Contributed by Anthony S. Aiello, The Gayle E. Maloney Director of Horticulture and Curator

Every year at this time our plant propagator, Shelley Dillard, and I start choosing plants for our annual spring planting.  While doing this last week, I was thrilled to see the pink flower buds and slightly-opened flowers of a horticulturally rare flowering cherry, Prunus hirtipes.  This is the earliest-flowering of all the ornamental cherries in our living collections, and it is also one of the rarest flowering cherries in the U.S.  It is so unusual in cultivation that it does not have common name and we simply call it “flowering cherry”. 

Our plant is growing in the ‘Medicinal House’, a semi-submerged glasshouse that is closed to the public.  This greenhouse is kept above 30 degrees in the winter, and it is here that we over-winter new cuttings and some of our most special or more tender plants.  P. hirtipes is known in only nine collections globally, and until two years ago, the tree at the Brooklyn Botanic Garden (BBG) was the only known specimen in North America (information provided courtesy of BGCI’s PlantSearch).  Since then, we have successfully propagated that tree, and hope to grow more for further distribution. 

We came to have this tree as part of a program to enhance the living collection aspect of our Cherry Blossom Festival.  Starting in 2009, we began a concerted effort to increase the length and diversity of our flowering cherry season by adding early and late varieties.  At that time I started to survey other botanic gardens along the East Coast to see what early- and late-blooming flowering cherry varieties we could propagate and add to our collection.  Once I had done this, I quickly realized that there were many varieties that were held uniquely at these various gardens - that is, varieties represented by only one or two plants at one location.  So what began as an effort to extend our season evolved into two things: first, backing-up these unique cultivars so they were replicated at other gardens; and second, verifying our collection and those at the other institutions. 

Among those uncommon varieties was P. hirtipes, with the only verified plant growing at BBG.  This species flowers in late winter or early spring, with small, delicate, and slightly fragrant pink flowers.  The flowers are tender for our area, being prone to open during a winter warm spell, and as a result are liable to get frosted; but all of this adds to the mystique and allure of the species.

I first saw Prunus hirtipes on a trip to England in early March 2011, where they had recently experienced these weather conditions - a hard frost that had followed milder weather.  The flowers that I saw were wilted frozen versions, not at all at their best, but still intriguing because of their precociousness.  My colleagues referred to the tree alternately as Prunus conradinae or P. hirtipes, the former name referring to the wife of Bernhard Adalbert Emil Koehne, the German botanist who gave it that name, and the latter (currently accepted) name, meaning “hairy foot”, a reference to the fine hairs on parts of its flowers.

The next time I saw this species’ flowers was at BBG on a frigid day in early March 2017, after a freakishly warm February had caused many cherries to flower, followed by temperatures in the teens.  Once again I was looking at frosted flowers.  So, you can imagine my excitement recently when I saw our plant in bud, with its pink petals starting to show.  Since then its flowers have continued to open, and with the protection of the Medicinal House, this is the first time that I have seen un-frosted flowers.

How did we come to have this plant?  My 2011 trip to England coincided with my explorations of other flowering cherry collections along the East Coast, and so at that time I realized that there was only one verified location of P. hirtipes in the U.S. – Brooklyn Botanic Garden.  We then set out to take cuttings to vegetatively propagate the Brooklyn tree.  The goal was to clone it by rooting cuttings, as you might do with basil or a houseplant on your window sill.  Our first attempt in June 2011 failed so we repeated this in 2012 and 2014.  But the tree resisted our efforts at rooting cuttings, even though we’ve been successful with many other species and cultivars of flowering cherries. 

With concern rising because of the potential impact of a construction project on BBG’s tree, by the winter of 2017, we decided on another propagation technique, grafting.  In this technique, a shoot (scion) of the species to be propagated is grafted (or attached) to another plant (rootstock).  This is an ancient technique of cloning plants and virtually every apple, orange, or other fruit that we eat is grown on trees produced this way.  Fortunately one of the grafts took, and the plant currently flowering in the Medicinal House is from this grafting effort two years ago.  It is growing so vigorously that we plan to try cuttings from it this June.  Plants, unlike humans, have a fountain of youth so to speak; once you restore vigor and juvenility to a plant, it becomes much easier to propagate.

I recently learned that the tree at Brooklyn survived the construction project.  If we can further propagate our one tree, we can return one to Brooklyn, and distribute it elsewhere.   As we always say in the world of horticulture, the best way to preserve a plant is to give it away.