Plant problems

Why Are My Arrhenatherum Leaves Curling?

Q: What is the best time to cut back arrhenatherum variegatum?

The best time to cut back Arrhenatherum elatius var. bulbosum 'Variegatum' (variegated bulbous oat grass) is in late summer, specifically in late July to September, after the plant has gone through its characteristic summer semi-dormancy and the tired, curling, scorched growth from the heat of summer has accumulated. Cutting back at this time — to 5 to 10 cm from the base — stimulates a flush of fresh, vivid new white-and-green growth through August to October, taking advantage of the cooler, moister conditions of early autumn to produce attractive new foliage that carries over into the spring season. This late-summer cut-back is the most important single cultural action for maintaining arrhenatherum 'Variegatum' in good condition throughout the year; plants that are not cut back accumulate tired, scorched, curled growth through summer and fail to produce the best spring display. In spring (March), new growth begins from the distinctive bulb-like stem bases; this fresh spring growth should not be cut — it is the most vivid season of the year for arrhenatherum 'Variegatum', with the most intense white-and-green striping visible from March to May. Cutting back in spring removes this prime display. A second cut-back in very early spring (late February to early March) can be appropriate if the previous autumn's re-growth has not been cut and looks tatty after winter; but the primary maintenance cut is always in late summer.

Q: How do I grow arrhenatherum elatius variegatum in the UK?

Arrhenatherum elatius var. bulbosum 'Variegatum' grows best in partial shade to full sun in moderately moist, moderately fertile, neutral to slightly alkaline soil; it is more sun and drought tolerant than some other cool-season variegated grasses but still performs best in partially shaded conditions where the soil remains moderately moist through summer, reducing the summer curl and scorch that develops in a hot, dry, fully exposed position. Full sun in freely draining, moderately moist soil is acceptable and the plant can be vigorous in these conditions, though the summer dormancy and leaf curl is more pronounced in full sun than in partial shade. The distinctive bulb-like swellings at the base of each stem are a characteristic feature of the bulbosum variety; these store energy and nutrients and allow the plant to regenerate vigorously after the late-summer cut-back. Plant from spring to autumn; space at 30 to 40 cm apart. Water during dry spells in summer to reduce the severity of summer leaf curl and scorching. No feeding is needed in moderately fertile soil; in very poor soil, a light spring application of balanced fertiliser improves spring vigour. Cut back to 5 to 10 cm in late July to September; this is the key maintenance action. Divide every three to four years in spring when the clump becomes congested or the centre dies out; replant the bulb-bearing sections and discard the rest. Fully hardy throughout the UK. The combination of the vivid spring colour display (March to May), the interesting bulb-like stem bases, and the compact, low-growing habit makes arrhenatherum 'Variegatum' a useful front-of-border or edging plant in a UK garden.

Q: Is arrhenatherum elatius native to the UK?

Yes, Arrhenatherum elatius (false oat grass, tall oat grass) is a native UK grass, one of the most common and widespread grasses of UK road verges, rough grassland, hedgerow bases, and dry meadows across England, Scotland, Wales, and Ireland; it is a characteristic species of UK road verge plant communities and is very frequently found on chalk downland, limestone grassland, and other dry, freely draining UK grassland habitats. In UK grassland communities, Arrhenatherum elatius is often considered a dominant and sometimes excessively competitive species that can suppress other grassland wildflowers if not managed by regular cutting or grazing; it is one of the species that needs to be controlled in a wildflower meadow to prevent it from overwhelming finer grassland species. In a UK road verge or rough grassland setting, the airy, tall, pale-green, oat-like flower heads (produced in June to August) are attractive in a naturalistic way and the grass associates well with native grassland wildflowers including ox-eye daisy, knapweed, and field scabious. The ornamental cultivar 'Variegatum' is a selected form of the bulbosum variety (which has the distinctive bulb-like stem base swellings) and is the garden selection used in ornamental planting; the species form is the common UK grassland grass, while 'Variegatum' is the compact, white-striped ornamental cultivar chosen for garden planting.

Arrhenatherum elatius var. bulbosum 'Variegatum' (variegated bulbous oat grass) is a compact cool-season ornamental grass with vivid white-and-green striped flat leaves to 30 cm and distinctive bulb-like swellings at the base of each stem. At its most vivid from March to June. Summer heat and drought cause leaf curl and scorch; the solution is a late-summer cut-back that stimulates a fresh flush of vivid growth through autumn and into the following spring.

