Asters, perennial

Native asters provide fall food for pollinators

Asters are fall blooming perennials that can add last minute color to flower beds and borders.  Perennial asters are easier to grow than mums are and more likely to survive the winter even when planted in full bloom in the fall.  There are dozens of varieties of asters and there is sure to be a color and form of aster that will suit any garden.

Aster comes from the Greek word for star, and our wild asters may seem as numerous as stars sparkling across a dry meadow in the fall.  Native asters are often tall; they have struggled up through tall grass and weeds to the sunlight.  They throw their froth of small daisy like flowers out above the brush and sprinkle them through the weeds.   Many cultivated asters have been developed from the natives that are more compact, have a mounding habit and larger flowers.  

Native aster species are wonderful for naturalized gardens and attract butterflies and bees and people sometimes move native asters to flower borders and butterfly gardens. (Take only plants from your own property or from areas where you have permission to dig the plants.) Individual native plants have different growth habits so choose carefully.  It might be best to choose the plant in the fall when it is in bloom, mark the plant, and return in the spring to transplant it, as wild asters seem to establish better when moved in the spring.

 Compact varieties of asters are excellent for fall containers.  Some asters can be used as ground covers.  Asters make good, long lasting cut flowers and also dry well. 

Growing asters

Almost all asters are upright plants with thick woody stems and long narrow leaves. There are some that hug the ground and one that is a climbing vine.  Aster flowers are small, 1-2 inches across, and daisy like.  They come in all shades of blue, purple, white, pink and red.  While the centers are often yellow, there are no yellow or orange perennial asters yet. Asters begin blooming in late summer and usually continue blooming until a hard freeze kills them.

Perennial asters are hardy from zone 3-9.   Asters tolerate a wide range of soils.  They will do well in dry areas but will also do fine in well-watered sites.  Most asters prefer full sun; some will tolerate light shade.  Unless your soil is extremely poor, native species of asters do not need fertilization.  Some of the cultivated varieties may bloom heavier if they are fertilized in the early spring with a timed-release fertilizer for flowers.

‘Alma Potschke’

You can start asters from seed but most gardeners will want to start with plants.  Potted asters can be planted in the garden from early spring to about 6 weeks before the ground freezes.  If you start with seeds you can sow the seed where you want the plants to grow or for best results, you can start the seed indoors 6-8 weeks before your last frost and transplant outside.  

Space asters from 1 to 3 foot apart, depending on the variety.  Asters form large clumps and need to be divided every 3 years or so.  Simply dig up the clump in the early spring and separate it into 2 or 3 parts, which you can then re- plant.   

If you want dense rounded clumps of asters and abundant flowers, pinch your aster plant back by about 6 inches at the beginning of July.  Take your fingers and “pinch” the stem off just before a set of leaves.  Don’t pinch asters after July 15.   If you don’t pinch your asters they will be taller and the display will be airy and lighter.  In the fall after a hard freeze has killed the plants, asters may be cut off to ground level.

Asters are prone to powdery mildew, a fungus disease that makes the leaves first get a white, powdery coating, then turn brown and fall off.  You can use a flower fungicide to prevent the disease, applying it from about July 1 through the blooming season.  Provide good ventilation by not crowding the plants and don’t keep asters overly moist.

Some aster varieties

The native New England Aster has lovely blue-purple flowers and cultivated varieties of this native include ‘Purple Dome’ - deeper purple flowers on a rounded, compact plant, and ‘Alma Potschke’ - rosy pink flowers.  

‘White Wood Aster’ is a native species that has loads of tiny white flowers with purple centers.  It will tolerate light shade.  ‘Silky Aster’ is a native that has silvery gray leaves and rose-violet flowers.

White Heath aster, a common wildflower

Other cultivated asters include ‘Lady in Black’ which has deep purple foliage and hundred of tiny white daisies with pink centers. ‘Wonder of Staffa’ has lavender flowers that begin in late June and keep blooming until frost.  ‘Pink Star’ is a 2 foot mounded aster smothered with small, soft pink flowers. 

Odd asters include the native climbing aster, Carolina aster, which is hardy only to zone 7.  It has light pink flowers with a light pleasant scent.  ‘Nanus’ is a tiny plant, 12 inches high, with shiny green leaves and sky blue flowers. ‘October Skies’ is a bright blue flowered plant only 18 inches high and excellent as a groundcover and ‘Alert‘ is a dwarf aster with red flowers. 

 Asters are great plants for fall color in the garden and since they survive dry conditions well are great for areas where water use is restricted.  They provide food for butterflies and bees when little else is available.  They deserve to be planted in the garden much more frequently than they are.

Stiff Asters, another wildflower.