Plant problems

Why Are My Thinopyrum Leaves Curling?

Q: What is thinopyrum used for in UK agriculture and conservation?

Thinopyrum intermedium (intermediate wheatgrass) and Thinopyrum ponticum (tall wheatgrass) have several uses in UK agriculture, conservation, and ecological restoration: Perennial grain crop: Thinopyrum intermedium is the parent species of 'Kernza', a perennial grain developed by the Land Institute (USA) through selective breeding that can be harvested annually for grain without reploughing; Kernza has been trialled in the UK and is of interest as a more sustainable, soil-health-positive alternative to annual wheat in some farming systems; the perennial root system reduces soil disturbance, prevents erosion, and supports more diverse soil biology than annual crops. Forage grass: Thinopyrum intermedium is a productive, palatable, and deep-rooted perennial forage grass that produces reasonable dry matter yields in dry conditions where more moisture-demanding grasses struggle; it is used in dryland forage mixes in North America and has potential for UK farms on lighter, drier soils. Erosion control and soil stabilisation: Thinopyrum ponticum (tall wheatgrass) has been widely used for erosion control, soil stabilisation, and revegetation of disturbed or saline soils; it has good salinity tolerance (one of the better salinity-tolerant perennial grasses) and can establish in difficult coastal, roadside, or industrial sites. Wildflower meadow and prairie planting: Thinopyrum intermedium can be used as a structural grass component in naturalistic, prairie-style, or low-maintenance wildflower meadow plantings on well-drained, low-fertility soils; its upright habit, blue-grey-green leaf colour, and slender flowering spikes provide foliage interest and structural contrast. Breeding resource: Thinopyrum species are valuable in wheat breeding programmes as sources of resistance to rust diseases, fusarium, and other wheat pathogens; genes from Thinopyrum have been introduced into bread wheat to improve disease resistance.

Q: What is the relationship between thinopyrum and couch grass?

Thinopyrum intermedium (intermediate wheatgrass) and Thinopyrum repens (syn. Elytrigia repens, formerly Agropyron repens) — common couch grass — are both members of the tribe Triticeae (the wheat tribe) and the genus Thinopyrum (following recent taxonomic revisions); the two are closely related but differ greatly in their garden behaviour and agricultural value. Thinopyrum repens (couch grass, twitch, scutch grass) is the familiar, deep-rooted, rhizomatous grass that is one of the most troublesome and persistent weeds in UK gardens and agricultural land; it spreads aggressively by rhizomes (underground stems) that penetrate deeply into the soil and produce new shoots from any fragment left in the soil; it is very difficult to eradicate once established; it was previously classified in the genera Agropyron and Elytrigia. Thinopyrum intermedium (intermediate wheatgrass) is an upright, clump-forming perennial grass that also has some rhizomatous spreading ability but is far less aggressively spreading than couch grass; it forms a well-behaved, slowly expanding clump that is manageable in a garden or field situation and is not considered a weed; it has been intentionally bred and developed as a useful agricultural crop. The key practical distinction for a UK gardener: Thinopyrum repens (couch grass) is an aggressive weed that should be eradicated; Thinopyrum intermedium (intermediate wheatgrass) is a useful, non-invasive, clump-forming grass that can be grown in a garden or agricultural setting without concern about it becoming a weed problem. The two species are genetically close enough that they can hybridise, which has been exploited in wheat breeding programmes.

Q: How do I identify thinopyrum intermedium in the UK?

Thinopyrum intermedium (intermediate wheatgrass) can be identified in a UK garden or field setting by the following characteristics: Leaves: flat, strap-like, with a distinctive blue-grey-green to grey-green colour (glaucous); the leaf surface is sparsely hairy on the upper surface; the leaves are 3 to 8 mm wide and up to 35 cm long; the characteristic bluish-grey colour distinguishes it from most common UK grasses, which are mid or dark green. Leaf sheath: the leaf sheath (the part of the leaf wrapping around the stem) is tight and glabrous (hairless) to sparsely hairy. Roots and rhizomes: has short rhizomes but does not spread aggressively; forms a slowly expanding clump rather than the wide-spreading rhizomatous mat of couch grass. Flowering stems: erect, to 90 to 120 cm tall; the flowering spike (ear) is a narrow, upright, elongated spike 10 to 20 cm long resembling a slender wheat ear with alternately arranged, two-rowed spikelets closely attached to the main stem axis (rachis); the spikelets are longer and narrower than those of most common UK grass species. Flowering time: June to July in the UK. Overall habit: upright, clump-forming, cool-season perennial; dormant or slow-growing in summer heat; most active growth in spring and autumn; similar overall form to tall fescue or sheep's fescue but larger and with a bluer leaf colour. The blue-grey leaf colour and narrow, wheat-like ear are the most distinctive identification features.

Thinopyrum intermedium (intermediate wheatgrass) is a cool-season, deep-rooted perennial grass in the wheat tribe, native to the dry continental grasslands and steppes of central and eastern Europe and central Asia. Closely related to wheat and couch grass; the parent of Kernza, a perennial grain crop. Valued in UK conservation, low-maintenance planting, and experimental agriculture. Leaves curl and roll from drought, waterlogging, or nutrient deficiency.

Drought and dry soil

Although thinopyrum is adapted to dry continental grasslands and is more drought-tolerant than most agricultural grasses, the flat, strap-like leaves roll inward along their length (a drought-stress response reducing transpiration surface area) and the leaf tips yellow when the plant is severely drought-stressed in an extended UK summer dry period. Most common in a light, sandy, or chalk soil without supplementary water.

