Trial rates catmint cultivars

Nepeta, or catmint, is part of the mint family (Lamiaceae), which includes giant hyssop (Agastache), bee balm (Monarda), lamb’s-ears (Stachys), lavender (Lavandula), rosemary (Rosmarinus) and thyme (Thymus). They share common traits, including bilabiate (two-lipped) flowers, square stems and opposite leaves, which often contain fragrant essential oils. There are approximately 250 species of Nepeta originating in temperate regions of Europe and Asia, with 20 species commonly grown in gardens. Unfortunately, like the neighborhood alley cat, the pedigree of many cultivated catmints is sketchy.

Chicago Botanic Garden evaluated 36 taxa of Nepeta from 1999-2006. Thirty taxa successfully completed a minimum four-year trial, although some taxa were evaluated for the full eight-year period. The goal of the comparative trial was to identify outstanding Nepeta through an assessment of ornamental traits, disease and pest resistance, cultural adaptability and hardiness.

Top-rated catmints

Four catmints received five-star ratings based on heavy flower production, robust plant habits, good health and winter hardiness. In general, the top-rated catmints featured abundant lavender-blue flowers over a protracted period and hoary green leaves. Plant habits were strong throughout the flower period and didn’t require shearing to rejuvenate habits or health.

Lavender-blue-flowered Nepeta ‘Joanna Reed’ was one of the tidiest catmints because its stems did not flop and new growth quickly concealed the declining flower stems. At 24 inches tall and 48 inches wide, ‘Joanna Reed’ is a bushy catmint producing a wealth of flowers from mid-May through October. Billowy ‘Six Hills Giant’ is taller than ‘Joanna Reed’ but exhibited a similarly floriferous and robust habit all summer.

Nepeta x faassenii ‘Select Blue’ is a low-mounded catmint, to 14 inches tall and 30 inches wide, that also remained tight and compact well into the late season. Although its flowers are touted as darker blue than typical Faassen’s catmint, they are in lavender with a dark calyx that gives the inflorescence an overall swarthier complexion.

Nepeta racemosa ‘ Walker’s Low’ lived up to its accolades and was a top performer. A profusion of luminous blue flowers clothed its upright stems beginning in mid-May. ‘ Walker’s Low’ is not as small as its name implies (it’s named for a garden in Ireland) but was comparable in height to ‘Six Hills Giant.’

Performance summary

The catmints in the trial were mainly lavender-blue-flowered, with little difference noted between ‘Dropmore,’ ‘Joanna Reed,’ ‘Kit Cat’ or ‘Blue Wonder.’ Flowers of Nepeta ‘Ice Blue,’ ‘Blue Whisper’ and ‘Blue Ice’ were the palest lavender fading to white, especially in bright sunlight. The purple-blue flowers of N. racemosa were the darkest in the trial, although blue-flowered N. yunnanensis was also quite dark. Some catmints featured flowers accentuated by a darker calyx. The pale-pink flowers of N. grandiflora ‘Dawn to Dusk’ were highlighted by violet calyces, while N. grandiflora ‘Pool Bank’ featured lavender-blue flowers and reddish purple calyces.

Flowers of Nepeta x faassenii, N. grandiflora and N. racemosa, as well as most of the hybrid cultivars, were typically small, between 1/4 inch and 1/2 inch long, although their inflorescences were often up to 12 inches or longer. The larger flowers of N. sibirica (1 1/4 inches long), N. subsessilis (1 inch long), N. ucranica (3/4 inch long) and N. yunnanensis (1 1/4 inches long) were borne in shorter inflorescences, usually to 6 inches long.

The majority of catmints were consistently strong bloomers, often with flower production greater than 80 percent during the peak period, which was usually two to three weeks after the first flowers opened. Distinct bloom periods, marked by a short interval without any flowers present, were occasionally observed. However, it was more common to see flowers blooming continually, albeit at low levels, until the end of the year. Plants were not commonly deadheaded or sheared after flowering.

For ease of comparison, catmints were grouped by foliage color; namely, gray-green or green. Describing the leaf color of Nepeta x faassenii, N. grandiflora and N. racemosa was somewhat subjective and depended on the amount of pubescence, level of sunlight and the size and age of the leaves. In general, most gray-green-leaved taxa were described as dusty green, referring to a medium to light green tinged with gray. When placed side-by-side, the individual leaves of these taxa were similar to or identical in color, although when viewed all together on their respective plants, the foliage appeared slightly more gray- to blue-green. The aromatic leaves of these species were up to 2½ inches long with heart-shaped or truncated leaf bases. Green-leaved species such as N. nervosa, N. sibirica, N. subsessilis and N. yunnanensis had larger leaves, ranging from 3-4 inches long.

