Planting multiple varieties increases plant establishment

Authors: Rinella, Matthew; LARSON, JULIE - University Of Washington; JAMES, JEREMY - University Of California

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Restoring desirable plants to degraded ecosystems is challenging because high mortality often results in low plant densities. To determine whether planting more varieties meaningfully increases densities, we considered published grass data from the northern Great Plains, Intermountain Region, and California annual grasslands of the U.S. Dividing the seeding rate among multiple varieties increased densities as much as 12-fold. In addition to increasing densities, seeding multiple varieties greatly reduced risks species failed to establish. When multiple, similarly priced varieties are available, we recommend dividing the total seed rate among all those varieties. One downside to this is the additional work of acquire and mixing seed from multiple suppliers. An additional benefit to this is increased genetic diversity, which could increase population fitness over the long term.

Technical Abstract: 1. Restoring desirable plants to degraded ecosystems is challenging because high mortality often results in low plant densities and establishment failures (0 plants m-2). Identifying varieties with greater survival rates has proven difficult. It was initially hypothesized local varieties would consistently survive better, but that is far from true. It was also believed traits could be identified that would consistently benefit survival, but it is now known different varieties with different traits can be most fit depending on unknown environmental conditions. Rather than identifying the best variety for a specific area, there are increasingly calls for planting multiple varieties. One effect of this can be established a priori: As the seeding rate for a species is divided among more varieties, chances of relatively low densities decline, and this decline is sharper when survival rates vary widely among varieties. 2. To determine whether planting multiple varieties meaningfully guards against low densities and establishment failures, we considered grass survival probability data from past experiments in three western U.S. grasslands. 3. Survival rates varied widely, so dividing seeding rates among multiple varieties showed high potential for increasing densities. For example, in experiments on Poa secunda J. Presl., dividing the seeding rate among four varieties instead of one variety would have increased minimum possible densities about five-fold (from 0.5-1.0 plants m-2 to 4.0 plants m-2). Similarly, with Elymus lanceolatus (Scribn. & J.G. Sm.) Gould and Elymus trachycaulus (Link) Gould ex Shinners, dividing the seeding rate among two varieties instead of one variety would have increased minimum possible densities roughly 14-fold (from 0.1-0.5 plants m-2 to 4.1 plants m-2) and nine-fold (from 0.1-0.5 plants m-2 to 2.8 plants m-2), respectively. In addition to increasing densities, dividing the seeding rate among multiple varieties instead of one variety would have eliminated risks of establishment failures in 15 of 48 species-seeding year combinations. 4. Synthesis and applications. When multiple, similarly priced varieties are available, we recommend evenly dividing the seeding rate among those varieties. One downside to this is the need to acquire and mix seed from multiple suppliers, but an additional benefit is increased genetic diversity, which could increase population fitness over the long term.