Maine Plants

Ornamental Research Results from UM

In the past five years, the faculty, staff, and students of the Landscape Horticulture Program in the Department of Biosystems Science and Engineering at the University of Maine in Orono have conducted many ornamental research projects. Some results and findings are highlighted in the following topics. The information is provided for your reference only. For more detailed information or unlisted projects (such as evaluation and trial of Hosta and Astilbe, plant materials were provided by Fieldstone Gardens), please contact Dr. Donglin Zhang, Horticulture Program, 5722 Deering Hall, University of Maine, Orono, ME 04469-5722, Phone: 207-581-2918, Fax: 207-581-2999, and Email: donglin@maine.edu.

Propagation and Production of Bunchberry (Cornus canadensis L.)

Soft-wood stem cuttings of Bunchberry were rooted in 5-9 weeks in 1:3 peat and perlite (v/v) under the fine mist (45 seconds every ten minutes). Rooting percentage was above 82% and was not affected by growth hormone (regulator) K-IBA. However, 3000 ppm KIBA enhanced growth and establishment of the root system and number of rhizomes.

Bunchberry sod pieces can be dug before the snow and left in cold storage room for overwintering. The sod pieces can be brought in and forced to grow in the greenhouse (18C, ambient temperature) in early February. The plants should be watered as needed and 300 ppm fertilizer should be applied weekly after new shoots emerge in March. Single stem divisions or three-node cuttings can be taken in early April and prepared as the above. Rooted cuttings with rhizomes and divisions should be moved out of the mist and transplanted into marketable pots with peat and perlite (1:1, v/v) (pH 3.5-4.0). Fertilizer should be applied weekly at level of 300ppm-N until September. Marketable plants can be sold since then.

For more: Haynes, J. 1999. M.S. Thesis, University of Maine, Orono, ME

Propagation and Overwinter Survival of Stewartia koreana and Stewartia pseudocamellia Rooted Cuttings

Cuttings of Stewartia koreana and Stewartia pseudocamellia were taken from seven different plants. Growth hormone K-IBA was applied at level of 10000 ppm and cuttings were placed under intermittent mist (8 seconds at each 8 minutes from 6:00am to 9:00pm) with perlite : peat medium (3:1, v/v). The rooting percentages range from 36% to 83% for cuttings from mature canopy and 100% for cuttings from vigorously-growing shoots arising from a wound near the base. It is possible that cuttings from the wounded base were more juvenile, i.e: cuttings of mature plants had less rooting potential than those of juvenile tissue.

The overwinter survival is a critical factor which is also a limiting factor in propagating a large quantity of Stewartia plants. Acclimation conditions (long day and short day in Greenhouse, outside winter conditions), post-winter photoperiod (16 hrs/day vs. 12 hrs/day), cutting types (softwood, semi-hard wood, and hard-wood), and cold storage duration (40F) had no or little effect on overwinter survival rate. All rooted cuttings from mature plants were dead in the second year. However, all cuttings from the wound base survived. Obviously, the cuttings from the juvenile plant had not only 100% rooting rate, but also 100% overwinter survival rate under regular cold storage conditions. Further studies should be conducted to address the overwinter problem.

For more: Haynes, J. 1999. M.S. Thesis, University of Maine, Orono, ME

Cold Hardiness of Selected Mountain Laurel (Kalmia latifolia) Cultivars

Kalmia latifolia (Mountain Laurel) is a native plant with great ornamental potential. It has been widely planted for its dark evergreen foliage and gorgeous white to pink flowers. Unfortunately, cold tolerance limits its distribution in the northern landscape. Based on the study of low-temperature tolerance in laboratory and evaluation in the field, a number of taxa were distinguished as having potential for use in USDA hardiness zones 4 and 5. Please be advised that the plant sources (north vs. south) have significant effect on winter survival rate (plant materials were provided by Broken Arrow Nursery and Pride’s Corner Farms Nursery).

Zone 4: ‘Bridesmaid’, ‘Pinwhell’, ‘Sarah’, ‘Snowdrift’, and ‘Willowcest’.

Zone 5: ‘Bullseye’, ‘Carol’, ‘Carousel’, ‘Kaleidoscope’, ‘Little Linda’, ‘Minuet’, ‘Olympic Fire’, ‘Pink Charm’, ‘Raspberry Glow’, ‘Tiddlywinks’, ‘Tinkerbell’, ‘Willowwood’.

