Complete Guide to Smooth Blue Aster – From Seed to Bloom


Want to get some beautiful light blue color into your garden late in the Summer? Want to attract a wide variety of bees and butterflies, including Monarchs? Smooth Blue Aster may just be for you then!

In this article:

What is Smooth Blue Aster?

Smooth Blue Aster is a herbaceous perennial wildflower native to North America that blooms baby blue, or light blue flowers in late Summer to early Fall, attracting many butterflies. Scientifically known as Symphyotrichum laeve, it will grow up to 3-4′ tall in full sun, dry to medium moist soil.

One of the first Asters to bloom in late Summer, Smooth Blue Aster looks exquisite in the garden, wildflower meadow, or micro-prairie. The pale blue/purple color looks wonderful. And the smooth to touch blue/green foliage is beautiful all season.

Although there are over 180 of different species of Aster [1], this is one of the more popular ones for cultivation. The attractive foliage and showy flowers make it a welcome addition to most gardens.

Reference Table – Facts

Scientific NameSymphyotrichum laeve, Aster laevis
Common Name(s)Smooth Blue Aster, Smooth Aster
Native Range, USDA ZoneAll of North America, except California. USDA Zone 3-8
Bloom TimeLate Summer to Early Fall
Bloom Duration, Color4-6 weeks, light blue to pale purple
Height2′-4′ (60-120 cm)
Spacing / Spread1′-3′ (30-90 cm)
Light RequirementsFull sun to partial shade
Soil TypesSandy loam to clay loam
MoistureDry to medium moisture
Fauna Associations / Larval HostsAttracts bees, numerous butterflies. Hosts the Pearl Crescent Butterfly
References [2]

What are the Benefits of Smooth Blue Aster

Smooth Blue Aster is an excellent nectar source for butterflies and numerous bees. Each plant will produce numerous blooms and generally stay erect and upright. It has a particularly long blooming season, with it’s bloom time lasting over 4 weeks.

One other stand out feature of Smooth Blue Aster is the attractiveness of the foliage. The blueish hue and texture remind one of Blue False Indigo in that they look cool and feel nice.

Identification and Characteristics of Smooth Blue Aster

Smooth Blue Aster is generally upright and erect as long as it receives sunlight from all sides, and is exposed to wind. If it is sheltered from the sun in a direction, the tendency is to lean towards where it does receive sunlight.

Stem

The stem of Smooth Blue Aster is round, light-green to blue in color. True to it’s common name it is generally smooth. The upper half of the plant will produce some branching.

Leaves

Smooth Blue Aster leaves are oblong-ovate or lance shaped, and alternate along the stalk of the plant with smooth margins/edges. Like the stems, the leaves are hairless and are anywhere from 1″ wide by 6″ long to about 1/2″ wide by 3″ long. The larger leaves are towards the bottom of the plant.

The top surface of the leaves are more of a greenish-blue, while the under side is more green. The leaves will clasp and wrap around the stems.

Flower

Clusters of individual flowers occur at the terminals of the branches, containing several blooms each. Individual flowers are daisy-like, light purple to light blue in color with yellow centers and generally 1/2″-1″ wide. As the season goes on, the flowers appear to change color from blue to purple.

After several weeks, and individual flower will stop blooming and turn brown. The seed head is now forming, and when ready will form the ‘feathery’ aster seed head. Seeds can be collected at this time, dried, and stored for a year or two in a cool dry place.

Root System

Smooth Blue Aster has a shallow fibrous root system that also produces rhizomes. However, the plant is not an aggressive spreader. It will slowly expand over time, forming a small colony.

Grow and Care for Smooth Blue Aster

If planted in it’s preferred growing conditions, Smooth Blue Aster will not require special care. Just make sure the plant is spaced enough to allow air circulation to prevent fungus.

Sunlight Requirements

The sunlight requirements for Smooth Blue Aster are Full Sun (6+ hours direct sun) to partial shade (4 hours direct sun). The more sun it receives the larger and more blooms the plant should produce.

Moisture Requirements

For water requirements, Smooth Blue Aster prefers drier to medium moist conditions. It will not do in soil that does not drain well and is wet.

Soil Requirements

For soil requirements, Smooth Blue Aster can tolerate sandy loam to clay loam – so quite a versatile range. The key is to make sure it drains well to avoid root rot.

How to keep Smooth Blue Aster from flopping or leaning

Like other Asters, Smooth Blue Aster may lean or arch substantially. This generally occurs if it is planted along a structure or has something that shades it from one of the primary directions of the sun (East, South, West). This can create two factors that cause it to lean.

1 – The plant will naturally arch toward the sunny directions. And keeping it shaded from one direction makes it lean more towards the others. Where as if it had exposure from all sides, it would be more erect.

2 – Planting along buildings sometimes shields the plant from the wind. This can result in a weaker stem, as the stems resisting the regular wind actually strengthen the stem (like lifting weights for plants).

As Smooth Blue Aster is naturally found in prairies and in the open, it likes to get sun from all directions. Plant it where it is most exposed to sun and wind to keep it upright and vertical.

One additional strategy is to give the plant a ‘haircut’ in June. Just go prune or trim the top 1/3-1/2 of the plant off in June, and it will start branching. This will reduce the overall height, and therefore reduce the amount of torque on the stem, making it more vertical.

