What Is a Soilless Potting Mix? Dig In to This Unique Growing Medium and Learn How To Make Your Own

What is soilless potting mix? It’s a mix of materials that serves the same purpose as potting soil but with unique properties based on the types and proportions of materials used.

Different plants benefit from different soil types and even mixes of materials that don’t include any soil at all. It’s a misconception that plants need soil to grow. They need some type of medium to contain their roots (although some, called air plants, don’t even need that), water, nutrients, and sunlight.

You can buy or make your own soilless mix. Here’s everything you need to know.

The Benefits of Soilless Potting Mix

So why not just use soil to grow plants? There are many benefits to using a soilless mix, either a store-bought product or a mix you make yourself:

• Soilless mixes are typically sterile. As compared to garden soil, you can be more certain that they do not contain pests or diseases that will harm your plants.
• Potting mixes without soil provide better drainage and airflow for roots. The larger materials in these mixes create little pockets of air, preventing soggy roots and allowing oxygen in. They won’t compact the way soil does. The loose nature of the mix supports healthy root growth.
• On the other hand, certain materials in potting mix improve moisture retention. These materials retain moisture more evenly, preventing the sogginess you get with soil while also reducing watering frequency.
• A soilless potting medium is customizable. You can create unique blends based on the needs of the plants you’re growing, from tropical rainforest plants to desert succulents.
• Soilless mixes are much lighter than soil, which makes them easier to handle and move from one place to another. They are also less messy.

It’s not practical to replace garden soil with soilless mix, but these blends are ideal for anything you grow in a pot. Soilless potting mix is particularly good for starting seeds, for air plants, for succulents, and really, for any houseplant. You can also add some of these ingredients to the soil in garden beds to improve aeration, drainage, and moisture retention.

Materials Used in Soilless Growing Medium

If you only have a few houseplants, it’s easy to buy a pre-made soilless mix. For example, if you have a cactus or an orchid, you’ll find good-quality potting mixes at your garden center designed just for these plants. You can also find a great organic, peat-free cactus and succulent mix from Rosy Soil on Amazon.

You might also want to make your own mixes for specific needs. These are the common ingredients that go into potting blends and what they offer your plants.

Sphagnum Peat Moss

Peat moss is one of the most common ingredients in potting mixes. It is good for retaining moisture and making mixes lighter to allow air in. It also has a low pH, so it’s great for a plant that naturally grows in more acidic soil. There are better alternatives to peat moss, like coco coir.

Important Note: Two issues arise with the use of sphagnum peat moss. One is that too much can make your mix overly acidic. The other issue is that the harvesting of peat moss from bogs poses an environmental issue. This process releases immense amounts of carbon dioxide, a greenhouse gas, into the atmosphere. As a result, this non-renewable resource has now been banned in several countries.

Coco Coir

Coco coir offers similar benefits to sphagnum peat moss and is a more environmentally friendly alternative. Coco coir is a natural byproduct of the processing of coconut fibers. It retains moisture very well and has the added benefit of natural resistance to fungal and bacterial pathogens. One downside is that coco coir often contains salt, so be sure to rinse it thoroughly before using. Back to the Roots offers organic coco coir through Amazon that comes in a convenient compressed brick which expands when you add water to it.

Perlite

Perlite is a lightweight mineral added to mixes for aeration. You’ll often see it in soil mixes, as it is used to lighten and aerate soil. Use perlite when you want to lighten the weight of a mix and improve drainage of either a soil or soilless mix.

Vermiculite

Vermiculite is also a mineral and is very similar to perlite. It differs in how it manages moisture in a potting mix. Vermiculite lightens mixes, as perlite does, but it also improves moisture retention. So, if you want a lighter mix with more drainage, choose perlite. If you want a lighter mix that retains moisture more evenly, choose vermiculite.

Though several types of vermiculite are available to the public, for using it within potting mixes, only choose those that are clearly labeled as “horticultural grade.” Burpee offers organic horticultural grade vermiculite for sale on Amazon or your local garden center.

Coarse Sand

Also known as builder’s sand or horticultural sand, coarse sand is used in potting mix to improve drainage and change the density. As compared to using perlite to improve drainage, coarse sand will make your mix denser and heavier. It’s a good choice for a potted plant that is top-heavy. The heavy mix will stabilize the container and prevent tipping.

Limestone

Limestone is a type of rock that is used in potting mixes to change the pH. If a mix or soil is too acidic, the addition of limestone will raise the pH, neutralize some of the acidity, or even make the mix alkaline.

Calcitic limestone raises the pH quickly, while dolomitic limestone is a mix that acts more like a slow-release product, raising the pH over a more prolonged period of time.

Compost

Compost is a great addition to soilless potting mix because it adds nutrients. You can purchase finished compost from a garden center or make your own.

If you have only just started a compost pile, use a purchased product until your own compost is ready. It’s essential that you use finished compost, as immature compost can damage plants. You can find organic, manure-free compost at the Home Depot.

Fertilizer

Finally, fertilizer allows you to fine-tune the nutrients in your potting mix. Compost is an important source of nutrients, but fertilizer gives you more control. Use products specific to the plants you’re growing to get the balance of nutrients just right. Slow-release products, like the Miracle-Gro Shake 'N Feed All Purpose Plant Food from Amazon, are the easiest to use and will ensure your plants get a good amount of nutrients over time.

Soilless Mix Starter Kit

How to Make Soilless Potting Mix

Several factors play a role in the development of a soilless potting mix recipe. Most notable among these are the specific needs of individual plants. Potting recipes involve simply mixing equal parts moss or coir with perlite or vermiculite. From there, continue to add amendments, as needed for your own specific use.

Making your own soilless potting mix is both an art and a science. Look for recipes based on the plants you’re growing or choose a basic recipe that works for most houseplants.

Frequently Asked Questions