Tree groundsel

Tree groundsel: how do you recognise it?

Habit

Semi-evergreen, dense, much-branched shrub of 1–4 m.

Leaf

Alternate, 3–7 cm, obovate to diamond-shaped, coarsely toothed in the upper part (often untoothed near the top of the branches), thick, grey-green and slightly sticky.

Shoots

Green, grooved, slightly sticky twigs, later brown.

Flower

Small, white to yellowish-green flower heads in clusters, in September–October; male and female plants.

Fruit

Masses of seeds with silvery-white fluff on the female plants (October–November), which blow far away.

Difference from sea buckthorn

Sea buckthorn has thorns, narrow silvery leaves and orange berries.

Difference from oleaster

Oleaster is evergreen, with untoothed, leathery leaves with a silvery underside.

Flowering: September–October

Looks like it, but isn’t

• Sea buckthorn Hippophae rhamnoides: thorns, narrow silvery leaves and orange berries. Difference from sea buckthorn
• Oleaster Elaeagnus: evergreen, with untoothed, leathery leaves with a silvery underside. Difference from oleaster

Why grow it?

• Why not plant it: it is an invasive alien species on the European list; selling, planting and propagating it is banned.
• Its seeds blow far and germinate on salt marshes, dunes, dykes and waste ground, where it crowds out native vegetation.
• Spot it early: a young plant is still easy to pull up, while an old shrub sprouts again after being cut down.
• For a wind-hardy coastal hedge there are good native alternatives, such as sea buckthorn and burnet rose.

Tree groundsel: where does it grow best?

• Grows in full sun, on wet and dry, salty and non-salty soil.
• Spreads mainly on the coast: salt marshes, dunes, dykes, port areas and the banks of brackish water.
• Still very rare in the wild here; in France and Spain it is already overrunning large areas of salt marsh and wetland.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry to wet

Size

3 m tall, 2.5 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Sea buckthorn: The native alternative for the coast: silvery leaves, orange berries for birds, resistant to sea wind and salt.
• Burnet rose: A low, native coastal rose with white flowers and black hips, ideal on sandy soil.
• Wild privet: A native shrub of the dunes, for a wind-hardy hedge with white flowers and black berries.
• Tamarisk: Not native, but not invasive either: an airy, salt-tolerant windbreak with pink flower plumes.

Good and bad companions

Best kept away from

• Do not plant under the dense crown of these trees: norway spruce, european silver fir, nordmann fir, douglas fir, yew, horse chestnut, norway maple, sycamore

Tree groundsel: when and how to plant it?

1. Do not plant it, and do not give away plants, cuttings or seed: it is banned.
2. Looking for a wind-hardy, salt-tolerant shrub for the coast? Choose sea buckthorn, burnet rose or wild privet.
3. For a taller windbreak, tamarisk will do: not native, but not invasive either.
4. If there is already a tree groundsel in your garden, remove it, preferably before it sets seed in October.

Care

Young plants

Pull or dig them up with the whole root, ideally when the soil is moist.

Old shrubs

Cut them down and dig out the stump with the largest roots; a stump left behind sprouts again.

Seed-bearing branches

Take them away in a closed bag with the household waste, not on the compost heap and never in the countryside.

Follow-up

Come back in the following years: new plants still appear from roots left behind and from seed.

Tip: Wondering whether a shrub by the sea is tree groundsel? Look in autumn: grey-green, coarsely toothed leaves and flower clusters that turn into silvery-white fluff on female plants are typical. Report a wild shrub outside your garden, for example on waarnemingen.be or waarneming.nl.

Tree groundsel: when to prune it?

When: Do not prune but remove, ideally before it sets seed in October.

How:

• Dig up young plants, roots and all. Older shrubs sprout again after being cut down: remove the stump too.
• If you cannot remove it straight away, cut the flowering branches off female shrubs in September, before the seeds ripen. Pruning alone will not stop it: it sprouts back vigorously.

Caution: Take seed-bearing branches away in a closed bag, never dump them in the countryside: the fluff blows away at the slightest breath of wind.

Pruning calendar and basic rules

Propagation

Do not propagate

Propagating, selling and giving it away are banned: you would only help it spread.

How it spreads

In autumn, female shrubs produce masses of fluffy seeds that blow far away. After being cut down, it also sprouts again from the stump.

Tree groundsel: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Fully hardy: even after a hard winter it sprouts again in spring.
• Semi-evergreen: in a mild winter it keeps some of its grey-green leaves, in a cold winter it loses them. Winter is a good time to dig shrubs up.

Diseases and pests

• Regrowth after cutting: A shrub that has been cut down sprouts many new shoots. Dig out the stump, or cut the regrowth several times a year until the roots are exhausted.
• Seedlings: Many seedlings come up around a female shrub. Pull them up as soon as you see them.
• Crowding out: On salt marshes and in dunes it forms dense thickets under which native vegetation disappears.
• Male or female: Only female shrubs set seed: you can recognise them in October–November by the silvery-white fluff. Tackle those first, but remove the male ones too.

Through the year

• January: Dig up or cut down shrubs and remove the stump, in mild weather.
• March: Pull up seedlings while the soil is moist.
• June: Cut the regrowth from shrubs that were cut down.
• September: Flowering: cut the flowering branches off female shrubs before the seeds ripen.
• October: Last chance to remove shrubs before the seeds blow away.
• November: Silvery-white fluff on female shrubs: take seed-bearing branches away in a closed bag; plant native alternatives.
• December: Dig up shrubs in mild weather.

What can you use it for?

Garden and landscape

Was once planted as a wind-hardy, salt-tolerant shrub by the sea.

Caution: Invasive alien species on the European list: selling, planting and propagating it is banned. It crowds out the vegetation of salt marshes and dunes.

Did you know?

• A single female shrub can produce more than a million seeds a year. It is on the European list of invasive species: selling and planting it is banned.
• A single female shrub can produce more than a million seeds a year. Since 2016 it has been on the European list of invasive species: selling and planting it is banned.
• It belongs to the daisy family, like asters and dandelions: each ‘flower’ is really a head of many tiny florets.
• ‘Halimifolia’ means ‘with leaves like Atriplex halimus’, a silvery-grey Mediterranean saltbush; the French name also refers to this plant.