Native trees and shrubs for bees: pollen, nectar, nesting and a bloom calendar from willow to witch hazel

If you plant one thing for bees in the eastern United States, plant a willow; if you plant three, add a basswood for June and a serviceberry or a redbud for April.

Most of the flowers in an eastern landscape are on trees and shrubs, not in beds, and most of them open before a perennial border has done anything. Honey bee colonies sampled for a year in Michigan, Texas and Florida took 61 to 83 percent of their spring pollen from trees and shrubs. An American basswood flowers for about two weeks in June over a crown as wide as a house, and 66 kinds of insects have been recorded pollinating it. Of the roughly 770 bee species native to the eastern United States, about a quarter raise their young on the pollen of one plant group. The largest set of them tied to any woody plant, 14 species, depends on one genus: willow.

Who the bees are

The United States has more than 4,000 species of native bees. The honey bee is not one of them. It came from Europe and lives in a hive of thousands. Most of our natives are solitary instead: one female digs or builds a nest and stocks each cell with pollen and nectar for a larva she never sees. About 70 percent of native species nest in the ground and about 30 percent in cavities, old beetle tunnels in dead wood or the hollow and pithy centers of stems. Bumble bees are the social exception, nesting in abandoned rodent burrows and under grass tussocks; their mated queens winter an inch or two down in the soil, under leaf litter where there is any.

Roughly a quarter of the 770 bee species native to the East are pollen specialists, whose larvae eat the pollen of one plant family or a few related genera and nothing else. Jarrod Fowler’s catalog for the Northeast counted 61 such species tied to 33 plant genera, and in the wider eastern list nearly 60 percent of the specialists are rare.

Why the woody plants carry most of the food

A tree holds its flowers in three dimensions over a crown 30 to 60 feet across; a bed holds them on one plane, and in the Mid-Atlantic mostly after mid June. Woody plants are more efficient forage because of their absolute resource density. Honey bees show a measurable preference for trees even where trees are sparse. In a year of sampling honey bee colonies in four states, spring pollen came 61 percent from trees and shrubs in Michigan, 78 percent in Texas and 83 percent in Florida. The important pollen types in Michigan over the year included maple, willow, plum, locust, chestnut and sumac.

The numbers for single plants are large. A male pussy willow catkin holds about 270 flowers; five catkins from a Maine bog averaged 200 nectar-bearing flowers each, with more sugar than any of the 17 other plants measured beside them. American basswood opens in June for about two weeks, 4 to 40 flowers to a cluster. Its nectar is heavy enough that beekeepers call it the bee tree. Its recorded visitors are 66 insect species from 29 families, bees and flies by day and moths at night.

Pollen, nectar and the trees that give only one

Nectar is sugar, the fuel for flight and, in a hive, for wax and honey. Pollen is protein and fat, and it is what a larva eats; a solitary female provisions her nest with pollen moistened with nectar and nothing else. A plant can be rich in one and useless for the other.

The wind-pollinated trees, oaks, hickories, walnuts, birches, alders, hazels and hornbeams, shed pollen by the pound and, needing no insect, offer no nectar. They still feed bees. Oak pollen was among the main pollen types honey bees brought home in California, Texas and Florida, and chestnut pollen turned up in Michigan colonies. American hazelnut sheds pollen in late winter and early spring, and our oaks, from dwarf chinquapin oak to cherrybark oak, shed theirs as they leaf out.

Chestnuts go further: honey bees carry their pollen home, and a mining bee, Andrena rehni, is a recorded chestnut pollen specialist from Georgia to Massachusetts. That bee gives an Allegheny chinquapin a claim no oak has.

The bloom calendar, March to November

Dates are for the Mid-Atlantic.

March and April

May

June to November

The bloom calendar draws the same months for every tree and shrub we grow, narrowed to your zone, sun and soil.

By November the year’s last bees are on asters and goldenrod, and the moths on the witch hazel are flying in cold that grounds everything else.

“These moths can remain active at cooler temperatures while other pollinators cannot, by vibrating their wing muscles to raise their body temperature.” (Penn State Extension, Native Shrubs for Pollinators)

The specialists: bees that need one kind of tree

Of the 200 eastern pollen specialists, 14 collect pollen from willow and nothing else, more than for any other woody genus. All are mining bees but one tiny Perdita, and they fly from March into June while the catkins are open. The blueberry genus has ten, and black huckleberry shares one of them, Andrena carolina. The best known is the southeastern blueberry bee (Habropoda laboriosa), which ranges north into New England. It emerges in early spring, lives three to five weeks as an adult and buzz-pollinates blueberry bells that honey bees handle poorly. In that time one female can visit 50,000 flowers and set more than 6,000 berries. Before the blueberries open she takes pollen from redbud, and the males visit plum, viburnum, azalea and even oak.

