What Is Vermiculite Seed Starter?

Seedlings emerging from seed starter.

Vermiculite seed starter is a soil-less planting medium that consists of either all vermiculite or vermiculite mixed with other seed starter media such as perlite and sphagnum moss.

Vermiculite Properties

Vermiculite is a naturally occurring phyllosilicate mineral resembling mica. When heated, vermiculite expands to many times its size and becomes capable of holding both air and water. Vermiculite seed starters contain vermiculite in its expanded form.

Types

The most common type of vermiculite seed starter is a loose potting medium that is readily available online and in local garden supply outlets. Another type, available to commercial seed processors, is a moisture-absorbing coating applied to individual seeds.

Benefits

Vermiculite seed starters are lightweight, making them easy to handle. They retain moisture and allow air circulation, encouraging healthy root production. Commercially available, sterilized vermiculite seed starters are free of soil-borne organisms such as the damping-off fungus that attacks emerging seeds and seedlings.

Considerations

Compacted vermiculite seed starter does not retain its aerating and water-absorbing properties. When preparing containers for starting seed, moisten the starter lightly and evenly. When planting the seeds, avoid pressing the seed starter down with your hands or gardening tools.

Warning

Almost all vermiculite distributed worldwide before 1991 contained asbestos. Use only vermiculite packaged and sold after 1991.

References

• IMA Europe Vermiculite Fact Sheet
• North Dakota State University, How to Succeed at Seed Starting
• University of Connecticut , Damping-Off

Resources

• About Vermiculite and Asbestos