Where Did Thuja Green Giant Come From?

Thuja Green Giant is the most popular and widely-grown hedging plant off all time. Millions of satisfied gardeners enjoy the benefits of its rapid growth and easy care. Most people take plants for granted, thinking they just ‘are’, but perhaps you have wondered, “Where did this plant come from? Does it grow somewhere in the wild? Did some scientists or nursery-person create it? Is there a connection between its origin and how fast-growing and sturdy it is?” Let’s see if we can answer these questions.

First of all, Thuja Green Giant is not a wild plant – it is the product of gardening itself, which has brought into being thousands and thousands of plants for us to eat and enjoy. Selecting certain plants for their special features is as old as agriculture. If we could only put on our tables plants that can be found growing wild, then we would have to ignore almost every fruit and vegetable we eat. There are plenty of ornamental plants growing in our gardens that can be found growing wild somewhere in the world, but many more that have been created for our enjoyment. Thuja Green Giant is such a plant, with a long and complex history.

The Origins of Thuja Green Giant

About 150 years ago, in 1878, a gardener and amateur botanist called Dorus Poulsen started a nursery to grow and sell plants, in Frijsenborg, Denmark. It soon became famous and very well-regarded, especially for its roses, which Dorus bred himself. He opened several branches across Denmark, and when he died in 1925 his sons continued the business, producing many new plants from their breeding programs. In 1937 they noted a novel Thuja growing, but it is not clear if this was an accidental seedling, or part of some breeding they had done.

History stepped in, World War II broke out, and Europe had more important things to think about than plants. After the war the nursery returned to normal activity, and eventually, in 1967, thirty years after that first chance discovery, the National Arboretum in Washington D.C. received a package of plants from one of the Poulsen nursery branches, in Kvistgaard, Denmark. Included in the shipment were several different Thuja plants, which the Arboretum staff planted out in a nursery area at the arboretum. The speed of growth on one of them was noticed, and that plant started to get some excited reactions when it reached 30 feet tall in 25 years.

When the staff looked back through their records, they quickly found that the book-keeping had been less than perfect. The plant numbering had become confused, and they could not figure out which Danish plant ths was. Suspecting the plant was a hybrid, something that had never been seen before among Thuja plants, three scientists became interested, and with the recent development of DNA analysis, they saw a way to solve the mystery. These three scientists, Susan Martin, from the National Arboretum; Robert Marquard, from the Holden Arboretum in Ohio; and Kim Trip, from the New York Botanic Garden got to work, and succeeded in analyzing the DNA all the plants at the Arboretum, and comparing it to that of the parents of those 1967 plants from Denmark.

A Hybrid Child

The scientists were able to link this mystery giant Thuja to the plant found in 1937 at the Poulsen nursery, and showed that it was indeed a hybrid between two species of Thuja. One parent was the Western Redcedar, Thuja plicata. This forest giant can reach 200 feet in height, and grows wild in Oregon, Washington State and British Columbia. It is the source of the lumber called red cedar, which is ideal for garden construction and furniture, since it is naturally resistant to decay and needs no paint or preservatives.

The second parent was the Japanese Arborvitae, Thuja standishii. This plant grows wild high in the mountains of the Japanese Islands of Honshu and Shikoku. It is also cultivated in Japan for its wood, which is aromatic and waterproof, and is used for sake cups and barrels.

Just what had happened in that nursery in Denmark in the 1930s is not clear, but somehow a trans-pacific hybrid had been created, a plant that had beautiful foliage all year round, grew vigorously and very quickly, and was graceful, upright and worthy of a place in every garden. Botanist already new that crossing together two different species of plants produced what they call ‘hybrid vigor’ – strength, hardiness, speed of growth and resistant to pests that neither parent has. Thuja Green Giant had hybrid vigor in spades.

Thuja Green Giant Takes Off

A nurseryman from Tennessee called Don Shadow was the person who suggested the name ‘Green Giant’, and a major US nursery group called Wayland Gardens decided to multiply and promote this plant to home gardeners. They propagated thousands of young plants of Thuja Green Giant from that original plant, and began a program to describe its benefits to gardeners. This great evergreen lived up to everything promised of it, and by 2004 it was the top-selling plant at Wayland Gardens. Other growers picked it up, and since there was no plant patent on it, everyone could freely reproduce it. In the south-east, many gardens had old hedges planted in the 50s and 60s, which were diseased and needed replacing. So the timing was perfect for the introduction of a new hedging evergreen. Millions of plants were sold to replace those old hedges, and Thuja Green Giant, the child of two trees from different continents, who met on a third, became the most popular and successful hedge plant in America.