Add mulch before or after seeding/planting

Supporting evidence from individual studies

1. A replicated, randomized, controlled study in 1981–1982 in two former pits used for disposal of waste from oil extraction in Texas, USA (McFarland et al. 1987) found that adding mulch after sowing seeds did not alter the density of six sown plant species in most cases compared to sowing without mulch. In 11 of 13 comparisons, after 6–7 months, the density of six plant species did not differ significantly between mulched and seeded areas (0–27 plants/m²) and unmulched and seeded areas (0–18 plants/m²). In two of 13 comparisons, there were more plants in mulched and seeded areas than in unmulched and seeded areas for king ranch bluestem Bothriochloa ischaemum (18 vs 2 plants/m² respectively) and kleingrass Panicum coloratum (28 vs 1 plants/m²). Before seeding, each pit was covered with soil which was then disturbed using a tractor and fenced to exclude herbivores. At each site, in six 6.1 x 6.1 m plots, the seeds of either king ranch bluestem, Lehmann lovegrass Eragrostis lehmanniana, kleingrass, alkali sacaton Sporobolus airoides, kochia Kochia scoparia, or fourwing saltbush Atriplex canescens was sown, and mulch was applied to half of the plots. After 6–7 months, ten 0.5 x 0.5 m quadrats were placed in each plot and the number of seedlings counted.

   Study and other actions tested

   Referenced paper

   McFarland M.L., Ueckert D.N. & Hartmann S. (1987) Revegetation of oil well reserve pits in west Texas. Journal of Range Management, 40, 122-127.

2. A replicated, randomized, controlled study in 1994–1999 in a species-poor wet pasture in the UK (Tallowin & Smith 2001) found that adding mulch before planting seedlings led to lower cover of planted species and similar cover of common knapweed Centaurea nigra compared to planting without mulch. No statistical analyses were carried out in this study. Cover of planted Cirsio-Molinietum species was lower in plots where mulch was added before planting (22–34%) than in plots where mulch was not added before planting (29–40%). Cover of common knapweed was similar in plots where mulch was added (54–67%) or not added (50–68%) before planting. In May 1994, ten 2 x 2 m plots were rotovated. Cereal straw was added as a mulch to five plots, while five other plots were left unmulched. In May 1995, all plots were sprayed with glyphosate herbicide and seedlings of 14 species were planted. Cover of all species was assessed in each plot every year between 1997 and 1999.

   Study and other actions tested

   Referenced paper

   Tallowin J.R.B. & Smith R.E.N. (2001) Restoration of a Cirsio-Molinietum fen meadow on an agriculturally improved pasture. Restoration Ecology, 9, 167-178.

3. A replicated, randomized, controlled study in 1995–1997 at a former landfill site in Seattle, USA (Ewing 2002) found that adding mulch after planting native prairie plants did not alter the growth of any of seven plant species. During two years after planting, there was no significant difference in the growth of Idaho fescue Festuca idahoensis, prairie lupine Lupinus lepidus, camas Camassia quamash, cinquefoil Potentilla gracilis, white-top aster Aster curtus, Oregon sunshine Eriophyllum lanatum, or long stoloned sedge Carex inops between fertilized and unfertilized plots (see original paper for data). In May 1995, twelve circular 4-m² plots at the landfill site were each planted with four individuals of seven native prairie species. Six plots were covered with 10 cm of mulch (a locally produced composted yard waste), and six plots were left untreated. The landfill site had been decommissioned in 1966 and sown with grass in 1971. All surviving plants were measured in June and September 1995, and in July 1996 and 1997. Measurements included height, diameter, area, spread, and/or branch and stem length depending on the plant species.

   Study and other actions tested

   Referenced paper

   Ewing K. (2002) Mounding as a technique for restoration of prairie on a capped landfill in the Puget Sound lowlands. Restoration Ecology, 10, 289-296.

4. A replicated, controlled study in 2004–2005 at a former mining site in Saxony-Anhalt, Germany (Kirmer et al. 2012) found that adding mulch before sowing seeds increased the cover of target plant species but did not alter target plant species richness compared to sowing without mulch. After one year, plots that were mulched and seeded had on average a greater cover of target plant species (67–70%) than plots that were unmulched and seeded (25–33%). However, the average number of target plant species was similar between mulched (7–23 species) and unmulched plots (6–22 species). In December 2004, three blocks were established on an unvegetated area (240 x 50 m) of boulder clay mixed with sand. In each block, two plots had a layer of mulch added (3–5 cm thick), and two plots were left unmulched. Mulch was obtained from a second cut of species-poor grassland. One of each of the two mulched and unmulched plots/block was sown with a high diversity mix of local seeds, and the other with a low diversity mix of non-local seeds. Vegetation was monitored within a 5-m² quadrat in each plot in 2005.

   Study and other actions tested

   Referenced paper

   Kirmer A., Baasch A. & Tischew S. (2012) Sowing of low and high diversity seed mixtures in ecological restoration of surface mined-land. Applied Vegetation Science, 15, 198-207.

5. A replicated, controlled study in 2012 in a former arable field in Alberta, Canada (Mollard et al. 2014; same experimental setup as Mollard et al. 2016) found that adding mulch before sowing seeds increased the number of seedlings in most cases compared to sowing without mulch. In three of four comparisons, there were more seedlings in plots where mulch was added alongside sowing of seeds (39–54 seedlings/m²) than in plots where seeds were sown but no mulch was added (9 seedlings/m²). However, in one of four comparisons, seedling emergence did not differ significantly in plots that were mulched and seeded (25 seedlings/m²) compared to those that were not mulched and seeded (9 seedlings/m²). In May 2012, the site was sprayed with glyphosate herbicide, tilled to a depth of 10 cm, and fenced to exclude livestock. Mulch (wheat straw or hay) was added to twenty-four 2 × 2 m plots, following which plots were sown with five grass species at a rate of 250 seeds/plot. In six plots, seeds were sown but no mulch was added. Seedling emergence was recorded in each plot every two weeks in July–September 2012.

   Study and other actions tested

   Referenced paper

   Mollard F.P., Naeth M.A. & Cohen-Fernandez A. (2014) Impacts of mulch on prairie seedling establishment: facilitative to inhibitory effects. Ecological Engineering, 64, 377-384.

6. A replicated, controlled study in 2012–2014 in a former arable field in Alberta, Canada (Mollard et al. 2016; same experimental setup as Mollard et al. 2014) found that adding mulch before sowing seeds did not increase vegetation cover compared to sowing seeds but not adding mulch. Vegetation cover did not differ significantly between plots where mulch was added and seeds were sown (23–82%) and plots where seeds were sown but mulch was not added (29–70%). In May 2012, the entire site was sprayed with glyphosate herbicide, tilled to a depth of 10 cm, and fenced to exclude livestock. Mulch (wheat straw or hay) was added to twenty-four 2 × 2 m plots, following which plots were sown with five grass species. In six plots, seeds were sown but no mulch was added. In August 2013 and 2014, vegetation cover was estimated using 1 × 1 m quadrats placed in each plot.

   Study and other actions tested

   Referenced paper

   Mollard F.P., Naeth M.A. & Cohen-Fernandez A. (2016) Mulch amendment facilitates early revegetation development on an abandoned field in northern mixed grass prairies of North America. Ecological Engineering, 97, 284-291.