Plant of the Month


Plant of the Month Archive


The Dew of the Sea



November is typically filled with a saturnalia of autumn color that ultimately tasks the gardener with the chore of leaf raking as they begin to fall.  It is a job I never disliked, since the two weeks of riotous color was always worth the resulting effort.  However, there are also plants that remain subdued until the days approaching Thanksgiving when they truly shine.  Of course, I am referencing our evergreen herbs and in particular, Rosmarinus officinalis or Rosemary!

With its prominent fragrance, it is not surprising that Rosemary is a member of the Lamiaceae or the Mint Family.  It is a small genus with only 2 or 3 species, all of which are found in the region surrounding the Mediterranean Sea.  The genus name was initially penned by Carl Linnaeus (1707-1778) in 1753.  The name is derived from the Latin Ros or Dew and Marinus meaning sea.  Hence, Rosmarinus literally means the Dew ofPOM the Sea, reflecting its Mediterranean origins.  The species epithet of officinalis was also penned by Linnaeus, but in a much earlier publication dated 1735. It stems from the Latin officina, which originally meant workshop or place of work.  Later, it became the name for the storage room in monasteries where medicines and medicinal plants were stored.  Officinalis means ‘belonging to an Officina’ and Linnaeus affixed this epithet to plants or animals that were known to have medicinal benefits.  Rosemary was in fact well known through the ages for its health benefits.  One of the main constituents of the foliar oils is rosmarinic acid, which is known for reducing inflammatory disorders and pain.  It also functions as an antioxidant and it relaxes the smooth muscles found in capillary and arterial walls, enhancing blood flow.  Perhaps due to improved circulation it was credited with improved memory and was often displayed at funerals to ensure remembrance for those who had passed.  On a happier note, it was also carried by a bride to enhance the love between couples!

Indeed, Rosemary is an herb with many wonderful and beneficial effects on people!  The challenge, is maintaining the health of the plants where winter temperatures dip lower than 15°F, is getting the plant to survive the winter!  Rosemary requires very well drained soils and full sun to prosper, and if the soil become waterlogged during the winter, death is certain to follow.  The plants also benefit from a slightly alkaline soil with a pH of 7-7.8.  The aromatic, needle-like foliage (picture above right) is leathery in texture, approximately 1” long and is arranged oppositely on the light tan branches.  The leaves are green on top and white beneath, POMwith a prominent central vein and margins that are rolled downward.  The foliage is evergreen in warmer climates, but it can scorch as temperatures dip below 15° F.  Flowers appear soon after winter retreats in warmer regions, but in NJ, the flowers do not begin to appear until mid-summer and often continue well into autumn.   The nearly tubular flowers range from white to light blue to pink, are up to 1” long and appear in the leaf axils in clusters of typically 2 or 3.  The flowers are labiate, meaning they have an upper and a lower lip, with the upper lip having two lobes and the lower lip divided into three.  Although sprigs of the plant can be harvested nearly year-round in warm climates, plants do not respond well to a late winter and spring pruning in NJ and harvesting is best restricted to summer and early fall.  Both the flowers and the leaves can be used for seasoning, with the somewhat bitter flavor making a nice compliment to lamb, beef and poultry.

As a rule, forms that are prostrate in habit or have a darker blue flower will be less hardy than the upright forms sporting light blue flowers.  For those gardening where temperatures frequently dip below zero, consider the selection named ‘Arp’.  It was found in Arp Texas in 1972 by Madalene Hill (1913-2009), who livedPOM in Cleveland Texas and was one of the preeminent proponents of herbs from the 1950’s onward. ‘Arp’ has proven to be very winter hardy, providing the soil is well-drained and the site is given some protection from winter winds.  Hardiness can actually be improved by siting it next to stonework that absorbs the warmth of the day (as seen on right).  Also, consider mulching it with gravel in lieu of bark, which helps to keep the stem dry as well as absorb some of the daytime heat.  Another very winter hardy cultivar is ‘Madeline Hill’, which is often sold under the name ‘Hill Hardy’.  It was named in honor of Madalene by fellow herb enthusiast Tom Debaggio in the late 1980’s.  It too is hardy to around -10°F, but is somewhat more densely branched with a more upright habit than ‘Arp’.  It also appears to flower more freely into the fall.

Less hardy selections that are potted can be overwintered indoors during the winter, but this has proven to be equally as challenging.  Plants should be watered far less during the winter, allowing the soil to become moderately dry between watering and exposed to 6 hours of sunlight throughout the day.  They also appreciate a cool room with temperatures in the 50’s and good air circulation, since indoor environments enhance the outbreaks of powdery mildew and mealybug. 

Without a doubt, Rosemary can be a bit challenging to grow in more northerly climates.  Fortunately, the cold hardy forms have proven to overwinter well at Rutgers Gardens and the rewards of adding fresh sprigs of the flavorful stems to your favorite meals or drinks at Thanksgiving makes the challenge worthwhile.  Although the foliage will turn color with the season, it remains attractive and the long bloom time makes this Dew of the Sea a most attractive addition to any garden.