Which tree sheds white fluff? Sort it by month, leaf and where the fluff sits

Late spring and early summer: cottonwood and the other poplars

If the air is full of cotton between May and July, look for a tall poplar. The USDA Forest Service's Silvics of North America says eastern cottonwood flowers from February to April before the leaves, then disperses seed from May through mid-July in the South and June through mid-July in the North. The seed is carried by wind with the "cotton" attached, often several hundred feet, and seeds that fall in water can travel much farther. The same source calls eastern cottonwood one of the tallest species east of the Rocky Mountains.

The leaf confirms it: triangular, coarsely toothed, on a stalk flattened from side to side, so it rattles in the wind. Only female trees make cotton. The Forest Service gives a sex ratio of about 1 to 1 and notes that male clones, which have none of the "objectionable cotton", are the ones preferred for planting, which is why one cottonwood on a street fluffs and its neighbour does not.

Quaking aspen sheds the same kind of fluff in smaller amounts. NC State's aspen profile describes female catkins up to 4 inches (10 cm) long splitting open in summer, each capsule holding 4 to 10 tiny seeds embedded in cottony hairs, spread by wind or water. Its leaf is nearly round and trembles on a flat stalk, and the bark is smooth and pale. In Canada the "trembling aspen fluff" search is the same tree. The poplar page separates cottonwood, aspens, Lombardy and white poplar.

Narrow leaves: willows

If the fluff comes from a tree with long, narrow leaves near water, it is a willow. The Virginia Tech black willow sheet describes lance-shaped leaves 3 to 6 inches long with finely toothed edges, catkins in early summer, and cone-shaped capsules full of small, cottony seeds that split open in midsummer. Black willow bark is brown to gray-black with thick, scaly ridges, unlike the smooth pale bark of an aspen.

Willows are also male or female. The Woodland Trust's white willow page explains that female catkins lengthen into small capsules holding minute seeds in white down, which the wind carries away. White willow leaves look paler than most willows because of silvery hairs underneath. Weeping willows produce the same down where the trees are female; the willow page covers how to tell the common willows apart.

Fluffy buds in March are a different thing. The Morton Arboretum describes pussy willow catkins about an inch long, fuzzy and silvery gray, opening before the leaves in early to mid spring. These are flowers; the cotton comes weeks later.

Seed balls that break into fluff: sycamore and London plane

A fuzzy brown debris of tiny seeds under a big tree with patchy bark in late winter or spring comes from sycamore seed balls. Virginia Tech's sycamore sheet describes a round cluster of achenes hanging on a stalk 3 to 6 inches long, maturing in November and dispersing in late winter. The Woodland Trust's London plane page says the fruits break up slowly over winter, each seed carrying stiff hairs that help wind dispersal. That fluff is short and brownish compared with cottonwood's white drifts. See sycamore for the leaf and bark.

White fluff in fall and in warm climates

Groundsel tree. On the coast of the eastern US, a shrub or small tree turning white in autumn is likely Baccharis halimifolia. NC State's groundsel tree profile describes frilly white seed plumes on female plants from September to November, dispersed by wind, on a plant 5 to 12 feet (1.5–3.7 m) tall with gray-green, coarsely toothed leaves 1 to 3 inches long, found in salt marshes, sandy places and wet disturbed sites.

Silk-floss tree. In south Florida and southern California, white floss hanging from a tree with a thick, spiny, green trunk is Ceiba speciosa. The UF/IFAS fact sheet describes pink and white flowers in fall and winter, followed by woody, pear-shaped capsules about 8 inches long filled with silky, white, kapok-like floss and pea-like seeds, on trees reaching 50 feet in USDA zones 10A to 11. Its relative the kapok tree (Ceiba pentandra) is in Tree Identifier's Collection.

White fluff in the UK

"Tree that sheds white fluff" in Britain usually means a poplar or a willow. The Woodland Trust's black poplar page says fertilised female catkins develop into fluffy, cotton-like seeds that fall in late summer, and that only about 600 of Britain's roughly 7,000 wild native black poplars are female, so a fluffing poplar on a British street is more likely a planted poplar than a wild native black poplar. London planes add their own hairy seed as the fruits break up over winter.

Fluffy flowers and fluff stuck to the bark

Two searches look like seed fluff but are not. Fluffy white flowers in April or May on a small tree with long, fringe-like petals belong to American fringetree, which NC State's fringetree profile describes as clusters 4 to 8 inches long with creamy white petals; the white flowers guide covers the other white-blossomed trees.

Fluff glued to the bark is usually an insect. The RHS describes woolly aphid as a white, waxy fluff over dark brown to black aphids, often mistaken for a fungus, found only on apple, cotoneaster and pyracantha, from about April to October, often around old pruning cuts. Diagnosing it is outside this guide; a local extension office can confirm the insect.

Using a photo

Fluff itself says little about the tree. Photograph a leaf with its stalk, or the whole tree with its open catkins, and Tree Identifier names it from that one photo; eastern cottonwood, black poplar, white willow, weeping willow and American sycamore are in its Collection. It shows no confidence score or alternatives, so check the answer against the month and the leaf in the table above. The follow-up chat under a result can tell you when that species sheds seed, and the Tree Map remembers where the fluffy tree stands for next year.