Aromatic Aster – How to Grow Aster oblongifolius

Aromatic Aster – General Description

Aromatic Aster close up blooms — Three Aromatic Asters in my garden. The flowers look like a purple/blue carpet!

The native perennial Aromatic Aster is a very late bloomer, but it is worth the wait! Blooming about two weeks after its cousin New England Aster blooms, it will prolong the color of your garden well into Autumn. I’ve never seen a garden flower bloom later than Aromatic Aster. It creates showy clusters of flowers that are generally low to the ground. Since it blooms so late, Aromatic Aster is very valuable to pollinators, as it is one of the last sources of food before winter dormancy. The ‘aromatic’ portion of the name refers to the leaves when crushed. This plant is frost tolerant, and will be one of the latest blooming flowers you will ever see. I’ve seen it bloom all the way into November in Pennsylvania.

If you like to have year round color in your garden, then Aromatic Aster is a must-have. The only real maintenance item for this plant is staking it if you don’t want it to flop over or pulling new volunteers. Alternatively, you can surround it with taller plants, packed close together to provide support. This plant will slowly spread via rhizome. So, it will fill out an area over time. The branching is pretty dense, making the plant appear to be a small shrub even if it falls over. As the nearby picture shows, even if the plant has fallen over, it still makes a stunning display in the flower bed.

Also, saving seed from Aster is a good idea, since in the wild an individual plant has been observed to live for a maximum of six years. My plants are currently in year 4, and I will update this article accordingly if they live beyond 6!

Aromatic Aster Growing Requirements

This plant is smaller than most prairie plants. So, keep that in mind in regards to where you plant it. It may have trouble if it is close to taller, aggressive species. However, this plant can thrive in clay/rocky soil as long as it drains. It is drought tolerant, so watering is typically not an issue. If you notice that the lower leaves are drying out, then you may need to give it water. If this plant gets too tall it might need staking. Or you can trim it back some earlier in the season around mid-June to keep its height lower. I’ve had it flop over before because I didn’t stake or trim it due to being too busy. It will generally look like a small carpet of purple/blue flowers even if it falls over. So – I don’t mind it laying down in the flower bed at all.

But, the best benefit of this plant is how late in the season it blooms! This study found that the earliest date this plant would bloom was August 25th. I have seen Aromatic Aster bloom much longer than mums, bloom through frost, and even past Halloween! So, this flower will give you the ‘last gasp’ of color until Spring. I currently have six of these, and plan on planting about 10 more in my meadow near the front.

Common Uses

This plant is fairly versatile! It naturally grows in prairies and open woodlands, getting full sun. It can handle a wide variety of soil as long as it is well drained. The pictures you see here are all in fairly tough, rocky Pennsylvania clay soil. But, as it is a Native Plant within Pennsylvania, that means it is well adapted! So, I generally keep these near the front of flower beds where they can prominently display their late Autumn flowers. Since the plant is native, that means it has co-evolved with the environment, making it less susceptible to disease and other pests. Recently I added several specimens to our micro-prairie in our backyard.

Click HERE to see some prairie garden designs!

Aromatic Aster leaves in Spring, about 1 month after emerging from dormancy.

How to Grow Aromatic Aster from seed

Aromatic Aster is very easy to grow from seed. Just plant it on the surface of the soil in a small pot, or direct sow in spring. Just ensure the seed doesn’t wash away during a heavy storm. Keep them moist by misting with a spray bottle as required. Then continue to ‘pot-up’ this plant as needed until transplanting into the garden. This plant can bloom the first year if started/transplanted early enough.

Aster Seedlings Symphyotrichum — Aster seedlings. Not long after germination.

Aromatic Aster Seedlings Symphyotrichum oblongifolium — Aromatic Aster Seedlings, ready for transplant into the garden.

Harvesting Aster Seed

Harvesting Aromatic Aster seed is incredibly easy. Just wait until the blooms have faded, and the flowers become fuzzy, dry seed heads. Then just pull the seed heads off and store in a paper bag for about a week in a cool/dry place. The individual seeds will be arrayed around the seed head, and each attached to a feather-like tail. Then, just grow more plants in the Spring, or scatter seed where you would like more plants!

Aromatic Aster with Spotted Bee Balm in background

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Aromatic Aster Reference Table

Common Name	Aromatic Aster
Scientific name	Symphyotrichum oblongifolium
USDA Zone	3-8
Bloom Time	Sep/Oct/Nov
Bloom Duration	4 weeks
Color	Blue/Purple
Bloom Size	1” (25mm) diameter, daisy-like flowers. Many blooms per plant
Characteristics	Branches coming from one stem, each supporting many blooms
Height	2’ (60 cm)
Spacing/Spread	1.5’ (50cm)
Light Requirements	Full sun
Soil Types	Well drained
Moisture	Dry to medium
Maintenance	Plant will likely flop over without staking.
Typical Use	Versatile flower – can go many places and look nice
Fauna Associations	Bees
Larval Host	None
Sowing Depth	Surface
Stratification	Not required
Native Range	Eastern half of the USA
Notes	This flower will bloom last in your garden. It will likely be the only flower blooming in your neighborhood.