Scentless mayweed

How to recognise it

Habit

Annual or short-lived herb of 15–80 cm, usually 30–60 cm, upright or spreading and much branched, often almost as wide as tall. The hairless stems are often tinged red.

Leaf

Two to three times finely pinnate, with narrow, thread-like, hairless segments. Crushed, they smell of almost nothing.

Flower

Heads 2–4 cm across at the tips of the branches, with 12–25 white ray florets around a yellow centre of disc florets, from June to October. The receptacle is domed and solid, without scales.

Fruit/Seed

Small dark brown achenes without a pappus, with three white ribs on one side and two small dark oil glands on the other.

Roots

A taproot with fine side roots: young plants pull up easily, large ones are more firmly anchored.

Confused with

Scented mayweed (German chamomile) has smaller heads, a hollow, conical receptacle and a strong chamomile scent. Corn chamomile and stinking chamomile have chaffy scales between the disc florets, and stinking chamomile smells unpleasant. Sea mayweed on the coast has thick, fleshy leaf segments.

Flowering: June–October · Pruning: September–October

Why grow it?

• Flowers for a long time, from June into October, so it still offers pollen and nectar late in the season.
• The open, flat flower heads are an easy food source for hoverflies, small solitary bees, small beetles and shieldbugs.
• Food plant for the caterpillars of a few moths that live on chamomiles, such as the chamomile shark (Cucullia chamomillae).
• A true pioneer: it quickly covers bare soil in a new garden, on a building site or in a freshly sown wildflower strip.
• Together with common poppy and cornflower it makes up the classic picture of a flowery field margin.

Scentless mayweed: where does it grow best?

• In the wild: arable fields and field margins, fallow land, verges, dykes, building sites, tips and gaps in grassland.
• Full sun; in shade it grows weak and floppy and flowers poorly.
• Any open, fairly fertile soil: sand, loam or clay, fairly dry to moist. It also tolerates a little salt, as on verges along gritted roads.
• In the garden: in a cornfield-flower strip, on a fallow patch, along the edge of the vegetable plot or in a newly planted, still open border.

Goes well with

• Common poppy: Red next to white in a cornfield-flower strip, on the same sunny, open ground.
• Cornflower: A blue cornfield flower that blooms at the same time and needs the same soil cultivation.
• Corn marigold: Large yellow flower heads that keep flowering just as long.
• Corncockle: A purplish-pink cornfield flower that rises above the mayweed.
• Scented mayweed: Looks similar but does smell: a nice way to learn the difference.

Scentless mayweed: when and how to plant it?

1. It usually turns up by itself on disturbed ground: the seed is often already in the soil.
2. If you do want to sow it, buy seed of native origin from a wild-plant nursery, on its own or in a cornfield-flower mix.
3. Sow in September–October or March–April on loose, weed-free soil. Sow thinly, press the seed in and cover it with no more than a very thin layer of soil.
4. Keep the soil moist until the seedlings are up and thin them to 20–30 cm apart.
5. Never dig up plants from the wild; seed from a few plants in your own garden is more than enough.

Care

Water

Not needed, except just after sowing in dry weather.

Feeding

Not needed. On soil that is too rich the plants grow big and heavy and flop open.

Keeping the soil open

As a cornfield flower it needs bare ground: rake or lightly cultivate the strip every autumn, or it will vanish into the grass.

Spreading

Too much of it? Hoe off or pull up young plants, or cut flowering plants before they set seed. It does not survive in a regularly mown lawn.

Self-seeding

Let a few plants ripen where you want to see it again next year.

Tip: Not sure whether it is scented or scentless mayweed? Slice a flower head lengthwise: hollow and conical is scented mayweed, solid and domed is scentless mayweed.

Pruning and mowing

Pruning months: September–October.

When: After flowering, in September–October, or earlier if you want to prevent seeding.

How:

• Cut faded plants off at the base or pull them up before the heads turn brown if you want fewer seedlings.
• If you want it to come back, let some ripen and shake the dry plants out over the strip.
• In a wildlife garden, leave a few dead plants standing over winter: small insects shelter in them.
• Plants without ripe seed can go on the compost heap; avoid it with ripe seed, as the seed survives an ordinary compost heap.

Caution: One plant produces thousands of seeds that stay viable for years: do not let it set seed in the vegetable plot.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Ripens from August. Sow in autumn or spring on bare soil, or let the plants self-seed.

Scentless mayweed: how does it get through the winter?

Hardy to −20 °C.

• Most plants die after setting seed. Those that germinate in autumn overwinter as a low rosette of fine leaves.
• The seed overwinters in the soil and germinates as soon as the ground is cultivated again.
• The rosettes are fully hardy; an ordinary Belgian winter does them no harm.
• Dead stems and seed heads give small insects a place to shelter.

Diseases and pests

• Weed in the vegetable plot: Germinates en masse on disturbed soil. Hoe on a dry day, as young as possible, and mulch the soil between the crops.
• Large seed bank: Letting it seed every year fills the soil for years. Remove plants before they set seed and do not dig deeply, so old seed is not brought back to the surface.
• Flopping plants: On rich soil they become heavy and fall apart. Do not feed and sow on poorer soil.
• Aphids and powdery mildew: Occur now and then, especially in dry weather. Usually just leave it: ladybirds and hoverfly larvae deal with the aphids.

Through the year

• March: Seedlings on bare soil. You can still sow a cornfield-flower strip.
• April: Overwintered rosettes start to grow. Weed the vegetable plot.
• May: Plants start to shoot up; hoe them off where they are in the way.
• June: First white flower heads.
• July: Full flower, with plenty of hoverflies and small bees.
• August: Flowering and first ripe seed. Cut back if you do not want seedlings.
• September: Last flowers and seed ripening. Sow for next year.
• October: Clear faded plants or leave a few standing for insects.
• November: Lightly cultivate the flower strip so the seed can germinate in spring.

Did you know?

• Inodorum means ‘without scent’. Tripleurospermum means ‘seed with three ribs’, after the three ribs on the achenes.
• It used to be placed in the genus Matricaria, together with scented mayweed; hence its French name matricaire inodore.
• The seed can survive in the soil for many years. That is why it sometimes appears in huge numbers after an old pasture is ploughed.