Logo

SHEFFIELD BOTANIC GARDENS 2004

As part of the Heritage Lottery funded restoration of the Gardens, I was invited to create an area (800m²)of North American Prairie as a constrast to the more conventional vegetation in the Gardens.  The site was previously a pond in the C19th resulting in a very nutrient rich, silty soil.   This lead to very high levels of prairie standing biomass, and the loss through competition for light of many of the smaller species.  What has been really interesting however is that this prairie biomass has proved to be extremely resistant to invasion of weeds from the outside, even though the only maintenance the vegetation has received over the past 10 years is cutting down and removal of the biomass in March, with an occasional flash burn over immediately after this. This shows that even highly productive  sites can support sustainable herbaceous plantings when highly productive species are employed as part of the design.


By late May 2004 the designed seedling density of approximately 150 seedlings/m² had been achieved.  Seed was sown in January, into a 75mm deep sand sowing mulch and then covered by jute erosion matting to reduce fox and cat digging.  No irrigation was used,  but spring 2004 was relatively wet.


By August 2004 the canopy of prairie seedlings had fused across much of the site.  Weeding was undertaken by the author  prior to this and 14 hours were expended in 2004 to keep the site essentially weed free in the first growing season.  Keeping weeds to a very low density in the first year is critical to long term resilience.


The sown prairie was initially very species diverse and included annual hemi-parasites such as the wild endangered scarlet Castilleja coccinea, plus relatively low growing species such as Penstemon digitalis (white flowers in the image). The high sowing density plus the sites high productivity inevitably however lead to dominance by taller, more productive species.


In September 2005 the flowering display was very dramatic, with many of the quick growing species, such as Aster, Ratibida and Rudbeckia subtomentosa particularly evident.


In the first few years the vegetation was flash burnt with a propane triple burner to kill weed seedlings, and particularly winter annuals and biennials that would otherwise dominate the site during the dormant season.  This has not occurred over recent years, but prairie dominance is now so complete that weed invasion is very, very limited.


By September 2013, the vegetation is still present and stable despite very low levels of maintenance, and remains very attractive.  The species composition has however changed significantly across the 10 years, with low growing and highly palatable (to slugs) species eliminated from the vegetation.