When many of the perennial flowers in your garden are wrapping up their performance for the year, Aster Purple Dome is just starting to step onto the stage. Known botanically as Symphyotrichum novae-angliae ‘Purple Dome’ (syn. Aster novae-angliae), this late-blooming plant is a true star of the fall garden. Yes, the dark green foliage looks unassuming all season long, but when the days begin to shorten and early autumn arrives, things change. The buds burst open to reveal clusters of hundreds of inch-wide, daisy-like blooms in rich shades of purple. But this plant’s beauty is more than skin deep. There are also plenty of other reasons to include it in your garden. In this article, I’ll share Purple Dome’s many noteworthy traits and offer tips for growing it successfully.
What makes Aster Purple Dome so special?
Beyond its gorgeous flower color (the exact shade of the flowers varies slightly, based on the light levels and the maturity of the blooms), Aster Purple Dome has a lot more to offer both the gardener and the late summer garden. A cultivar of the North American native New England aster, Purple Dome is fully hardy in winter temperatures as low as -20°F (USDA zone 5). Plus, it tolerates summer’s heat like a champ (unless you live in the deep south where, admittedly, it will struggle). Purple Dome is a dwarf cultivar that reaches only 18-20” in height, making it perfect for flanking walkways, edging garden beds, or accenting small landscapes.
Aster Purple Dome is clump forming, which means it won’t spread and take over the garden, and its rounded growth habit stays neat and compact all season long. When the buds open to reveal a cushion-like blanket of plum-purple petals, you’ll also catch a glimpse of the flowers’ yellow centers. Those yellow centers are filled with nectar that’s enjoyed by many types of late-season pollinators. On my plants, I frequently find numerous species of native bees, butterflies, syrphid flies, and other pollinators feeding. Asters in general are a terrific autumn nectar source, and Purple Dome is a true standout among them.
When does Aster Purple Dome bloom?
If left to its own devices, Aster Purple Dome comes into flower around late August and stays in bloom for 6 to 8 weeks. If the weather is extremely hot, the flowers may fade a bit faster, but in the typically cooler temperatures of autumn, this doesn’t become an issue.
Pinching back asters
Pinching back the plants once or twice earlier in the growing season delays the bloom time by a few weeks and keeps the plant even more compact (much like you would do for a mum). This isn’t necessary by any means, but it is a great way to ensure you’ll have color in your garden through October’s end. To pinch back all aster varieties, trim off the top 2-3 inches of every stem once in late May and again in early July. Don’t pinch any later in the growing season or the plant may not have enough time to develop flowers before the arrival of a killing frost in the fall. Again, pinching Aster Purple Dome isn’t necessary, but you may find it’s something worth experimenting with.
Caring for the plants
Thankfully, this variety of aster is easy to care for. Because of its compact habit, the plants don’t flop over or split open in the middle. Yep, that means – No staking required! It’s naturally small statured, so, as I mentioned above, unlike some other asters that can grow tall and floppy if they aren’t pinched, there’s no need to pinch back Aster Purple Dome to keep it compact.
Since the plant blooms so late in the season, there’s no need to deadhead it or otherwise fuss over the plant. I do suggest dividing Aster Purple Dome every four to five years to keep it bloom-filled and healthy. Give each plant plenty of room because good air circulation around the plants reduces the chance of developing powdery mildew (more on this in a later section).
Aster Purple Dome truly is carefree. The only regular maintenance that’s required is an annual “haircut”. Trim the entire plant down to the ground in the spring when you start to see new green growth emerge from the ground at the base of the plant. The old stems can be left to stand all winter long. The goldfinches and other birds enjoy eating the seeds, and the pollinators and other beneficial insects can take shelter in the dead stems through the winter.
Where to plant Aster Purple Dome
Like other New England asters, Purple Dome prefers full sun to partial shade. In partial shade conditions, the stems may grow longer and leggier, forcing you to stake the plants if they flop over. The more sun it receives, the sturdier the stems will be.
Average garden soil is all that’s needed. No amending or fertilizing necessary. This perennial tolerates moist soil and is a great candidate for a rain garden or another low-lying area. You’ll want to make sure it isn’t located in a spot that stays sopping wet all winter long, though, as that encourages crown rot.
Mix Aster Purple Dome into perennial beds and meadow plantings, or plant a few around your mailbox or front steps. As long as they get plenty of sun and decent air circulation, they’ll be happy and healthy.
What to plant with Aster Purple Dome
Since Aster Purple Dome comes into its own in fall, I love to partner it with other late-season lookers. Ornamental grasses are a favorite partner (try switchgrass or little bluestem). Their textures complement each other in the most beautiful way. For a pop of bold color, pair Aster Purple Dome with a smaller-statured goldenrod (Solidago) such as ‘Golden Fleece’ or ‘Goldkind’ (also known as Golden Baby).
I also love to see Aster Purple Dome with Helenium plants as the two are in bloom at the same time. ‘Mardi Gras’ is my favorite orange variety, and ‘Moerheim Beauty’ is a coppery red. Artemisias (wormwoods) make another great partner for Purple Dome. Though they aren’t covered in blooms, the lacy gray foliage makes an excellent textural backdrop to the purple aster flowers.
Potential problems with Aster Purple Dome
Though the plant is as carefree as they come, unfortunately, Aster Purple Dome does have problems from time to time. I’ve faced a handful of spider mite infestations over the years (cured by 2 or 3 applications of horticultural oil) as well as nibbles from rabbits and deer (cured by monthly applications of my favorite spray repellent).
Probably the biggest troublemaker is powdery mildew. While Purple Dome is noted for its powdery mildew resistance, in hot, humid summers, the lower leaves of the plant may show signs of infection. Starting with the classic white talcum powder-like dusting on the leaves and progressing to brown, crunchy foliage, powdery mildew can be a real bummer. Give the plants plenty of air circulation. You can use preventative sprays of an organic fungicide such as Monterey Complete, Revitalize, or Safer Neem Oil, but powdery mildew is largely an aesthetic issue. In other words, it doesn’t cause any long-term damage; it just makes the plant look not-so-good. You can learn more about powdery mildew in this article.
Where to buy
Now that you know the many positive attributes of this wonderful fall-blooming beauty, I hope you’ll find a home for a few of these great plants in your garden (here’s one of my favorite sources). The people and the pollinators will thank you!
For more on growing flowering perennials, please visit the following articles:
- Purple flowering perennials
- Hardy hibiscus
- When to cut back irises
- When to cut back peonies
- Shasta daisies