Image by Michael Lehet
By Nikki Phipps
(Author of The Bulb-o-licious Garden)
Even with the healthiest of soils, dirt is still prone to carrying harmful bacteria and fungi. Soilless growing mediums, on the other hand, are usually cleaner and considered sterile, making them more popular with container gardeners.
What is a Soilless Mix?
Gardening with soilless potting mix does not include the use of soil. Instead, plants are grown in a variety of organic and inorganic materials. Using these materials rather than soil allows gardeners to grow healthier plants without the threat of soil-borne diseases. Plants grown in soilless mixes are also less likely to be bothered by pests.
Types of Soilless Growing Mediums
Some of the most common soilless growing mediums include peat moss, perlite, vermiculite, and sand. Generally, these mediums are mixed together rather than used alone, as each usually provides its own function. Fertilizers are also commonly added to the mix, providing important nutrients.
- Sphagnum peat moss has a coarse texture but is lightweight and sterile. It promotes adequate aeration and holds water well. However, it’s usually difficult to moisten on its own and is best used with other mediums. This growing medium is ideal for germinating seeds.
- Perlite is a form of expanded volcanic rock and is usually white in color. It provides good drainage, is lightweight, and holds air. Perlite should also be mixed with other mediums, like peat moss, since it does not retain water and will float to the top when plants are watered.
- Vermiculite is often used with or instead of perlite. This particular form of mica is more compact, and like perlite, does not retain water. Vermiculite does not provide good aeration either.
- Coarse sand is another medium used in soilless mixes. Sand improves drainage and aeration but doesn’t retain water.
In addition to these common mediums, other materials, such as bark and coconut coir, can be used. Bark is often added to improve drainage and promote air circulation. Depending on the type, it is reasonably lightweight. Coconut coir is similar to peat moss and works much the same way, only with less mess.
Make Your Own Soilless Mix
While soilless potting mix is available at many garden centers and nurseries, you can also make your own soilless mix. A standard homemade soilless mix contains equal amounts of peat moss, perlite (and/or vermiculite), and sand. Bark can be used in lieu of sand, while coconut coir can replace peat moss. This is a personal preference.
Small amounts of fertilizer and ground limestone should be added as well so the soilless mix will contain nutrients. There are numerous recipes for preparing soilless potting mixes online so you can easily find one to suit your individual needs.