There is increased interest in using native plant alternatives to invasive species for landscaping. Several invasive shrubs are used extensively in landscaping since they perform well in challenging landscapes, such as parking lot island plantings, which are dry, nutrient-poor, and sun and heat exposed. This study evaluated the landscape suitability of six underused Connecticut native shrubs [american filbert (Corylus americana), buttonbush (Cephalanthus occidentalis), northern bush honeysuckle (Diervilla lonicera), steeplebush (Spiraea tomentosa), sweet fern (Comptonia peregrina), and sweet gale (Myrica gale)] by planting them in a large commuter parking lot on the University of Connecticut (UConn) campus in Storrs. Two nonnative invasive species, ‘Crimson Pygmy’ japanese barberry (Berberis thunbergii) and ‘Compactus’ winged euonymus (Euonymus alatus), were also planted as controls. Buttonbush, sweet fern, and sweet gale performed as well as controls and had aesthetic quality index (AQI) ratings similar to controls throughout the study, which spanned three growing seasons. These findings were surprising for buttonbush and sweet gale, which are found in the wild occupying predominantly wet areas. Buttonbush plants readily established at the site as indicated by a 930% increase in plant size over the first growing season. Sweet fern and sweet gale produced attractive, dense, and uniform mounds consistently throughout the study. Northern bush honeysuckle and american filbert were slower to establish, but by the second and third year, respectively, plants were highly attractive and had AQI ratings similar to controls. Despite its attractive floral display, steeplebush performed poorly and developed powdery mildew (Sphaerotheca) symptoms in the first and second years, which contributed to a lower AQI compared with controls. Aesthetic quality for american filbert, buttonbush, and steeplebush was reduced because of variation resulting from seed propagation. For certain native species, plants received from the nursery were not robust, which may have had a greater influence on establishment and early performance than their inherent landscape adaptability. This study identified five underused native shrubs that are adaptable and able to replace invasive plants in landscapes.
Pragati Shrestha and Jessica D. Lubell
Nursery and landscape professionals are interested in white-tailed deer (Odocoileus virginianus)–resistant native plants to replace invasive species used in difficult landscape sites, such as parking lot islands, which are dry, nutrient-poor, and exposed to sun and heat. Eight native shrubs [creeping sand cherry (Prunus pumila var. depressa), elderberry (Sambucus canadensis), gray dogwood (Cornus racemosa), highbush blueberry (Vaccinium corymbosum), round leaf dogwood (Cornus rugosa), northern spicebush (Lindera benzoin), sweetbells (Eubotrys racemosa), and virginia rose (Rosa virginiana)] were planted in a large commuter parking lot on the University of Connecticut campus to evaluate their suitability for use in difficult landscapes. The non-native, invasive shrubs ‘Compactus’ winged euonymus (Euonymus alatus) and ‘Crimson Pygmy’ japanese barberry (Berberis thunbergii) were also planted as controls representing non-native species typically planted in such sites. Aesthetic quality ratings for sweetbells matched the controls (rating of 4.5 out of 5.0) and plants exhibited a high level of white-tailed deer resistance. Virgina rose and creeping sand cherry had similar aesthetic quality to controls, despite light grazing of plants by white-tailed deer. Elderberry was damaged by moderate white-tailed deer grazing and snow load, but plants regenerated to 485% of initial size in one growing season with white-tailed deer exclusion. Gray dogwood, round leaf dogwood, and northern spicebush exhibited the least resistance to white-tailed deer grazing. Both dogwood species had lower aesthetic quality than the controls, and round leaf dogwood had the lowest survival rate (68%) after 2 years. However, several individuals of gray dogwood, round leaf dogwood, and northern spicebush that were less heavily damaged by white-tailed deer grew into attractive shrubs after white-tailed deer exclusion. Highbush blueberry had significantly lower aesthetic quality than controls and only 75% survival after 2 years, indicating that this species is an unsuitable replacement for invasives in difficult landscape sites. This study identified the underused native shrubs sweetbells, virginia rose, and creeping sand cherry as suitable replacements for invasives in difficult landscape sites with white-tailed deer pressure.
