Trial rates Shasta daisy cultivars

Shasta daisy (Leucanthemum x superbum) is prized for the simplicity of its bright-white, yellow-eyed flowers and its long flower season. Its quiet charm allures gardeners and nongardeners alike -- perhaps due to nostalgia for summers past, memories of a hopeful game of “loves me, love me not” or simply the cheery blossoms that shine in the summer garden. Cultivars introduced in recent years have surpassed many of the earliest ones, ensuring a place in contemporary gardens for the venerable Shasta daisy.

The trial

The Chicago Botanic Garden (USDA Hardiness Zone 5b, AHS Plant Heat-Zone 5) evaluated 36 cultivars of Leucanthemum x superbum and L. vulgare between 1999 and 2006. The goal of the comparative trial was to identify outstanding Leucanthemum for Northern gardens. Twenty-seven taxa completed a minimum four-year trial, although some were evaluated longer.

Eight plants of each taxon were grown in side-by-side plots for easy comparison. The evaluation site received approximately 10 hours of full sun during the growing season and was openly exposed to wind. The well-drained, clay-loam soil was amended with composted leaves and had a pH of 7.4 throughout the evaluation term.

Maintenance practices were kept to a minimum to simulate home garden culture. Water was provided as needed, and no fertilizer was applied. Plants were routinely cut back each year between late August to rejuvenate foliage and improve plant health before the end of the growing season. Mulch consisting of shredded leaves and wood chips was placed around the plants for water conservation and weed suppression; no winter mulch was used.

The taxa in the comparative trial were evaluated for ornamental traits; cultural adaptability to the soil and environmental conditions of the test site; disease and pest problems; and winter hardiness. Final ratings are based on floral display (flower production and duration of bloom); plant health and vigor; habit quality; disease and pest problems; and winter injury. Plant traits and overall ratings for the 27 taxa that completed the trial are noted in the table, which can be found in PDF form here.

Nine cultivars of Leucanthemum x superbum are not included in the results because they either did not finish a four-year trial or are synonyms of other cultivars.

Top-rated daisies

Leucanthemum ×superbum ‘Amelia,’ L. x superbum ‘Becky,’ L. vulgare ‘Filigran’ and L. vulgare ‘Maikönigin’ received five-star excellent ratings. Plants were consistently healthy with heavy flower production and robust habits throughout the evaluation period.

‘Amelia,’ a seed cultivar donated by Jelitto Perennial Seeds, had strong stems, a robust habit and 5-inch blossoms -- the largest flowers in the trial. Variability in plant height within the test group was not unexpected given the fact that ‘Amelia’ was grown from seed.

On the other hand, ‘Becky’ exhibited a uniform habit with sturdy stems to 40 inches tall and an abundance of 3 1/2-inch flowers from July to September. ‘Becky’ was named the 2003 Perennial Plant of the Year by the Perennial Plant Association.

Leucanthemum vulgare ‘Filigran’ and ‘Maikönigin’ (‘May Queen’) were comparable in habit and floral display but were not the same size. ‘Filigran’ featured single, 2-inch-wide flowers on stems to 26 inches tall; whereas, the larger ‘Maikönigin’ had single, 3-inch flowers on stems to 36 inches tall. Both cultivars began blooming in May, but ‘Filigran’ typically bloomed two weeks earlier.

Performance summary

Shasta daisies are generally strong bloomers over a long period. The majority of taxa exhibited excellent (80-100 percent) to good (60-80 percent) flower production at peak bloom, roughly three to four weeks after the first flowers opened. The high levels of flower production were often maintained for several weeks following peak bloom, eventually tapering off to sporadic bloom up to the end of the flowering period.

Bloom dates were fairly consistent over the course of the evaluation period, except in 2004 when a number of Leucanthemum ×superbum cultivars flowered two to three weeks earlier. Temperatures above 90°F in early June likely contributed to the precocious bloom dates.

All taxa in the trial had white ray florets, with the exception of ‘Cobham Gold’ and ‘Sonnenschein,’ which had creamy to light-yellow rays. Flowers were predominantly single, although flower forms ranged from crested to semi-double to fully double.

Erect stems and robust plant habits during the bloom period were commonly observed for the majority of taxa. No taxon seemed predisposed to floppiness, but weak or lodged stems were sometimes noted. Periodically, strong wind and heavy rainfall caused stems to flop or to be beaten down during the storm.

Few taxa displayed exceptional uniformity within their test groups. ‘Aglaia,’ ‘Becky,’ ‘Filigran,’ ‘Maikönigin,’ ‘Rijnsburg Glory,’ ‘ Switzerland’ and ‘Wirral Pride’ had reliably full habits with all stems the same height.

Daisy basics include white flowers

Leucanthemum x superbum, a reputed hybrid between L. lacustre and L. maximum, was introduced by Luther Burbank in 1901, and named Shasta daisy for the snowy peaks of Mount Shasta in Northern California.

Surprisingly, given the simple nature of Shasta daisy, the RHS Plant Finder lists 69 cultivars, representing a variety of single- to double-flowered forms. While the parents of Shasta daisy are native to Europe, L. vulgare, oxeye daisy, is a ubiquitous native of temperate Eurasia that has naturalized in fields and roadsides in North America.

Like many members of the Asteraceae family, Leucanthemum flowers are comprised of petallike ray florets and tube-shaped disc florets. In the case of L. x superbum, the showy rays are typically white. The yellow disc florets, which make up the eye of the flower, are encircled by the prominent ray florets. Floral habits vary from the classic daisy form (single row of rays) to crested or anemone-centered (perimeter disc florets are petallike and center disc florets remain yellow) to double-flowered (disc florets resemble the color and form of ray florets).

Flowers may also be frilly double, marked by a profusion of narrow rays that give the blossoms a shaggy appearance. Flowers range from 2-5 inches in diameter and are produced from late spring throughout summer.

Leucanthemum vulgare, oxeye daisy, is similar in general appearance to Shasta daisy. The white and yellow flowers are typically smaller, 1-3 1/2 inches wide, and bloom up to four weeks earlier. Oxeye daisy is readily available to gardeners and frequently confused with Shasta daisy. Both species self-sow in the garden, although oxeye daisy is particularly fruitful.

Growing conditions

Shasta daisies prefer fertile, well-drained soils in full sun and are intolerant of wet or poorly drained soils at any time. Crown rot will likely occur under heavy winter mulch. A loose covering of conifer boughs, pine needles or whole leaves applied after the ground is frozen will protect the semievergreen crowns without smothering them.

Shasta daisies are generally hardy in USDA Hardiness Zones 5-8. Since Shasta daisies are often short-lived perennials, dividing the clumps every few years will keep plants robust and may increase their life span.

They benefit from regular deadheading to prolong flowering and to reduce reseeding. Taller selections may need to be staked to prevent floppiness. Shasta daisies can be troubled by aphids, spider mites and verticillium wilt caused by poorly drained soils.

- Richard G. Hawke

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Richard G. Hawke is plant evaluation manager, Chicago Botanic Garden, (847) 835-5440; www.chicagobotanic.org.

June 2008