Due to the tendency of many catmints to relax after flowering, plant habit rating was based on the habit in the early season, up to and directly following primary bloom. Ratings were not unduly reduced because stems relaxed or flopped after flowering, unless stem regeneration was weak and habit quality did not rebound quickly. Conversely, taxa with stems that flopped consistently before or during the primary bloom period received a lower rating.

The gray-green-leaved catmints typically produced a second flush of new shoots during the primary bloom period, which eventually caused the early-flowering stems to be pushed to the outside of the developing shoots. This occasionally resulted in a temporary flattened appearance until the new growth covered up the older stems. It is not essential that the older stems be cut back at this time, because many catmints are self-rejuvenating and retain robust habits without any maintenance.

Plants were generally left alone to determine how quickly and to what extent plant health and habit quality rebounded following a period of heavy flower production. In most cases, plant health improved on its own within a few weeks after the primary bloom cycle ended. In some cases, plant health declined sharply and was slow to improve without maintenance. The removal of older stems each year quickened recovery and improved the overall ornamental display of Nepeta ‘Blue Whisper,’ N. ‘Dropmore,’ N. ‘Ice Blue’ and N. grandiflora ‘Wild Cat.’ Unfortunately, a few catmints suffered serious decline in health after flowering and did not rebound well, whether left alone or sheared; among this group were N. amethystina ssp. laciniata, N. nervosa, N. nervosa ‘Forncett Select’ and N. yunnanensis. Nepeta yunnanensis was the only taxon with little or no stem regeneration after shearing each summer.

Summary from the trial

In general, the catmints were well-adapted to the growing conditions of the test site and untroubled by diseases or pests.

Overall, the catmints were determined to be winter hardy.

Seven of the 30 taxa that completed the trial received fair or poor ratings based on inferior habits (Nepeta ‘Veluw’s Blauwtje’), low flower production (N.grandiflora ‘Dawn to Dusk’), severe foliar chlorosis (N. subsessilis var. sensibilis) and/or winter injury (N. grandiflora ‘Dawn to Dusk’ and N. yunnanensis). Nepeta amethystina ssp. laciniata, N. nervosa and N. nervosa ‘Forncett Select’ suffered from a general lack of health and vigor throughout the trial, as well as plant losses in successive winters.

Award-winning ‘ Walker’s Low’ is just one of many outstanding catmints that received top performance ratings. Twenty-two of the 30 catmints that completed the trial were rated highly for heavy flower production, robust plant habits, good health and winter hardiness. In addition to ‘ Walker’s Low’, ‘Joanna Reed’, ‘Six Hills Giant’ and ‘Select Blue’ took top honors.

Catmint qualities

Flowers. Catmint flowers are clustered in many-flowered verticillasters (false whorls) above the foliage. Flower color ranges from purple-blue to lavender and white, although Nepeta govaniana has yellow blossoms. Catmints have a long flower period, beginning in late spring to early summer and continuing well into late summer and fall.

Foliage. Many common catmints have pubescent, grayish-green leaves, although a number of less-familiar species have green leaves. Catmints generally have bushy habits with shoots emerging early in the spring and quickly developing into sizeable mounds. The leaves and stems of many catmints contain nepetalactone, an essential oil which, when vaporized, triggers a variety of behavioral responses in cats. The narcotic effect of catmint affects cats differently, causing them to become mellow, frisky or aggressive.

Growing conditions. Catmints prefer to grow in full sun and well-drained soils. They may be drought-tolerant once established. In contrast, Nepeta subsessilis is adaptable to partial shade and prefers moist soils. Catmints are rarely troubled by diseases or pests, but their health and vigor will quickly decline in poorly drained soils. Fertilizer is unnecessary and encourages floppy stems.

Uses. Catmints are free-flowering, easy-care perennials combining handsome foliage with an exuberant floral display. Their adaptability to average gardens as well as droughty conditions attests to their landscape versatility. Whether in a public parkway or garden border, their vivid-blue flowers over many weeks in summertime are an incomparable sight.

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- Richard G. Hawke

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