Black Gum

A tough, adaptable native shade tree with the best fall color in the eastern woods - it turns fluorescent scarlet weeks before anything else, feeds fall migrant birds with high-fat fruit, hosts moths that live on nothing else, and can outlive almost every hardwood around it.

Full sun to part shade and acidic to neutral soil, wet or dry - it is genuinely adaptable. The rules that matter: plant a small tree, plant it in spring, and water it deeply for three summers.

Black gum takes full sun to part shade (full sun gives the strongest fall color) and an unusually wide range of soils. It grows in the seasonally flooded edges of swamps and ponds and equally on dry upland slopes, tolerates clay and periodic standing water, and handles zones 4 through 9. Its one soil preference is acidic to neutral ground; on limy, high-pH soil the leaves yellow between green veins and the tree never really thrives.

The difficulty is not growing it — it is getting it established. Black gum sends down a deep taproot early and does not rebuild a cut one quickly, so a large field-dug tree moved at the wrong time of year is a common and expensive failure. Buy container-grown, or the smallest tree that will do, and plant in spring only. Set it at the depth it grew, skip the soil amendments, mulch wide, and water deeply through the first three summers. Then expect it to do very little above ground for a season or two while it works below.

Give it room: 30 to 50 feet tall and 20 to 30 wide is the usual mature size, more on a good site. Site a female tree back from patios, walks, and parked cars, because ripe fruit stains and makes paving slippery for a couple of weeks each fall.

Almost nothing once it is established - no feeding, water only in real drought, and minimal dormant-season pruning. The tiered, low-branched shape is the whole point, so resist limbing it up.

An established black gum is close to maintenance-free. It needs no fertilizer in reasonable soil, and water only in an extended drought. Keep a wide mulch ring, keep mowers and string trimmers off the bark, and otherwise leave it be.

Pruning is minimal and belongs in the dormant season: dead, damaged, or crossing wood, cut back to the branch collar. Black gum builds a strong central leader and evenly spaced horizontal branches without help, and a tree that has been shaped by a person almost always looks worse than one left alone. In particular, resist the urge to limb it up — the low, tiered branching is most of its character.

Expect and tolerate some leaf spot in humid summers; purple-rimmed spots and a bit of late-August leaf drop look worse than they are and never trouble a healthy tree. Watch for sticky honeydew and black sooty mold underneath, which means scale. And leave the caterpillars — on a native tree, chewed leaves are the tree doing its job.

No crop for the kitchen. The fruit is a sour, stony bird food that vanishes into migrating thrushes each fall, and the flowers become honey by way of bees - both harvests belong to something other than you.

There is nothing here to pick. Black gum's fruit is a half-inch blue-black drupe that is almost entirely stone, wrapped in a thin, intensely sour flesh. It is not poisonous — country cooks have made preserves and a sharp jelly from it — but between the sourness, the stone, and the fact that birds usually clear the tree within days of ripening, it is not a food crop, and this catalog lists no edible part on black gum.

The fruit's real value is timing and fat content. It ripens in September and October, precisely when migrating songbirds need dense fuel, and high-lipid fall fruits like this one are what carry thrushes and thrashers south. Only female trees bear, and only when a male is somewhere nearby.

The second harvest goes to the bees. Black gum is a first-rate nectar tree and its honey is excellent. One point of accuracy: the famous commercial tupelo honey of the Florida panhandle comes from a different species, the Ogeechee tupelo (Nyssa ogeche) of the Apalachicola river swamps. Black gum makes fine honey under its own name; it is not the source of the bottled article.

Nothing to store from the tree. Seed must be cleaned of pulp and kept moist and cold, never dried out, and the tree's off-season value is its bark and branching silhouette in winter.

There is no crop to put away. If you are saving seed, treat it as a living thing rather than a dry good: clean the pulp off ripe fruit promptly, since the flesh inhibits germination, and either sow the stones outdoors in fall or hold them moist and cold in damp sand in the refrigerator for two to three months. Do not let black gum seed dry out on a shelf, and do not expect all of it to come up in the first spring — a fraction routinely waits a second year.

What the tree stores up is winter presence. Once the scarlet leaves are gone, black gum is one of the more sculptural trees in a bare landscape: a straight central leader, tiers of branches leaving the trunk at right angles, and, on older trees, that deeply blocked alligator-hide bark. Old hollow trunks are among the best natural den and roost cavities in the eastern woods, which is why an aging black gum is worth keeping rather than removing.

Buy a small container-grown tree, or sow cleaned seed in fall where the tree will stand. Cuttings are difficult, transplanting an established tree rarely works, and the taproot is the reason for both.

For nearly everyone the answer is a small container-grown tree, planted in spring. Black gum has become far easier to find as its fall color has gotten its due, and container stock avoids the cut taproot that sinks so many field-dug trees.

From seed it is straightforward if slow. Collect ripe fruit in fall, clean off the pulp, and sow the stones about an inch deep either in a nursery bed or directly where the tree will grow, letting winter supply the two to three months of cold, moist conditioning they need. Cage the spot against rodents. A directly sown seedling keeps its taproot intact and, given a few years, will outrun a nursery tree planted the same season.