For more: Wachter, J. 1998. M.S. Thesis, University of Maine, Orono, ME

Cold Hardiness of Selected Magnolia Taxa

After a long winter in the northern regions, Magnolia is one of the earliest woody flowering plants to bring us the spring. Actually, these plants are among the oldest and most popular woody ornamental plants on the market. I have enjoyed a more exquisite Magnolia bloom here in Maine than in the south. Unfortunately, cold tolerance limits its distribution in the northern landscape. Based on the study of low-temperature tolerance in laboratory and evaluation in the field, a number of taxa were distinguished as having potential for use in USDA hardiness zones 4 and 5. Please be advised that the plant sources (north vs. south) have a significant effect on winter survival rate (plant materials were provided by Dr. John Frett at the University of Delaware).

Zone 4: Magnolia ‘Butterflies’, M. ‘Yellow Lantern’, M. acuminata, M. accuminata ‘Meogi Dori’, M. fraseri, M. globosa, M. kobus var. loebneri ‘Ballerina’, M. sieboldii, M. sinensis, M. virginiana var. australis.

Zone 5: Magnolia ‘Ann’, M. ‘Betty’, M. ‘Florence’, M. ‘Helen’, M. ‘May’, M. ‘Galaxy’, M. ‘Pristine’, M. ‘Yellow Bird’, M. ‘Yellow Fever’, M. ashei, M. × loebneri ‘Merrill’, M. stellata ‘Rosea’, M. stellata ‘Royal Star’, M. macrophylla, M. × soulangiana ‘Dottie Grosse’, M. × soulangiana ‘Lilliputian’, M. × soulangiana ‘Lombardy Rose’, M. × soulangiana ‘Verbanica’, M. tripetala.

For more: Wachter, J. 1998. M.S. Thesis, University of Maine, Orono, ME

Viburnum is one of largest and most popular groups of flowering shrubs. Plant habit varies from small shrubs to small trees. Spring to summer flowers, fall leaf and fruit colors bring great attention to our everyday gardens. Unfortunately, cold tolerance limits its distribution in the northern landscape. Based on the study of low-temperature tolerance in the laboratory and evaluation in the field, a number of taxa were distinguished as having potential for use in USDA hardiness zones 3, 4, 5, and 6. Please be advised that the plant sources (north vs. south) have significant effect on winter survival rate (plant materials were provided by Bailey’s Nursery (Oregon), Bailey’s Nursery (Minnesota), and Spring Meadow Nursery).

Zone 3: Viburnum ‘Alfredo’, V. ‘Emerald Triumph’, V. dentatum ‘Northern Burgundy’, V. dentatum ‘Red Feather’, V. lantana ‘Mohican’, V. opulus ‘Roseum’, V. trilobum ‘Bailey’s Compact’, V. trilobum ‘Compactum’, V. trilobum ‘Hahs’, V. trilobum ‘Wentworth’.

Zone 4: Viburnum dentatum ‘Autumn Jazz’, V. dentatum ‘Chicago Lustre’, V. sargentii ‘Onondaga’.

Zone 5: Viburnum × burkwoodii ‘Chenaultii’, V. opulus ‘Nanum’, V. plicatum var. tomentosum ‘Mariesii’, V. rufidulum.

Zone 6: Viburnum × pragense ‘Decker’, V. utile ‘Chesapeake’.

For more: Wachter, J. 1998. M.S. Thesis, University of Maine, Orono, ME

Ornamental Grass Trial at UM

Selected ornamental grasses have gained their position in the horticultural trade because of their four-season interest, especially in the winter garden. A handsome clump of grass against snow background will invoke a lot of imagination from your daily gardening experience. In 1997, a total of 25 ornamental grass taxa planted in the Lyle E Littlefield Ornamentals Trial Garden for evaluation. Mulch was not found to help the plant survival and growth in their early stage.

Short Ornamental Grasses: Only Deschampsia ‘Bronzschleier’, ‘Fairy’s Joke’, and ‘Goldschleier’ survived in the last two years. Carex hachijoensis ‘Evergold’, C. glauca, Festuca glauca ‘Silver Lining’, Koeleria glauca and Molinia aurndinacea did not survive.

Tall Ornamental Grasses: Calamagrostis ‘Karl Forester’, ‘Overdam’, ‘Stricta’, Helicotrichon sp., Miscanthus sinensis ‘Purpurascens’, Panicum virgatum, and Spartina pectinata overwintered for the last two years. Erianthus ravennae, Miscanthus sinensis ‘Gracillimus’, ‘Graziella’, ‘Morning Light’, ‘Sarabende’, ‘Silberfedder’, ‘Strictus’, ‘Variegata’, Pennisetum alopecuroides, P. alopecuroides ‘Little Bunny’ did not make it through the second winter (Plant materials were provided by Walter’s Gardens and Quansett Nurseries).

