Flowers for Pollinators: 2018 Update
By: Julie Weisenhorn
Associate Extension Professor
Department of Horticultural Science
Planting for pollinator health is on every gardener’s mind these days. But in all the talk about pollinators, little is said about annual flowers. While there’s lots of research on how native plants help pollinators, there’s not much on the interaction of pollinators and annual flowers. Favorites of gardeners, they just didn’t get much notice by entomologists and native plant purists. We thought they needed to be looked at more closely and started pollinator counts on selected varieties of annual flowers popular with gardeners in the retail garden center and online. As we like to say, “Gardeners love them, but do the bees?”
Why are annual flowers such a big deal? For one, they are popular with consumers as annual plants comprise $2.3 billion of US horticultural crop sales. Many people want to do their part to help pollinators, but for various reasons, they may only have space for annual plantings:. Some gardeners like the diversity of mixing annuals with perennial flowers, shrubs and trees. There are also claims about annuals that we wanted to test: "they will be a-buzzin' with bees".
So I set out to study whether pollinators are attracted to annual flowers with features that attract pollinating insects. Thirty varieties of annual flowers were selected and trialed to see how many and what kinds of pollinating insects visit them. Flowers were selected based on characteristics known for attracting insects such as patterns, colors, size, and flower form, and volunteers and staff observe and collect data on the numbers and types of insects - bees, butterflies, flies, moths, beetles, wasps, etc. - that visit our flowers over the growing season. My ultimate goal is to be able to provide annual flower selection guides to citizens who want to grow annuals that attract and provide for pollinators in their landscapes. I am also working with artist Ursula Hargens on a creative and artistic way to communicate this information.
I am in my second year of the 30 variety study. To-date, data is still being compiled from 2018. Some noticeable points of interest: (1) Bloom time of annuals: Some have very long bloom times, others much shorter, and understanding this allows the gardener to stagger plantings while providing pollinator attractive varieties; (2) different sites are prone to different pollinators attracted to the same flowers: in 2017, bumble bees were most present at the Farm, flies at the U horticulture display garden in Morris, and honey bees at the U horticulture display garden on the St. Paul campus.
This project has produced a tangential project called Pollinators for Food where I try to answer the question "Will pollinator-attractive plants result in higher yields" - even if the crop doesn't depend on insects for pollination? The hypothesis is yes. This past year, I and Master Gardener volunteers tested this hypothesis by planting 36 'Ace' bell pepper plants (wind-pollinated) near three of the Flowers for Pollinators leading varieties. We left 18 plants open to pollination and excluded the remaining 18 using a mesh so that pollinators would not be able to reach them. I chose the annual flower varieties based on their continuous season-long bloom and attractiveness to all bees (honey, bumble and other natives) on some level. Peppers from each sector - open and excluded - were harvested as they began to ripen indicating they had reached their mature size, weight and seed count. We counted, weighed and measured the peppers and weighed the seeds. We are still compiling the data at this time.
I would like to combine these two studies by planting top attractive annual flowers from Flowers for Pollinators along with 72 peppers - half open and half excluded from pollinators. I'd like also to analyze the flower features and reach into the lineage of the top performers to see if their relatives are also attractive. Could we possibly say all Helenium are attractive to pollinators and why? I'd like to know!