How Chicago Botanic Garden Approaches Perennial Breeding

This past July, I participated in the Perennial Plant Association’s National Symposium in East Lansing, MI, where I spoke during a session featuring breeders discussing their current work. My goal was to explain what differentiates the breeding program at the Chicago Botanic Garden from its for-profit industry counterparts. To my knowledge, ours is the only breeding program at a botanic garden in the country. As part of a non-profit institution, our breeding program leads us to target genera and traits differently, which I believe is worth exploring further.

Which Genera to Breed?

When it comes to selecting genera to breed, we prioritize natives, though not exclusively. People have different standards when it comes to deeming a species native (that is, whether the species needs to be growing in their county, state, or region). I prefer the latter category, as plants do not care about the artificial borders between counties or states, especially when these borders aren’t marked by physical barriers that keep plants from spreading.

If considering an exotic genus for breeding, we look at two factors related to seed reproduction that can contribute to its invasive potential. The first is fecundity, or how much seed is produced, and the second is dispersal, or how readily those seeds spread, whether just a few feet or much farther. In some cases, vegetative spread should also be considered, since a species may expand through rhizomes, stolons, suckers, or other non-seed means. Kudzu (Pueraria montana) is an extreme reminder of what can happen when a plant’s ability to spread is underestimated.

Native or not, we largely focus on niche genera. Due to the small size and limited resources of our breeding program, we cannot compete head-to-head with larger commercial breeding programs. Even if we could, many mainstream genera are already saturated with dozens, if not hundreds, of cultivars on the market. Do we need another Echinacea or Hosta when there are comparatively esoteric genera with untapped potential?

Which Traits to Target?

The traits we focus on vary greatly by genus, so it may be easier to discuss some of those we are not focused on. The most prominent example is highly compact cultivars. These have proliferated in industry breeding over the past decade or two because they look great in pots and can be shipped more efficiently. While I would not be against releasing a compact cultivar should a promising selection arise, this is not something I actively seek out.

I should clarify that “compact” in the context of this example means about 30 inches or shorter in height. I would not consider a 4-foot-tall cultivar bred from a species that is normally 5 or 6 feet tall to be very compact. There is a difference between reining in the size of an unruly species and releasing a cultivar that is half, or less, the height of the species it is bred from.

Another trait we avoid when breeding is sterility, which can sometimes take the form of “double” flowers in ornamental horticulture. In these cases, additional petals may replace the pistils and/or stamens, potentially reducing available pollen or making other floral resources less accessible to pollinators. To broaden this beyond sterility, we do not seek to breed cultivars with traits that hinder their ecological function.

Pollinator support is an important consideration for many home gardeners. We hope to collaborate with the Garden’s Science Department, which is partnered with Northwestern University, to study pollinator visitation to our breeding selections and compare their performance with straight species. This could help us to better understand how the abundance and diversity of pollinator visitation compared between the two.

Focused on Function

One cultivar that encapsulates these points is Eutrochium maculatum ‘Summer Snow’, which we released about 10 years ago. It was bred from germplasm collected roughly 90 miles from the Garden. Despite that germplasm coming from three counties away, I still consider ‘Summer Snow’ a native selection because its species is also native to our county. At 5 feet tall, it is not significantly shorter than the straight species, and its highly upright stems bear white flowers that support pollinators from mid-to-late summer.

Aesthetics are understandably a major consideration when breeding perennials for the commercial market, especially when it comes to how a plant looks in a pot. Ecological function may not always receive the same emphasis. Because we are a non-profit organization, we are not seeking to release a certain number of cultivars each year or maximize the sales of each one. This lack of pressure allows us to breed perennials differently from many commercial breeding programs.

Hopefully, that means gardens won’t someday consist entirely of perennials 2 feet or shorter.