What to do

The deep root system of thinopyrum intermedium allows it to access subsoil moisture that shallower-rooted grasses cannot reach; in most UK soils, established plants tolerate dry spells without irrigation. On very light, sandy soils in a prolonged dry summer, a single deep watering every two to three weeks is sufficient. Mulching around the base helps retain soil moisture and moderates soil temperature. Once established, thinopyrum generally needs no irrigation in UK conditions outside of extreme droughts.

Waterlogging and root oxygen deficiency

Thinopyrum requires well-aerated soil and is not tolerant of prolonged waterlogging; in a heavy, compacted, or poorly draining clay soil that becomes waterlogged in winter or after heavy rain, root oxygen deficiency causes leaves to yellow, wilt, and roll. The characteristic blue-grey-green leaf colour is replaced by a pallid yellow-green as chloroplast function is disrupted. Severe or prolonged waterlogging in cold wet winters can kill the roots and cause the clump to fail to regrow in spring.

What to do

Plant in well-drained, free-draining soil; thinopyrum performs best on lighter loam, sandy loam, or clay-loam soils with good drainage; avoid heavy, impermeable, or compacted clays. Improve drainage before planting on heavy soils by incorporating grit and organic matter. In a wet, poorly draining site, raise the planting area or plant on a slope. A well-drained, slightly raised, sunny position is ideal and prevents both waterlogging stress and root disease.

Nutrient deficiency

In a low-fertility, nutrient-poor, sandy, or chalk soil, thinopyrum may show leaf yellowing, tip dieback, and leaf roll when nitrogen or other key nutrients are deficient. Nitrogen-deficient plants have pale yellow-green leaves (rather than the characteristic blue-grey-green), produce fewer flowering stems, and are smaller and weaker overall. Most apparent in a long-established clump that has depleted the available nutrients in a poor soil without supplementary feeding.

What to do

In a garden setting, an annual application of a balanced granular fertiliser (such as Growmore) in spring restores good leaf colour and vigour. In a conservation or low-input agricultural context, thinopyrum intermedium is generally grown without fertiliser on low-fertility soils where its drought tolerance and deep rooting are the main assets; mild nutrient deficiency in these contexts is normal and the plant remains functional. Avoid excessive nitrogen fertiliser, which can reduce drought tolerance and cause excessive lush growth that is more susceptible to disease.

Frequently asked questions

Why are my thinopyrum leaves curling?

Thinopyrum leaves curl most commonly because of drought and dry soil (more drought-tolerant than most agricultural grasses but leaves roll inward and tips yellow in severe summer drought; deep roots access subsoil moisture; established plants rarely need irrigation in UK conditions; mulch to retain moisture on sandy soils), waterlogging and root oxygen deficiency (not tolerant of prolonged waterlogging; leaves yellow, wilt, and roll in heavy, compacted, poorly draining clay soils in winter; plant in well-drained loam or sandy loam; avoid heavy impermeable clays), or nutrient deficiency (pale yellow-green leaves in nitrogen-poor soils; smaller, weaker plants; fewer flowering stems; balanced granular fertiliser in spring restores colour; avoid excessive nitrogen). Well-drained, moderately fertile soil in full sun is ideal.

What is thinopyrum used for in UK agriculture and conservation?

Perennial grain crop: parent of Kernza (developed by the Land Institute), a perennial grain harvested annually without reploughing; trialled in the UK; benefits soil health and reduces disturbance versus annual wheat. Forage grass: deep-rooted, drought-tolerant perennial forage on drier, lighter UK soils. Erosion control: Thinopyrum ponticum used for soil stabilisation and revegetation of difficult, saline, or disturbed sites. Naturalistic planting: structural grass component in prairie-style or low-maintenance wildflower meadow planting on well-drained, low-fertility soil. Wheat breeding: source of rust resistance and disease resistance genes introduced into bread wheat. Blue-grey leaf colour and upright habit provide foliage interest in mixed plantings.

What is the relationship between thinopyrum and couch grass?

Both are in the genus Thinopyrum (wheat tribe, Triticeae) following recent taxonomic revision. Couch grass is Thinopyrum repens (formerly Elytrigia repens, Agropyron repens): the aggressive, deep-rhizomatous UK garden weed that is very difficult to eradicate. T. intermedium (intermediate wheatgrass) is clump-forming, slowly spreading, and non-invasive; a useful agricultural grass, not a weed. Key distinction: T. repens = eradicate it; T. intermedium = a useful, manageable plant. The two are genetically close enough to hybridise, which has been exploited in wheat breeding programmes to transfer rust resistance genes.

How do I identify thinopyrum intermedium in the UK?

Distinctive blue-grey-green (glaucous) flat, strap-like leaves, 3 to 8 mm wide, to 35 cm long; sparsely hairy on the upper surface; the blue-grey colour distinguishes it from most common UK grasses. Short rhizomes; slowly expanding clump; not aggressively spreading. Flowering stems erect, to 90 to 120 cm; narrow, upright, elongated spike 10 to 20 cm resembling a slender wheat ear with alternately arranged, two-rowed spikelets; flowers June to July. Cool-season perennial; most active growth in spring and autumn. Blue-grey leaf colour and slender wheat-like ear are the most distinctive identification features.