White wood aster Eurybia divaricata is a perennial that produces small, white daisy-like flowers that bloom in late summer to early fall. Perfect for a natural garden, it attracts butterflies and is deer-resistant. Will grow to 61 to 91 cm tall in partial to full shade and tolerates average to dry soil.
I. Appearance and CharacteristicsÂ
Eurybia divaricata (syn. Aster divaricatus), the white wood aster, is an herbaceous plant native to eastern North America. It occurs in the eastern United States, primarily in the Appalachian Mountains, though it is also present in southeastern Canada, but only in about 25 populations in the provinces of Ontario and Quebec. In the U.S. it is abundant and common, but in Canada it is considered threatened due to its restricted distribution. It has been introduced to a number of countries in Europe. It can be found in dry open woods as well as along wood-edges and clearings.Â
Eurybia divaricata is a late summer to fall-flowering herbaceous perennial, typically growing to heights between 30 and 90 cm, though some specimens may be up to 1.2 m (3.9 ft) tall. The plant emerges each year from rhizomes and forms dense colonies of clones that lack sterile rosettes. The rhizomes are branched, elongated and become woody with age. One simple erect stem is present per plant. It is flexible and nearly hairless to finely hairy near the base, though densely covered with fine hair towards the extremities. It is very similar to and often confused with E. chlorolepis, E. schreberi and Symphyotrichum cordifolium, though E. schreberi differs in having wider leaves with more teeth, while E. chlorolepis has more rays, longer involucres, and only occurs in the southern U.S. from Virginia to Georgia.
Three types of leaves with differing morphology are present: cauline leaves, or those that appear on the stem from the middle of the plant upwards; basal leaves, or those that are present at the base of the plant; and distal leaves, which are those found on the extremities of the plant. All types are thin and sharply serrated with 6 to 15 pointed teeth per side. They are ciliate, meaning they have small hairy projections emerging from the margins of the leaf, while the apices, or tips of the leaves, are acuminate, meaning they taper to a point. The adaxial (i.e. upper) surfaces of the leaves are nearly hairless or sparsely hairy, while the abaxial (i.e. lower) surfaces are sparsely hairy with the veins being more villous, or covered in shaggy hairs.
The basal leaves are ovate, or egg-shaped, with bases that are cordate, or heart-shaped. The blades measure 1.9 to 6.5 cm in length by 1.7 to 6 cm (0.67 to 2.36 in) in width and have petioles ranging in length from 2 to 7 cm. They wither when the plant flowers. The cauline leaves have petioles measuring 2.5 to 7 mm (0.098 to 0.276 in) long that are often winged. Their blades are also ovate, though the bases may be cordate to rounded. They measure 2 to 20 cm (1 to 8 in) long by 1 to 10 cm (0.5 to 4 in) wide, making them often much longer than the basal leaves. The distal leaves are typically sessile, meaning that no petiole is present, though they are sometimes sub petiolate, meaning a very short petiole is present. The blades are ovate to lanceolate, meaning lance-shaped, with rounded bases and are 0.5 to 2 cm (0.20 to 0.79 in) long by 0.1 to 0.8 cm (0.039 to 0.315 in) wide.
The capitula, or flower heads, are arranged in relatively flat-topped corymbiform arrays. The capital number is anywhere from 4 to 50 and up to 100 or more in exceptional cases. The peduncles, i.e. the flower stalks, are up to 1.5 cm (0.59 in) in length and are densely covered with non-glandular hairs. Bracts, modified leaves that appear at the axil of a peduncle, are typically absent, though in some cases up to two are present. The involucres, which are the whorls of small, scale-like modified leaves that appear at the base of the capitulum, are in between cylindrical and campanulate (i.e. bell-shaped) in shape and measure 4.2 to 6 mm (0.17 to 0.24 in) long, making them much shorter than the pappi.
The phyllaries, which are the small leaves that make up the involucre, number from 25 to 30 and are arranged in 4 to 5 series. The inner phyllaries are between linear and lanceolate in shape with a purplish colouration towards the apices, while the outer ones are more oblong. All of the phyllaries are strongly unequal with hardened bases, margins that are somewhat scarious (i.e. thin, membranous and dry) as well as fimbriate-ciliate, meaning fringed with hair at the margins. Their apices are rounded to acute in shape, while the surfaces are sparsely haired, though sometimes sparsely covered in stipular glands. Their chlorophyllous zones, a darker green zone where chlorophyll is concentrated, appear on the upper half of the outer phyllaries, to the upper third or along the outer mid veins of the inner phyllaries. The outer phyllaries typically measure 0.7 to 1.5 mm (0.028 to 0.059 in) wide with the lengths rarely exceeding 2.5 times the width.
