Establishing Perennials By Seed – A case study in London Parks
Establishing perennials by open ground sowing requires a carefully thought-out approach, especially on large scale, high-profile sites and under the scrutinous eye of the general public. Not something for the faint-hearted!
Richmond Borough Council, (RBC) had enjoyed some great success using 'Pictorial Meadows’ annual mixes for three consecutive years. This had gone down well with park users and the response was positive, ensuring that ‘wildflower’-type planting in local parks had been accepted by its communities.
However, moving from annuals to perennials by sowing seed proved to be quite a leap of faith as now there were many more requirements. As well as the need for good quality seed, irrigation, weed control, an extended two-year establishment period, regular site-monitoring and public perception were all now critical to a successful meadow. Portia Baker, Consultant Landscape Architect for RBC, who took on the challenge, commissioned ‘Green Estate’ meadow specialists to help overcome these additional tasks.
Sowing annuals can give the quick wins with their aggressive nature, germinating within three days and flowering from as early as 6 weeks after sowing. However this is not the case with perennials. While annuals grow so fast they can out-compete most weeds and grasses, the slow nature of perennials from germination to established plants means they are the underdog in a battlefield of highly competitive weeds.
To overcome this problem, ‘Green Estate’ recommended spraying off the ground and using a sterile-growing material to be spread as a 100mm depth blanket over the site. This provided a much greater advantage to the slow perennials by giving a clean seed-bed for germination but also gave a mulch to hold back the weeds.
Although the perennials now had a toe-hold in the field, the young seedlings were at a critical stage. Temperatures were rising in London and a lack of water would mean a loss of seedlings burnt off by the wind or sun. ‘Continental Landscapes’ were commissioned to undertake irrigation throughout the dry periods. Eight weeks or more after sowing and people were starting to wonder when the plants would flower. Public patience was running out.
After the initial growth spurt from April to June , taller foliage from the faster growing perennials had overshadowed the slower growing species. A ‘cut and collect’ was required at this stage to prevent the taller plants dominating the slower species but this also helped other plants to put on root growth and basal foliage. From the public’s point of view, however, they had waited long enough for any signs of flowers only to see them being cut down as soon as they had appeared.
To overcome the public’s perception, Richmond Council decided to erect some information panels to help the public understand the process required to establish the long-term meadows in their parks.
Well-established meadows with good species composition are very resistant to weed invasion. Despite the mulch, there is always some in-blown seed which will exploit any opening and, although the sterile mulch can hold back competition, over time the pernicious weeds, such as creeping thistle and nettles, can start to push up through the mulch. These were dealt with as a means to an end by eradication through selective herbicidal treatment.
The desired result came well into the second growing season. Finally, people were appeased by the impact and, along with the pollinators, were now able to enjoy the flowers.
“I’ve just come back from Crane Park and it is looking fab!”
Yvonne Kelleher, Parks Development Officer
This sterile mulch technique used by ‘Green Estate’ has now proved to be successful in many other location by reducing the risk of failure in open ground sowing.
The main challenges and solutions for successful perennials from seed were;
“Pictorial Meadows’ annual meadows were a great success with our parks users and residents, but after sowing them for three consecutive years we decided to make the transition to more sustainable perennial meadows at a few key sites. We are currently establishing four of Pictorial Meadows perennial meadows from seed and a further three from their PM Turf. Composed of a mixture of native and non-native species, we hope these will provide colour and interest for many years as well as providing nectar, pollen and seed heads for the wildlife”.
Portia Baker, Consultant Landscape Architect to the Council