Designing a pollinator-friendly herbaceous scheme for roundabouts
– By Peter Cuthbert, Horticultural Services
Roundabouts can provide the opportunity for very attractive herbaceous planting schemes and excellent resources for pollinators. Successful long-lasting herbaceous schemes need considerable plant knowledge, both in terms of selecting and sourcing the right materials. Roundabouts can be a difficult growing environment, so attention to detail is essential. In my experience, they can easily go well, but they can also go wrong without the correct design and technical input.
Given that the primary purpose of a roundabout is a traffic control device, there are health and safety issues which need careful consideration. Due to high traffic volumes of traffic circulating, care needs to be taken when carrying out works, be it initial planting or subsequent maintenance.
I’ve tried to summarise the key things I’ve learned through my years of experience in this area:
- A successful roundabout planting scheme requires good plant knowledge in terms of things like longevity (you want plants that will last at least 10 years); which plants will spread and how competitive they will be with other plants in the scheme; how quickly they will establish and if self-seeding may occur. I believe it’s very important to use only good quality plants from a reliable source. Where possible, I think we should buy Irish plants rather than importing from Europe so that we are supporting local industry.
- Often the soil in roundabouts may be poor. It can sustain grass but may be inadequate for the establishment of a colourful herbaceous scheme. If this is the case, you will need to improve the soil before planting.
- Good initial ground preparation is also key to minimise future maintenance. Initial removal of all root weeds (scutch grass, bindweed, etc.) will reduce the need for weeding later.
- Roundabout planting needs to take place in autumn or spring as this allows for quick establishment. Planting later than April may result in need to irrigate which is unrealistic on a roundabout.
- I believe it’s best to use pot size p.9 at a high planting density of 9-11 plants per square metre. Dense planting will reduce the need for weeding.
- You should aim for a small range of plants for maximum colour. I usually recommend planting in bands.
- Perhaps the most important thing I’ve learned is that a pollinator-friendly roundabout might look easy, but to be successful it must be adequately maintained. During the establishment phase, weeding is essential. This may need to be done 3-4 times in year 1, depending on the weed population. When the perennials have established and provided dense cover, the frequency of weeding can be reduced. In year 2 and onwards, weed at the beginning and end of the growing season.
- Leave dead stems on plants for the winter as they provide protection for the plants, as well as offering food and nesting materials for wildlife. The dead foliage can be removed in spring by mass pruning to 10cm height when there is new growth appearing. Some plants, such as grasses, provide year-round structure and colour on a roundabout and won’t need pruning.
- The lifespan of a well-planted and maintained roundabout is 10-12 years or longer. Small amounts of replacement planting may be required, but generally they should be trouble free.
Below is a typical example of one of my pollinator-friendly roundabout designs:
All-Ireland Pollinator Plan: Technical blog series www.pollinators.ie