Family: Myrtaceae

Genus: Leptospermum

Species: Over 80

Origin: Australia, New Zealand, and Southeast Asia

Height and Spread: From groundcovers to trees

Bloom time: Varies by species, mostly spring and early summer

Location: Several species can be seen in the Pacific Connections Australia Entry Garden, Leptospermum scoparium is also prevalent in the New Zealand Forest.

You may be familiar with tea trees from the myriad of products containing oils from these plants. From shampoo and soap to lotions and candles, tea tree oil infused products seem to be everywhere you look. Manuka honey, made when honey bees use nectar from Manuka (Leptospermum scoparium) is another product you will likely find in your local grocery store. What you may not know is that many tea trees thrive in our Pacific Northwest climate and several species can be admired in the Australian section of the Pacific Connections Garden at the Arboretum.

The tea tree genus, Leptospermum, is in the Myrtaceae (myrtle family), and includes about 85 species, almost all of which are endemic to Australia. A few species are distributed throughout Southeast Asia and New Zealand. The common name ‘tea tree’ comes from Captain James Cook who made tea from the leaves of the plants to prevent scurvy in his crew. Manuka, the most commercially used species, is native to New Zealand and Australia. Confusingly, another Australian plant in the Myrtaceae family, Melaleuca alternifolia, is also known as tea tree and essential oils from this plant are also widely commercially available. This post focuses exclusively on plants in the Leptospermum genus.

Manuka has long been recognized for its unique healing properties by the Māori people of New Zealand. Traditional uses include using it to treat skin infections and burns and inhaling the vapors from steaming the plant to treat colds and respiratory ailments. In addition to medical uses, durable wood from manuka is prized for a variety of tools including canoe paddles, spears, and gardening tools. Tea tree oil extracted from the leaves of manuka has been the subject of many western scientific studies and has been shown to have antibacterial and antifungal properties. Manuka honey originated much later when European honeybees were introduced to New Zealand in the 1830s. Although manuka honey was being used medicinally for decades, its popularity exploded in the 1980s after western scientists confirmed its unique antimicrobial properties. It is currently used for treatment of burns and other skin wounds where infection risk is high.

Several tea trees species can be seen in the Pacific Connections Australia Entry Garden at the southern end of the Arboretum. All the species in our collection are evergreen, thrive in full sun, are drought tolerant once established, and have the distinctive tea tree scent when their leaves are crushed. One of my favorites is the evergreen creeping alpine tea tree, Leptospermum rupestre, which is from the high mountains of Tasmania. In summer, this ground cover is covered with small white flowers and is popular with the bees. Alpine downy tea tree, Leptospermum namadgiensis, is a larger species growing up to eight feet tall and wide with tiny delicate leaves. Even larger is the wooly tea tree, Leptospermum lanigerum, which has silvery foliage and can reach up to twelve feet high. Manuka, Leptospermum scoparium, grows as a narrow shrub in our climate typically topping out around eight feet high, and four feet wide. Manuka can be viewed in the New Zealand Forest section of the Pacific Connections Gardens.

During these dark months of Seattle winter I find it helpful to have a destination to get me out of the house. This is a great time to come admire the evergreen foliage and lovely scent of the Arboretum’s tea trees.

Sources:

Mandal MD, Mandal S. Honey: its medicinal property and antibacterial activity. Asian Pac J Trop Biomed. 2011 Apr;1(2):154-60. doi: 10.1016/S2221-1691(11)60016-6. PMID: 23569748; PMCID: PMC3609166.

Song, C.-Y., Nam, E.-H., Park, S.-H. and Hwang, C.-Y. (2013), In vitro efficacy of the essential oil from Leptospermum scoparium (manuka) on antimicrobial susceptibility and biofilm formation in Staphylococcus pseudintermedius isolates from dogs. Vet Dermatol, 24: 404-e87. https://doi.org/10.1111/vde.12045