Plant problems

Why Are My Anthoxanthum Leaves Curling?

Q: What does anthoxanthum odoratum smell like?

Anthoxanthum odoratum (sweet vernal grass) has a highly characteristic, sweet, hay-like, vanilla-tinged scent produced by the chemical compound coumarin, which is concentrated in the leaves and seed heads of the plant and released when they are crushed, cut, or dried. The scent is most strongly produced when the leaves are dried, as coumarin is released in higher concentrations from drying plant tissue than from fresh tissue; this is the reason why a newly mown or newly dried UK wildflower meadow that contains a good proportion of anthoxanthum has such a distinctive, sweet, warm, complex scent compared to a plain ryegrass lawn that lacks it. The coumarin scent of anthoxanthum odoratum is very similar to that of Hierochloe odorata (holy grass, sweetgrass), which also contains high coumarin levels; both grasses share the same chemical basis for their scent. In the context of UK wildflower meadow management and restoration, anthoxanthum odoratum is one of the grasses most associated with the characteristic sweet scent of a traditionally managed UK hay meadow, and its presence in a meadow seed mixture or an established meadow sward contributes significantly to the sensory character of the meadow in late spring and early summer when the seed heads are maturing and the first cut approaches. In hay-making, the presence of anthoxanthum in the sward adds to the quality and attractiveness of the dried hay, which is one of the reasons it was traditionally regarded as a desirable component of hay meadow grass mixtures in UK farming.

Q: Is anthoxanthum odoratum good for a UK wildflower meadow?

Yes, Anthoxanthum odoratum (sweet vernal grass) is one of the most recommended and most characteristic grass species for a UK wildflower meadow seed mixture, both for its ecological value as a native grassland grass and for the distinctive sweet, hay-like coumarin scent that it contributes to the meadow sensory experience. It is a non-aggressive, relatively low-growing, loosely tufted grass that flowers early (from April, making it one of the earliest-flowering UK grasses) and sets seed in May to June, providing a valuable early source of pollen and the seed structure of a spring-active wildflower community. It is adapted to a wide range of moderately fertile to low-fertility, acid to slightly calcareous, moderately moist to moderately dry soils and is included in commercial wildflower and native grass seed mixtures for a wide range of UK grassland habitat types, from neutral lowland meadow to slightly acid grassland to chalk and limestone meadow. As a characteristic species of unimproved, traditional UK hay meadows (a UK Biodiversity Action Plan priority habitat), anthoxanthum odoratum is a useful indicator of meadow quality and grassland continuity; its abundance in a sward is often a sign that the meadow has not been recently fertilised, ploughed, or re-seeded with modern agricultural grass mixtures. It associates naturally in a UK meadow with other native grassland grasses (Festuca rubra, Agrostis capillaris, Cynosurus cristatus) and with characteristic meadow wildflowers including cowslip, oxeye daisy, yellow rattle, common knapweed, and meadow cranesbill.

Q: Is anthoxanthum odoratum native to the UK?

Yes, Anthoxanthum odoratum (sweet vernal grass) is a native UK grass, one of the most widespread and ecologically important native grassland grasses in the British Isles; it is found in a very wide range of grassland, meadow, pasture, heath, and open woodland habitats across England, Wales, Scotland, and Ireland, from sea level to the upland zone. It is one of the earliest-flowering UK grasses (from late March to April), which makes it an important early pollen source for pollinators in UK meadow and grassland habitats. Sweet vernal grass is a characteristic species of UK lowland meadow (MG3, MG4, MG5 NVC communities), upland hay meadow (MG3 NVC), acid grassland (CG, U series NVC), and a wide range of other UK grassland NVC communities, reflecting its very wide ecological range across UK grassland types. It is a UK Biodiversity Action Plan (BAP) priority grassland species indicator for several of the traditional UK grassland habitat types that have declined dramatically as a result of agricultural intensification (ploughing, fertilising, re-seeding with modern grass mixtures, and changes in cutting and grazing management). Anthoxanthum odoratum has also been the subject of some of the longest-running ecological research in UK science; the Park Grass Experiment at Rothamsted Research in Hertfordshire, which has been running continuously since 1856, has used anthoxanthum as a study species for long-term research on grassland biodiversity, soil fertility, and plant community ecology, making it one of the most scientifically studied UK native grasses.

Anthoxanthum odoratum (sweet vernal grass) is a native UK grass of meadows and open grassland, one of the earliest grasses to flower in spring (from April), notable for its sweet, coumarin-rich, hay-like scent when cut or dried. Adaptable across a wide range of UK soil conditions, it is a valued component of wildflower meadow mixtures. Drought and excessive fertility cause the most problems in cultivation.

