Yellow seems the very essence of summer. Emulating the sun with their golden blooms, and reigning supreme in the landscape, are some of our tallest and most stately native perennials, representatives of the genera Silphium, Rudbeckia, and Helianthus. These are big, tough beauties, performing when most other garden favorites have had their day and are beginning to fade. With these three golden genera, you can lead your garden from one season to another.
The silphiums begin the bloom parade in June or July, the rudbeckias follow, and those in the helianthus crowd can extend the show well into October or beyond. This length of bloom time is a boon for wildlife. The butterflies and bees, naturally attracted to the bright yellow blossoms, have a smorgasbord of nectar and pollen. Later, when the flowers go to seed, the birds have their time of feasting. The statuesque nature of these plants adds a distinct dimension to the summer landscape. They can serve as sculptural elements or even as “architecture” when used as a seasonal screen or hedge.
The silphiums are native to the eastern half of the United States, and they attracted botanist William Bartram’s attention when he was exploring the Southeast in the 1770s. In the records of his travels, as he describes the flora of the fields, he notes: “The most conspicuous, both for beauty and novelty, is a tall species of Silphium.” Despite the beauty and novelty Bartram remarked on, the silphiums have been largely overlooked as garden specimens and may be hard to find except in native plant nurseries.
All members of the genus are tall, in the range of 7 to 10 feet, and display 2- to 3-inch wide, yellow, daisy-like flowers with gold centers. All of the silphiums are sun lovers. Being creatures of wild meadows and fields, they are tough and tolerant of a wide range of conditions. The foliage is quite variable within the genus and displays some fascinating forms.
Silphium laciniatum is known as compassplant because the large, deeply incised leaves line themselves up in a north-south direction to minimize exposure to the harsh midday sun. One of my favorite silphiums is Silphium perfoliatum, commonly called cup plant due to the configuration of the foliage. The leaves are opposite one another on the stem, and the larger mature leaves, which can be up to a foot long, are fused at their bases, forming a “cup” around the stem. Rainwater pools in these living vessels, providing birds with a drink.
The Rudbeckia genus includes several dozen species, including annuals, biennials, and perennials, all having their origin in North America. The nursery industry has created many hybrids over the years, resulting in untold numbers of cultivars. Rudbeckias now come in all shapes and sizes, but to my eye, the most magnificent are the perennial giants of the genus, R. laciniata (green-head coneflower) and R. maxima (great coneflower).
R. laciniata is the largest of the rudbeckias, topping out at 6 to 10 feet tall. Attractively lobed lower foliage emerges in late winter, and the plant develops a branching habit as it matures. From mid-summer into autumn, numerous yellow flowers appear, which are 2 to 3 inches across with gracefully reflexed petals surrounding a green central disk.
Rudbeckia maxima is another native giant of the genus. It enjoys popularity with garden designers due to its attractive, gray-green, oval foliage and its tall flower stalk that is topped with a 4-inch bloom consisting of yellow petals surrounding a brown cone. This rudbeckia can provide a decidedly vertical accent in the garden.
You can extend the bloom time of the golden rulers by including some of the perennial sunflowers in your gardening repertoire. These robust specimens put on their big show beginning in late summer and continuing well into fall. Again, all are native to North America, and there are several excellent species from which to choose. All sport bright yellow blooms and perform best in full sun. One perennial sunflower to consider is Helianthus angustifolius (swamp sunflower). It is native to most of the eastern half of the United States, and as its common name implies, it prefers a moist, rich soil.
Helianthus maximiliani (Maximilian sunflower) is perhaps the toughest of the perennial sunflowers, being drought tolerant and able to survive in a variety of soil conditions. William Bartram was notably enchanted with these three genera as he explored the “expansive savannas, charmingly decorated with late autumnal flowers, as Helianthus, Rudbeckia, Silphium...” These magnificent beauties can rule your summer and fall garden with a golden touch, as they did the landscape over two centuries ago.