This Aromatic and Useful Plant Has Earned a Place in Gardens Around the World and Across Time
UT Gardens’ September 2019 Plant of the Month: Rosemary
Submitted by Holly S. Jones, Horticulturist, UT Gardens, Knoxville
Humans have been growing and using rosemary (Rosmarinus officinalis) for more than 5,000 years. It has been documented as far back as the ancient Sumerians who inscribed it on their stone cuneiform tablets. Not only is it a beautiful plant, with its evergreen, conifer-like leaves and light blue or pink flowers, but rosemary is so useful that it has earned a place in gardens across time and around the world. Greeks and Romans grew it for medicinal, metaphysical and culinary use. Egyptians included it in their funeral preparations, and many other cultures have used it to symbolize remembrance of loved ones.
The connection between rosemary and memory has proven to be more than just an anecdote. In 2013, researchers at Northumbria University in Newcastle (in the United Kingdom) found that the scent of rosemary had a positive impact on memory. Participants who spent time in a rosemary-scented room scored 15% higher on memory tests than those who were placed in an aroma-free environment. Scientists are continuing to study the link between rosemary phytochemicals and cognitive function.
Whether you grow it for aromatherapy, for culinary purposes, or simply for its beauty, rosemary is a must have for your garden. This woody-stemmed member of the mint family can grow up to four feet tall or more when given the right growing conditions. There are also prostrate forms like ‘Dancing Waters’ that can grow along the ground or drape over the edge of a rock wall or container.
Rosemary grows best in full sun and requires excellent drainage. If your soil doesn’t drain freely, consider growing it in a raised bed or container. Even the hardiest rosemary plant will not survive a winter with waterlogged soil. During the growing season, it is best to allow it to dry out between waterings. Once established, rosemary is drought tolerant and overwatering can lead to root rot.
For Tennessee gardeners, rosemary is generally considered a half-hardy plant, which means it doesn’t always survive the winter. Most varieties are rated hardy for zones 8-10 with the exceptions being ‘Arp’, ‘Hill Hardy’ and ‘Salem’, which are rated for zone 7. ‘Arp’, is an upright, quick-growing variety that has been flourishing in a raised bed in the kitchen garden at the UT Gardens, Knoxville, for more than five years. If overwintering is a concern, you can simply treat rosemary like an annual and purchase a new plant each year. If you prefer, you can bring the plant inside for the winter and keep it in a sunny window until the danger of frost has passed the following spring.
Another option is to propagate your rosemary plant towards the end of the summer. This will give you small plants that won’t take up a huge amount of space indoors. Using a sharp pair of clean pruners, take 4- to 6-inch cuttings from healthy non-flowering, pest- and disease-free growth. Trim up the leaves, leaving about three or four leaves at the top. Dip each cutting end in rooting hormone, which can be purchased at most garden centers. Fill plastic pots with a free-draining, sterile potting mix, and insert each cutting all the way up to the first set of leaves. Firm them in the mix. Next water them well and let them drain. Seal your pots in a plastic bag to create a humid environment, place them out of direct sunlight, and wait about three to six weeks. Be sure to check the moisture level periodically to ensure the potting mix does not dry out completely. As soon as your plants take root they can be removed from the bag and moved to a sunny window. Rosemary is one of the easiest plants to propagate and doing so is a great way to ensure that you will have this useful, beneficial plant in your garden.
The UT Gardens includes plant collections located in Knoxville, Jackson and Crossville. Designated as the official botanical garden for the State of Tennessee, the collections are part of the University of Tennessee Institute of Agriculture. The Gardens’ mission is to foster appreciation, education and stewardship of plants through garden displays, educational programs and research trials. The Gardens are open during all seasons and free to the public. For more information, see ag.tennessee.edu/utg.