UMD Extension doesn't have local research on which Solidago species appears to attract the most pollinators. Complicating factors (and these are not specific to Solidago) will include:

• habitat (not all potential pollinators for one species occur in the same area, or are active at the same time)
• yearly fluctuations in insect populations (if an insect species becomes less abundant for a year or two based on natural factors, it will be under-represented in trial garden observations)
• weather (periods of rain or chilly weather will keep many pollinators grounded)
• plant genetics (some plant individuals of a species might produce more or less nectar, pollen, fragrance, or other pollinator attractants, even if they are not cultivars)

A rating of pollinator attractiveness is a difficult trait to measure with accuracy for many plants, especially to avoid accidental bias from the observer documenting flower visitors. For example...

• How many insect species visit after dark, like moths and beetles?
• Would an observer notice just as many tiny wasps, flies, ants, or other insects as they would the more showy butterflies, bees, beetles, or hummingbirds?
• How many times a day would the plants be observed for pollinator visits? (Some bees are active early in the day, others near midday, and so on, so not every species using the blooms would be present in the same window of time.)

Fortunately, by growing a diversity of native plants where feasible, a gardener can still support a lot of pollinating insects and hummingbirds. Generalist pollinators appreciate the abundant blooms on Solidago, and species active late in the season that might be specialists for aster-family plants will also find it useful. Some pollinators might not rely on its flowers but can still use the foliage (such as a caterpillar host plant) or stems (like for stem-nesting bees), so the plant's ecosystem value can go beyond blooms all season long.

Our recommended approach to deciding which Solidago to grow is simply to pick one that both appeals to your aesthetic while also being a good match for the site conditions (amount of summer sun, soil moisture and drainage, etc.) Species plants grown from local seed (with local genetics) are ideal, but might not be easy to find in all cases.

Miri