Seed Bombs & Dryland Revegetation

By Felicia Fredd

Revegetation seeding has been a major theme for me this month. Examples of projects include reveg. of a former horse corral, cut slope treatments, monitoring seedling emergence from a post-construction planting, and consultation on extensive grass and wildflower reveg. to suppress weeds - mostly the all-too-familiar kochia and tumbleweed duo. Each project has its own unique set of conditions and challenges, but I’d say problems that consistently define the work of revegetation seeding are:

Timing

Establishment of landscape seeding hinges on aligning seeding with temperature, rainfall, and dormancy cycles. For residential properties, there is usually supplemental irrigation involved, which helps, but success requires ongoing observation and adjustments to moisture & drying cycles throughout critical establishment stages.

Degraded Soils and Persistent Weeds

Revegetation seeding is often aimed at disturbed areas with long histories of weed dominance. Weed seed loads in such soils can be massive, and viable for several years. This means that irrigation to support desired seed establishment can also trigger an explosion of weed growth. Over time, some weeds may even alter native soil structure, chemistry, and microbial communities, and may introduce allelopathic effects that inhibit native plant germination.

Exposure and Predation

Most revegetation projects involve larger areas of exposed landscapes where intense sun, heat, wind, and seed displacement pose significant challenges. Seeds are also highly susceptible to predation by birds, rodents, rabbits, and ants—often resulting in substantial losses before germination even begins.

Rediscovering the Seed Bomb

While thinking about one of my current seeding challenges, I recalled something I hadn’t thought about in years: seed bombs. Seed bombs, or seed balls, are rolled balls of compost, clay.  Masanobu Fukuoka, the Japanese farmer-philosopher who developed important concepts for natural farming outlined in his cult classic book, One Straw Revolution, is credited for reintroducing the ancient Japanese technology for both seed storage and field planting called Tsuchi Dango, meaning ‘Earth Dumpling’, and applying it specifically to dryland restoration.

I can attest to seed bombs working. About 20 years ago, I used the technique to establish a pasture grass area for my horse in a previously weed infested area. I didn’t know anything about Fukuoka. A friend just told me about seed bombs, and gave me a ratio recipe of compost, red clay, seed, and water. After two initial flushes of weeds that had to be removed, my horse did finally get to enjoy a grazing pasture. It was work, but effort that in hindsight probably wouldn’t have been half as bad if I had not tilled. Tilling, a form of soil disturbance, encourages weeds.

The seed bomb technique does not guarantee germination, but it does help with every seeding issue mentioned above. I found a great webinar from The Institute For Applied Ecology that presents current seed ball studies from a seed ball science nut, Elise Gornish, at the University of Arizona.

“ These structures can ameliorate conditions that contribute to failure in arid land restoration, including dry conditions that exacerbate seed desiccation stress and create soil crusts that limit seedling establishment, as well as seed loss via predation. Seed balls also serve to enhance seed to soil contact and reduce seed redistribution by wind. https://www.youtube.com/watch?v=o7KcgbIu8dM

THE RECIPE:

I can’t find any two recipes alike. I did find this from Native American Seed, https://seedsource.com/content/pdfs/NAS_seedballinstructions.pdf:

6 parts dry sifted clay, preferably red (others say 5 parts)

1 part dry sifted compost

2 parts seeds (for native grasses and wildflowers)

1 part water

The recipe above emphasizes clay. I have seen recipes that omit clay altogether. I do not think this is a good idea. It is the dried clay shell that protects the seeds, and requires adequate available moisture to soften and break apart, helping to ensure proper germination timing. I think the omission may stem from a general notion that clay soil is ‘bad’ vs. compost being good in all ways. This is not true. Clay particles are essential for nutrient transfer.