Transplanted grasses in a forest
Plant Material Application

 

There are multiple approaches to plant material application, including broadcast seeding, drill seeding, hydroseeding, outplanting, and even passive restoration. The best choice depends on ecosystem type, site conditions, project goals, and available budget or capacity. Steep, rough, or unprepared terrain might favor broadcast or hydroseeding; well-prepared seedbeds can benefit from more precise drill seeding; outplanting gives control when establishment from seed is unreliable; and passive recovery can work where local propagules and low disturbance allow natural regeneration. Matching method to constraints and objectives (and often combining tactics) is key to efficient and effective restoration.

 

Broadcast Seeding

Broadcast seeding is a technique where seeds are distributed across the soil surface without incorporation, making it a practical option for a variety of restoration scenarios. This method can be implemented using equipment mounted on a wheelbarrow, ATV, or tractor that spins or drops seed onto the ground. It is an appropriate method in situations where large areas need seeding (i.e. industrial reclamation) and the soil is too rocky, the site unprepared, or the terrain too steep/uneven to use drill seed or hydroseed equipment. For smaller or fragmented areas, or sites that are inaccessible to machinery, hand broadcasting may be the most effective approach. Although this method can result in less uniform coverage, it is useful for reaching irregularly shaped areas and navigating challenging terrain where equipment cannot operate.

To improve the evenness of seed distribution, seeds can be mixed with a bulking agent such as rice hulls, sterile seeds, or non-clumping cat litter [1]. Bulking materials help improve flow through spreaders and ensure more consistent coverage, especially when working with small or lightweight seeds. After broadcasting, enhancing seed-to-soil contact is critical for successful germination. This can be done by lightly pressing seeds into the soil using a cultipacker, roller, or even a simple flat tool such as a board or piece of cardboard stepped on by foot. This additional step of pressing seeds into the soil can significantly improve seedling establishment and cost-effectiveness [2].

Because seeds are not incorporated into the soil with this method, broadcast seeding typically requires a higher seeding rate to achieve successful establishment. In most cases, this means applying approximately twice the amount of seed compared to more targeted methods like drill seeding [3].

Resources

References

  1. Meyer SE. Artemisia L.: sagebrush. In: Bonner FT, Karrfalt RP, editors. The woody plant seed manual. Agricultural Handbook No. 727. Washington (DC): US Department of Agriculture, Forest Service; 2008. p. 525–527. PDF

  2. Kimball, S., Lulow, M., Sorenson, Q., Balazs, K., Fang, Y.-C., Davis, S.J., O'Connell, M. and Huxman, T.E. (2015), Cost-effective ecological restoration. Restoration Ecology, 23: 800-810. https://doi.org/10.1111/rec.1226 

  3. Shaw, N., Barak, R.S., Campbell, R.E., Kirmer, A., Pedrini, S., Dixon, K. and Frischie, S. (2020), Seed use in the field: delivering seeds for restoration success. Restor Ecol, 28: S276-S285. https://doi.org/10.1111/rec.13210

Drill Seeding

Drill seeding is a commonly used method in native plant restoration that places seeds directly into shallow furrows in the soil at a consistent depth and rate. This technique enhances seed-to-soil contact, reduces seed predation, and can improve germination rates compared to surface broadcasting. As a result, drill seeding typically uses about half the amount of seed needed for surface broadcasting or hydroseeding, making it a more efficient option in terms of seed use. In California, drill seeding has proven effective for many native species, including for restoration of coastal sage scrub [1], perennial grasslands [2], and oak woodlands [3]. Species generally perform well when placed ¼ to ½ inch deep into a prepared seedbed.

When using drill seeding for native plant restoration, seed characteristics should be considered carefully. Small-seeded species can shift or separate from the main seed mix during the seeding process, leading to uneven distribution. One solution is to use seedballs or pelleted seed, which add bulk and weight to small seeds, helping them flow more evenly through seeder equipment. Seeding rates should be calibrated to account for seed size and mix composition, ensuring even distribution and desired species ratios in the restored plant community.

