Aesculus parviflora Walt.

In the woody plant identification courses at the University of Illinois, students are usually unimpressed when they first learn about bottlebrush buckeyes. The dark green, relatively boring leaves mounded over an oval habit, giving way to coarse, lanky stalks in winter with dried flower stalks atop don't help much. They come to know the plant as a diminutive member of the horsechestnut family with opposite palmately compound leaves and large buds bearing waxy white residue which unfortunately reminds them of bird droppings.

Late summer is a time of reckoning, however. As the students leave for summer internships or full-time jobs, they often get a first-hand opportunity to see a specimen in full bloom. Large, upright feathery plumes borne atop the rich, dark green color appreciated by so many gardeners are compelling arguments, strong enough to convince even the most skeptical. But if that weren't enough, the uniformity of the broad-rounded habit, lending itself to tremendous mass plantings and its ability to thrive in sun or shade remove any last shreds of doubt.

Foliage:

Easy to identify, the palmately compound leaves are composed of 5, or occasionally up to 7, leaflets which in combination produce an umbrella-like effect. The leaflets are 3 to 8 inches in length with short petiolules, obovate to oblong in shape and with finely round-toothed margins. The leaves are dark green above and have rounded-cuneate bases and acuminate apices.

Flowers:

Prized for their mid-summer displays, the brush-like white flowers stand out in any garden. The small, individual 1/2" diameter flowers are 4-petaled and tubular with long thin white filaments extending for more than an inch from the petals. The presence of small red anthers adds a faint touch of pink to the overall display. On most specimens, the flowers are borne in erect terminal panicles held above the nicely contrasting dark green foliage. Panicles on var. serotina tend to droop because of their greater length (12 - 18+"), and are borne 2 to 3 weeks later than the species. A specimen of the variety serotina at the Missouri Botanic Garden resembles a large shaggy white dog when it is in flower in mid-July. Although the panicles are significantly longer on this variety, I personally feel the drooping tendency of the flowers makes it much less attractive than the upright panicles of the species. The cultivar 'Rogers' was selected from this variety for long drooping panicles that range from 18 to 30" in length.

Fruit:

Although looking more like a nut than anything else, the fruits of Aesculus species are classified as capsules. Within these capsules, only one seed develops to full size while the others remain much smaller or undeveloped. The tan-brown colored capsules are pear-shaped, smooth, 1 - 2" in length and are borne in early fall. They provide little ornamental contribution to the plant.

Fall Color:

Variable in its effect, the fall color on this species is sometimes an ineffective yellow-green. However, it does have the potential to become a clear, bright yellow or a yellowish bronze.

Pathology:

This is generally a very trouble-free species the leaves of bottlebrush buckeye are usually free of the leaf blotch and leaf scorch problems associated with some of the other buckeyes. I have experienced young plant loss due to a wilt disease which may have been Verticillium wilt (unconfirmed). Established plantings are usually not troubled by serious problems.

Propagation:

Seed needs to be collected in fall before drying or becoming squirrel chow. The capsules can only be allowed to dry slightly without losing viability. After the husks are removed, they should be stratified in moist sand for about 2 months. This species can also be propagated by root cuttings; pieces of root several inches in length can be dug in late fall. When placed in sand under cool conditions, shoots should be produced by spring. Softwood cuttings collected in May and treated with 1000 ppm of IBA will root fairly readily under mist (Burd and Dirr, 1977).

Comments:

This is a handsome shrub with an attractive broad-rounded habit, interesting dark green foliage and wonderful flowers. It is available in balled and burlapped and container forms and should be transplanted into acid to neutral soils with average soil moisture. It adapts to a range of light conditions ranging from full sun to moderate shade. It does not require pruning to maintain its uniform habit, although it tolerates rejuvenation through cutting back to several inches above the ground. The suckering nature of the species will allow it to gradually spread into adjacent areas, although the plant is not aggressive enough to be considered invasive.

Suggested uses:

The ability of this species to tolerate either sun or shade makes it a useful landscape plant in many sites. I have seen it grown quite effectively under the shade of large oak trees or in the open full-sun heat of the South. Plants tend to broaden with time as they sucker and mass together extremely uniformly. The potential size of this plant may limit you to a single plant in smaller yards, but its full beauty is best seen in larger sites. It makes an eye-catching specimen as a result of its mid-summer flowering. Even without flowers the interesting foliage and broad rounded habit of this shrub are appealing. It can make an effective summer screen due to its size. The dark green foliage color makes a nice background for perennial and annual flower beds. Beautiful specimens can be observed at Bernheim Forest, Kew Gardens, and Missouri Botanical Gardens.

Companion plants:

Aesculus octandra, Dirca palustris, Euonymus americanus, Fagus grandifolia, Hamamelis virginiana, Hydrangea arborescens, Liriodendron tulipifera, Magnolia acuminata, Stewartia ovata.

Medicinal uses:

The species has no significant medicinal uses.

References:

• Bailey Hortorium. Hortus III. New York: Macmillan, 1976.
• Burd, Susan and Michael Dirr. 1977. The Plant Propagator 23(4):6-7.
• Dirr, Michael. Manual of Woody Landscape Plants. Champaign: Stipes Publishing, 1990.
• Dirr, Michael and Charles Heuser, Jr. The Reference Manual of Woody Plant Propagation: From Seed to Tissue Culture. Athens: Varsity Press, 1987.
• Hightshoe, Gary L. Native Trees, Shrubs, and Vines for Urban and Rural America. New York: Van Nostrand Reinhold, 1988.
• Johnson, Warren T. and Howard H. Lyon. Insects That Feed on Trees and Shrubs. Ithica: Cornell University, 1994.
• Krussmann, Gerd. Manual of Cultivated Broad-Leaved Trees & Shrubs, vol. I. Beaverton: Timber Press, 1976.
• Poor, Janet Meakin and Nancy Peterson Brewster. Plants That Merit Attention, Vol. II: Shrubs. Portland: Timber Press, 1996.
• Rehder, Alfred. Manual of Cultivated Trees and Shrubs. New York: MacMillan Publishing.
• Sinclair, Wayne A. et al. Diseases of Trees and Shrubs. Ithica: Cornell University, 1993.
• Wyman, Donald. Wyman's Gardening Encyclopedia. New York: MacMillan, 1986.