Some invasives you don’t want to grow


Too often, a new species of plant or plant pest arrives in Hawaii. They are missed in entry inspections or we simply don’t realize the risk they pose to our fragile environment.

Once invasive species arrive, it is very hard to control their spread. Some, such as the coqui frog, coffee berry borer and kahili ginger, thrive here with little natural competition. Frog cacophony has driven folks from their homes, the borer is making coffee farming very challenging and the kahili is invading native habitats in places including Hawaii Volcanoes National Park.

We can help stop the spread of invasive plant species by keeping them out of our gardens, asking nursery owners not to sell them and reporting their location to the Big Island Invasive Species Council at 933-3340, 961-3299 or 643-7378. You may also contact Page Else at pageelse@hawaii.edu or 933-3345 to discuss the problem.

Several plant families have invasive members in their ranks. The Melastomataceae family includes several serious weedy plants that are destructive enough to be prohibited further entry into the state. Some are already wreaking havoc in native forests and fallow areas in the state. Beyond not planting a pest, we can educate our communities and help folks safely dispose of these plants.

The three Melastomataceae family genera that are particularly invasive are Tibouchina, Medinilla and Miconia. Some of these are present in local gardens and all are on the Hawaii Invasive Species list. Visit plantpono.org, hawaiiinvasivespecies.org or state.hi.us/dlnr/dofaw/hortweeds for more about invasive plants.

Tibouchina semidecandra is a shrub that can grow to 15 feet and is commonly known as the princess flower. It produces lovely purple flowers up to 5 inches across and has dark green, velvety leaves of about 5 inches long. In our tropical climate, these plants multiply rapidly and can quickly take over an area.

Dissotis rotundifolia is an ornamental ground cover that also spreads quickly. It is now crowding out native species in many locations.

Medinilla magnifica and M. cumingii are on the Hawaii Invasive Species list as they are capable of spreading beyond initial plantings and becoming naturalized as weeds. M. magnifica can grow to 10 feet tall with 10-inch leathery, ovate leaves that come to a short point. The small pink, red or violet flowers grow in long, attractive panicles that often measure 20 inches long. The fruits that follow flowering are small violet, fleshy berries that birds consume. The birds drop seeds in forested or open areas where they grow into invasive weeds. M. cumingii is a smaller version of the plant that poses the same weedy problem.

Miconia calvescens is native to Central and South America but has spread worldwide to become one of the world’s most invasive species. It came to Hawaii as an ornamental in the mid-20th century.

The tree can grow to 50 feet and has large leaves, up to 3 feet long. These purple and green leaves have attractive white veining. The trees produce large panicles of white to pink blossoms several times a year followed by tiny purple fruits that contain more than 200 miniscule seeds. The sweet berries are eaten by animals and birds that disperse the seeds. A young miconia tree can produce as many as 200,000 seeds in its first fruiting season. The seeds germinate quickly or lie dormant as long as 12 years, awaiting the proper conditions for germination. Plants grow quickly and, at full height, shade out understory plants. Their shallow root system is problematic as it facilitates soil erosion in the area.

You will see these plants in cultivation as well as in the wild. In either case, you should do what you can to get rid of them, report them to BIISC and certainly don’t take them home to your garden.

Tropical gardening helpline

Lorraine asks: I have some beautiful medinilla plants growing in a hedge across the back of my property. I have recently learned that they are on the invasive species list. What should I do?

Answer: You should get rid of them, but while you are getting a replacement ready, you certainly can help reduce their invasiveness by carefully removing all the flowers once they start producing berries. It is the berries that cause most of the problems. Birds or animals will eat the berries and disperse the seeds wherever they poop.

Visit plantpono.org for replacement suggestions. Brunfelsia americana, known commonly as “yesterday, today and tomorrow,” grows into a full shrub that could serve as a good hedging plant. It produces violet flowers that lighten as they age. It produces a wonderful fragrance at night.

Several gardenia varieties grow well as hedges here. They offer dark green foliage and bright white fragrant flowers. Consider the native Gardenia brighamii or the Tahitian variety, Gardenia taitensis.

Another good hedging plant that not only has beautiful flowers but also a delicate fragrance is one of the native hibiscus varieties. Hibiscuswaimeae is a particular favorite because of its red stamen that protrudes from the large, pure white, fragrant blossom.

Your efforts to reduce invasive species from your garden are a good start that hopefully will inspire others to do the same.

Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.Diana Duff is a plant adviser, educator and consultant with an organic farm in Captain Cook.

Diana Duff is an organic farmer, plant adviser and consultant.