Side by side
Common alder or grey alder? How to tell them apart
Alnus glutinosa · Alnus incana
You can tell a common alder by its round leaf with a rounded or notched tip, its sticky young leaves and its dark, cracked bark; a grey alder has a pointed, double-toothed leaf with a grey, hairy underside and smooth, light grey bark.
Look at the leaf tip and the trunk. Round and notched, with a dark trunk: common alder. Pointed, greyish green and hairy underneath, with a smooth, light grey trunk: grey alder.
| Common alder | Grey alder | |
|---|---|---|
| Leaves | Alternate, round to obovate, 4–10 cm, double-toothed, tip rounded or notched. Young leaves sticky. | Alternate, 5–10 cm, oval with a pointed tip, sharply double-toothed; underside grey-green and softly hairy. Not sticky. |
| Flowering | Long, hanging male catkins as early as February (February–March). | Hanging male catkins in February–March, before the leaves (February–March). |
| Fruit | Small woody cones 1–2 cm long. | Small woody cones 1–1.5 cm long, stalkless or short-stalked, in small clusters. |
| Bark | Dark grey to blackish-brown, cracked into small plates. Buds purple and stalked. | Smooth and pale grey, even on older trees; twigs hairy. |
| Shape and height | Broadleaf tree, 15–25 m | Broadleaf tree, 10–20 m |
| Site | Sun or partial shade, any garden soil, moist to wet | Sun or partial shade, any garden soil, dry to wet |
| Native to Belgium | Yes | No, naturalised |
| Good for bees, butterflies and birds | Yes, for butterflies and birds | – |
| Poisonous to people and pets | Not known to be poisonous | Not known to be poisonous |
| Pruning months | November–March | November–March |
The best feature in each season
- Spring
- Both flower as early as February–March with long hanging catkins, before the leaves. The young leaves of the common alder are sticky, those of the grey alder are not.
- Summer
- Turn a leaf over: greyish green and softly hairy on the grey alder, green with tufts of hair in the vein axils on the common alder.
- Autumn
- Alders hardly change colour: the leaves fall while still green. The little cones of the grey alder are mostly stalkless or short-stalked in groups; those of the common alder hang on clear stalks.
- Winter
- Both keep their woody little cones all winter. The buds of the common alder are purple and stalked; the twigs of the grey alder are hairy and its trunk stays smooth and light grey.
Where do they grow?
The common alder is native: the tree of stream banks, alder carr, wet meadows and ditch sides. The grey alder grows naturally in the mountains and along rivers of central and northern Europe; here it has been planted as a pioneer and windbreak, and has naturalised in places. It also copes with drier, poorer soil.
Which one for your garden?
- If you have wet soil, a stream or a pond, choose the native common alder, free-growing, coppiced or pollarded. It feeds many insects, and siskins and goldfinches eat the seeds from its cones.
- The grey alder suits a windbreak or pioneer planting on drier, poor soil, but it sends up suckers: not right next to a lawn or border. The pollen of both can trigger hay fever as early as February–March.
Did you know? Both alders take nitrogen from the air thanks to bacteria in nodules on their roots: that is how they thrive on soil where other trees go hungry.
Read on
- Plant profile: Common alder
- Plant profile: Grey alder
- Common alder: when and how to prune
- Grey alder: when and how to prune
- Identification key