“Since blueberry plants have naturally heavy and adherent pollen, it is harder for non-buzz-pollinating bees (such as the honeybee) to extract pollen.” (University of Georgia Extension, Southeastern Blueberry Bee: Native Blueberry Pollinator)

The rest of the woody list:

• Shrub dogwoods, four mining bees restricted to them; silky dogwood and gray dogwood are two of the dogwoods they use.
• Hollies, three specialists, among them Colletes banksi, recorded from New England to Florida, whose season covers winterberry and American holly.
• Sumac, one: Andrena brevipalpis.
• Chestnut, the Andrena rehni above.
• Native azaleas, Andrena cornelli, on pinxterbloom azalea among them, and rosebay rhododendron.
• Mountain laurel and maleberry, with specialists on mountain laurel and four on maleberry alone.

Willow, blueberry, dogwood, holly and sumac between them account for most of the specialists a woody planting can support.

Honey plants, and what the honey trait means in our catalog

Honey bees are not native, but a plant that yields a honey surplus is producing nectar in bulk, and native bees drink from the same flowers. In our catalog the honey trait marks the plants beekeepers count on:

• American basswood, which makes choice honey.
• Black locust, planted for honey production on three continents; Hungarian selections have raised its nectar yield 74 percent.
• Sourwood, whose honey is sold under its own name where the tree is common.
• Black gum, a good honey tree in its own right, though the famous tupelo honey comes from Ogeechee tupelo along the Apalachicola River in Florida.
• American persimmon, in flower in May and June, and sweet pepperbush, from late June to August.

Redbud, silverbell, holly and tuliptree are honey plants too. Three of the honey-trait trees, basswood, black locust and black gum, we sell as a set that gives a hive a flow from May into June: the Honey Tree Trio.

A colony’s foragers routinely work flowers up to 3 miles from the hive, so no single yard can feed one. In a study of one colony in a deciduous forest, half its foraging lay within about a mile of the nest and 95 percent within 4 miles. In the East the nectar flow thins out in July, and the summer dearth follows: weeks of little nectar, when strong colonies may rob weak ones, until the goldenrod flow of August. Of the trees and shrubs we grow, sourwood flowers from late June into August, sweet pepperbush in July and August, buttonbush from June to September and devil’s walking stick in July and August.

Nesting: pithy stems, dead wood and bare ground

The 30 percent of bees that nest above ground want beetle tunnels in dead wood and the soft centers of stems. The Xerces Society names three native shrubs for the job: elderberry, sumac and raspberry.

• Small carpenter bees hollow last year’s dead canes and nest a few inches from the flowers that feed them.
• Yellow-faced bees take narrower stems, and leafcutter bees wider ones.
• Mason bees and leafcutters both use the holes that long-horned and jewel beetles leave in a snag or a log.

Leave dead stems standing through winter. In spring cut them to stubble of mixed heights, 8 to 24 inches, so the open ends are available; new growth hides the stubble by summer. Leave that stubble through the following spring as well, because the bees that nested in it are still inside. Keep a snag where it threatens nothing, and a log or a stick pile where a snag is not possible.

The 70 percent that nest underground need something most yards have removed: bare or thinly vegetated soil in the sun. Mining bees, cellophane bees and the blueberry bee dig in loose, well-drained ground, and wood chips or landscape fabric lock them out. Mulch only the first foot in from a path, use fallen leaves rather than bark under shrubs, leave patches of bare ground on a sunny bank and do not till. Leaf litter shelters the bumble bee queens as well, and it beats wood chips under a tree anyway.

“Females prefer underground nesting chambers in deep, well-drained, sandy or loose soil in sunny (and often bare) open areas, including along the periphery of blueberry fields.” (University of Georgia Extension, Southeastern Blueberry Bee: Native Blueberry Pollinator)

Pesticides, including the ones already in the plant

Neonicotinoid insecticides are systemic: a plant takes them up and expresses them in every tissue, nectar and pollen included. Home garden products can legally be applied at concentrations as much as 120 times greater than the same chemicals on a farm.

What that does to a bee tree was measured in June 2013 in Wilsonville, Oregon. There, 55 flowering littleleaf lindens in a parking lot were treated with dinotefuran, 46 sprayed and 9 drenched at the roots. An estimated 45,830 to 107,470 bumble bees from as many as 596 colonies died under them, the largest documented pesticide kill of bumble bees in North America. Oregon has since prohibited four neonicotinoids on any linden or basswood by any method.

