention crystals: These commercially produced sterile granules can absorb up to 500 times their weight in water and can reduce watering frequency.
• Worm castings: Also known as vermicompost, this worm byproduct is one of the richest organic fertilizers available. It’s mineral-rich, retains moisture, and protects plants from disease.

Choosing a Soil Media

No one soil medium on its own boasts all the properties a plant needs to thrive. Therefore, you often encounter blends of various media to create the perfect mix. You’ll commonly find soil media, for instance, that contain an organic ingredient such as bark, sphagnum peat moss, or compost that retains water and provides nutrients, plus a coarse mineral ingredient such as sand, perlite, pumice, or vermiculite that will facilitate drainage and aeration.

The soil media you choose depends on the type of gardening you’re doing and what you’re planting. Container plants grow well in a blend of various components, such as coco coir, peat moss, or vermiculite. Foliage plants and tropicals tend to prefer moist conditions; therefore, you might choose a soil medium with high water retention. Succulents and herbs, on the other hand, grow best in well-drained soil media such as sand and perlite.

How to Properly Use Soil Media

Read package instructions to learn how to use your growing medium or soil media blend properly. You want to follow a few basic steps, however, with almost all of these materials:

1. Moisten the material slightly by placing it in a bucket or tub, adding water, and mixing until it’s consistently damp throughout. 
2. Create your soil media. For instance, you might mix equal parts garden soil, coco coir, and perlite into your own custom blend. 
3. If you’re planting in a very large container, fill the bottom quarter or third of it with a filler such as plastic bottles or packing peanuts, topped with a layer of landscape fabric. This will keep the pot’s weight and materials’ cost down.
4. Fill your plant container with media, leaving an inch of space between it and the pot’s rim.

Soil media are key components to growing healthy, thriving plants, flowers, and vegetables. Choose a blend of materials that will best support what you’re trying to grow, where you’re trying to grow it.