From 2014 through 2023, The Chicago Botanic Garden (USDA Hardiness Zone 5b-6a, AHS Plant Heat Zone 5) evaluated 49 cultivars of Salvia nemorosa or related hybrids. Each cultivar was planted in a row of five plants and data was collected on overall health and habit of the variety, any disease or pest issues, winter hardiness, floral production, and other ornamental considerations or notable morphological characteristics. All cultivars with surviving plants were kept in the trial for a minimum of four years.

The first year was considered an establishment year, and data taken during that period was for monitoring purposes only and did not affect the final rating of each cultivar (see Table 2 for the years each individual cultivar was trialed).

The trial garden has a clay-loam soil with a pH of 7.4. During the trial period, plants were exposed to wind in all directions and up to 10 hours of full sun during the growing season. Maintenance practices were kept to a minimum, thereby allowing the plants to thrive or fail under natural conditions. Trial beds were irrigated via overhead sprinklers when necessary, mulched with composted leaves once each growing season, and weeded regularly. Plants were not deadheaded, fertilized, mulched for winter, or treated for insects or diseases.

Table 2: Evaluation Periods

 

Table 1 shows morphological and phenological data, as well as overall ratings for 40 of the 49 Salvia cultivars in the trial. Overall ratings were based on average health, habit quality, and floral production, with an emphasis on the latter. While data was collected on pest and disease pressure, neither was noted to be a significant issue in the trial, so the data was ultimately not factored into the overall ratings. Cultivars that lost plants during the winter received a penalty to their overall score.

Salvia nemorosa ‘Lurie Strain Mix’ is a seed strain introduced by Intrinsic Perennials in Hebron, Illinois. The mix is based on a seedling selected by Piet Oudolf and Roy Diblik in the Lurie Garden in Millennium Park, Chicago, Illinois. As a seed strain, various plant sizes, flower colors, and flower sizes were observed on the five plants in the trial. Due to these variations, the data in Table 1 for ‘Lurie Strain Mix’ does not include morphological data and is limited to bloom timing and flower coverage.

Nine of the original 49 cultivars in the trial were lost after only one year due to an extreme flood event, where the bed remained waterlogged for a significant amount of time. These taxa were not re-trialed, did not receive ratings, and are not included in Table 1 The cultivars lost to flooding were 'Burgundy Candles', Sensation^® Compact Bright Rose ['Florsalbro'], Sensation^® Compact White [‘Florsalcwh’], Sensation^® Deep Blue [‘Florsaldblu’], Sensation^® Medium Deep Rose [‘Florsaldro’], Sensation^® Medium Light Pink [‘Florsaliro’], Sensation^® Medium White [‘Florsalmwh’], Sensation^® Medium Pink [‘Florsalpi’], and Sensation^® Medium Purple [‘Florsalpur’].

Table 1: Overall Ratings and Observational Data

Salvia nemorosa 'Bumblesky’

Salvia nemorosa 'Burgundy Candles’

Flowers of Salvia 'Snow Kiss'

Open habits of Salvia nemorosa 'Sixteen Candles' exposing lighter inner foilage.

New growth of Salvia nemorosa 'Trinity' was not vigorous enough to fill the open habit.

On average, floral displays were strong, though some year-to-year variation in productivity levels were noted. Flower color fell into one of three broad categories: violet, pink, or light-colored. Of those categories, the lightcolored varieties are the easiest to further split into subcategories. While some cultivars had flowers that were nearly pure white, many of the light-colored flowers had a small amount of blue or violet pigment, resulting in a perception of an icy blue or delicate lavender color. In that category, Salvia ‘Snow Kiss’ was notable for having peach-colored buds and nearly white flowers with just a touch of pinkish pigment. While they read more as white than pink, the flowers did give an impression of a warmer white than the flowers of other light-colored varieties.

The calyx color was almost as powerful as the flower color regarding the floral displays. Flowers with darker colors stood out more when combined with an even darker calyx, as was the case with Salvia ‘Rose Marvel’ as well as the early stage of S. ‘Indiglo Girl’ (see comparison in Figure 2.), whereas light-colored flowers displayed better against a lighter or more neutral calyx, such as with S. ‘Perfect Profusion’.

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Figure 2. Comparison of the effect of calyx color on perception of flower color between (a) Salvia nemorosa ‘Tidal Pool’ and (b) Salvia ‘Indiglo Girl’. Though a similar color, the flowers of ‘Indiglo Girl’ appear to be more colorful because they have both brightness and chromatic contrast against the dark calyces. With ‘Tidal Pool’, both contrasts are reduced by the lighter calyces.

The calyces of some cultivars held their color and/or transitioned to an attractive tan after the faded flowers fell away. One example of this was Salvia nemorosa ‘Blueberry Beret’, where the calyces transitioned from a dark purple to a golden brown and were noted as being quite attractive for a period of about four weeks after the initial flowers had faded (see Figure 3). In other cases, plants held their calyces, but their color transitioned to a muddier brown and they became more of a detriment to the overall display.

