Holcus mollis L.
Perennial Grass Weeds
Creeping soft-grass is a rhizomatous perennial grass native in woods and hedgerows. It is favoured by conditions in woodland clearings and at the early stages of coppicing. Growth and flowering are restricted as the tree canopy develops. It is often a relict of former woodland vegetation, surviving woodland clearance despite being a shade lover. It is found in open grassland mostly on acid soils but is absent from areas of calcareous or base rich soil. It occurs on moist, freely drained soils, normally light to medium texture and high in organic matter. On grassy heaths it is often in association with bracken.
Creeping soft-grass occurs at the edges of arable fields. It is a troublesome weed on light, acid arable soils. In a survey of weeds in conventional cereals in central southern England in 1982, creeping soft-grass was found in 1% of winter barley but not at all in winter wheat or spring barley.
Within a natural population, many of the plants are derived from a single colonising seedling. A clonal patch may reach 100 m across. A pentaploid variant of creeping soft-grass is common in Britain, it is sterile but spreads vegetatively. Natural hybrids are formed with Yorkshire fog (H. lanatus). The hybrids tend to resemble creeping soft-grass in morphology.
Creeping soft-grass flowers from June to July. The flowers are wind pollinated and cross-pollination predominates. Seed is set from July to September. A plant may flower in its first year. The seeds germinate from March to June.
Creeping soft-grass has rhizomes that occur 5 to 10 cm deep in soil. In woodland the rhizomes occupy the litter layer. The horizontal length of the rhizomes varies with habitat and can range from 7 to 494 cm. The average internode length is 2 cm. Rhizome growth occurs in the period from May to November but is greatest from mid-June to mid-July. Only the apical bud is active and rhizomes extend from the apex. The lateral buds remain dormant unless the rhizomes are disturbed and then fresh aerial shoots may arise from the broken fragments. Even the buds on older rhizomes retain the ability to grow when separated from the rest of the rhizome system.
The rhizomes grow horizontally for a year before turning erect to form an aerial shoot. New shoots are produced mainly in the autumn. The young shoots are able to overwinter but prolonged hard frosts may damage the shallow rhizomes. The following year the shoots begin to grow actively in March/April and initiate new rhizomes.
Persistence and Spread
Creeping soft-grass is spread by seed and through fragmentation of the rhizome. In natural habitats, the spread is mainly vegetative. Rhizomes generally survive for 7 to 9 years and can extend by 15 cm per year to form large clonal patches. The plant also spreads by tillers that develop along prostrate shoots.
Seed shedding and the introduction of seed as an impurity in crop seed should be prevented. Once established creeping soft-grass can be difficult to eradicate but does not persist under heavy grazing being slower to recover compared with other grasses and with clover. It survives moderate treading and disturbance. Growth becomes more luxuriant when soil fertility is increased.
In stubble, thorough cultivations to disturb and fragment rhizomes should be carried out soon after crop harvest. Rotary cultivations are best for this. Subsequent regrowth should be killed off by further cultivations that stop the foliage persisting for more than 2-3 weeks. Ploughing to 30 cm will bury the rhizomes and cover them with 15-20 cm depth of soil. Deep tine cultivations such as chisel ploughing cause more fragmentation of the rhizome than ploughing.
Pigs and slugs feed on the rhizomes but creeping soft-grass is rarely grazed by rabbits. The developing flower head fails to emerge when it is attacked by the fungus Dilophosphora alopecuri.
Updated October 2007.