Drought and dry conditions

Anthoxanthum is more drought-tolerant than many UK grassland grasses, but prolonged drought on thin, light, freely draining soil in a hot UK summer causes the flat, softly hairy leaves to curl and yellow at the tips. In a wildflower meadow context, summer browning and leaf curl during the driest period is a normal seasonal feature of many native grassland grasses and the meadow typically recovers with autumn rains.

What to do

In a lawn or border context, water during prolonged dry spells to maintain the appearance of the grass. In a wildflower meadow context, summer drying and leaf curl is natural and needs no intervention; the meadow recovers with the return of autumn moisture. The species is better adapted to managing summer drought naturally than many introduced ornamental grasses.

Too much fertility

Anthoxanthum is a characteristic grass of unimproved, low to moderate fertility UK meadows; in highly fertile, heavily fertilised soils it is outcompeted by more vigorous species and gradually disappears. If anthoxanthum in a garden or meadow shows poor vigour and leaf curl, excessively high soil fertility may be the underlying cause, shifting competitive balance in favour of ryegrass or Yorkshire fog.

What to do

Do not fertilise a meadow containing anthoxanthum; applying nitrogen fertiliser rapidly increases the competitive advantage of vigorous, fertility-tolerant species. In a wildflower meadow context, remove cut material after each cut rather than leaving it to rot and return nutrients to the soil; this gradual nutrient depletion over several seasons helps maintain the low-fertility conditions that anthoxanthum and associated wildflower species need. Yellow rattle (Rhinanthus minor) sown into the meadow sward is a highly effective tool for reducing overall grass vigour and increasing wildflower diversity by parasitising the roots of the more vigorous grasses.

Cutting before seed set

Anthoxanthum is a relatively short-lived perennial that depends on self-seeding to maintain its presence in a meadow sward. A cutting regime that cuts too frequently or too early (before May to June, when the seed has matured) gradually reduces the anthoxanthum component over several seasons as seeds cannot set and the older plants die without replacements. Individual plants cut before seeding also produce weaker subsequent growth.

What to do

In a wildflower meadow, do not take the first cut before late July; this allows anthoxanthum to flower (April to May) and set seed (May to June) fully before the first annual cut. Remove all cut material from the site to prevent nutrient return. In a lawn context where cutting is unavoidable, accept that anthoxanthum will be present in a reduced form as short vegetative growth and will not contribute its characteristic flower display or scent.

Frequently asked questions

Why are my anthoxanthum leaves curling?

Anthoxanthum leaves curl most commonly because of drought (more drought-tolerant than many UK grasses but prolonged drought on thin soil causes leaf curl and tip yellowing; water in a border context; accept natural summer drying in a meadow), too much fertility (grass of unimproved, low to moderate fertility meadows; in highly fertile soil outcompeted by ryegrass and Yorkshire fog; do not fertilise; remove cut material after cutting; use yellow rattle to reduce overall grass vigour), or cutting before seed set (short-lived perennial; needs to self-seed; do not cut before late July in a meadow; allows flowering April to May and seed set May to June). Low fertility and late-summer cutting are the keys.

What does anthoxanthum odoratum smell like?

Sweet, hay-like, vanilla-tinged; produced by coumarin, concentrated in leaves and seed heads and most strongly released when cut or dried. The same compound gives Hierochloe odorata (holy grass) its scent. The characteristic scent of a traditionally managed UK hay meadow in late spring and early summer is substantially due to anthoxanthum. In hay-making, anthoxanthum's presence adds to the quality and sweetness of dried hay. One of the most distinctive and pleasant scents associated with traditional UK grassland management.

Is anthoxanthum odoratum good for a UK wildflower meadow?

Yes; one of the most recommended and most characteristic native grasses for a UK wildflower meadow seed mixture. Non-aggressive, loosely tufted, flowers early (from April), sets seed May to June. Adapted to a wide range of moderately fertile to low-fertility, acid to slightly calcareous, moderately moist to moderately dry soils. Associates naturally with Festuca rubra, Agrostis capillaris, Cynosurus cristatus, and meadow wildflowers including cowslip, oxeye daisy, yellow rattle, common knapweed, and meadow cranesbill. An indicator of long-established, unimproved UK grassland.

Is anthoxanthum odoratum native to the UK?

Yes; one of the most widespread native UK grassland grasses, found across England, Wales, Scotland, and Ireland from sea level to the upland zone. One of the earliest-flowering UK grasses (March to April); an important early pollen source. A characteristic species of UK lowland and upland hay meadow, acid grassland, and a wide range of other NVC grassland communities. Subject of long-term ecological research at the Park Grass Experiment at Rothamsted Research (running continuously since 1856), one of the most scientifically studied UK native grasses.