What is in a seed bomb?
There are many variations on the humble seed bomb. The vital ingredients are clay, compost (or potting soil) and seeds. There are a few considerations for each of these:
Clay – can be dry bentonite, natural clay soil, potters clay or air-drying clay. If using natural clay soil, beware of weed seeds that may already be present. If using dry clay, wet it with water and/or seaweed solution until you get a good consistency. Air-drying clay can be purchased at hardware and craft stores.
Compost (or potting soil) – compost may have worms that should be removed before use. Compost also may contain seeds that could sprout before your desired seeds. Potting soil often contains bits of wood and large pieces that make mixing and rolling difficult. A commercial seed-raising soil should have finer particles than a general purpose mix.
Seeds – Seeds are the most important part of a seed bomb. Be sure to choose species that are native to your area. You do not want to spread weeds!
Why use a seed bomb?
If you have a level garden that you water regularly, you can easily plant seeds and care for them. Steep, rocky or dry sites that are difficult to revegetate with normal planting methods are ideal for seed bombs. You don’t have to dig to plant the seeds and they have a bit of starter soil around the outside. Seeds are protected from wind and seed eaters inside their clay and soil coverings.
Case study – seed bombs for revegetation at the Gold Fields’ arid mine sites
A good example of the use of seed bombs is for revegetation after mining. Gold Fields has used bentonite-encased seeds (professional seed bombs) at Agnew Gold Mine. They compared the success of bentonite-encased seeds, hand spread seeds and machine spread seeds.
This photo shows where seeds were spread for revegetating at Agnew Gold Mine. On the left, in grey outline, is the area that had rocks spread over it, to prevent erosion. The area on the right had topsoil applied as well as rock. Topsoil is a finite resource, especially in arid regions. Photo courtesy of Gold Fields, taken December 2020.
After a year and a half in a challenging desert environment, bentonite encased seeds were most successful on the slopes with topsoil. The protection offered by the clay and soil coating kept the seeds in place and allowed them to grow better than unprotected seeds. Monitoring of vegetation performance will continue to help inform seed decisions for rehabilitated areas.
With good success in these comparative trials, bentonite seeds will be used more frequently for rehabilitation in arid areas. The seeds are protected until rain falls and conditions are suitable for growth. Seeds are less likely to blow away, erode or be eaten. This leads to a better environment after mining.
- This AusEarthEd video shows how to make seed bombs.
- This article describes uses for seed bombs and how to make them.
- Students and staff at the University of Newcastle created seed bombs with mosquito-repellent plants and used these for an interactive activity across the campus. The plants that grew were used to create a natural mozzie spray.
- Gardening Australia’s fact sheets (1 and 2) explain how to make seed bombs.