Resources

References

  1. Montalvo, A. M., McMillan, P. A., & Allen, E. B. (2002). The relative importance of seeding method, soil ripping, and soil variables on seeding success. Restoration Ecology, 10, 52–67. https://doi.org/10.1046/j.1526-100X.2002.10106.x
  2. Kimball, S., Lulow, M., Sorenson, Q., Balazs, K., Fang, Y.-C., Davis, S. J., O'Connell, M., & Huxman, T. E. (2015). Cost-effective ecological restoration. Restoration Ecology, 23, 800–810. https://doi.org/10.1111/rec.12261
  3. Palmerlee, A., & Young, T. P. (2022). Drill-seeding blue oak acorns: Testing the (cost-) effectiveness of a new restoration technique across years and microsites. Ecological Restoration, 40(1), 25–29. https://doi.org/10.3368/er.40.1.25

Hydroseeding

Hydroseeding is a method of applying seed in a water-based slurry that may also include mulch, fertilizer, and a tackifier to help stabilize soil. It is especially useful for restoration on steep slopes, rocky terrain, and other areas that are too difficult or unsafe for conventional seeders. This approach is well-suited for large sites and is commonly used in erosion control projects. Hydroseeding and hydromulching can be particularly useful for post-fire revegetation and erosion control.

The mulch component, often made from wood fiber, paper, or excelsior, helps keep seeds in place, retains moisture, and protects against erosion and seed predation. Mulch is often dyed (usually green) to improve visibility during application and ensure even coverage. Hydroseeding can efficiently cover large areas, typically in 1 to 2 hours per acre depending on tank size [1].

Despite its benefits, hydroseeding has several limitations. It can be costly, with prices ranging from $2,000 to $4,000 per acre, and may result in poor plant establishment if not applied carefully. To improve results, practitioners may scarify or roughen the soil surface before application and consider using hydromulching [2]. Care should be taken to avoid applying hydromulch too thickly, as this can inhibit germination and prevent seed-to-soil contact if done before seeding [3]. Hydroseeding may also limit the natural regeneration of woody species following fire [4] and can harm existing vegetation if it is applied directly on top of established plants.

Resources

References

  1. Steinfeld, D. E. (2007). Roadside revegetation: an integrated approach to establishing native plants. Federal Highway Administration, Western Federal Lands Highway Division, Technology Deployment Program. PDF
  2. Montalvo, A.M., McMillan, P.A. and Allen, E.B. (2002). The Relative Importance of Seeding Method, Soil Ripping, and Soil Variables on Seeding Success. Restoration Ecology, 10, 52–67. https://doi.org/10.1046/j.1526-100X.2002.10106.x
  3. VinZant, K. (2019). Restoration in type-converted and heavily disturbed chaparral: lessons learned. In Proceedings of the chaparral restoration workshop, California. Gen. Tech. Rep. PSW-GTR-265. Albany, CA: US Department of Agriculture, Forest Service, Pacific Southwest Research Station: 67-83 (Vol. 265, pp. 67–83). PDF
  4. Vourlitis, G. L., Griganavicius, J., Gordon, N., Bloomer, K., Grant, T., & Hentz, C. (2017). Hydroseeding increases ecosystem nitrogen retention but inhibits natural vegetation regeneration after two years of chaparral post-fire recovery. Ecological Engineering, 102, 46–54. https://doi.org/10.1016/j.ecoleng.2017.01.041

Seed Balls

Seedballs, also known as seed pellets or seed bombs, are small, compact structures made by combining seeds with a mixture of clay, compost, water, and occasionally other materials such as sand, soil, or beneficial microbes like mycorrhizal fungi. The clay serves to encase and protect the seeds, while the compost provides a localized nutrient source to support early seedling growth. This method is particularly useful in arid or degraded landscapes where direct seeding often fails due to poor seed-to-soil contact, seed predation, or rapid desiccation [1]. By shielding seeds until rainfall breaks down the outer coating, seedballs can improve germination conditions and enhance establishment without requiring intensive site preparation.

