January 2007 Culture

Nepeta x faassenii ‘Walker’s Low’ By Paul Pilon

With its aromatic, silver-green foliage and impressive, long-lasting display of lavender-blue flowers throughout the summer months, it's no wonder that nepeta 'Walker's Low' has caught the attention of gardeners, landscapers and perennial enthusiasts everywhere. With its ease of production and great landscape appeal, Nepeta x faassenii 'Walker's Low' has been named the 2007 Perennial Plant of the Year by the Perennial Plant Association.

'Walker's Low', contrary to its name, is not a dwarf cultivar and commonly grows 24-36 inches high and spreads 24-36 inches across. From late May until frost, it bears numerous, soft lavender-blue flowers on long, arching, aromatic, gray-green stems. With its arching habit, the actual height in the landscape is typically 18-24 inches. The flowering season can be extended or renewed by trimming the plants back by one-half to two-thirds when the initial flush of flowers begins to fade.

Nepeta 'Walker's Low' is commonly produced throughout USDA Hardiness Zones 3-8 and AHS Heat Zones 9-1. It thrives in sunny locations with dry soils and, once established, is considered to be drought tolerant. Nepeta is intolerant of the heat and humidity of the Deep South and requires afternoon shade in these hot climates.

In the landscape, nepeta, also known as catmint, is an easy-to-grow, versatile perennial that performs best in full sun where it attracts bees, butterflies and birds when blooming. Nepeta is considered to be resistant to deer and rabbit feeding, which is an additional selling point for gardeners. 'Walker's Low' is commonly used in flower borders, as a tall edging or groundcover, in herb gardens or container plantings. Propagation

'Walker's Low' is vegetatively propagated by tip cuttings or divisions. Propagation of tip cuttings usually occurs during the spring and summer months. Cuttings that are in bloom will root successfully, but they will take longer and have a lower survival rate than purely vegetative starting materials.

Nepeta roots readily with or without the use of rooting compounds. The cuttings tend to root slightly faster and more uniformly when rooting hormones, such as IBA, are used. After sticking, the cuttings should be placed under low misting regimes for the first 7-10 days of propagation. Misting can gradually be reduced as the cuttings form calluses and root primordia. They are generally well rooted in 3-4 weeks, provided the soil temperatures are maintained at 70-74¡ F. It is beneficial to begin feeding using 150-ppm nitrogen with each irrigation beginning 10 days from sticking.

Production

'Walker's Low' is commonly produced in 1-qt. or larger containers with a single liner planted in the center of each pot. Catmint performs best in well-drained media with a pH between 6.0 and 6.6. At time of transplanting, the soil line of the liner should be even with the growing medium of the container it is transplanted into. When produced in containers, 'Walker's Low' requires an average or moderate irrigation regime. When watering is necessary, water pots thoroughly and let plants dry out slightly between irrigations.

'Walker's Low' are light to moderate feeders requiring only modest amounts of fertility. Generally, when planting nepeta, I recommend incorporating a controlled-release fertilizer into the growing media at a rate equivalent to 1 lb. of elemental nitrogen per yard of growing medium. Another method to deliver fertility to this crop would be using a constant liquid fertilizer program, delivering 100- to 150-ppm nitrates to the crop at each watering. Plants grown under high fertility regimes generally will become very lush and may take longer to flower.

With its growth habit, it is often necessary to manage plant height during production. Pro-viding adequate spacing between the plants will reduce plant stretch caused by competition. If additional height control is necessary, several of the commercially available PGRs are effective at controlling plant height when they are applied using the appropriate rates, frequency and timing. In the northern parts of the country, I recommend applying 2-3 spray applications of Bonzi, Paczol or Piccolo (paclobutrazol) at 30 ppm or Concise or Sumagic (uniconazole) at 5 ppm at 7-10 day intervals beginning when the plants are 4-6 inches high.

Pests And Diseases

The presence of insects on nepeta is not uncommon but rarely do they become problematic. The most common insects that feed on catmint include aphids, leafhoppers, slugs, snails, spider mites and whiteflies. Routine scouting will allow for early detection of these pests and can be useful to determine if control strategies are necessary.

There are relatively few diseases affecting the production of nepeta, and seldom does significant plant injury or loss occur. Crown and root rots are likely to occur when plants are produced under wet growing conditions. In situations where there is a dense plant canopy with little air movement, Botrytis infestations in the foliage are likely to appear when water is allowed to remain on the leaves for long durations. In southern climates where the conditions are often hot and humid, growers have observed the presence of the bacterial pathogen Pseudomonas. When the conditions are optimum for bacterial infestations, preventative applications of copper-based fungicides such as Phyton 27 or Camelot (copper sulfate) may be helpful. Carefully discard all infected plants to prevent the spread of Pseudomonas, as bacterial diseases cannot be controlled using fungicides. Forcing Nepeta 'Walker's Low' can be easily forced into bloom throughout the growing season provided a few guidelines are followed. Nepeta do not require cold (vernalization) for flowering but are classified as cold-beneficial plants. Providing a cold treatment to plugs or small containers for 6-9 weeks at 40¡ F will enhance uniformity and reduce the time it takes to reach flowering.

'Walker's Low' is an obligate long-day plant and will not flower when grown under short photoperiods. Growers can provide long days using either day-length extension or night interruption lighting during the middle of the night (10 p.m. to 2 a.m.), providing a minimum of 10 foot-candles of light at plant level. After long days are provided, the time it takes to reach flowering is a function of temperature. Plants grown at 64¡ F will flower in about seven weeks, while plants grown at 68¡ F will flower in as little as five weeks.

Availability

Nepeta x faassenii 'Walker's Low' is widely produced and readily available to the industry as unrooted cuttings, rooted liners and finished containers. Many plant brokers will be able to help you locate this variety in its various forms and sizes.