Trifolium pratense L., Red Clover
Account Summary
Native and introduced, common and widespread, locally abundant.
Eurosiberian temperate, but widely naturalised and now circumpolar.
1881; Stewart, S.A.; Co Fermanagh.
Throughout the year, peaking in April.
Growth form and preferred habitats
Red Clover is a wintergreen, deeply penetrating, tap-rooted, short-lived perennial legume of leafy, tufted habit, 5-100 (usually 30-70) cm tall, common and widespread on grasslands on and off the limestone, including pastures and in silage and hay meadows. It is also common but sometimes sparse in rough, open areas on roadsides and waste ground, on damp or marshy lakeshores, rock outcrops and lightly-shaded, artificial, disturbed sites and waste ground below about 360 m. Despite the wide range of habitats occupied, T. pratense is most frequently found on ± unshaded, productive, lowland disturbed ground and it reaches its highest altitude in B & I at around 850 m in the Scottish Highlands (D.A. Pearman, in: Preston et al. 2002). T. pratense can grow on all types of soil except strongly acidic peatland (ie below about pH 4.5), waterlogged ground, or in permanent wetlands.
This was an extremely important agricultural grassland legume for pasture, silage, hay and green manure soil improvement and it is second only in importance to T. repens (White Clover). Clovers are components of natural grasslands and they are almost always cultivated in association with companion grasses or with crop species such as Brassica rapa (Wild turnip) in simple or complex seed mixtures supplied by the agricultural trade. The proportion of clover is usually between 30-50% in these seed mixtures. The principal ley grassland species used with Red Clover are Timothy (Phleum pratense), Meadow Fescue (Festuca pratensis) and Perennial Rye-grass (Lolium perenne).
The main value of clovers to the farmer lies in their ability to fix atmospheric nitrogen through the Rhizobium bacteria which inhabit their root nodules (Evans 1976). This fixed nitrogen is the main driver for the growth of the accompanying grass or crop species. The nodules of T. pratense var. sativum are such efficient nitrogen-fixers, the species becomes heavily suppressed if additional nitrogen fertiliser of any sort (organic or inorganic) is unnecessarily applied (Grime et al. 1988, 2007). In addition to their nitrogen capturing ability, clover plants are also rich in protein, minerals and trace elements contributing to their fodder value (Evans 1976). Around the world, about 25 Trifolium species are of significance as food for grazing animals and, of these, about ten are agriculturally important.
Variation
T. pratense shows considerable genetic variation and as a species has wide ecological tolerances, although it is not strongly competitive, especially in fertile, wet, or shaded conditions. In common with most VCs in B & I, the Fermanagh database records do not distinguish the two widely recognised varieties of Red Clover, the native var. pratense (diploid with 2n=14 chromosomes) and the cultivated var. sativum Schreb. (of which there are at least ten strains currently in agricultural use in these islands). It is likely, however, that the larger, more vigorous, erect, short-lived (surviving 2-3 years only), cultivated variety (which is hollow-stemmed and has less heavily toothed leaflet margins) is nowadays more common in all types of lowland grassland compared with the longer-lived native var. pratense (Stace 1997). The numerous cultivars of var. sativum include both diploid and tetraploid chromosome forms (2n=14 & 28) and, in terms of flowering, they vary from early to intermediate and late-season types. Polyploidy is not common in Trifolium and most species are diploid with 2n=14 or 16. T. repens is, however, a tetraploid with 2n=4x=32, but it shows regular bivalent formation at meiosis and thus is an allotetraploid, formed by spontaneous chromosome doubling after hybridisation.
Both of these T. pratense varieties are less tolerant of heavy grazing and trampling pressure than T. repens and T. pratense var. sativum is probably the more sensitive variety due to its erect growth habit and hollow stems (Grime et al. 1988, 2007). Before the expansion of silage making, Red Clover was used in ley mixtures with several grass species, mainly for cutting as a hay legume. While it is quick to establish and releases nitrogen to the grasses in its first year and subsequent years, it is a tall plant and only survives for two or three years. On the other hand, when sown with grasses, White Clover is slower to establish and does not release much nitrogen until its third or fourth year of growth. However, on account of its low, creeping nature, it persists and can becomes a long-lived meadow or pasture legume in permanent grassland (Dr John Orr, pers. comm., 2 May 2021).
Alsike Clover (T. hybridum) is another perennial that can replace T. pratense on more acid soils in N Europe and in Canada. T. dubium (Lesser Trefoil or Yellow Suckling Clover) is an annual that is sometimes included in clover-grass seed mixtures in B & I for short leys, where it may persist by self seeding. The three perennial clovers mentioned are all mainly or almost entirely self-incompatible and they require insect-pollination to set seed (Evans 1976).
