The Dana Greenhouses celebrate sixty years—and a newly renovated facility for wintering plants

Dana Greenhouses with solar array by Jon Hetman
Front of the Dana Greenhouses, with solar array visible at top. Jon Hetman

As the Arnold Arboretum of Harvard University embarks on an exciting new chapter in its 150th anniversary year, the Charles Stratton Dana Greenhouses observe 60 years as the hub of the institution’s plant propagation and production activities. For the Arboretum—as a 281-acre outdoor museum of the world’s temperate trees and shrubs—the Dana Greenhouses serve as the birthplace, nursery, and initial testing ground for every plant destined for the living collections. New seed acquired on expedition or a clone from an invaluable Arboretum centenarian all get their start at the greenhouse, and are dutifully nurtured throughout infancy, eventually joining the other 17,000 plants in the permanent collections in a few years’ time.

Dana Greenhouses construction, summer 1961 by Heman Howard
View of Dana Greenhouses under construction, summer 1961. Photograph by Heman Howard. Arnold Arboretum Archives

Construction of the greenhouse complex at the Arboretum was made possible by the Mercer Trust, established by Mrs. Martha Dana Mercer, which noted that a third of her estate be bequeathed to the Arnold Arboretum in honor of her late father, Mr. Charles Stratton Dana, due to his admiration of the Arboretum.  The donation came at a most opportune time—the Arboretum was fast outgrowing the shared facilities at the former Bussey Institution (the site of the Hinton State Laboratory Institute of the University of Massachusetts). Arboretum propagules were cultivated in a handful of different locations prior to the Bussey Institution: first at the Harvard Botanic Garden in the 1870’s; followed by a small land plot next to the 1090 Centre Street house, where plant propagator Jackson Dawson resided at the time; and afterwards in a glasshouse constructed on Orchard Street (off of the Arborway rotary) from 1917-1928.

Greenhouses, fall, Arboretum greenhouses at the Bussey Institution, 1928
Arboretum greenhouses at the Bussey Institution, fall 1928. Photograph by Lord & Burnham Company. Arnold Arboretum Archives

Then Arboretum Director Richard Howard and staff broke ground for the Dana Greenhouses on May 12th, 1961, with construction proceeding through that autumn and culminating in a grand opening in March 1962. The complex today comprises a two-story headhouse with four glasshouse bays, with specialized equipment for seed and clonal propagation, outside benches for container production, an evaluation nursery, three longer-term nurseries, a cold storage building, and the Bonsai Pavilion. Over the past decade, the greenhouses have undergone a number of renovation and sustainability projects aimed at updating technologies and increasing energy efficiency, including the installation of LEDs in the propagation glasshouses in 2014, high performance thermal windows in the headhouse in 2016, and solar panels on the roof in 2017.

Dana Greenhouses, spring 1962 by Heman Howard
Dana Greenhouses in spring 1962, with construction nearly completed. Note cold storage facility in the foreground, and layout of the shade nursery. Photograph by Heman Howard. Arnold Arboretum Archives

Since its earliest days, the Arnold Arboretum has developed its plant collections primarily through the acquisition of seeds, either through plant exploration efforts or exchanges with individuals and other institutions. The journey from seed or cutting to tree takes several years as a plant moves throughout the aforementioned areas of the 1.5-acre production complex. Relying on our own knowledge and experience of propagation and years of documentation on successes and failures at the Arboretum, we germinate seeds in a warm, humid greenhouse and root cuttings in a mist room. Individuals are later transplanted into containers, grown indoors initially and then later outside in open air.

Seed propagation greenhouse at the Dana Greenhouses today
The seed propagation greenhouse at the Dana Greenhouses today. Many germinating seedlings come from recent expeditions from the Campaign for the Living Collections. Tiffany Enzenbacher

When they are ready, the next location in the complex for many small plants is the evaluation nursery, affectionately called the Shade House. It is covered by polyethylene fabric which permits just half of the light to pass through, providing essential protection to delicate, young transplants. Growing plants in the Shade House gives us the information we need to make a rough assessment of cold hardiness, along with habit and vigor. After approximately two years of evaluation here, specimens transition into longer-term nurseries in our complex to grow them to a size appropriate for planting in the landscape. The whole process can take 4 to 7 years depending on the growth rate of the species.

Shade Nursery at the Dana Greenhouses, spring 1966 by Heman Howard
The shade nursery behind the Dana Greenhouses, photographed by Heman Howard in spring 1966. Arnold Arboretum Archives

Plants not channeled through the Shade House―mainly the marginally hardy ones―spend the winter in a dedicated building for cold storage until our horticulture staff finds permanent spots in warm microclimates in our landscape for them to best survive Boston’s Zone 6 winters (average annual minimum temperatures -10 to 0°F). With five expedition seasons now completed in the Arboretum’s 10-year Campaign for the Living Collections―and over half of our target list, including many marginally hardy taxa, already acquired ―our cold storage building was in dire need of an overhaul. A generous gift from the Powder Mill Foundation, established by Arboretum friends Louis J. and Josephine Appell, turned our visions into reality in 2021.

Evaluation nursery or shade house in 2021
The evaluation nursery or Shade House where plants remain for approximately two years before transitioning into nurseries. Tiffany Enzenbacher

Part of the original complex dedicated in 1962, the 15 x 100-foot cold storage building provides dormant winter storage for all containerized plants from the months of November to April. Plants acclimate to the cooler temperatures and shortened days of autumn outdoors, and as temperatures near the low 30’s overnight, plants are brought in to prevent freeze damage. Constructed of concrete and insulated with two-inch slabs of a Styrofoam-like material, the facility was built into the side of hill, and is surrounded on three sides by soil to help buffer temperatures within.

Frank Wolfe inspects plants in the cold storage facility at the Dana Greenhouses, 1966
Arnold Arboretum Mercer Fellow Frank Wolfe inspects plants in the cold storage facility at the Dana Greenhouses in 1966. Photograph by Heman Howard. Arnold Arboretum Archives

In 2020, we selected new mobile stainless-steel carts with adjustable shelving (and a lifetime warranty) to replace the original 1961 stationary shelving in the building.  This switch allows us to maximize the amount of space available for overwintering our expanding inventory. The existing gravel floor was replaced by concrete in summer 2021, allowing us to wheel the new carts throughout the building as needed. The structure’s compromised roof was also replaced, increasing its insulation factor. Upgrades to the cooling system that keeps our plants in the dormant sweet spot of just above freezing are planned for summer 2022. The cold temperatures needed in late fall and early spring to preserve plant dormancy are extremely difficult to maintain, particularly in a changing climate, and new evaporative coolers will help us moderate these conditions as the seasons change. On the opposite extreme, more efficient heaters are also being installed to protect our plants if temperatures drop below freezing inside during spats of extremely cold weather.

New mobile carts with adjustable racking installed in the cold storage facility in December 2021. Concrete replaced the original gravel floor so carts can be moved easily within the space and throughout the building. Tiffany Enzenbacher

As we increase our holdings through the Campaign for the Living Collections and work to safeguard crucial Arboretum lineages by clonal propagation, providing the optimal environment during this next generation’s first few years sets the stage for success. Although the Dana Greenhouse facility is behind-the-scenes and relatively modest in scope, it is at the very heart of this extraordinary living museum, giving life to all new plants that are soon to be used for research, education, and the enjoyment by all.