Ornamental Horticulture


Our outreach program is based on people using our research. Research and outreach priorities are driven by stakeholders, from whom we seek advice and feedback. In part, ornamentals outreach is conducted through a liaison with the Cooperative Extension Center. The Center organizes and coordinates most of our training programs in ornamental horticulture through its GreenShare, Learning Landscape, and Master Gardener programming. The RI ornamental plant industry relies heavily on the outreach efforts of our faculty with extension responsibility (Maynard, Englander, Mitkowski,Casagrande).

Sustainable Landscape

Plant Development: Our outreach emphasizes sustainable landscapes: We focus on plant materials that are economical to grow and maintain—in home, work, and recreational plantings—and that require a minimum of water, fertilizer, or pest control chemicals. Our goal is to minimize the environmental impact of landscape plant management. Development of plant materials includes selecting, breeding or modifying plants through biotechnology, and promoting market acceptability through outreach.

The focus of the tree and shrub development program is to develop and evaluate novel ornamental plant germplasm for use in New England landscapes. Priority is given to trees and shrubs suitable for cultivation by RI growers and for use by RI landscapers. A second focus is to obtain and evaluate plant materials that may be substituted for pest-prone taxa, such as salt-tolerant conifers suitable for replacement of Japanese black pines dying along the RI seaboard, and replacements for infested Canadian hemlocks

Tree and shrub evaluation is conducted at the RI AES East Farm, as well as at test sites sited around the state to take advantage of mesoclimactic conditions (eg. salt spray tolerance). We regularly engage the industry to participate in the evaluation program, through field days, twilight seminars, and presentations. This research objective is tightly linked to the Sustainable Landscapes Program, Master Gardener curriculum, and new Invasives Species Management program discussed below.

Relevance to Stakeholders: The Green Industry benefits greatly from having a greater selection of plant materials to grow and offer to consumers. As we have promoted the use of sustainable plants to the public through our Outreach programs, the industry has been hard pressed to give up growing pest-prone crops that are central to their production programs. It is our responsibility to evaluate concurrently the plants we promote, including production and marketing issues, for the industry. Plant Selection and Development have been identified as priority concerns by the Rhode Island Nursery and Landscape Association, New England Nursery Association, and Horticulture Research Institute.

Plant Management

Ornamentals plant management has the following foci:

  • Increase the efficiency of novel methods, developed at URI over the last 5 years, for clonally propagating trees and shrubs using less water and chemicals
  • Improve treatment of nursery fertilizer and chemical runoff using ornamental plant biofiltration systems that produce a saleable crop while addressing pollution concerns
  • Evaluate the loss of nutrients and pesticides through above-ground and pot-in-pot production systems using a newly developed total-capture irrigation system
  • Reduce the impact of growing deer populations on the Green Industry by evaluating and devising solutions to the problem of deer damage to trees in nurseries and landscapes, specifically that caused by antler rubbing.

Relevance to Stakeholders: Nursery and landscape organizations at the state, regional and national levels have all identified production efficiency, water quality and wildlife control as top issues for Land-Grant institutions. Results of research are disseminated to the Green Industry through a variety of outreach channels, including newsletters, popular and research articles in national-level professional magazines, refereed publications, and presentations at conferences and short courses.

Pest Management

Our tree and shrub pest management outreach program emphasizies getting producers and users of nursery plants to avoid pest-prone plants and use pest-resistant alternatives. To this end, we have produced and widely distributed a URI bulletin that lists and describes ornamental plants that are sustainable in this region. We have also facilitated locating these plants through the publication of a RI Nursery Stock Source List. Revision and promotion of these lists is an ongoing process.

We are also r esearching biological control of key nursery pests, including the hemlock woolly adelgid and the birch leafminer. (Discussed under Invasive Species – Biological Control.) Research on plant pathology in trees and shrubs is derived from both local needs (eg. Phytopththora on Rhododendrons) and national problems (eg. Sudden Oak Death, below). Locally, Rhododendrons provide a major revenue source for nurseries. Unfortunately, they are highly susceptible to Phytopththora, which causes significant losses annually. We wamt to identify and quantify resistance to this disease in available germplasm.

A problem commonly seen problem in commercial apples is “apple replant disease”. This disease complex is found nationwide and frequently makes it impossible for growers to plant new trees in established orchards. While it has yet to be identified on crabapples, it is likely that it does occur on them. Crabapples are planted widely in the Northeast and a crabapple orchard exists at the University of Rhode Island. Using this facility as a resource, we are attempting to determine the severity of apple replant on crabapples and appropriate management strategies for landscapers and homeowners wishing to grow crabapples.

A new fungus species was found recenty to be causing rapid death of oaks in California(Sudden Oak Death). The fungus has been found since on a multitude of under-story shrubs, forest trees, and woody nursery plants, with the host list growing by the week. Nursery crops frequently are moved about the country and may act as vectors of the disease, potentially devastating oak forests and urban/landscape plantings throughout North America. Despite severe quarantines against movement from affected areas in California, the pathogen has been found killing trees in Oregon (a major source of plant materials for the RI Green industry). The USDA recently funded a cooperative project between URI (L. Englander) and the USDA-ARS Plant Quarantine facility in Ft. Detrick MD to provide essential knowledge about the environment and biology of this pathogen.

