Abstract
Seed balls, also known as seed bombs, pods or pellets, are a mechanism for seed encapsulation and dispersal increasingly being used in the context of ecological restoration. For seed balls to achieve their desired effect they need to be stable enough to facilitate handling but then be able to uptake water to allow for seed imbibition. Little quantitative data has been published on the specifics of seed ball formulations or their physical properties. This study aimed to test the effect of seed ball composition on structural integrity and water uptake in the absence of seeds. We firstly compared two types of commercially available organic matter (OM), sieved coconut coir and humate, mixed in clay:OM ratios of 2:1, 1:1 and 1:2. We used pure bentonite clay powder rather than natural clay soil for ease of mixing and to reduce the risk of microbial or seed contamination. Balls handmade with humate absorbed water more rapidly than balls made with coir, and balls with a ratio of 1:2 clay:humate disintegrated almost immediately in water. We then compared the effect of vermiculite, dried sphagnum moss, water crystals and biochar as additives on handmade ball structural integrity and water uptake. Balls containing water crystals or Biochar proved fragile so were omitted from further trials. The remaining formulations were manufactured into balls in a commercial compression machine using a clay: humate:additive ratio of 1:2:1. Commercially available seed balls made using a proprietary formulation were also included in experiments for comparison. The commercially available balls and balls made using vermiculite proved more resistant to shaking than other formulations but differed in response to wetting. Our study provides useful information for restoration practitioners interested in vegetation restoration using seed balls.