How to Grow Smooth Blue Aster from Seed

Germinating seeds of Smooth Blue Aster is easy. There is no special treatment required to germinate the seed! Just sow the seed directly in loose potting soil and tamp down. Aster seeds do not like to be planted deep at all!

  1. Fill a container (4″ square) with moist potting soil, leaving a 1/2″ gap at the top
  2. Scatter 5-10 Smooth Blue Aster seeds
  3. Add a handful of loose potting soil on top, partially covering the area.
  4. Mist the pot using a spray bottle or pump sprayer to avoid washing seed away
  5. Place pot in a location that receives morning sun and afternoon shade, and keep moist (water early in the morning)
Smooth Blue Aster Seedling

Germination should occur within a couple of weeks if seed is viable.

Purchase Seed

We have ordered a variety of native flower seeds from Everwilde Farms, which you can order right from Amazon through our link on our RECOMMENDED PRODUCTS PAGE. (We may earn a small commission when you purchase through our links, at no cost to you. This helps support our website.)

Transplanting Smooth Blue Aster

Smooth Blue Aster can be transplanted and moved around the garden in early Spring or late Fall. Just dig up the root ball, giving about a 2″ extra distance to make sure you get as many roots as you can. Dig at a 45 degree angle. And replant as soon as you can, within an hour or two. Water after transplanting.

Although it isn’t 100% necessary, just about any plant being transplanted will benefit from having a handful of compost added to the bottom of the hole. It will provide a nice source of nutrients while it is in transplant shock.

Transplanting in early Spring or late Fall when the plants are dormant, or nearly dormant is the safest time for transplanting. The ground is generally more moist, and there is less of a heat load on the plant, so watering is less of a concern.

Wildlife, Pests, and Diseases

Bees

Many different species of bees will visit Smooth Blue Aster. Bumblebees, mason, leaf-cutters and many more frequent this flower.

Butterflies

Asters are one of the more popular flowers for many species of butterflies. I frequently observe skippers, clouded sulphers, Monarch, and other species visiting to get the nectar.

Deer and Rabbits

Some references will tell you that the foliage is occasionally browsed by deer and rabbits. My experience has been that both Deer and Rabbits will completely devour Smooth Blue Aster.

Protect this plant throughout the growing season with Liquid Fence! It really works! It is the only way I am able to enjoy this flower. You can find Liquid Fence at our Recommended Products page.

Dogs

Smooth Blue Aster is not poisonous to dogs. [3]. Per the ASPCA, almost no member of the Aster genus is poisonous to dogs.

Diseases

Like many plants, Smooth Blue Aster can get certain fungus diseases such as powdery mildew. Although there are fungicides available, prevention is often better than curing a disease! Make sure the plants are spaced enough to allow airflow, and planted in direct sunlight.

Where you can buy Smooth Blue Aster

Smooth Blue Aster is sold in certain specialty nurseries that mainly deal in Native Plants. But really, this plant is so easy to grow from seed that one should consider attempting germination. We recommend Everwilde Seed, and they carry this species. You can find a link to their Amazon store at our RECOMMENDED PRODUCTS PAGE.

Uses of Smooth Blue Aster

Smooth Blue Aster makes an excellent addition to many different garden settings. The attractive foliage make it a nice addition to a formal flower bed. It’s height also make it a great choice for a wildflower garden, micro-prairie, or border garden.

One thing of note, Smooth Blue Aster can get ‘lost’ amongst taller plants. It does not tolerate aggressive competition from larger species. So, try to ensure it has its own ‘space’.

Smooth Blue Aster (pale blue) with New England Aster (Pink/Purple), Spotted Bee Balm, Late Boneset, and Echinacea purpurea

Companion Plants

For some companion plants that bloom concurrently or overlapping with Smooth Blue Aster, and prefer the same growing conditions, consider the following:

Smooth Blue Aster vs. New England Aster

Asters can get a bit confusing sometimes, as there are just so many different species! But there are probably more similarities with New England Aster than differences, but in the table below I’ve summarized the key facts:

CharacteristicSmooth Blue AsterNew England Aster
Height3′-4′4′-5′
Bloom TimeLate Summer – Early FallLate Summer – Fall
Bloom ColorLight Blue – Light PurpleDark Purple – Pink
Foliage ColorBlueish-GreenGreen

I’ve observed that the blooming period for both Smooth Blue Aster and New England Aster overlap by a few weeks. With Smooth Blue usually starting it’s blooming period 2-3 weeks earlier than New England Aster.

Find more native plants here….

References:

[1] – Elizabeth Pennissi (2001). “Linnaeus’s last stand?”. Science. 291 (5512): 2304–2307. doi:10.1126/science.291.5512.2304. PMID 11269295. S2CID 83724152.

[2] – Sullivan, Symphyotrichum laeve, US Forest Service. 1992. Accessed 29MAR2021. USDA.https://www.fs.fed.us/database/feis/plants/forb/symlae/all.html

[3] – Plants poisonous to dogs. ASPCA. Accessed 29MAR2021. https://www.aspca.org/pet-care/animal-poison-control/dogs-plant-list

Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over six years. I hope to share some of my knowledge with you! Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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