By Kit Raven
The plantings at the Swarthmore roundabout are already morphing from scraggly trees and weedy-looking little plants into specimens that are beginning to fill out, flower and spread.
Jeff Jabco, Scott Arboretum’s director of Grounds and coordinator of Horticulture, took some time away from the many plantings he is now overseeing to explain how the design came about, the new concepts evident at the roundabout, and how, soon enough, we’ll be seeing an interesting, gorgeous and frequently changing landscape.
Jabco pointed out that all gardens and landscape plantings need a few years to grow, to develop from promising to actually looking great. However, some long-blooming perennials are already in flower, including Coreopsis verticillata ‘Zagreb,’ with tiny, canary yellow flowers; Salvia nemorosa ‘Blauhugel’ (‘Blue Hill’), with blue spires; Ruellia humilis, a wild petunia with sprinklings of small lilac-blue flowers; Eragrostis spectabilis, purple love grass topped with clouds of rosy purple panicles; and Pycnanthemum flexuosum, mountain mint, with frizzy balls of white flowers.
More than a dozen varieties of perennials will fill in the planting areas and will bloom in overlapping succession, from spring through fall. The effect will be like a meadow, delightfully dense, varied and often changing.
Not only are the currently blooming perennials giving a sneak preview of what’s to come in much greater profusion, but these and the trees and shrubs will also provide food and habitat for beautiful and necessary winged creatures.
The roundabout’s design includes some trees and shrubs, as a traffic-calming measure required by PennDOT. The native trees are Gymnocladus dioicus, Kentucky coffee trees (the roasted seeds are a poor substitute for coffee, so Hobbs won’t be harvesting them) which will eventually provide high shade and evergreen Juniperus virginiana, eastern red cedar or aromatic cedar.
The native shrubs are Ilex verticillata ‘Winter Red,’ with red berries in winter; Diervilla sessifolia ‘Coolsplash,’ variegated bush honeysuckle with yellow flowers and red fall leaves; and Juniperis chinensis ‘Angelica Blue,’ a silver spreading juniper. These structural plants were selected by Jabco and former curator Andrew Bunting.
Some residents have been curious about why the Scott Arboretum used gravel to cover the planting areas and what the little colored flags are for.
The design approach for the plantings is quite unusual. Last October, the German landscape architect Cassian Schmidt gave a Scott lecture on landscape planting that is sustainable and low-maintenance, yet also naturalistic and stunningly beautiful. The low maintenance starts with natural, unfertilized soil, which is then covered with gravel. This creates a lean environment for tough plants, which are only watered their first year and never fertilized. As the desired plants fill in and cover the gravel, weeding will be minimal, only a few times per year.
The Arboretum invited a number of horticultural professionals to participate in a one-day workshop to apply Schmidt’s principles for the roundabout and nearby areas. As a group, they selected perennials in four categories and decided how much of each category to use: 15% structural ones, such as Baptisia ‘Lemon Meringue’; 35% companions, ones that will grow well with the structural plants, such as the salvia above; 50% groundcovers, including the purple love grass; and 10% fillers, such as the coreopsis.
The group came up with a recommended plant list and proportions, which Jabco and garden supervisor Adam Glas revised to consider conditions of all day sun on an open site surrounded by cement, asphalt and constant traffic. Accordingly, a number of selections are natives that thrive in poor soil and adverse conditions.
To get a naturalistic look, Schmidt’s method uses a grid. On the roundabout, the colored flags marked a four square yard grid.
First, the featured or structural plants were placed. Then, in each square, the correct proportion of each type of perennial was randomly placed. The Arboretum intends over time to use this system all along Field House Lane, as the sustainable, low-maintenance method is also easy to plan and vary.