We all love a list, I think, as long as it is not a list of chores to be done. Particularly fun at this time of year is a list of plants we wish to add to our gardens in the season ahead. I have lists of seeds I want to grow, lists of plants I want to move, and lists of projects I want to tackle in the garden.

Last week I came upon a list that made me sit up. It was first published in 2009, and I wish it were better known than I think it is. Douglas Tallamy, professor of entomology at the University of Delaware, published a study describing the impacts of planting nonnative genera in the garden and in the urban/suburban landscape in particular, on insect populations and the implications for life up the food chain.

I am embarrassed to admit that, while I believe in and use organic gardening principles and try to employ conservation methods for pollinators, I had never given much thought to the larger ecological interconnections. I’m growing Asclepias (milkweeds) this year because I’m concerned for the welfare of Monarch butterflies, and every little bit of effort helps. I try to relax when I see caterpillars making feasts out of fresh green leaves, because I know those caterpillars will grow into moths or butterflies. And those guys will pollinate my plants, plus they’re pretty to watch. 

But they might not grow up to be butterflies. They might get eaten by hungry birds instead:

“…a single pair of Carolina chickadees needs to bring 6,000-9,000 caterpillars to the nest to rear a clutch of a half-dozen nestlings. Black-capped chickadees probably need more. If you want the birds, [Tallamy] says, you need the caterpillars, and to get the caterpillars you need the right trees.”  

Songbird populations are on the decline nationwide due in part to the inclinations of housecats let loose in the garden for the day.  Compound that with habitat loss due to development, climate change, and the additional pressures presented by landscaping choices (however benign the intentions behind those choices may be), and it adds up to substantial challenges coming from all corners.

Tallamy’s list uses Lepidoptera (butterflies and moths) to stand in for all herbivorous insects, because data on them are plentiful and they represent a substantial food source for birds. But understand that if you have these plant genera in your garden, they’re benefitting more than butterflies and birds.

What beneficial choices can gardeners make to help sustain not only pollinators, but birds as well?

Ten best genera for hosting butterflies, moths, and the life they support:

1. Quercus (oaks): 532 total Lepidoptera species
2. Prunus (peaches, plums, cherries, almonds, etc.): 456 species
3. Salix (willow): 455
4. Betula (birch): 411
5. Populus (poplars, aspens, cottonwoods): 367
6. Malus (apples and crabapples): 308
7. Acer (maples): 297
8. Vaccinium (blueberries and cranberries): 294
9. Alnus (alders): 255
10. Carya (pecans, hickories, etc.): 235

While the ten best all happen to be woody plants, herbaceous plants are also on the list. Tomorrow I’ll outline the best herbaceous host plants.

Consider studying Tallamy’s full list before you begin your plant shopping this spring.

Other resources of interest:

• National Audubon Society: Birds in Decline