Today’s column comes to you from the Royal Botanic Gardens of Kew. We are here for a meeting of the International Palm Society. For those who have not experienced this amazing 500 acre plus garden, it is like the Walt Disney World of horticulture. The gardens date back to the early 18th century as royal palace gardens to today’s globally renowned scientific institution for plant and fungal research. In 1759, Princess Augusta, mother of King George the third, started it all. Today it employs over a thousand people. Kew is London’s largest UNESCO World Heritage site and houses over 50,000 species both native and introduced from all over the world. We are here primarily to study the family of palms.
It would take a lifetime or two to even scratch the surface of all the horticultural knowledge represented here. Most interesting is how many plants from temperate regions are used to create a tropical look. Because of Kew, one can see the impact in unique landscapes all around London and beyond. What a surprise to see many cold hardy palms, bamboos and even bananas throughout England, Wales and even north to Scotland creating a tropical ambiance.
Visiting tropical places like Hawaii is the treat of a lifetime to millions of people a year. One of the highlights for them is to experience the lush tropical gardens and forests that are unlike any place in the continental United States. Many folks who enjoy gardening go home wishing they lived in a tropical place where they could have yards and homes filled with palms and other exotics. Some mainlanders create a mini oasis with lots of houseplants. Others even build solariums or small greenhouses to get their tropical fix, but ambiance can be created in colder parts of the country with the selection of tropical looking plants with the right landscape design.
The air of freedom and informality in Hawaiian gardens is partly due to the exotic plant materials used. It is also due to the casual style of design found throughout the islands. This consists of mixing many bold and colorful shrubs, ground covers and trees in a relaxed, unregimented manner. This type of landscaping gives a sort of well-maintained jungle effect.
The best part is that the look can be done anywhere there is a place to grow things. It can be achieved with almost any plants, but to develop that kind of look, the selection should be those with a bold lush look. There are very hardy warm temperate trees like some species of rhododendron, magnolia and camellia that can give the tropical effect. This combined with global warming has allowed gardeners to grow some plants that could not be grown in the region 100 years ago.
One tree that is finding its way northward is the albizzia julibrissin or Persian silk tree. Although very tropical in appearance, with its poinciana-like foliage and pink pompon flowers, this tree will tolerate conditions below zero degrees. The silk tree is native to Asia and can reach heights of up to 40 feet but is usually much smaller, spreading like an umbrella to 20 feet. The tree’s filtered shade allows grass and other plants to grow underneath. It also makes a very good patio tree.
The gingko biloba, or maidenhair tree, is another from China that will tolerate sub-zero temperatures. This tree is a living fossil from the era when tree ferns and palms were growing throughout North America. Cities like New York are using them as street trees to reduce the negative effect of concrete and asphalt. Another close relative of our ohia (Meterosidos polymorpha) is s species from New Zealand (Meterosidos tomentosa} that is almost identical but cold hardy. There are probably selections of our ohia from the high mountains that are also very tolerant of cold.
When it comes to palms and ferns to create a tropical look, there are those that are fairly hardy. If you live in an area where temperatures seldom reach 10 degrees or colder, the Trachycarpus fortunei or windmill palm is a great one for the ultra-tropical look. It is relatively fast growing to about 30 feet. This palm should be used in groups of three to seven for a dramatic effect. The many healthy specimens in Seattle, Washington attest to this tree’s ability to withstand cold. They may even be found in Scotland and Switzerland. Another much slower palm that is equally hardy is the Chamaerops humilis or European fan palm. This clumping type has been known to sustain temperatures of six degrees above zero. There are several other palms that will grow as far north as coastal Oregon.
There are several hardy bamboos that will take temperatures below zero. Close relatives of bamboo, like the arundo from the Mediterranean, can be used in areas where temperatures are below zero. Although this giant reed may freeze down in winter, give it a protective mulch with a good rich soil and it will grow from six to fifteen feet in a summer. Another popular bamboo relative is pampas grass, or Cortaderia sellowana, from Brazil and Argentina. This versatile clumping grass will tolerate dry to wet soils and temperatures close to zero if protected by mulching. Two bananas, Musa sikkimensis and Musa basjoo will also winter over with protective mulch as will our taro.
The list of tropical-looking but hardy plants is extensive. You might consider trees like the hardy eucalyptus species. These include the cider gum and snow gum,that survive temperatures close to zero.
When it comes to fruits, the fig, pomegranate, olive and loquat can all be found growing as far north as Seattle, Washington on the West Coast.
Your mainland friends can experiment with these and others that nurseries and garden centers carry, or try some from more southerly locations. To avoid discouragement, check with garden books that cover plant hardiness. One good reference is Sunset’s Western Garden Book that may be found in garden shops. You may also call the UH master gardener helpline at 322-4893 in Kona or 981-9155 in Hilo.
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Norman Bezona is professor emeritus, University of Hawaii College of Tropical Agriculture and Human Resources.
