The magic of seedballs

Ecological restoration is hard to do right. Its especially hard to do successfully in arid systems. This is because conditions that tend to be ideal for plant germination, growth and survival (such as adequate rainfall events) occur infrequently and irregularly. One approach that shows promise for enhancing restoration in dryland habitats is the development and deployment of seed pellets.

Seed pellets (also referred to as seed balls or seed bombs) are stand-alone structures typically made of clay, soil, water and seed (but can include a huge range of ingredients including rock dust, cat litter, coffee grounds, cayenne pepper, sand, worm castings, activated carbon and mycorrhizal fungi). These structures serve to ameliorate conditions that mainly contribute to failure in arid land restoration, including dry conditions that exacerbate seed desiccation stress and create soil crusts that act as barriers to seedling establishment. These structures share properties with other seed treating technologies, such as seed pillows and encrusted seed, which largely serve to protect seeded species from herbicide application and enhance seed to soil contact. In theory, seeds are protected in the seed pellet structure until adequate rainfall removes the surrounding clay and a small pocket of nutrients from the soil component of the seed pellet nourishes the seedlings as they emerge. Although seed coating technologies, including the use of seed balls, have been used in agriculture since ancient times, seed pellets only started to gain traction for use in large scale restoration in the 1940’s and has only been investigated formally by researchers and non-governmental practitioners very recently.

One of the projects my lab works on is investigating fundamental attributes that might enhance seed pellet restoration outcomes. We ask questions such as what should the pellets be made out of? How many seed should go in each pellet? What is the ideal density and broadcast method for seed pellet dispersal. These questions are basic, but they are critical for the development of best management practices. Our work is conducted in the field and in the greenhouse and we work with a variety of partners including the Audubon Society, the Buenos Aires National Wildlife Refuge, the Altar Valley Conservation Alliance, Tucson High School and several local mines.

In addition to developing science based recommendations for managers based on our research, the lab is involved in outreach that enhances science application on the ground. For example, although seed pellets are easy and inexpensive to make by hand, it is infeasible for managers to make adequate numbers for large scale restoration. To address this issue, the lab developed a seed bike that can create thousands of pellets in under six minutes. Guidelines of how to make the bike (approximate cost =$130) can be found here: https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az…