The decline of Red Clover on most (but not all) farms: Before the widespread use of nitrogen fertilisers, ie post-World War II, Red and White Clover were the main source of nitrogen for grass swards (the soil releases a small amount into the atmosphere each year) and both clover species were included in commercial grass seed mixtures to give 'mixed swards'. Red Clover grew well in the first two years and its upright growth habit made the sward suitable for haymaking. After the second year, the Red Clover died out and the White Clover took over the provision of nitrogen as the driver of grass growth. T. repens was less suitable for haymaking because the tall grasses tended to shade it out, so the sward was grazed and was converted into long-term pasture. These clover/grass seed mixtures were known as 'hay and grazing mixtures' and they were the basis of grass farming for many years (Dr John Orr, pers. comm., 2 May 2021).
Post-World War II, the introduction of 'artificial' nitrogen fertilisers (NPK), meant that intensive farmers (mainly dairy farmers) could get a 'quick fix' for growth in the first year of the sward and silage making meant they did not need hay, so the use of Red Clover declined rapidly. White Clover was retained because its spreading growth habit meant it filled in spaces in the sward and gave some yield, but its nitrogen fixation was very little since it was suppressed by the NPK fertiliser. Less intensive farmers (mainly cattle and sheep) used less nitrogen fertiliser and still used White Clover for some nitrogen fixation.
In the first eight decades of the 20th century, vast quantities of commercial strains of Red Clover seed were sown by farmers each year in B & I. In Britain and NI, the Ministry of Agriculture, Fisheries and Food (MAFF) estimated, in figures released in 1984, a seed weight use of around 200 metric tonnes/year. As a result of its heavy sowing rates, var. sativum was a frequent escapee from cultivated fields and was most commonly found on fertile disturbed ground near the agricultural fields where it was being repeatedly sown (Grime et al. 1988, 2007). However, from the late 1940s onwards, there was a gradual move on farms towards developing intensive managed and fertilised pastures and meadows using applied agrochemical NPK fertilizers. This was accompanied by a move away from hay production towards the use of fermented grass silage as animal fodder. This happened in tandem with an increasing application of farm-produced cow and pig slurry, sprayed on grassland as a cheaper alternative to expensive chemical fertiliser mixtures produced by the petrochemical industry. Clover species, and especially short-lived Red Clover, could not tolerate additional N fertiliser being added to the soil as it heavily depressed their growth. Furthermore, T. pratense fermented poorly in silage, the leaves breaking down excessively, so it quickly became redundant (Morrow 2010; pers. comm. J. Crea, May 2021).
The increase in organic farming in recent decades renewed the interest in Red Clover. Organic farmers cannot use nitrogen fertiliser (its manufacture uses a massive amount of energy) and they therefore rely on clovers for their grass production. They found that Red Clover, mixed with suitable varieties of grass and properly managed, could produce large quantities of silage (as much as farmers using large amounts of sprayed chemical or organic fertiliser). The organic clover/grass ley was also of higher nutritive value than ordinary silage, because of the additional protein provided by the T. pratense and it was made without any nitrogen fertiliser. Some conventional farmers tried to grow T. pratense, but they often did not know how to properly manage it, so there has been very limited uptake outside organic farming (pers. comm. J. Orr, May 2021).
The cultivated clover strains most often grown by farmers are early-flowering ones and they tolerate or survive at least two hay or silage cuttings per growing season (Proctor & Yeo 1973).
The downside with Red Clover swards is that they generally only last around three years and expensive ploughing and cultivations are required to establish new ones. As a result, organic farmers have to plough more often than traditional grass farmers. However, there has been sufficient demand for T. pratense seed in recent years that one seed supply company has developed a variety called 'AberClaret' that can persist for up to five years. This appears to be a good step forward and is an indication of expected growth in this seed market (pers. comm. J. Orr, May 2021; https://germinal.co.uk/top-tips-for-growing-red-clover/; https://www.dlf.co.uk/forage-grass-seed/species/dlf-uk/clovers, both websites accessed by RSF in May 2021).
Clover-Herbal leys
Another innovation which should increase demand for Red Clover seed is the development of herbal leys. These are complex mixtures of deep rooting pasture grasses, clovers and herbs, principally Chicory (Cichorium intybus) and Ribwort Plantain (Plantago lanceolata) and they have promising features including resilience to drought, improved animal health and greater biodiversity above and below ground.
The mixture of plants contained in the herbal ley brings multiple benefits. Red Clover, for instance, has a deep root structure and can fix nitrogen into the soil. A potentially large herb like Chicory provides an even deeper root, mining the soil for minerals, improving the life and health of the soil. Mixes containing Sainfoin (Onobrychis viciifolia), Bird's-foot-trefoil (Lotus corniculatus) and Chicory also have natural anthelmintic properties and the growing times of the different plants also have the great advantage of providing year-round forage. It is standard agricultural practice to lightly graze a herbal ley in the year of sowing to control annual weeds and to thicken the sward. It is also important not to over-graze too early after sowing and to leave plenty of leaf on the sward to provide ground cover and prevent weed colonisation of vegetation gaps.
