CONIFER COLLECTION
What is a conifer?
Conifers are a group of woody plants that produce cones with scales that contain their seeds. Many of these plants produce needles instead of leaves and many are also evergreen. Contrary to popular belief, some conifers do in fact lose their leaves or needles in the winter. Some conifers even produce cones that resemble fleshy fruit! Most conifers are wind pollinated, so the pollen floats on the wind and hopefully finds a receptive female cone. Seeds are usually hard with a strong seed coat and are often called a “nut” despite not being closely related to true nuts.
The Iowa Arboretum & Gardens has been planting conifers since the beginning, with our first established conifer collection planted in 1982. The original trees still stand to the north of the Hughes Education Center in what is now the Perennial Garden. This group of towering trees and spreading shrubs includes pines, spruces, firs, and junipers. More of collection was planted in the Founder’s Grove, Jacobson Conifer Garden, and Alpine Garden as the arboretum grew. Unfortunately, many of our more unique conifers were destroyed during the 2020 derecho, as evergreens are not particularly resistant to extreme winds.
Today the arboretum’s conifer collection numbers well over 400 individual plants across 16 genera, over 65 species, and nearly 200 unique varieties. Included are large, mature specimens, a sizeable number of dwarf varieties, and an extensive list of ginkgos.
American Conifer Society Reference Garden
The combination of the extensive collection of dwarf conifers planted in the Alpine Garden and Jacobson Conifer Garden led to the Iowa Arboretum & Gardens receiving the distinction of an American Conifer Society Reference Garden. This program allows us to continue our mission of educating the public about plants while helping provide funding for projects related to conifers.
Conifer Conservation
Spurred by a seed exchange with Steven Roesch of New Berlin, WI in 2022, the Iowa Arboretum & Gardens started a special conservation project working specifically with the genus Hesperocyparis. Now in partnership with the California Botanic Garden Seed Conservation Program, the arboretum is working to evaluate the hardiness of several species in the genus in the hopes to conserve them through horticulture.
Listed with International Union for Conservation of Nature (IUCN) as endangered or vulnerable, members of the genus Hesperocyparis need some help. Their reproductive cycle is completely dependent on low-intensity fire to open ripe cones and disperse seed. With decades of fire suppression in their native ecosystems, they have lost the ability to reproduce and subsequent fires are too intense, killing trees and burning seed. These species also have an extremely low germination rate and have little success in long-term seed storage.
So far, the arboretum has successfully grown from seed and overwintered four species: Hesperocyparis arizonica (Arizona cypress), H. bakeri (Modoc cypress), H. glabra (smooth Arizona cypress), and H. nevadensis (Paiute cypress). Our hope is that they prove to be totally hardy and eventually grow large enough to set seed, preserving their genetics for further conservation efforts.
If any particular plant proves to be a handsome specimen, propagation and distribution will keep the genetics alive in gardens for many years into the future! Native to high elevations from Arizona, California, and Oregon, these plants regularly experience temperatures below freezing and snowfall. While we are most optimistic about the species from the northern Sierra Nevada mountains, species from further south have surprised us with their hardiness. Foliage color can range from fresh green, to pewter silver, to even a cool blue, providing ample potential in the landscape. Many varieties of H. glabra (smooth Arizona cypress) and H. arizonica (Arizona cypress) are readily available on the market, others are on the way. Native historical distribution maps below are provided by the Biota of North America Program (BONAP).
The arboretum’s Hesperocyparis trees can be found in the Jacobson Conifer Garden, Perennial Garden, and Shrub Border.
How to use the Woody Plant Record:
The West 40 Acres of the Iowa Arboretum & Gardens is divided into a 13 x 13 grid of 100′ x 100′ squares. This was done at the inception of the arboretum to map each individual tree and shrub to a precise location. While we anticipate converting to a more contemporary system in the future, this curatorial document currently allows us to keep track of every plant.
Every tree that is still documented as alive in 2025 is mapped on this document:
Each page is an individual 100′ x 100′ square with the accession number, Latin name, and cultivar of each plant listed. Plants are then labelled with a corresponding number on the map. Use the “find and edit” tool in your web browser to search the document for particular plants by Latin name or the “find and edit” tool in Adobe if viewing as a downloaded PDF. The letter at the top of each page represents an East-West grid column of the whole 40 acres while the number represents a North-South row.
It’s a large document, so it may take several seconds for the plant to be found using the “find and edit” tool. If searching for a particular plant on the grounds, a display label should be present at the base of the trunk of the tree, facing the nearest pathway.
A Conifer Collection Plant List is available at the bottom of this page.
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Conifer Collection Plant List:
Below is a complete list of conifers currently in the Iowa Arboretum & Gardens’ collection. Accession numbers are included for germplasm requests and for documenting the acquisition of varieties. For six digit accession numbers, the first two digits correspond to the year the arboretum acquired the plant, eight digit accession numbers have a four digit year. Accessions for 2022 may be misleading. An extensive survey of all woody plant material on grounds in 2022 revealed many plants that were present in gardens that were never properly documented. These plants were assigned a 2022 accession number if their identity and acquisition date couldn’t be found. Woody Plant Record grid numbers and specific garden locations are also included.