Seedballs are inexpensive and simple to produce [2], making them especially appealing for restoration projects with limited budgets or for community-based efforts where volunteers can help with production and distribution. They are well-suited for areas with minimal access, steep terrain, or sites where mechanical seeding is impractical. However, despite their potential benefits, seedballs are not always effective in all environments. Germination rates can be inconsistent, especially if rainfall is insufficient to break down the clay coating, and they may not always offer advantages over traditional seeding. Additionally, large-scale application can be labor-intensive. Seedballing could also damage seed and inhibit germination in some species [3]. Still, seedballs remain a promising and flexible tool in the ecological restoration toolbox, particularly for challenging, dryland systems.

Resources

References

  1. Gornish, E., Arnold, H., & Fehmi, J. (2019). Review of seed pelletizing strategies for arid land restoration. Restoration Ecology, 27(6), 1206–1211. https://doi.org/10.1111/rec.13045
  2. Pedrini, S., Merritt, D. J., Stevens, J., & Dixon, K. (2017). Seed coating: science or marketing spin? Trends in Plant Science, 22(2), 106–116. https://doi.org/10.1016/j.tplants.2016.11.002
  3. Griffiths, J. W., Lord, J. M., Paull, J., Pritchard, A. S., Butler, A., Alderton-Moss, J., ... & Moran, K. (2024). Viability of seed balls for large-scale restoration of native plant communities in New Zealand. New Zealand Journal of Botany, 1–17. https://doi.org/10.1080/0028825X.2024.2432314

Outplanting

Outplanting, or transplanting nursery-grown plants into the field, is a common and often highly effective method for ecological restoration, particularly in situations where seeding alone is unlikely to succeed. This approach is especially useful for small-scale sites, species with low germination or slow establishment rates, or meeting restoration goals that require faster canopy development or specific plant placement [1]. Outplanting allows for more control over species composition, spacing, and timing of establishment compared to seeding. It also yields higher survival rates [2].  Before planting, develop a strategic design for installation. Grasses and forbs are often installed as plugs, while larger shrubs and trees may be transplanted from larger containers. For woody plants, using lower planting densities, typically one meter or more between individuals, can improve survival by reducing competition. For bunchgrass plugs, maintaining a distance of at least 7 inches can improve plant growth and reproduction early during restoration [3].

For some species, applying drought-conditioning treatments to seedlings in the nursery can improve survival and drought tolerance after outplanting [4]. Similarly, pre-planting clipping of bunchgrasses may promote stronger growth and increased resistance to herbivory [5]. However, these responses can vary widely by species and site conditions. Practitioners should pilot these treatments at a small scale before applying them more broadly.

While transplanting offers several advantages, it also involves tradeoffs. Larger plants in bigger containers generally show higher survival rates, but they are more expensive, heavier, and more challenging to transport and install. This can significantly increase labor and material costs, particularly on large-scale projects. Smaller containers are easier to handle and allow for higher planting densities but may result in lower survival and slower growth. Additionally, transplanted individuals often require initial irrigation or protection from herbivory to ensure successful establishment. Despite these considerations, outplanting remains a valuable restoration strategy, particularly when precision, survival, and early vegetation structure are important restoration goals.

When using nursery-grown plants in restoration projects, it is critical to avoid introducing plant pathogens [6], such as Phytophthora ramorum, the causal agent of sudden oak death. These pathogens can be unintentionally transported in contaminated soil or plant material and have devastating impacts on native plant communities. To reduce risk, practitioners should source plants from nurseries that follow best management practices for disease prevention.

Resources

References

  1. Young, T. P., & Evans, R. Y. (2000). Container stock versus direct seeding for woody species in restoration sites. In Combined Proceedings - International Plant Propagators Society (Vol. 50, pp. 577–582). IPPS; 1998. PDF
  2. McGuire, K. D., Schmidt, K. T., Ta, P., Long, J. J., Yurko, M., & Kimball, S. (2022). Is it best to add native shrubs to a coastal sage scrub restoration project as seeds or as seedlings? PLOS ONE, 17(2), e0262410. https://doi.org/10.1371/journal.pone.0262410
  3. Huddleston, R. T., & Young, T. P. (2004). Spacing and competition between planted grass plugs and preexisting perennial grasses in a restoration site in Oregon. Restoration Ecology, 12, 546–551. https://doi.org/10.1111/j.1061-2971.2004.00009.x
  4. Valliere, J. M., Zhang, J., Sharifi, M. R., & Rundel, P. W. (2019). Can we condition native plants to increase drought tolerance and improve restoration success? Ecological Applications, 29(3), e01863. https://doi.org/10.1002/eap.1863
  5. Valliere, J. M. (2019). Effects of defoliation and herbivore exclosures on growth and reproduction of transplanted bunchgrass seedlings. Ecological Restoration, 37(4), 213–217. https://doi.org/10.3368/er.37.4.213
  6. Frankel, S. J., Alexander, J. M., Benner, D., Hillman, J., & Shor, A. (2020). Protecting restoration plantings from pathogens. Fremontia, 48(1), 39. PDF

