We tend to think of asters only in fall. Surrounded by spring’s emergent beauty, it is easy to lose oneself in the flowering tree families of Magnoliaceae, Rosaceae, Cornaceae, and Fabaceae. Add to that the living picture of nesting songbirds, blossoming shrubs, bulbs, and wildflowers, then followed by summer’s luxuriant bounty — understandably so — we often fail to adequately plan in spring for fall blooms and butterflies. I encourage you to consider integrating native species of asters in your overall garden design. Plant aster seeds collected, a nursery-grown pot, or a pass-along from a friend, and, come next fall, you will be richly rewarded for your foresight. The luminous lower angle of light gilding the late summer New England landscape creates an ethereal haze when seen through the purples, lavender-blues, rosy-pinks, and white inflorescence of calico, New York, New England, late-purple, and smooth asters, to name but a handful, transforming roadside, meadow, and garden.
Asters are one of the most important plants for providing nectar in late summer and autumn for all categories of pollinators. Listed on the website of the Connecticut Botanical Society are perhaps thirty or so asters native to New England. The following three beauties I have in mind for your gardens not only provide nectar; they are also larval host plants for many species of Lepidoptera: smooth aster (Aster laevis), flat-topped white aster (Aster umbellatus), and New England aster (Aster novae-angliae). The neatly compact Wood’s asters that are commonly available at garden centers have their place in the landscape design when a low mounding plant is desired. We see comparatively far fewer butterflies on Wood’s asters than the three aforementioned straight species.
The flower clusters of flat-topped aster are usually flat, but occasionally may appear dome shaped. The lacey white ray flowers surround the yellow disk florets and the leaves are a larval food plant for the Harris Checkerspot butterfly (Chlosyne harrisii). Aster umbellatus grows anywhere from 2 to 7 feet. Typically, in the well-tended garden, it will grow towards the taller side, as does New England aster. Plant both in the back of the border. The foliage on the lower part of the stems of New England aster tends to dry out towards blooming time; plant lower- growing perennials such as Montauk daisy and goldenrods in the foreground to disguise the ratty looking foliage. Flat-topped asters, New England, and smooth asters begin to bloom in September. They tolerate a variety of soil and light conditions, however, they will thrive when planted in full sun and in rich, moist soil.
New England asters bloom in shades of deep purple and pink, more intense in color when compared to other native asters. I can’t talk about New England asters without mentioning my friend Joe Ann’s patch. Hers runs along the back length of her luxuriantly lush vegetable garden. In mid- to late September, the blossoms become a nectar magnet for all manner of pollinator on the wing. The combination of masses of Persian pink blossoms, bees, and butterflies are truly a sight to behold.
Not only are smooth asters a top source of nectar for Monarch butterflies (and many species of butterflies) during their annual fall migration, they are also a larval host plant for the Pearly Crescentspot (Phyciodes tharos) butterfly (see photo in last week’s column) and Northern Crescent (Phyciodes selenis). If I had to choose a favorite of the favorites, it would have to be smooth aster. The cheery lavender-blue ½ inch button-sized flowers are a lovely addition to the butterfly garden. I like that they reseed prolifically throughout the borders, realizing however, that this trait may not be to every one’s taste. Smooth aster is a common sight in our neighborhood and grows vigorously along the shoreline, particularly in wet swampy areas.
Generally speaking, the majority of native wildflower seeds will germinate without pretreatment when planted outdoors in fall or early winter. To plant in spring or summer, a physical modification to the seed’s coat is often needed to allow the embryo to mature or break dormancy. New England aster seeds require a period of moisture and cold after harvesting before they will germinate. If planting in spring, this period is artificially simulated by placing the moistened seed in a refrigerator for a certain length of time. Place the seeds in a small container with moist (not wet) sand, peat or vermiculite, and leave in the refrigerator for four to six weeks. This procedure is known as stratification, because of the layering of the seeds within the medium. Look at the seeds from time to time. The seeds must be kept moist while pre-chilling but it doesn't usually benefit them to be actually in water or at temperatures below freezing. Light is also beneficial after pre-chilling. Pre-chilled New England aster seeds should have only the lightest covering of compost or soil, 1/4 to 1/8 inch.
End Notes: — Weston Nurseries often carries ‘Alma Potchke,’ a lively, almost hot pink, cultivar of New England aster. Garden in the Woods at the New England Wild Flower Society offers the straight species of New England aster. I am giving away seeds of New England asters with purchase of book. — If you are planning to attend my class (first class is this coming Tuesday, May 5th) at the Arnold Arboretum, “Your Garden as Habitat,” please register at your earliest convenience to assure a spot. — Oh Garden of Fresh Possibilities! would make a terrific Mother’s Day gift. Please come join me, if you can, the weekend of Mother’s Day at the upcoming book signings and events: — Barnes and Noble at the Prudential Center, Boston. Thursday May 7, 2009 at 4:30 pm. — Jabberwocky Bookshop at the Tannery in Newburyport on Friday May 8, 2009 at 7:00 pm. — The Stevens-Coolidge Place Annual Plant Sale on Saturday, May 9, 2009 from 10:00 am to 2 pm. Butterfly walks and book signing.