Cold Hardiness and Overwinter Methods of Heath and Heather

Ten different heath and heather cultivars (24 each) were tested using different overwinter methods (Micro Foam, Reemay (2 layers), and control). Compared with the control (no winter protection), both Micro Foam and Reemay have significantly increased the survival rate and growth rate. Based on controlled freezing test in laboratory and field trial data, you can probably grow one cultivar (out of 10), Calluna vulgaris ‘Tenuis’, without winter-protection in Orono, Maine (Zone 4). If you covered with Reemay, you can extend your list to six (Calluna vulgaris ‘Gold Haze’, ‘Mairs Variety’, ‘Robert Chapman’, Silver Knight’, ‘’Tenuis’, and ‘Tib’). You may grow all listed cultivars if you covered them with Micro Foam. For the cultivars we studied, Calluna cultivars survived better than Erica in Orono, Maine (Zone 4).

Compared with July planting, September planting had significantly higher survival rate. The wet soil in early summer in Maine is probably a important factor. Freezing tests in the laboratory of heath and heather plants have great potential to predict the plant survival in the field. Although it is hard to get funding for this type of research, we believe that all of us would like to do more research projects like this one. We are looking forward to further collaboration with all of you (Plants materials were donated by Sylvan Nursery Inc. They are Erica carnea ‘Winter Beauty’, Erica vagans ‘Mrs. D.F. Maxwell’, Erica tetralix ‘Rosy Pink’, Calluna vulgaris ‘Mairs Variety’, Calluna vulgaris ‘Tib’, Calluna vulgaris ‘Gold Haze’, Calluna vulgaris ‘Robert Chapman’, Calluna vulgaris ‘Sliver Knight’, and Calluna vulgaris ‘Tenuis’).

Growing Full-charged New Guinea Impatiens hanging baskets for Customers

New Guinea Impatiens (Impatiens × hawkeri ‘Guadaloupe’ (Paradise KNG)) requires low-fertility. Mature plants can survive for about three months without any extra fertilizer. All three different fertilizers can be used to charge New Guinea Impatiens. If you use Sierra Tablets Plus Minors 16-8-12 (8-9 month) fertilizer, better performance can be reached by applying 3 tablets (= 3.6 grams pure Nitrogen) in each hanging basket. The same performance can be achieved if you use 8 grams (= 1.2 grams pure Nitrogen) or more Osmocote Plus 15-9-12 (8-9 month) fertilizer. For F & B All & Only organic garden 5-5-5 fertilizer, 48 grams (= 2.4 grams pure Nitrogen) or more should be applied per basket.

The slow release or organic fertilizers should be applied at least three weeks before the sale date of the hanging baskets. During these three weeks, be sure to continue the liquid fertigation at 100ppm and gradually reduce the concentration to 0 ppm. Then, your customers can enjoy the hanging baskets without adding fertilizer (Supported by Mid-Maine Greenhouse Growers Association. Plant materials were provided by Pleasant View Gardens).

Growing Full-charged Ivy Geranium hanging baskets for Customers

Compared with New Guinea Impatiens, Ivy Geranium (Pelargonium peltatum ‘Bartlett’s Pink’) requires much high fertility. The hanging baskets could not survive for three months without extra fertilizer. The best performance was observed by applying 32 grams (= 4.8 grams Nitrogen) of Osmocote Plus 15-9-12 (8-9 month) fertilizer. If using F & B all & only organic garden 5-5-5 fertilizer, the highest amount, 96 grams (= 4.8 grams Nitrogen) did not achieve better performance (3.5 or above). For Sierra Tablets Plus Minors 16-8-12 (8-9 month) fertilizer, 4 tablets (= 4.8 grams of pure nitrogen) or more should be applied per basket.

The slow release or organic fertilizers should be applied at least three weeks before the sale date of the hanging baskets. During these three weeks, please be sure to continue the liquid fertigation at 200ppm and gradually reduce the concentration to 0ppm. Be sure to remove the dead flowers continuously (Supported by Mid-Maine Greenhouse Growers Association. Plant materials were provided by Bartlett Nursery).

Selection and Evaluation of Chamaecyparis thyoides

With the support of Dr. Michael A. Dirr at the University of Georgia, a total of 50 different clones (three plants for each clone) have been planted in the research area in the Lyle E. Littlefield Ornamentals Trial Gardens and Research Center in Orono, Maine.

Chamaecyparis thyoides (Atlantic Whitecedar) grows in swamp or bog areas along the Atlantic coast, ranging from Maine to Florida. Wide ranges of habitats and artificial selections have contributed the great diversity of this species. The growth forms range from upright (‘Emily’) to compact mounding globe (‘Heatherbun’). The foliage colors rang from rich green (Dirr’s Form), light green (‘Select Tree’), golden (‘Aurea’), to blue (‘Blue Sport’). Also, selections for needle foliage (‘Top Point’ and ‘Red Star’) and scale foliage (‘Glauca’) have enriched its attraction for our gardens.