Over the years, there has been a commitment to adapting the rotation to fully incorporate herbal leys, which are left in place for 2-4 years to really build root mass and organic matter in the soil. The grasses in the herbal ley typically include Dactylis glomerata (Cock's-foot), Festuca arundinacea (Tall Fescue) and Festuca pratensis (Meadow Fescue), that have very good root systems which create pore spaces and a large amount of root mass in the soil that breaks down over a long time. Plants in the mix that have anthelmintic properties (ie natural wormers) benefit livestock health. The legumes in the mix – Clover, Bird's-foot-trefoil, Lucerne (Medicago sativa) and Sainfoin – are used to fix atmospheric nitrogen, reducing the reliance on inputs. Forage herbs with deep roots like Chicory, Burnet (Sanguisorba minor), Yarrow (Achillea millefolium) and Ribwort Plantain mine trace elements from further down the soil profile. This system of soil improvement has made land easier to work, requiring less cultivation. It also increases the soil's resilience to extremes of weather, causing it to act as a sponge after heavy rainfall, yet hold moisture in dry summers. The herbal leys are usually undersown into a cereal such as winter rye or spring barley to provide a cash crop whilst the ley develops, which reduces the amount of time land is left out of production. The herbal ley is left down for between two and four years – longer when required to control weeds, improve soil structure and drainage, before returning to three years of cereal crops.
It is important to choose the right combination of species for the right situation. The diversity of ingredients in a herbal ley means that mixtures can be tailored to suit individual soil types and circumstances and can be matched to a farmer's particular needs or preferences. For instance, Simple Herbal is an entry level herbal ley which can be used as a stepping stone to more complex mixtures, while the Heavy Land Herbal is tailored to wetter and heavier soils.
Although Red Clover can be grown as a monoculture, most farmers incorporate it into a mixture with Lolium perenne (Perennial Ryegrass). This combination ensures both the clover and grass reach the optimal stage to silage at the same time. As Red Clover can in some circumstances be slower to establish and grow, it is not recommended to mix it with fast growing L. multiflorum (Italian Ryegrass (IRG)), as this can result in the T. pratense being overwhelmed. IRG will also be at or past its best when the clover is ready to ensile, reducing the grass quality. Leys which include Red Clover should always be part of a rotation to control stem eelworms and Sclerotinia (Clover Rot). These parasites and disease are always present in the soil, but as Red Clover is a host plant, regular sowing can result in a substantial build-up. To prevent this, a six- to seven-year rest period from Red Clover is required, the break allowing the populations of these pests to reduce before reintroducing T. pratense.
Harvesting leys that include Red Clover must be done carefully. Much of the protein content of Red Clover is in the leaf, so it is important to prevent leaf damage during harvest in order to maintain the nutritional value of the silage. Mowing needs to be done as gently as possible since the clover leaves can be brittle and may shatter. Turning the crop when there is moisture on it, such as during early morning dew, also helps prevent leaf breakage. The cutting height is also very important, going no lower than 7-10 cm avoids taking out the crown of the plant. If the crown becomes damaged, the clover persistency in the field is severely compromised (https://www.cotswoldseeds.com/ accessed by RSF in May 2021).
Species variation recorded in wild habitats in B & I. Five varieties of T. pratense are listed by Sell & Murrell (2009) as occurring beyond cultivation in B & I, the other three not yet mentioned here being var. parviflorum Bab., stems 15-35 cm, with few appressed hairs; var. villosum Wahlb., stems up to 20 cm, with dense, long, appressed hairs on the upper stem; and var. americanum Harz., stems up to 80 cm, with numerous stiff, spreading hairs. These are quite rare forms, but they occasionally appear in so called 'wild flower seed mixtures' commonly sown by councils on roadsides and increasingly by gardeners.
The degree of persistence of any of these escaped cultivars is not known, nor the extent of hybridization and introgression between the two most common varieties. As with T. repens, these are examples of possible research studies the results of which would certainly be interesting to know.
Fermanagh occurrence
In Fermanagh, T. pratense is slightly less frequent than T. repens in terms of record numbers. However, in contrast, it is slightly the more widespread of these two commonly cultivated clover species in terms of tetrad distribution, being found during the Fermanagh survey in a total of 470 squares, representing 89% of those in the VC. In fact Red Clover ranks as the 31st most frequently recorded vascular plant in the local Flora Database.
