Ornamentals and Flowers Feb. 2010 OF-46 Non-invasive Landscape Plants with Fragrant Flowers Patti Clifford1 and Kent Kobayashi2 1Hawaii Invasive Species Council, 2CTAHR Department of Tropical Plant and Soil Sciences eeds are not friends to my garden. They cause To have a plant screened by one of the Hawaii Inva- more work and displace the flowers or vegetables sive Species Council’s weed risk assessment specialists, thatW I am trying to grow. But I do understand that in e-mail [email protected]. our multicultural world, a weed to one person may be a medicine, food, or ornamental to another. Plants have Characteristics of invasive plants many uses to humans; that is why we transport them with Many of the attributes that we appreciate in our garden us as we traverse the planet. and landscape plants contribute to their ability to invade In Hawai‘i, many of the native plants are endemic— natural and agricultural ecosystems. These include they are not found anywhere else in the world. This rarity • rapid growth has made them vulnerable to impacts from non-native • early maturity species. Some of the plants introduced here from other • heavy seed production regions become weeds and displace the native plants. • vegetative reproduction (i.e., pieces of roots, stems, While invasive weeds may cause trouble in my garden, or leaves can break off and grow into new plants; this they create havoc in Hawai‘i’s delicate native ecosystems. can happen when green waste or plant trimmings are Hawai‘i’s natural ecosystems have one of the worst discarded) weed problems in the world. To help understand and • tolerance of dense shade (conferring ability to spread cope with this problem, scientists developed a system, the into the understory of native forests) Hawaii-Pacific Weed Risk Assessment (HPWRA), which • having non-specific pollinators can predict a plant’s ability to become a weed here. This • having a “seed bank” (i.e., seeds last for a long time in system is based on the plant’s biological and ecological the soil and may germinate many years later, or they characteristics (its natural history, performance in its na- can accidentally be moved around with the soil). tive environment, and behavior in other parts of the world). By considering the information the system has assembled, How to use this resource we can predict how the decision to plant a particular plant This document gives a brief outline of the characteristics may affect the native Hawaiian environment. of seven plant species with fragrant flowers. Because Preventing invasive species from becoming estab- of their low risk of invasiveness, they are suitable for lished in Hawai‘i is the most economically and envi- planting in Hawai‘i landscapes. Resources for in-depth ronmentally efficient method of dealing with unwanted information on plant care are included in the references weeds. The plants in this publication have been screened section. The HPWRA is a predictive tool based on by the HPWRA. They are considered to be of low risk for current knowledge about a plant species. The system invasiveness to Hawaii’s agricultural systems and native correctly classifies 80–85% of non-pest (low-risk) spe- environments. For more information on the HPWRA, cies. If one of the species described in this publication visit www.hear.org/wra. starts to exhibit invasive characteristics, please contact [email protected]. Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in coopera- tion with the U.S. Department of Agriculture. Andrew G. Hashimoto, Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822. An equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, age, religion, color, national origin, ancestry, dis- ability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. CTAHR publications can be found on the Web site <http://www.ctahr.hawaii.edu/freepubs>. UH–CTAHR Non-invasive Landscape Plants with Fragrant Flowers OF-46 — Feb. 2010 Champaca (miulana melemele) Forest and Kim Starr Scientific name: Michelia champaca Native distribution: China, Bangladesh, India, Myanmar, Thailand, Vietnam, Indonesia, Malaysia Family: Magnoliaceae (magnolia family) HPWRA score: low risk www.oramsnurseries.com.au Preferred conditions Plant description Soil: fertile, well-drained, pH neutral to slightly acidic Evergreen tree Light: full sun Height: 20–70 ft Water: moist to moderate Spread: 10 ft USDA Hardiness Zones: 9–11 Growth rate: slow Elevation: 30–4900 ft Dispersal mechanism: birds Management Propagation methods: Flowers from seed Fertilizer: general purpose fertilizer before growth Fragrance: musky begins in the spring Color: deep yellowish-cream to orange