Passive Restoration

Passive restoration is a low-intervention approach that promotes ecosystem recovery by removing or reducing environmental stressors rather than actively planting new vegetation. This might include actions such as halting grazing [1] or controlling invasive species [2]. In some cases, especially where native seed sources are nearby and invasive species pressure is low, desired vegetation can return over time without the need for planting. The success of passive restoration depends on the condition of the site and the surrounding landscape, especially whether native species are present in the soil seed bank or nearby and able to recolonize the site [3].

While passive restoration can be cost-effective and require fewer resources than active planting, it also comes with important considerations and limitations [4]. It is most successful in sites with existing native vegetation nearby, minimal soil degradation, and low levels of invasive species. Ongoing invasive plant management is often key to the success of passive restoration [2]. Additionally, passive approaches often require longer timeframes to achieve visible results, and their success can be less predictable. In more degraded systems, or in areas where native seed sources are absent or invasive species dominate, active restoration may be necessary to jump-start recovery. Monitoring is essential to assess whether passive restoration is leading to successful recovery.

Practitioners must weigh factors such as cost, restoration goals, site history, and timelines when determining whether passive, active, or a hybrid approach is most appropriate. In that regard, it may be useful to view restoration as a continuum of interventions, rather than a strict division between active and passive approaches, allowing strategies to be tailored to an ecosystem’s recovery potential and the specific barriers that may limit it [5].

Factors to Consider When Choosing Passive Restoration

  • Has the site been severely degraded (e.g., soil loss, heavy disturbance, invasive dominance)?
  • Are native plant propagules (seeds, roots, rhizomes) present in the soil seed bank or nearby?
  • Is natural recolonization likely, based on nearby intact habitat?
  • Are there ongoing stressors (e.g., invasive species, grazing, altered fire regimes) that might inhibit recovery?
  • Do the project goals align with the potentially slower pace of passive recovery?
  • Is there capacity and funding to support long-term monitoring?

Resources

References

  1. Beltran, R. S., Kreidler, N., Van Vuren, D. H., Morrison, S. A., Zavaleta, E. S., Newton, K., ... & Croll, D. A. (2014). Passive recovery of vegetation after herbivore eradication on Santa Cruz Island, California. Restoration Ecology, 22(6), 790–797. https://doi.org/10.1111/rec.12144
  2. DeSimone, S. A. (2011). Balancing active and passive restoration in a nonchemical, research-based approach to coastal sage scrub restoration in southern California. Ecological Restoration, 29(1–2), 45–51. https://doi.org/10.3368/er.29.1-2.45
  3. Hall, S. A., Holmes, P. M., Gaertner, M., & Esler, K. J. (2021). Active seed sowing can overcome constraints to passive restoration of a critically endangered vegetation type. South African Journal of Botany, 138, 249–261.
  4. Prach, K., Šebelíková, L., Řehounková, K., & del Moral, R. (2020). Possibilities and limitations of passive restoration of heavily disturbed sites. Landscape Research. https://doi.org/10.1080/01426397.2019.1593335
  5. Chazdon, R. L., Falk, D. A., Banin, L. F., Wagner, M., Wilson, S. J., Grabowski, R. C., & Suding, K. N. (2024). The intervention continuum in restoration ecology: Rethinking the active–passive dichotomy. Restoration Ecology, 32, e13535. https://doi.org/10.1111/rec.13535