Vermiculite

Vermiculite is a naturally occurring mineral that is widely used in the horticultural industry for its beneficial properties in soil and growing media. When heated, vermiculite granules expand into lightweight, spongy particles with a characteristic golden-brown colour.  

In horticulture, vermiculite is used primarily as a soil amendment or as an ingredient in potting mixes due to its ability to hold water and nutrients. When added to soil, vermiculite helps create a loose, well-draining structure that facilitates root growth, making it particularly useful for plants in containers or other confined growing environments. Most commercial seedling nurseries use vermiculite as a 2 mm topping over new germination trays. The water holding capacity of vermiculite keeps a high relative humidity near the seeds to facilitate fast and even germination.  

Vermiculite is often compared to perlite, another common growing medium. While both improve aeration and drainage, perlite is more focused on improving drainage, while vermiculite excels in moisture retention and nutrient buffering. 

• Water Retention: Vermiculite can absorb and retain large amounts of water, releasing it slowly to plant roots as needed. This is especially beneficial in dry climates or for plants that require consistent moisture. 

• Aeration and Drainage: Its airy texture helps prevent soil compaction, improving aeration and drainage, which is critical for root health and preventing overwatering or root rot. 

• Nutrient Retention: Vermiculite has a high cation exchange capacity (CEC), meaning it can hold and release essential nutrients like potassium, calcium, and magnesium to plant roots. 

• pH Neutral: Vermiculite is typically pH neutral, making it suitable for a wide range of plants, from acid-loving species to those that prefer alkaline conditions. 

• Lightweight: Its light weight makes it easy to handle, transport, and mix into potting soils, contributing to a less dense growing medium. 

• Different Grades: While medium grade vermiculite is the most commonly used, large grade vermiculite is available for those wishing to make coarser mixes for increased aeration and the accommodation of plants with more robust or specialised root systems such as orchids. On the other hand, fine grade vermiculate is ideal for assisting in the germination of all fine to small-sized seed types. 

Common Uses: 

• Potting Mixes: Vermiculite is often blended with other materials like peat, compost, or perlite to create a balanced growing medium for indoor and outdoor plants. 

• Seed Starting: Because of its moisture retention and fine texture, vermiculite is often used for starting seeds, ensuring consistent moisture and promoting healthy germination. 

• Hydroponics: Vermiculite can also be used in hydroponic systems, where it serves as a substrate to anchor plants and retain moisture.