Jessica D. Lubell and Mark H. Brand
Interest in hemp (Cannabis sativa) for its medicinal compounds, cannabidiol (CBD), and Δ-9-tetrahydrocannabidiol (THC), continues to increase. Maximizing yield of CBD and/or THC requires female plants because female inflorescences accumulate significantly greater concentrations of these compounds than male inflorescences. Production of all female seed requires induction of female plants to develop male flowers that produce genetically female pollen. Growers would like access to feminized seed to produce all-female crops. We evaluated the efficacy of 0, 0.3, and 3 mm silver thiosulfate (STS) applied as a foliar spray (on three occasions 7 days apart) to produce male flowers on four strains of female hemp (having a THC concentration of ≤0.3%), designated CBD hemp A, CBD hemp B, CBD hemp C, and industrial hemp. Silver thiosulfate at 3 mm was the most efficacious treatment for all strains. The majority of inflorescences had 100% male flowers at 3 mm STS, and terminal inflorescences had ≥95% conversion to male flowers. Silver thiosulfate at 0.3 mm produced partial conversion to male flowers, whereas most inflorescences had around 50% male flowers, except for CBD hemp A, which demonstrated greater levels of masculinization. At 0.3 mm STS, terminal inflorescences of CBD hemp A had 91% conversion to male flowers. This study demonstrates that male flowers can be produced easily and consistently on female plants through application of foliar sprays of STS under short-day conditions.
Jessica D. Lubell and Jacob A. Griffith Gardner
American fly honeysuckle (Lonicera canadensis), hobblebush (Viburnum lantanoides), and sweetbells (Eubotrys racemosa) are eastern U.S. native shrubs with ornamental value, which might become successful nursery crops if they propagate readily from stem cuttings and grow uniformly in containers. We evaluated rooting success for hobblebush and sweetbells using stem cuttings treated with indole-3-butyric acid (IBA) in talc at concentrations of 0, 1000, 3000, or 8000 ppm. For hobblebush, IBA at 1000, 3000, or 8000 ppm will yield 70% rooting success. For sweetbells, IBA treatment did not enhance rooting, and 88% rooting success can be achieved with untreated cuttings. Stem cuttings of american fly honeysuckle root at 49% (previously published). We also evaluated all three native shrubs grown in nursery trade #1 containers under shade levels of 0%, 40%, or 70%. American fly honeysuckle grown under 40% or 70% shade were larger, had a greener hue angle, and higher chlorophyll fluorescence (Fv/Fm) than plants grown in full sun. Throughout the study period, Fv/Fm values for full-sun american fly honeysuckle were 0.6 or below, indicating plants were stressed. Hobblebush in 40% and 70% shade were wider, had more leaves, and enhanced foliage color compared with full-sun plants. Hobblebush in 70% had the highest Fv/Fm values at 0.78 or higher across the study period. For sweetbells, plant width increased as shade level increased. Even though sweetbells in 70% shade were wider and larger, they lacked density and had a less appealing habit than 40% shade and full-sun plants. Of the three study species, sweetbells might be the easiest plant for growers to incorporate into production because it propagates readily from stem cuttings and can be grown in full sun to 40% shade. Hobblebush and american fly honeysuckle may present more challenges for growers because hobblebush requires considerable shade to grow and american fly honeysuckle is more difficult to propagate.
Jessica D. Lubell and Mark H. Brand
Red-flowered elepidote rhododendrons (Rhododendron sp.) are favored by consumers, but cold-hardy red-flowered rhododendrons frequently have blue-red flower hue rather than the preferred red flower hue. Flower longevity, color, and color stability over 14 days were studied for the following eight elepidote rhododendron cultivars possessing red flowers: Besse Howells, Burma, Cary’s Red, Firestorm, Francesca, Henry’s Red, Low Red Frilled, and Nova Zembla. The eight cultivars were separated by flower hue into two distinct groups of four cultivars each. Rhododendron cultivars Burma, Firestorm, Francesca, and Henry’s Red produced flowers with red hue and Besse Howells, Cary’s Red, Low Red Frilled, and Nova Zembla produced flowers with blue-red hue. Flower longevity among rhododendron cultivars varied with Francesca blooms lasting the longest at over 14 days, and Besse Howells and Firestorm blooms lasting the shortest at ≈10 days. As flowers aged, hue angle decreased (became bluer), lightness increased, and chroma decreased or remained unchanged. The degree of change in flower color over time differed among cultivars, with ‘Francesca’ demonstrating the least change (ΔE 00 ≈ 3) and ‘Besse Howells’ the most change (ΔE 00 ≈ 11).