As with most members of the family Asteraceae, the actual flowers appear in two different forms: as ray florets, which have strap-like appendages that look like petals and project around the outside of the capitulum, and as disc florets, which appear at the center of the flower head and are very small. The ray florets number between 5 and 10, though as many as 12 may be present. Their straps are white and measure 6 to 12 mm long by 1.5 to 2.2 mm wide. The disc florets number from 12 to 19 and up to 25 and have yellow corollas (i.e. petals, though they are fused into a tube) that are 4.1 to 4.8 and exceptionally 5.5 mm long. Their corollas are abruptly ampliate, or enlarged, with tubes that are longer than their campanulate throats. The tubes measure 2.3 to 2.6 mm while the throats are typically only 0.9 to 1.2 mm long. The lobes, i.e. the friges of the throat, are reflexed and lanceolate in shape, measuring 0.7 to 1.4 mm.
The fruit are cypselae, a type of achene, which are brown in colour, slightly compressed and are between cylindric and obovoid, or inversely egg-shaped. They are between 2.6 and 3.8 mm (0.10 and 0.15 in) in length and sparsely strigillose, or set with stiff bristly hairs, with 7 to 10 ribs, which themselves are tan to stramineous (i.e. straw-coloured). The pappi, which are modified sepals, are made up of reddish to cream-coloured bristles that are 3.7 to 5 mm (0.15 to 0.20 in) long, making them equal to or longer than the disc corollas in length. The bristles are fine and barbellulate, or barb-like, though they may be sometimes more or less clavate, or club-shaped, towards their apices.
II. How to Grow and Care
Sunlight and Soil
The best location for E. divaricata is a partially to fully shaded area with average soil and a neutral to slightly acidic pH of 6.8 to 7.2.
The drainage should be excellent, as standing water invites pests and fungal diseases and may result in rotting.
Watering
White wood aster may be a drought-tolerant plant but appreciates weekly watering. Keep the soil moist until blooms stop appearing. First-year plants require about 1 inch of water a week. Water the base of the plant and avoid wetting the foliage and overwatering to avoid mildew and fungal growth. Wilting is a good indicator of overwatering.
Fertilizing
It is best to add fertilizer to your white wood aster once in the spring before the growing season. This can be done by incorporating a balanced, slow-release, or granular solution into the soil followed by a saturating watering. Another option would be to rake organic compost into the soil.
Pruning and Maintenance
Trimming the foliage by up to one-third in early summer promotes more compact, less leggy growth for a more uniform, mounded appearance at bloom time with less need for staking.
Even without early pruning, E. divaricata is less likely to require staking than other aster species.
Additional maintenance includes removing broken, diseased, or pest-infested foliage as needed, cutting all stems to the ground at season’s end, and discarding cut stems to deprive rodents and other pests of shelter during and after the growing season.
In the spring, apply an all-purpose, slow-release, granular fertilizer to support a healthy start to the season.
Propagation
For nursery plants, seedlings, and rooted soft stem cuttings, note the depth they sit in their containers, and set them at the same depth in the garden soil when they’re ready to transplant. For divisions, replicate their depth in the ground before you dug them up.
Allow 18 to 30 inches between plants.
Tamp soil firmly around the stems. Water and tamp again to squelch air pockets.
Apply a slow-release, granular, all-purpose fertilizer around the stems. Don’t let the product touch any plant tissue, as it may burn.
If planting seeds, moisten the soil lightly, and scatter several seeds at intervals of 15 to 18 inches.
Once they have two sets of true leaves, you can thin seedlings to intervals of 18 to 30 inches and apply a slow-release fertilizer to damp soil, as we did above.
Maintain even moisture, about an inch of water per week, including rain, to establish healthy roots without oversaturation.
Weed Control
Pests and Diseases
White wood asters are not prone to pests or diseases.
However, as shade plants, they may become vulnerable to both when plants are too close together and/or drainage is poor.
Slugs and snails are drawn to dark, moist foliage and may chew voraciously, leaving telltale holes or consuming entire leaves.
And fungal conditions, like fusarium wilt and powdery mildew, may proliferate on perpetually wet surfaces.
Advanced fungal disease may lead to rotting and plant death.
III. Uses and BenefitsÂ
The best way to showcase this large, bushy perennial with many tiny florets is to plant it en masse as a filler in the understory of naturalistic woodland settings.
Consider including specimen plantings in existing butterfly, native plant, and shade gardens where it can pair with flowering plants with similar cultural requirements.
Additional practical and attractive uses include scattering seeds to naturalize randomly in woodland settings, especially where erosion is problematic or along perimeters, for an informal herbaceous late summer to fall privacy hedge and wildlife habitat.