Phenology and flowering reproduction
Being a tufted perennial, Red Clover does not reproduce vegetatively, but instead relies completely on seed for long-term survival and dispersal to fresh sites. T. pratense is wintergreen, but it is late spring before the plant puts on any growth and flowering does not begin until May. However, anthesis may continue into September, depending upon any grazing or cutting it undergoes. The flowers are borne in large, round, or subglobose, dense sessile inflorescences 15-40 mm in diameter. Each inflorescence consists of up to 100 reddish-purple to pink (rarely cream or white) almost stalkless flowers, subtended by two sub-opposite, reduced, bract-like leaves with very broad stipules (Sell & Murrell 2009). The flowers have a lovely honey-like fragrance and the foliage give off a pleasant clover scent.
The flowers are highly self-incompatible and require insect pollinator visits to effect fertilisation. Insect visitors to Red Clover blossoms need a long proboscis to reach the nectar concealed at the base of the tubular flowers. The proboscis must be longer than that of the European Honey-bee (Apis mellifera), which cannot reach the nectar, but can nevertheless transfer pollen which it collects to feed its larvae and, in doing so, effect flower pollination.
The natural pollinators of Red Clover are bumble-bees of various species, whose importance seems to vary with the corolla tube length of the clover cultivar being grown: short, medium or long. In an English study, the worker bees of the short-proboscis Bombus terrestris group were found to be persistent corolla-biting, nectar robbers, though less troublesome in this respect on the shorter-tubed Red Clover flowers than on the longer-tubed strains (Hawkins (in Mittler 1962) in Proctor & Yeo 1973, p. 346). While bumble-bees are essential for the pollination of the longer-tubed cultivars of Red Clover and particularly for the valuable tetraploid cultivars which have larger flowers than the diploids, honey- bees may be used in some countries as pollinators of the remaining clover cultivars, and hives are hired for this purpose. They are more effective on the flowers of the second flush of the season, since the blossom of later inflorescences tend to have shorter corolla tubes and perhaps the nectar is also sweeter and more abundant in warm, dry weather conditions (Proctor & Yeo 1973).
After fertilisation, the one- or two-seeded fruit pod develops (usually a solitary seed) and is completely concealed by the persistent calyx and withered brown corolla (Meikle 1977). The pod eventually splits (dehisces) to release the seed, or else the fruit is consumed by a grazing animal, such as a horse, cow, elk or bird (eg members of the Crow family) (Ridley 1930) and the seed is gut transported and released in dung. Seed is long persistent in the soil, some surviving for five or more years (Thompson et al. 1997).
its most usual modern day a
T. pratense is frequent to common and widespread throughout both B & I, except in the Scottish highlands and on the most acidic boglands of western Ireland and N & W Scotland. There has been no significant change in the hectad T. pratense distribution (including both the wild form and cultivated varieties) between the two BSBI atlases of 1962 and 2002 (D.A. Pearman, in: Preston et al. 2002). T. pratense var. pratense is the commonest form on non-agricultural ground in B & I, while var. sativum has spread out beyond the field boundaries where it was previously sown and became widely naturalised in both islands. In agriculture, despite something of a revival on organic farms, T. pratense is not quite as much used now as previously was the case. Beyond the farm gate it is probably in decline to some extent, although nowadays it is introduced in so-called wild flower seed mixtures that are frequently and increasingly sown by local councils on roadside banks, verges and in also in gardens by private individuals keen to conserve insect visitors (Sell & Murrell 2009).
s for both colour and flavour
As a polymorphic species with many varieties, T. pratense was originally restricted to Europe and adjacent parts of Africa and Asia until it became a forage crop widely introduced worldwide. It is now to a varying extent naturalised in S Africa, E Asia, N & S America, S Australia and New Zealand. Taken in the broad s.l. sense, it is now circumpolar temperate (Hultén & Fries 1986, Map 1245).
Other uses
Apart from its most usual modern day application in agriculture as nutritious animal fodder and soil nitrogen supplier and green manure conditioner, T. pratense has an ancient reputation in herbal medicine in B & I as a fluid extract of it was used as an antispasmodic and for the treatment of bronchial and whooping coughs. In addition, "Fomentations and poultices of the herb have been used as local applications to cancerous growths." (Grieve 1931, p. 208).
Back in the mid-17th century the juice of the plant was applied to adder bites and to clear the eyes of any film obscuring them, or to soothe them when hot and bloodshot. Infusions of the plant were also applied to rashes and used to treat coughs and colds in Norfolk and Cumbria. The leaves were chewed in the Isle of Man to relieve toothache and in Offaly, Ireland they were applied to soothe bee stings (Allen & Hatfield 2004). Red Clover contains isoflavones and a herbal product sold in tablet form is taken by women during and after the menopause.
The plant is also edible and young leaves and flowers have been used in salads for both colour and flavour, or cooked and made into soup or used as spinach substitutes. The flowers in the past have provided not only popular sweet snacks for children, but were used to make both tea and wine (Darwin 1996).
Threats
None.