Relevance to Stakeholders: Stakeholder input largely drives our programs in pest management in ornamentals. We meet frequently with RINLA members, both formally (research committee) and informally to determine their research needs. We use many outreach venues including the URI GreenShare program, locally-produced articles (RINLA Newsletter), seminars, presentations at RINLA meetings, and the annual Disease-Resistant Crabapple Open House.

Invasive Species

Of the thousands of exotic plants that were introduced and distributed in this country for horticultural or agronomic uses over the past three hundred years, several species are now widely regarded as pests. Well-known examples include kudzu, crabgrass, dandelion, barberry, and purple loosestrife. Some important ornamental plants (Norway maple, winged euonymous, Korean dogwood) have invasive tendencies, which may present problems in minimally managed landscapes. Our focus is on continuing to identify invasive species and select, evaluate and promote suitable alternative species for the nursery and landscape industries. Our specific goals are toInvasive Ornamentals: Non-native plants and animals that are introduced into North America typically come without the natural enemies that keep them in check in their native habitats. Freed from these natural controls, these aliens often reproduce and spread with abandon. Our department is addressing this issue on two fronts: a) we are attempting to reduce the risk from purposeful plant introductions, and b) we work on biological control of select insect and weed problems.

  • Evaluate existing and potential new ornamental plant introductions for potential invasiveness
  • Develop ornamental plants which do not reproduce and spread in the landscape, and
  • Promote plants which are non-invasive alternatives to current invasive ornamentals.

Relevance to Stakeholders: Invasive plants affect many stakeholders, as well as the ecosystems that are altered by the proliferation of non-native species. Resource managers, environmentalists, green industry professionals and the public all recognize the impacts of invasive plants and animals on native species. However, the perception of best solutions to the invasives problem varies widely among stakeholders. All agree that more research is needed on the invasiveness of the many non-native plants in cultivation, as well as mechanisms for removing existing infestations. The Green Industry plays a central role as producers of many invasive ornamental plants. It is our role to discourage nursery growers and landscapers from using known invasive plant species, and to promote the use of alternative sustainable plants.

The concept of engineering sterility into popular and commercially important ornamental plants, which also happen to exhibit invasive tendencies, is exciting and could have hugely beneficial implications, regionally, nationally, and globally. Examples that would have a tremendous impact on the green industry include Berberis thungergii (Japanese barberry), Euonymus alatus (burning bush). and Acer platanoides (Norway maple). This would be an ideal focus for horticulture biotechnology research and infrastructure building using the recent USDA Special Agriculture Appropriation. Invasive plants are a Presidential initiative and directly impact the nursery industry.

We have actively promoted non-invasive plants and alternative species for years through the Sustainable Landscapes Program. At present, we are tightly engaged with the nursery industry on the issue of producing invasive plant species. A segment of our faculty are actively involved with the Rhode Island Invasive Species Council, and will be increasing efforts to identify potentially invasive species that are presently in production by the industry.

Biological Control

There are about 1,700 introduced insects in this country and over half of them are identified as pests. The 300 species of invasive plants in North America have already infested 100 million acres and infest another 3 million acres per year (about 4.5 times the land area of R.I.). Combined with the other exotic invasive animals (such as zebra mussels) these invasive species cause roughly 123 billion dollars in damages annually in the USA. In many cases these problems can be solved by “reacquainting” these “pests” with their effective natural enemies in a deliberate process called “Classical Biological Control”.

We have a USDA-approved primary quarantine laboratory: the only such university-based lab in the Northeast. This facility allows us to import and study potential biological control agents that do not exist elsewhere in North America. Our biological control programs concentrate on invasive insects and plants, particularly those of consequence to landscape plants in the Northeast. We are currently working on a range of pests including birch leafminer, hemlock woolly adelgid, lily leaf beetle, purple loosestrife, Cypress spurge, and Phragmites australis (common reed).

Relevance to Stakeholders: We select our pest problems based upon stakeholder needs presented to us by individuals (farmers, nurserymen) and organizations (North American Lily Society, Massachusetts Horticultural Society, Rhode Island Nursery/Landscape Association, Rhode Island Invasive Species Council). The biological control program has many outreach venues including the URI GreenShare program, locally-produced articles (RINLA Newsletter, Maritimes, RI Audubon Newsletter, Wild Plant Society Newsletter), presentations (RI Natural History Survey, SeaGrant and US Forest Service workshops, etc.). We regularly organize and participate in a Northeast Biocontrol Workshop through the Entomological Society of America. We provide our expertise (and our insects) to clients to solve problems with invasive species including solving the purple loosestrife problem at Roger Williams Park Zoo (and elsewhere in RI) and controlling Cypress Spurge at URI’s Alton Jones Campus and at Watson Farm in Jamestown.