The growth of Atlantic Whitecedar is cultivar dependent, from 7 inches to 2 feet a year in Maine. It can be grown as a single specimen, dwarf evergreen, Christmas trees, or in commercial plantation for its valuable wood. Can we grow all of the above cultivars in Maine and northeastern United States? Please follow our newsletter and we will keep you updated. Do not forget the cultivars selected from Maine. ‘Luce’s Blue’ (Maine Selection), ‘Appleton’, and ‘Yankee Blue’ do love our Maine cold and survive well in the northeastern regions.

Temperature and Gibberellin Acid on Seed Germination of Iris versicolor

Iris versicolor (Blue-flag Iris) is a native plant in wetland areas. The blue flowers in late spring or early summer bring much more attention to the swampy areas. The plant is not only an important species for wetland restoration, but also popular in the everyday gardens. The demand has increased in recent years. However, seed germination seldom occurs in the wild and the commercial production relies on division.

Four to six months of cold treatment (41F) is required for Iris versicolor seed germination. Alternating temperatures (75/65F or 81/59F for day/night) improved the germination percentage compared with constant 71F. The average germination percentage for three temperature treatments are 54.4% (71F), 96.5% (75/65F), and 96.0% (81/59F). Gibberellic Acid had significant influence on germination rate, only the temperature was not in favor the germination. The concentration 1000ppm is better than 500ppm, 1500ppm, and control. Iris versicolor germinated within 10 days after cold treatment.

Seed Germination of February Daphne (Daphne mezereum)

February Daphne is a great plant for early spring flowers. The small rounded growth habit (to 2' tall) loaded with flowering buds attracts your attention in winter time. The plant is doing well in the Ornamentals Trial Gardens in Orono except the poor fall color. Seed gemination of Daphne is difficult because of its complicated germination cycle and rapid rotting after contacting with moisture. To avoid these problems, this study was designed to investigate the effect of seed sources and cold treatment methods on seed germination.

Regardless of cold treatment, fresh seeds (collected with flesh seed coat from the plant) had significantly higher germination rate (43.3%) compared with that (20%) of dry seeds (seed coat is dried). The better cold treatment (with wet sphagnum moss, at 41F) is one month. The highest average germination rate (55%) occurred in one month cold with fresh seeds. Germination took place in six months. Obviously, to collect the fresh seeds and treat with cold immediately will enhance the seed germination percentage of plants, such as Daphne spp.

Magnolia stellata ‘Lyle’s Legacy’ (Growing ME Green, Vol. 3, No. 3, Page 5).

With support from all of you and funds from the Research and Development program, the New Maine Garden Plant Production project was established in 1998. Since then, the list of potential new garden plants from Maine has increased to more than 30 taxa. Magnolia stellata ‘Lyle’s legacy’ is one of them.

Eighteen years ago, Professor Lyle E. Littlefield grew many Magnolia stellata ‘Centennial’ from seeds. He then distributed the seedlings to different trial areas. Dr. John Smagula received some plants and evaluated them in a trial area in Orono. One of the seedlings has grown well and shown distinguished characteristics, including flowers with a large number of tepals. When Dr. Paul Cappiello joined the University of Maine faculty, both professors carefully examined the plant and found the unique characteristics of this seedling worth of introduction. In recognition of the great contribution of Professor Lyle E. Littlefield to horticulture, the new cultivar was named after him and Magnolia stellata ‘Lyle’s Legacy’ was "born" here in our beloved Maine.

The original plant is now about 14 feet tall and 12 feet wide. It consistently produces abundant flower buds and usually blooms in mid April and early May, about two weeks earlier than ‘Centennial’ plants in Lyle E. Littlefield Ornamentals Trial Garden in Orono. Leaves are similar to ‘Centennial’ and the tepals are twice as many as its species and the ‘Centennial’ cultivar. Last spring, I counted 59, 61, and 57 tepals in three randomly picked flowers.

Mr. Brad Libby, the greenhouse and garden Manager, has done some cutting propagation. Preliminary data showed that more than 80% soft-wood cuttings can be rooted with Hormodin #3 (8000 IBA). The same results have been observed using 8000 ppm KIBA. Other reproduction methods will be studied in order to produce large number of this wonderful new cultivar and satisfy the market.

For the last two years, the rooted softwood cuttings survived well in containers. The cold hardiness should not be a problem because the plant originates from Maine. "Lyle’s Legacy’ is still in the evaluation period and I hope you can have it in your garden sometime soon.

Conclusion

New garden plant production is a long term commitment. Your support and contribution are essential to keeping this program alive. Next time, if you plan to send a plant as a gift or cultivate one in your lovely garden, please be sure to ask for plants that originated in Maine. A good garden plant not only makes our living environment better, but also improves the quality of our daily life. Please join us and bring our Maine garden plants to national or worldwide attention.