Care: space 15–20 ft apart; pruning is rarely needed Size and shape: 1.5–2 inches long; cup Flowering period: throughout the year Pests and diseases Pollinator: beetles, other insects Aphids cause leaf curling, a fungus causes a leaf-spot disease Low-risk characteristics not a weed elsewhere no vegetative reproduction limited seed production no seedbank 2 UH–CTAHR Non-invasive Landscape Plants with Fragrant Flowers OF-46 — Feb. 2010 Chinese confederate-jasmine (maile haole) Forest and Kim Starr Forest and Kim Starr Scientific name: Trachelospermum jasminoides Preferred conditions Native distribution: China, Japan, Korea, Vietnam Soil: well-drained, acidic pH Light: full sun to partial shade Family: Apocynaceae (dogbane family) Water: moderate HPWRA rating: low risk USDA Hardiness Zones: 7–11 Elevation: sea level to above 3000 ft Plant description Management Evergreen woody climber Propagation methods: cuttings Height: 10–30 ft Fertilizer: complete fertilizer, twice a year Spread: depends on supporting structure Care: space 6–8 ft apart; prune after flowering Growth rate: fast to control spread Dispersal mechanism: vegetative fragments moved as Pests and diseases garden waste oleander scale, sooty mold Flowers Low-risk characteristics Fragrance: nutmeg-scented Color: white no evidence of seed production in cultivation Size and shape: tube 0.2–0.4 inches; star requires specialist pollinator Flowering period: warm months limited dispersal mechanisms Pollinator: hawkmoth no seedbank when cultivated 3 UH–CTAHR Non-invasive Landscape Plants with Fragrant Flowers OF-46 — Feb. 2010 Gardenia jasminoides (kiele) Forest and Kim Starr Forest and Kim Starr Scientific name: Gardenia jasminoides Preferred conditions Soil: high in organic matter, well-drained; acidic pH Native distribution: China, Japan, Taiwan, Vietnam (5.0–5.5) Family: Rubiaceae (madder or coffee family) Light: full sun in cooler areas, light shade in hotter areas Water: moist HPWRA score: low risk Temperature: 60–75˚F Elevation: 10–2500 ft Plant description Management Evergreen shrub Propagation methods: cuttings 4–6 inches long; Height: 2–6 ft grafted cuttings on nematode-resistant rootstock Spread: 4–5 ft Fertilizer: ratio of 3:1:2 or 3:1:3 Growth rate: moderate Care: space 5 feet apart; prune after flowering Dispersal mechanism: birds (fruits rarely seen) Pests and diseases Flowers aphids, mealybugs, spidermites, scales, whitefly, thrips; Fragrance: rich, sweet, mimics jasmine powdery mildew, root-knot nematode, sooty mold Color: white Size and shape: 2–5 inches; round Low-risk characteristics Flowering period: late spring to early summer not tolerant of a wide range of soil conditions Pollinator: possibly moths limited seed production doesn’t reproduce vegetatively 4 UH–CTAHR Non-invasive Landscape Plants with Fragrant Flowers OF-46 — Feb. 2010 Plumeria (melia, pua melia) Forest and Kim Starr Forest and Kim Starr Scientific name: Plumeria obtusa Preferred conditions Native distribution: Mesoamerica; Caribbean Soil: well-drained, slightly acidic Light: full sun Family: Apocynaceae (dogbane family) Water: moist HPWRA score: low risk Temperature: 60–90°F Elevation: 10–2000 ft Plant description Management Small tree Propagation methods: tip cuttings, seed (not com- Height: 3–30 ft mercially available) Spread: 30 ft Fertilizer: use 10–30–10 every three to four months Growth rate: fast Care: space 10–15 ft apart, prune in the winter Dispersal mechanism: wind (rarely produces seed) Pests and diseases Flowers long-horned beetle, thrips, whiteflies, mites, blossom Fragrance: sweet midge; plumeria rust, leafspot, shoot blight, Color: white with yellow center powdery mildew Size and shape: 2–3 inches diameter; tubular Low-risk characteristics Flowering period: March to October Pollinator: possibly hawkmoth not shade tolerant limited dispersal mechanisms limited seed production no seed bank 5 UH–CTAHR Non-invasive Landscape Plants with Fragrant Flowers OF-46 — Feb. 2010 Southern magnolia (mikinolia) Forest and Kim Starr Scientific name: Magnolia grandiflora Native distribution: southeastern and south-central United States Family: Magnoliaceae (magnolia family) Forest and Kim Starr HPWRA score: low risk Preferred conditions Soil: deep, sand, humus-rich, acidic pH Plant description Light: full sun to partial shade Evergreen tree Water: wet to moderate Height: 45–80 ft (25 ft in Hawai‘i) USDA Hardiness Zones: 7–10A Spread: 30–40 ft Elevation: 0–500 ft Growth rate: medium Dispersal mechanism: birds Management Propagation methods: grafting or by seed Flowers Fertilizer: general fertilizer every three months in the Fragrance: lemon–scented