Spring stirrings in Arboretum gardens


After a mild winter, the gardens at the Arboretum are showing early signs of spring. Changes in day length, thawing, budding, greening in cool season plants, and emerging sprouts initiate a new year.

The earth is stirring and gardeners are compiling plant orders, checking out new tools and planning for new projects.

The Friends of the Arboretum are offering tools and native plants. More information and order forms can be found on the Friends website at

Early orders for plant mixes, trees, and shrubs are due by March 26. Don’t miss this opportunity to enhance your native plantings and promote conservation at the same time.

Speaking of garden tools, a new plant hardiness zone map is now available on-line, with links to print versions. Go to

For the first time, the map is GIS-based and interactive. Effects of features such as topography and water bodies were included in the models used to represent areas between weather stations.

Based on weather data from 1976-2005, the values corresponding to each zone are the 30 year average annual extreme low temperatures. The new map shows a shift of zone boundaries about 5 degrees F warmer.

The Madison area has not “changed” zones; we are still listed in zone 5a (-20 to -15 degrees F). However, on this version you may find your garden or restoration located in a different zone than before, perhaps agreeing with season-to-season garden observations.

With shifts in climate (e.g., as shown in changes in hardiness zones) come changes in plant and animal range distributions, ecological relationships, phenology and seasonal length.

Native plant gardeners do not generally evaluate plants on the basis of zone hardiness. Instead, we consider geography and ecology and grow plants of our region while considering local site factors like soil type, exposure and microclimate.

Native gardens enhance local and regional biodiversity, and aid conservation and restoration goals appropriate across the landscape.

How does that big picture link to actual garden plans and practices? Here is an example:

You may already know that we promote habitat for native pollinators on Arboretum land and beyond. For bumblebee conservation, we offer simple steps to support bumblebee queens at the vulnerable time when they emerge from overwintering sites and establish colonies:
1) Plant native species that bloom early in the season, such as woodland phlox (Phlox divaricata),bellwort (Uvularia grandiflora), bluebells (Mertensia virginica), waterleaf (Hydrophyllum virginianum), geranium (Geranium maculatum), and Mayapple (Podophyllum peltatum);
2) Keep some areas relatively untended, where the queen may find an underground nest spot in an old burrow or under bunch grass;
3) provide continuous pollen and nectar for the mid and late season (when the colony size could reach 400 bees and workers are foraging).

To create bumblebee habitat in your garden, you could plant a mix like the Friends of the Arboretum “Butterfly and hummingbird prairie mix” (available through advance ordering) and supplement with partial flats of mountain mint (Pycnanthemum virginianum), additional purple prairie clover (Dalea purpurea) and showy goldenrod (Solidago speciosa). This particular plant mix as well as single-species flats are available through the Friends of the Arboretum plant sale orders due March 26 (for you to pick up on May 10).

E-mail me with any questions you might have about native plants for your garden, and enjoy your spring gardening!

Susan Carpenter, Native Plant Gardener

Located between Lake Wingra and the West Beltline Highway at 1207 Seminole Highway, the University of Wisconsin-Madison Arboretum features the restored prairies, forests and wetlands of pre-settlement Wisconsin. This 1,260-acre arboretum also houses flowering trees, shrubs and a world-famous lilac collection. Educational tours for groups and the general public, science and nature-based classes for all ages and abilities, and a wide variety of volunteer opportunities for groups, families and individuals are available.