Cuttings are difficult — only soft early-summer wood roots at all reliably, and it is a job for someone with mist and patience — which is why named cultivars are usually budded or grafted by specialist growers. And do not plan on moving an established black gum: past the first few years it very rarely survives the attempt.

Not a human food. Its ecological role is specific and valuable: high-fat fruit timed to fall bird migration, top-tier nectar for bees, host foliage for moths including a Nyssa specialist, and hollow old trunks that shelter everything.

Black gum feeds no gardener, and it feeds a great deal else. Its fall fruit is unusually high in fat, and it ripens in September and October in step with songbird migration — the moment when a bird needs calories most and finds them hardest. Thrushes, robins, catbirds, brown thrashers, bluebirds, flickers, and pileated woodpeckers all work it heavily, and black bear, foxes, raccoons, and wild turkey take fallen fruit. A single good female tree can be emptied within a week.

Its late-spring flowers are among the most productive nectar sources of the eastern forest, worked by honey bees and a long list of native bees. As host foliage it supports a modest but genuine set of native moths, including the Hebrew moth (Polygrammate hebraeicum), whose caterpillars feed on Nyssa and nothing else — lose the tree from a landscape and that species goes with it.

Then there is age. Black gum is one of the longest-lived hardwoods on the continent, and old trees characteristically go hollow while remaining perfectly healthy, producing exactly the cavities that owls, wood ducks, bats, and honey bee colonies depend on and that young forests almost never provide. Keeping an old black gum standing is a real conservation act.

A tree of extraordinary age and one durable piece of folk technology - hollow black gum logs were the standard American beehive, which is why old-timers still call a hive a 'bee gum'.

Black gum's history is mostly a history of hollow logs. Old trees hollow out while staying alive and structurally sound, and settlers across the Appalachians and the South cut sections of hollow black gum trunk, capped them, and kept bees in them. Those log hives were called bee gums, and the phrase outlived the practice: in parts of the South an old beekeeper will still call a hive a gum, whatever it is made of. The same hollow sections served as storage barrels, well curbs, and stock troughs.

Its wood is stubbornly cross-grained and nearly impossible to split, which made it poor firewood and excellent for anything that had to take abuse without cracking — mauls, wheel hubs, chopping blocks, factory flooring, and later shipping pallets and veneer. The names are a tangle worth untangling: black gum is not sweetgum (Liquidambar, the tree with spiky gumballs), and though it is sometimes called sour gum, it is also not sourwood (Oxydendrum arboreum), the other great Appalachian honey tree.

What has changed recently is its standing as a garden tree. Long known to foresters as an ordinary bottomland species, black gum has been recognized over the last few decades as one of the finest fall-color and wildlife trees available — and dendrochronologists have found individuals in New Jersey, New Hampshire, and the Carolinas exceeding 500 and even 650 years, making it the oldest known flowering tree of the eastern forest.

Nearly every black gum problem is the same problem: it was planted too big, or in fall, or both. After that come cosmetic leaf spot, scorch on young trees, and no fruit - which usually just means the tree is male.

Newly planted tree sulks, leafs out thinly, or dies within two years: the signature black gum failure — a large field-dug tree with a cut taproot, usually planted in fall. Replace with a small container-grown tree planted in spring, water deeply for three summers, and accept two seasons of almost no top growth. Purple-rimmed spots and leaf drop in late summer: leaf spot, cosmetic on an established tree; rake fallen leaves, give the tree airflow, and consider 'Red Rage' or 'Green Gable' if it recurs yearly. Brown, crisp leaf margins in summer: scorch, almost always on a young or recently planted tree, or one in reflected heat off paving — water deeply and mulch wide. Pale leaves with green veins: the soil is too alkaline; black gum wants acidic to neutral ground and will not settle on limy soil. Sticky leaves, black sooty film, ants on the trunk: scale insects — check the twigs and treat with dormant oil. Never any fruit: most black gums are functionally male or female, so either the tree is male or there is no pollen source nearby; nurseries seldom label sex. It colors red in August: not stress — that is the tree doing the thing it is famous for.

Hardy and native across the whole eastern US, zones 4-9, and unusually indifferent to wet or dry soil. Its limits are alkaline ground and the transplanting window, not climate.

Black gum is native from New England to Florida and west to east Texas, and it is hardy across zones 4 through 9. Zones 4-5: at its northern edge, slower and smaller but fully hardy, and the fall color is if anything more intense; buy northern-grown stock where you can. Zones 6-8: its heartland, and about as trouble-free a large shade tree as the region offers, thriving on everything from pond margins to dry ridges. Zone 9 and the Deep South: excellent, handling heat and humidity easily; expect more leaf spot in wet summers and choose a tolerant selection.

Its genuine flexibility is with water. Few trees this size will grow in seasonally flooded ground and also shrug off summer drought on an upland slope, which makes black gum one of the better choices for a rain garden, a low wet corner, a pond edge, or a site whose drainage you frankly do not understand. It also tolerates clay and moderate compaction.

Where it will not go is high-pH soil, which rules out much of the limestone Midwest and the alkaline West without amendment. It is also only moderately tolerant of road salt and urban pollution, so it is a better lawn, park, and woodland-edge tree than a hard-surfaced street tree.