Some neonicotinoids stay in flowers at lethal levels for eighteen months after application, so a treated basswood, locust or holly is a trap, not a resource. Ask any nursery, us included, what has been applied to its stock, and never treat a woody plant for aphids or scale while it is in flower or about to be.

Cultivars and doubled flowers

Most native shrubs sold are cultivars, and the question is what the selection cost the bees. A Connecticut trial over two summers compared six native shrubs with their cultivars and found no general rule. Sweet pepperbush ‘Hummingbird’ and ‘Ruby Spice’ drew the same insects as the wild plant. Purple-leaved ninebark ‘Diabolo’ matched the species for bees. The compact chokeberries drew as many mining bees per flower cluster as the wild plant, only fewer clusters.

The failure was wild hydrangea ‘Annabelle’, bred for big heads of sterile flowers. Of its florets, 42 percent were fertile against 99 percent in the species, and the cultivar received one third the bumble bee visits. The traits that can matter are anthers and pistils converted to petals, flower color, flower density and flower size. So avoid doubled flowers, which trade stamens for petals, and be relaxed about leaf color and compact habit.

A seed-grown plant is the species by definition. Everything Blue Whale Trees sells is grown from seed rather than from cuttings, so the question of what a selection cost the bees does not arise with our plants. The invasive ornamentals count for less than nothing, because they take the ground.

Our plants for bees, ranked

1. The willows, for a wet corner: the first and most important bee forage of the year in many places, in March and April, and the only pollen 14 specialist bees collect.
2. American basswood: the largest nectar flow in the eastern woods, two weeks in June.
3. Black locust: a fast honey tree for poor dry ground.
4. Sourwood: the honey tree of July, in a size that fits a yard.
5. Eastern redbud: April pollen and nectar for half a dozen bee groups, the blueberry bee among them.
6. Downy serviceberry and Allegheny serviceberry: a week of April flowers for mining bees, then fruit for birds.
7. Black huckleberry: a low heath for dry acid ground that shares a blueberry specialist.
8. American holly and winterberry: holly specialists, honey and a screen.
9. Sweet pepperbush: the bumble bee shrub of July and August.
10. Staghorn sumac and black elderberry: June nectar, then the best nesting stems on the list.
11. Silky dogwood: the shrub dogwood the four dogwood specialists want.
12. American plum and beach plum: thicket plums for April.
13. Allegheny chinquapin: June pollen and a specialist mining bee of its own.
14. Rosebay rhododendron and mountain laurel: bumble bee shrubs for shade, each with a specialist.

Put the plants in this ranking on a request list, keep the ones you choose, and we reply with what is ready and current pricing.

Red maple and tuliptree are not in our catalog, and a bee garden should have them from wherever it can get them. Four more of ours fill gaps the ranking leaves:

• Devil’s walking stick, whose two-foot flower heads open in August when little else does.
• New Jersey tea, a June shrub of dry ground with two rare pollen-specialist mining bees of its own.
• Deerberry, a blueberry of dry woods with specialists tied to its section of the genus.
• Pinxterbloom azalea, the April azalea Andrena cornelli depends on.

How to plant for bees

• Cover every month from March to October with at least one woody plant in flower, and preferably three: willow or red maple, serviceberry, redbud, plum, holly, basswood, sumac, sourwood, pepperbush, then asters and goldenrods. The bloom calendar, opened here on the ones we grow, shows the gaps they leave. Pick any one of them in the companion species tool to see what else belongs beside it.
• Plant each species in a group, not a scatter; a clump is found faster and worked longer.
• Leave dead stems through winter, cut them to 8 to 24 inches in spring and leave the stubble a second year; keep a snag, a log or a stick pile.
• Leave bare soil on a sunny bank, keep wood chips to paths and put the leaves under the shrubs instead.
• Put no systemic insecticide on anything that flowers, buy plants that have never had one and choose single flowers over doubled ones.
• Pull the invasive shrubs first; they hold ground that willow, plum and sumac would fill for free.

Common questions

What is the best tree to plant for bees?

A willow, if you plant one thing, for the 14 specialist bees that collect its pollen and the March forage that queen bumble bees depend on. We grow five willows, and among the bigger trees American basswood gives the largest nectar flow in the eastern woods, two weeks in June.

Do native bees need nesting stems as well as flowers?

Yes: about 30 percent of native bees nest in hollow or pithy stems and old beetle holes, and the other 70 percent dig in bare, sunny ground. Leave dead stems standing through winter, cut them to 8 to 24 inches in spring and keep a patch of bare soil.

Are nursery plants treated with neonicotinoids safe for bees?

No, because a systemic insecticide moves into nectar and pollen and can stay at lethal levels for eighteen months. Ask what was applied before you buy, and never treat a woody plant while it is in flower.