Jessica D. Lubell and Mark H. Brand
Epimedium is a genus of shade tolerant herbaceous perennials and groundcovers that are slow growing and command high prices. This research examined the influence of division size and timing on propagation success and growth of E. pinnatum ssp. colchicum Boiss., E. × rubrum Morren, E. × versicolor `Sulphureum' Morren and E. × youngianum Fisch. To determine an appropriate division size for each species, small (single bud) and large (three bud) divisions were made in mid-June 2002 and 2003. For the timing study, uniform divisions (three to five buds for E. pinnatum ssp. colchicum and E. × versicolor `Sulphureum'; four to seven buds for E. ×rubrum and E. × youngianum) were made in March, late June and late August, when plants were dormant, had just completed foliage expansion, or were summer dormant. Half of the plants were destructively harvested in the fall and half were overwintered and forced in the greenhouse in early spring. By the end of the growing season, plants grown from large divisions were larger than those grown from small divisions and had produced more buds, however, plants from small divisions produced more buds per initial bud than plants from large divisions, demonstrating a faster increase in growing points. For each species, March divisions produced more vegetative growth, buds, buds per initial bud and potential propagules than June and August divisions, by the end of the growing season. However, by the following spring, both March and June divisions had produced plants of similar size and appearance, while plants grown from August divisions were smaller and of lower quality.
Julia A. Cartabiano and Jessica D. Lubell
Interest in native plants for landscaping is increasing and nursery growers must expand their product offerings by adding new native species. Softwood stem cutting propagation of four underused northeastern U.S. native species [Ceanothus americanus (L.), Corylus cornuta (Marsh.), Lonicera canadensis (Bartr.), Viburnum acerifolium (L.)] was studied. V. acerifolium cuttings containing two nodes taken mid-June to mid-August rooted at nearly 100% with at least 15 roots per cutting. Exogenous auxin application did not enhance rooting of two-node V. acerifolium cuttings. Single-node V. acerifolium cutting success and quality of rooting increased with increasing concentration of auxin applied and reached a maximum of 80% rooting, whereas untreated cuttings only rooted at 53%. C. cornuta cuttings taken mid-June to mid-August rooted at greater than 85%. Hormone concentration did not affect rooting percentage for C. cornuta; however, cuttings treated with 3000 and 8000 ppm indole-3-butyric acid (IBA) had more and longer roots than untreated cuttings. June was the optimal time to collect cuttings of C. americanus (57% rooting) and L. canadensis (49% rooting), and rooting hormone did not significantly impact propagation success. C. cornuta and V. acerifolium could be propagated at a level necessary for consideration as a new commercial crop by general wholesale nurseries looking to add select native shrubs to their product lines. All four species evaluated could be viable commercial crops for nurseries that specialize in native plants.