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Figure 3. Stages of floral aging of Salvia nemorosa 'Blueberry Beret': (a) active flowering; (b) the oldest flowers begin to drop and calyces fade starting at the bottom of the inflorescence; (c) all calyces transition to a golden brown before eventually dropping.

A significant factor in the effectiveness of the floral displays was the combination of flower size (see Figure 4) and flower color. Larger flowers tended to merge into a much bolder display, whereas smaller flowers tended to be a role player in a more textured, complex visual. Neither of these is objectively better, but having lesser variation in the visual, as was the case with larger flowers, caused gaps in flower production to appear more pronounced. A similar observation can be made about flower color. Of the available flower colors, pink has the highest hue contrast with green. For that reason, pink-flowered cultivars were some of the boldest when flower production was high, but those same flowers also attracted the eye to any inconsistencies in habit or floral display.

Some hardy salvias have much better rebloom than others. In all cases except for one, coverage of the plants in actively blooming flowers dropped dramatically after the primary bloom period. For the remainer of the growing season, active blooms never rose above 10% coverage of the plant. The only exception was Salvia ‘Fortunate Night’, which had a second bloom peak during late-summer that averaged 20% coverage. While all cultivars in the trial showed some level of continuous blooming or late summer rebloom, the level of rebloom in all cases was insignificant compared to the primary bloom period. A controlled comparison of deadheading was not performed as a part of this study. However, a previous trial of hardy salvias performed by the Chicago Botanic Garden showed that deadheading the plants did not increase stem regeneration in most cases but did enhance the perception of floriferousness by removing any obstructive elements and improving the overall health and form of the plants in the late season (Plant Evaluation Notes, no. 14).

Each spring, most of the plants emerged as tight, well-behaved mounds. Once the primary flowering period was complete, habits generally began to decline, but to varying degrees. In the best cases most stems remained upright with the occasional gap forming as the plants loosened and older growth started to fade. A more severe decline in habit involved most stems collapsing outward leaving the center of the crown exposed. The worst decline in habit was exhibited by cultivars that started opening before the end of the primary bloom. In the case of ‘Sixteen Candles’, the habit opened and revealed chlorotic inner foliage, which tended to draw the eye in and emphasize the deficiency in the habit.

Open habits were occasionally improved by later season growth that filled the vacant centers, though the degree of improvement was dependent on how deficient the habit was and the vigorousness of the new growth.

Seedlings were occasionally observed throughout the trial period, but their numbers and spread were never noted to be a concern. Infrequently, some seedlings were able to establish themselves and eventually out compete and smother some of the original trial plants. While perhaps not an ideal in most situations, some seeding is not necessarily a negative trait as it may introduce a satisfying level of variation into a planting area.

With little deviation, the overall health of the trial plants was good, especially during the initial bloom period. No recurring disease or pest issues were noted during the trial. The only observations of significant pest pressure were recorded during an outbreak of thrips in 2021. During the outbreak, all plants suffered some amount of foliar damage. Observations related to the outbreak did little to differentiate the performance of the affected cultivars, so data related to the outbreak was ultimately not factored into the final ratings.

A total of 33 plants died during winter, or about 17% of the total trial population. Out of the 40 cultivars listed in Table 1, only seven received poor ratings. Six of those seven cultivars received a poor rating due to losses during winter: Salvia ‘Ballerina Pink’, S. nemorosa ‘Blue Marvel’, S. nemorosa Lyrical^™ White [‘Florsalwhite’], S. nemorosa ‘ New Dimension Rose’, S. nemorosa ‘Royal Crimson Distinction’, and S. nemorosa 'Salute Pink'. Salvia nemorosa ‘New Dimension Rose’ and S. nemorosa ‘Royal Crimson Distinction’ lost all plants during winter after only one season of active evaluation (see Table 4 for more details on winter losses).

Table 3: Flower size measurements and calculations

Table 4: Winter losses

The hue of the pink flowers of Salvia nemorosa ‘Pink Wesuwe’ contrast with the green foliage more than if they were violet or a near-white color, so the gaps in flower coverage are emphasized.

 

Overall, the trial results show that there are many appealing cultivars of hardy Salvia to choose from, with 19 cultivars having received a good rating and seven having received an excellent rating. Health-related observations show that these Salvia cultivars are generally easy to care for and have few major health concerns. Maintenance is not required but deadheading and/or a light prune may aid in creating a tidier aesthetic in the late season. The primary concern for most gardeners will be ensuring proper drainage to support longer-term survivability. Any site that is prone to holding excessive moisture or flooding is not appropriate for these plants. 

While most varieties can be expected to have some amount of rebloom, the level of rebloom is typically only a small fraction of the coverage generated by the primary bloom and expectations should be set appropriately. For that reason, the level of rebloom should not generally be considered a primary factor in selection of a cultivar for the typical gardener. 

The best rated plants in the trial were those with exceptional and consistent flower coverage that did not lead to any deterioration of habit. Performance metrics were not significantly correlated with morphological characteristics such as flower color, flower size, or overall plant size, which means that gardeners should have a relatively easy time selecting good and excellent performers that also match their aesthetic preferences.