June 2011 Culture

Perennial Solutions: Perovskia atriplicifolia ‘Lacey Blue’ By Paul Pilon

Ever since the Perennial Plant Association selected Perovskia atriplicifolia as the 1995 Perennial Plant of the Year, Russian sage has become a staple item in perennial programs and landscapes across the country. This long-lived perennial has silver stems, grayish foliage, and produces small light blue to lavender flowers in the mid summer. With these landscape attributes, perovskia is a reliable and highly valued landscape perennial.

Historically, there have been relatively few named cultivars introduced and grown by commercial growers; in fact, the straight species P. atriplicifolia is more widely grown than any named cultivar to date. However, due to efforts in plant selection, new cultivars are being discovered. 'Lacey Blue' is a recent discovery of Peter Catt from Liss Forest Nurseries Ltd. from the U.K. This cultivar has many desirable attributes sought by commercial growers and landscapers and is sure to bring new excitement to an already popular and reliable genus.

'Lacey Blue' forms compact 18- to 20-inch, bushy mounds with fragrant grey-green foliage. It is a profuse bloomer, setting masses of blue-purple flowers from mid-summer and into the fall. Its compact size does not jeopardize the quality of the plant in bloom; in fact, 'Lacey Blue' has the largest flowers of any Russian sage in production today.

Perovskia 'Lacey Blue' has outstanding garden performance and grows well in sunny locations throughout USDA Hardiness Zones 4 to 9. Russian sage is commonly used in containers, as border and mass plantings, and as cut or dried flowers. Additionally, perovskia are drought tolerant, attract hummingbirds into the garden and are resistant to deer feeding. With these attributes, uses and ease of production, 'Lacey Blue' will make an excellent addition to most perennial programs.

Propagation

Perovskia 'Lacey Blue' is vegetatively propagated using tip cuttings. Since a plant patent is being sought (PPAF-Plant Patent Applied For), unlicensed propagation of this cultivar is prohibited.

Cuttings can be successfully rooted by sticking them directly into liner trays containing a pre-moistened, well-drained growing medium. Rooting compounds are not necessary as perovskia will root well without them. Russian sage prefers to be propagated using high humidity over misting. Place the cuttings under a low misting regime for about the first week of propagation and gradually decrease the misting provided over time. Begin feeding with 150-ppm nitrogen weekly using complete water-soluble fertilizer as the cuttings begin to develop roots (usually between 10 and 14 days). The average rooting time is four to five weeks with soil temperatures ranging from 68 to 74¡ F.

Production

Perovskia 'Lacey Blue' is suitable for 1-quart to 1-gallon containers. When spring planting large containers, such as 1-gallon pots, I recommend planting at least two liners per container (depending on the size of the pot) to properly fill out the pot for same year sales; fewer liners per pot is often sufficient when planting in the late summer the year before the containers are to be sold.

Russian sage performs best when they are grown in a moist, well-drained medium with a slightly acidic pH: 5.8-6.5. Most commercially available peat or bark based growing mixes work well, provided there is adequate drainage. When planting, the liners should be planted so the original soil line of the plug is even with the surface of the growing medium of the new container. The best quality is achieved when plants are grown in full sun or in greenhouses with high light intensities (greater than 4,000 foot-candles).

Pinching is not usually required, but in some instances may be helpful to increase lateral branching, plant fullness and increase the total number of flowers produced on each plant. This is generally a soft pinch, only removing the growing point of the plant, and should leave at least four to six leaves (nodes) on each stem.

Perovskia require average to slightly below average amounts of irrigation. Avoid overly wet growing conditions as delayed growth, root rots and plant mortality could result. When irrigation is necessary, water them thoroughly and allow the soil to dry moderately between irrigations.

Russian sage requires moderate amounts of plant nutrients. Growers often apply water-soluble fertilizers using 150- to 200-ppm nitrogen as needed or constant liquid fertilization at 75- to 100-ppm nitrogen with each irrigation. Controlled-release fertilizers are commonly used by incorporating 0.9 to 1.2 pounds of elemental nitrogen per cubic yard of growing mix prior to potting.

With its compact growing habit, 'Lacey Blue' usually does not require height control. Plant height can be effectively controlled with water management, avoiding high nutrient levels, and by providing adequate spacing between the plants. If desired, the plants can be toned using spray applications of 2,500-ppm daminozide (B-Nine, Dazide) or the tank mixture of 2,000-ppm daminozide plus 3-ppm uniconazole (Concise, Sumagic).

Insects and Diseases

There are only a few problems with insects or diseases that growers are likely to experience when growing perovskia. Aphids, leafhoppers, spider mites and whiteflies may occasionally be observed feeding on Russian sage, but rarely do these pests cause significant crop injury.

The plant pathogens growers may observe on occasion include Cylindrosporium leaf spot, stem canker caused by Phoma, root rots and Sclerotinia stem blight. Routine scouting is useful and recommended to detect insect pests and plant diseases early, allowing the appropriate control strategies to be implemented before significant crop injury or mortality occurs.

Forcing

When producing 1-gallon or larger-sized containers, I recommend growers transplant 'Lacey Blue' during the late summer in the year before the plants are to be marketed; this allows adequate time for bulking and will result in fuller, higher quality plants.

Perovskia are cold beneficial plants and will flower with or without vernalization. Plants that have been vernalized will generally have better branching and more flowers than plants that have not received a cold treatment. The benefits of vernalization are most apparent with plants that have been bulked up prior to receiving a cold period (six to nine weeks at 35 to 44¡ F). In general, Russian sage requires long day lengths for flowering unless they have been vernalized; following a cold treatment, they will bloom under any day length. After vernalization, perovskia can be forced into bloom in 10 to 12 weeks when they are grown at 65 to 68¡ F.

Availability

Perovskia atriplicifolia 'Lacey Blue' is available to the industry as rooted liners from Ball Ornamentals (www.ballhort.com/Nursery/_Sales.aspx) and can be acquired from your Ball Horticultural sales representative (www.ballhort.com).