Helping Gardens Grow: How volunteers nurture new plants to support the Arboretum Foundation

If you’ve ever wandered the Washington Park Arboretum delighting in the year-round plant displays and wishing you could take a piece of the experience home, then be sure to explore the Pat Calvert Greenhouse on your next visit.

A Camellia in a decorative pot is ready for sale
A Camellia in a decorative pot is ready for sale

The greenhouse—and the volunteer effort behind it—were established by its namesake in 1959. Pat Calvert was inspired to create a space for Arboretum Foundation members to practice propagation, and she worked with the Foundation to secure funds to build the structure and start the program. Volunteers continue to propagate and sell plants to benefit the Foundation.

The volunteer greenhouse can be found adjacent the Graham Visitors Center parking lot, tucked behind the larger greenhouse that borders the lot. Visitors can browse young trees, shrubs, and perennials to buy—most clipped from the Arboretum’s collection.

Purchases can be made during Arboretum Shop hours, 10 a.m. to 4 p.m., Monday to Friday (and occasionally open on weekends; call 206-543-8800 to confirm). On Tuesdays and Thursdays, from 10 a.m. to noon, greenhouse volunteers are on site and happy to help you pick the perfect plant and answer horticulture questions.

On a recent Tuesday, long tables in the rain-protected greenhouse and sun house were filled with potted conifers, camellias, broadleaf evergreens and rhododendrons. (When summer brings more intense sunlight, plants will also be protected in the shade house.)

During our visit, volunteer Lynn Schueler talked through the process that generates this array of young plants:

  • The greenhouse volunteers have special permission to propagate from the arboretum collection (which is otherwise not allowed without special arrangements through UW Botanic Gardens). Cuttings may also be collected from volunteer gardens or from prominent local gardeners.
  • Each cutting is potted in pumice, or a mix of pumice and coconut coir. Schueler explains that coir— a waste byproduct of coconuts—is a renewable substitute for sphagnum moss.
  • The cutting is documented. Date, name, from where it was cut, and the results are noted. This data is used to analyze and plan future cutting efforts.
  • From there, cuttings are placed under a mister where leaves will absorb moisture until roots are formed. Misting is controlled by a simple machine called “the leaf.” A lever device controls the mister based on the weight of water droplets collected on its leaf-like mesh sensor. As water dries and “the leaf” grows light, the mister starts. When heavy, it stops.
  • Once roots are formed the plant is potted and moved to a non-misted section of the greenhouse and prepared for sale.

Volunteers know the many nuances of different species, and customize this process as needed. For instance, some cuttings do best when a liquid hormone is added to the stem base to encourage root growth. Other plants thrive when their roots are crowded, and will be moved to tighter pots as they grow.

Plants that are ready to take home are clearly marked with price tags. A selection is also featured on the plant cart outside the Graham Visitors Center.

Whether you’re interested in adding to your home collection, or simply curious about the propagation process, a visit to the Pat Calvert Greenhouse will reward—with all proceeds benefiting the Arboretum Foundation.

At a glance:

Planted cuttings under the greenhouse mister
Planted cuttings under the greenhouse mister
Plants available to take home from the sun house
Plants available to take home from the sun house
The Shade House as it appears in sunnier months.
Resource: Arboretum Foundation's how-to manual, “Cuttings through the Year,” is available in the Arboretum store.
Resource: Arboretum Foundation’s how-to manual, “Cuttings through the Year,” is available in the Arboretum store.