One of the greatest challenges of germinating seeds is managing moisture so they do not become too wet and succumb to damping off diseases. The following method of using a combination of seed raising mix and perlite minimizes the threat of overwatering and makes growing plants from seed a lot easier.
What is Perlite?
Perlite is a natural occurring mineral with a high silica content. When exposed to very high heat it softens and expands up to 15 times its volume, in a process similar to what happens to popcorn when it is heated. Perlite is light-weight and used in horticulture as a soil amendment and media for hydroponics.
Why use perlite for seed sowing?
- It is porous and allows air to enter freely
- Can hold water, but also provides excellent drainage
- Is sterile and contains no disease spores or weed seeds
Selecting a container for sowing seeds
When choosing a container the main requirement is that it has holes in the bottom for drainage. The size will depend on the size of the seeds and how many you are sowing. I don’t recommend using a container smaller than 4 in. as once the seedlings get larger they will dry out too quickly between watering’s. I like to use short, squat containers, as tall, skinny pots dry out quickly at the surface making it difficult to maintain the correct moisture content. Also, don’t forget to make sure the container has been thoroughly cleaned (preferably with a 10% bleach solution) to prevent the spread of soil borne diseases.
Creating a reservoir
We’re now going to fill our container to within 1 to 2 in. of the top with a standard seed sowing or peat-based potting mix. Read the label to make sure it doesn’t have any fertilizer added to it – we don’t want to burn the roots of newly emerging seedlings. This base is going to act as a reservoir and hold water for the seedlings to tap into. Level out the media and lightly press it down to remove large pockets of air.
Add approximately 1 in. of perlite on top of the seed sowing mix and level it out.
Perlite contains dust particles you should avoid breathing. Handling this material in a well-ventilated area and wetting it down with water helps minimize down. If you have respiratory problems, use a dusk mask.
Are there any seeds this method doesn’t work with?
I haven’t had the best of luck with some very fine seeds, such as Sarracenia and fern spores, but have had great results with native Azalea’s, Sourwood, and Penstemon seeds. One method I sometimes use when sowing very fine seed is to mix seed-raising media with perlite, at a 50:50 ratio. I then sieve the surface layer to remove larger pieces and then sow the seeds. Doing this increases water holding capacity while still providing a moderately well-drained media.
My next post will cover sowing the seeds and where to store them before germination.