Kristoffer J. Barker and Jessica D. Lubell
Nursery producers are interested in supplying sedum (Sedum sp.)-vegetated modular units for the green roof industry. This research examined the influence of three rates of controlled-release fertilizer (CRF) (50, 78, and 108 g per unit of 15N–3.9P–10K, 8- to 9-month formulation) on production of modules containing one or two Sedum species. Six Sedum species were evaluated independently: ‘Angelina’ sedum (Sedum rupestre), gray sedum (S. pachyclados), ‘John Creech’ sedum (S. spurium), tasteless sedum (S. sexangulare), ‘Weihenstephaner's Gold’ sedum (S. kamtschaticum var. floriferum), and white sedum (S. album). The species were then paired as follows: white sedum/‘John Creech’ sedum, ‘Weihenstephaner's Gold’ sedum/‘Angelina’ sedum, and gray sedum/tasteless sedum. For each pair, three starting proportions of cuttings were studied. In 8 weeks, the medium and high fertility rates produced significantly more units with at least 95% vegetation coverage than the low rate. In general, increasing the fertility rate increased the fresh weight at time of harvest, except for ‘Weihenstephaner's Gold’ sedum and tasteless sedum at the high rate, which developed “melt out.” Melted-out tissues turned brown, desiccated and detracted from the visual appearance of units. ‘John Creech’ sedum and white sedum had the greatest fresh weight followed by ‘Weihenstephaner's Gold’ sedum, ‘Angelina’ sedum, and tasteless sedum. Gray sedum grew substantially slower than all other species and had the lowest fresh weight. For white sedum/‘John Creech’ sedum units, harvest fresh weight proportions were similar to starting cutting fresh weight proportions. For gray sedum/tasteless sedum units, tasteless sedum outgrew gray sedum and gray sedum was barely noticeable in finished units. Harvest fresh weight and digital image analysis (DIA) of ‘Weihenstephaner's Gold’ sedum/‘Angelina' sedum units indicated that ‘Weihenstephaner's Gold’ sedum colonized units faster than ‘Angelina’ sedum, and had greater visual impact in finished units. Units started with 25% ‘Weihenstephaner's Gold’ sedum cuttings, the smallest proportion tested, were roughly 73% covered with ‘Weihenstephaner's Gold’ sedum at harvest. We recommend growers use the medium fertility rate to produce the most units with 95% vegetation or more in the least amount of time and with reduced risk of melt out. To achieve desired final species proportions, growers may need to adjust the ratios of cuttings based on uneven species vigor.
Mark H. Brand, Jessica D. Lubell and Jonathan M. Lehrer
Winged euonymus [Euonymus alatus (Thunb.)] is an important landscape shrub that has demonstrated its potential to be invasive in numerous states across the central and northern United States. Nine cultivars were evaluated for their potential to produce fruits and seeds in a randomized, replicated field planting. Seeds from all cultivars were evaluated for germination rate and initial survival in a deciduous woodland. Seeds collected from ‘Compactus’ were also sown in five natural environments (full sun meadow, edge of woods, moist woods, dry woods, pine woods) to determine which habitat types support its germination and establishment. Seed production for cultivars varied from 981 to 6090 seeds per plant. The dry deciduous woods and pine woods were the only environments that supported significant germination rates that could be as high as 37.8%. Seedling survival was at least 77% in the deciduous dry woods and at least 55% in the pine woods. In the first replication, establishment rates for cultivars in the dry deciduous woods ranged from a low of 6.5% for ‘Odom’ Little Moses™ to a high of 42.5% for ‘Monstrosus’. In the second replication, all cultivars achieved over 30% establishment and most exceeded 40% establishment. An estimate of the annual seedling contribution per plant per cultivar was calculated by combining seed production data with establishment data for each cultivar. This estimate was predicted to range from 588 to 3763 and therefore none of the nine cultivars evaluated should be considered non-invasive based on our findings. Our findings show that germination and seedling survival rates are high for E. alatus and because the species is long-lived, cultivars will likely have to be completely seed-sterile to be considered non-invasive according to demographic models.
Jacob A. Griffith Gardner, Jessica D. Lubell and Mark H. Brand
Comptonia peregrina is a desirable native ornamental plant for challenging landscapes, but it cannot be produced using conventional softwood stem cuttings. We demonstrate that C. peregrina can be successfully propagated using young shoots (6 to 8 cm in length) recently emerged from rhizomes taken as cuttings. Although significantly more cuttings rooted using intermittent mist (99%) than propagation dome (70%), cuttings under propagation domes had greater shoot counts. Due to the drier and warmer conditions under propagation domes, cutting shoot tips were killed, which relieved apical dominance and stimulated lateral budbreak. Cuttings rooted under propagation domes produced plants having greater height, width, and size after 90 d than cuttings rooted under intermittent mist. Treatment of cuttings with talc-based rooting hormone at 3000 and 8000 ppm indole-3-butyric acid (IBA) significantly improved rooting percentage and shoot count over untreated cuttings. Cuttings treated with 8000 ppm IBA produced the most roots. Container plants grown from cuttings and pruned to 7 cm in height produced twice as many shoots as unpruned plants. Using cuttings taken from young shoots (6 to 8 cm) produced from rhizomes, 3000 or 8000 ppm IBA, and intermittent mist nursery growers can achieve rooting percentages for C. peregrina above the 80% benchmark preferred for commercial plant production.