Hawaii gardeners have the advantage of a year-round growing season that allows us to pick up plants any time of year and add them to our backyard collection. And local garden centers carry an abundance of ornamental shrubs, trees and herbs from which to choose.

The University of Hawaii Cooperative Extension Service wants to help home gardeners to be knowledgeable when choosing plant material. The UH Master Gardeners on Oahu have teamed up with the Hawaii Invasive Species Council to provide classes and demonstrations to the public. (See the Star-Advertiser’s Home & Garden calendar for class listings.)

What is an invasive species? Technically, according to HISC, an invasive species is an alien species — plant, animal, or microbe transported by humans to a location outside its native range — whose introduction has caused or is likely to cause economic or environmental harm or harm to human health.

Basically, foreign plant material that propagates at warp speed and those seeds or plant parts that can travel long distances to naturally forested areas are termed invasive. These plants often demonstrate rapid and aggressive growth, production of numerous seeds that are spread easily by wind, wing or water, and the ability to grow under many different soil and climatic conditions.

What is the impact of invasive species? It’s the plants whose "keiki" reach the natural forested areas that take the largest toll on our native species and ecosystems. They threaten native plant habitats, reducing the number of native plants and affecting plant biodiversity, as well as the insect biodiversity that depends on those plants.

Aside from harming the environment, the control of invasive plants costs manpower and money. The elimination of infestations requires herbicide applications or back-breaking work cutting down or pulling out plants, and can take years. The small efforts to prevent the spread of invasive species or catch an infestation early on are still the most cost-effective ways to keep invasive plants out of our local landscapes.

Urban gardeners in Hawaii can help by becoming knowledgeable about invasive species. Several UH College of Tropical Agriculture and Human Resources publications have been produced to inform the public about non-native plant alternatives. For example, "Non-Invasive Landscape Plants with Fragrant Flowers" lists Champaca (miulana melemele), a beautiful evergreen tree with yellowish-cream to orange flowers that blooms year-round. Other plants listed include plumeria, Tahitian gardenia and southern magnolia, all widely available in local garden centers.

Please call your local UH Master Gardener Helpline to be directed to these publications for full details of each plant (call 453-6055 on Oahu to inquire about your local Helpline number).

Prevent the introduction of invasive species in the landscape by learning to identify those plants with invasive potential and being knowledgeable about alternative noninvasive species.

"Plant Pono!" is the theme of this month’s Second Saturday from 9 a.m. to noon Saturday at the Urban Garden Center in Pearl City. Classes on invasive species will be held at 9:30 and 11 a.m. The cost is $5. Other activities include guided tours and a seed sale. For more information, visit www.ctahr.hawaii.edu/ougc or call 453-6055 or 453-6050.

Jayme Grzebik is an urban horticulturist with the University of Hawaii-Manoa Cooperative Extension Service, part of the College of Tropical Agriculture and Human Resources. Reach her at grzebik@hawaii.edu.