Summer heat and drought

In a hot, dry, fully exposed position, the leaves of 'Variegatum' curl inward and the white margins scorch brown from June onwards. Even in partial shade, if the soil dries out significantly in summer, curl and scorch develop. The vivid white-and-green striping is most prone to scorching at the margins under drought and heat; the plant looks its worst in August in dry, sunny conditions and its best in March to May.

What to do

Grow in partial shade with moderate moisture; water during dry spells. In a hot, sunny, dry position, the summer semi-dormancy and leaf curl is more pronounced. Mulch to retain soil moisture. If summer appearance is important, a position with afternoon shade and morning sun produces the best compromise between spring colour and summer freshness.

Summer semi-dormancy

Even in a good position, arrhenatherum 'Variegatum' is a cool-season grass that enters a semi-dormant state through the warmest part of a UK summer; the leaves flatten, curl slightly, and lose some vivid striping. This is normal behaviour for the species, not a sign of failure. The plant revives with the cooler, moister conditions of early autumn and the following spring display is the most rewarding season.

What to do

Accept summer dormancy as part of the plant's cycle; plan the planting scheme around it by combining arrhenatherum with summer-interest plants that carry the border through July to August. The spring display (March to May) is exceptional and worth the position despite the summer quietness. A late-summer cut-back (late July to September) restores the plant's appearance for the autumn season.

Skipping the summer cut-back

The most common cultural error: without a cut-back in late July to September, tired, scorched, curled summer growth accumulates and the plant looks untidy through autumn and into the following spring. The bulb-like stem bases store enough energy for a vigorous re-growth after cutting; plants cut back properly in late summer consistently produce a better spring display than those left uncut.

What to do

Cut back to 5 to 10 cm in late July to September; do not cut in spring. New vivid white-and-green growth appears within two to three weeks of cutting in the cooler autumn conditions. The following March, fresh growth from the distinctive bulb-like stem bases produces the most vivid white-and-green striping of the year. Divide every three to four years in spring when the centre dies out or the clump becomes congested.

Frequently asked questions

Why are my arrhenatherum leaves curling?

Arrhenatherum leaves curl most commonly because of summer heat and drought (cool-season grass; white margins scorch in hot, dry, exposed positions; partial shade with moderate moisture; water in dry spells; mulch), summer semi-dormancy (normal cool-season behaviour in warm UK summer; plan the planting scheme around it; best from March to May), or skipping the late-summer cut-back (cut to 5 to 10 cm in late July to September; do not cut in spring; restores appearance for autumn; stimulates the best spring display). Late-summer cut-back is the key maintenance action.

What is the best time to cut back arrhenatherum variegatum?

Late July to September; cut to 5 to 10 cm to remove tired, scorched, curled summer growth and stimulate a flush of vivid new white-and-green growth for early autumn. Do not cut in spring; the March to May growth is the most vivid display of the year and should be left to develop fully. A second cut in late February is appropriate only if the previous autumn's re-growth looks tatty after winter. The primary maintenance cut is always in late summer.

How do I grow arrhenatherum elatius variegatum in the UK?

Grow in partial shade to full sun in moderately moist, moderately fertile, neutral to slightly alkaline soil. Plant from spring to autumn; space 30 to 40 cm apart. Water in dry spells. Light spring feed in very poor soil. Cut back to 5 to 10 cm in late July to September (not in spring). Divide every three to four years in spring. Fully hardy throughout the UK. The bulb-like stem base swellings store energy for vigorous re-growth after each cut-back. Good front-of-border or edging plant for spring interest.

Is arrhenatherum elatius native to the UK?

Yes; one of the most common UK grasses of road verges, rough grassland, hedgerow bases, and dry meadows across England, Scotland, Wales, and Ireland. Dominant and competitive in UK road verge and chalk downland communities; needs management in wildflower meadows to prevent overwhelming finer grassland species. The ornamental cultivar 'Variegatum' is a selected garden form of the bulbosum variety with distinctive bulb-like stem swellings and vivid white-and-green striping; the species form is the common UK grassland grass.