Restharrow: species, cultivation & health benefits

Restharrow is a bee-friendly perennial that has been valued for its medicinal benefits for thousands of years. Read on to discover more about this creeping plant with pink flowers.

As it attracts many wild bees, the restharrow (Ononis) should definitely be in your garden. Restharrow thrives in sandy and sunny locations. In this article, you will learn how to grow this low-growing plant with many flowers, which species there are, and how the plant is used as a medicinal herb.

Restharrow: origin and properties

The genus Ononis belongs to the legume family and is therefore part of the same plant family as peas (Pisum sativum) and the common bean (Phaseolus vulgaris). The 88 or so restharrow species are mainly found in the Mediterranean region, particularly in Morocco and Spain. Only two species are commonly found in the UK: common restharrow (Ononis repens), which is native to the UK and grows on chalk grasslands and in coastal areas, and spiny restharrow (Ononis spinosa), which is found in central and south-eastern England and will be the main focus of this article.

Spiny restharrow is a perennial that grows 10 to 80 cm tall. This means that the shoots near the ground become woody, and the restharrow sprouts again after winter from these woody shoots. The red stems contrast beautifully with the dark green leaves, and their pointed thorns give the species its name. The tripinnate leaves are alternately arranged on the stems. Spiny restharrow flowers appear in moderately dense clusters in the leaf axils from April to September. Their pea-like flowers show their relation to peas and beans.

During the flowering season, the pink flowers of the spiny restharrow emit a very sweet, almost unpleasant scent, attracting many bees – the spiny restharrow flower is a pollen source for 15 different wild bee species. However, bees are not the only ones who enjoy the plants; they are also the primary source of food for the caterpillar of the common blue butterfly (Polymmatus icarus). Following flowering, small, hairy, kidney-shaped legumes form. The spiny restharrow has a distinct taproot that grows up to 60 cm long and is used as a naturopathic medicine.

The most beautiful species and varieties

• Spiny restharrow (Ononis spinosa): The thorny shrub may seem a little rough in spring, but its many pink flowers break this impression from June to September.

• Large yellow restharrow (Ononis natrix): The large yellow restharrow gets its name from its yellow flowers. The semi-shrub grows up to 70 cm tall and is mostly used as an ornamental plant in Mediterranean gardens. The still closed flowers have red veins on the underside of the petals. Large yellow hawthorn thrives in dry, calcareous, warm, permeable, stony soils. These specific conditions means it can only be grown in certain locations.

• Common restharrow (Ononis repens): Native to the UK, Ononis repens is a subspecies of spiny restharrow that attracts a lot of bees; in fact, about ten different wild bee species collect pollen from its pink flowers, which bloom from July to September. Common restharrow makes an excellent ground cover and grows best in stony, dry, well-drained soils in full sun. In the wild, it is found in grasslands and coastal areas.

• Round-leaved restharrow (Ononis rotundifolia): This species also grows as a small shrub and flowers in pink. Unlike its relatives, it has spoon-shaped leaves. Furthermore, unlike its relatives that prefer full sun, the round-leaved restharrow prefers partial shade. It thrives in dry, well-drained soil.
• Ononis spinosa subsp. hircina: Also known as Ononis arvensis, this is another subspecies of the spiny restharrow. It is considered to be an invasive weed by farmers in Europe. Its pink flowers have a strong fragrance.

Planting and caring for restharrow

The spiny restharrow flourishes in sunny and dry locations with well-drained, humus-rich but nutrient-poor soil. For example, a slightly loamy sand would be ideal, but a stony, gravelly subsoil can work too. To improve the site conditions for the restharrow, mix a nutrient-poor, loose soil into the existing garden soil. Our Plantura Organic Herb & Seedling Compost is ideal for this because of its loose and airy structure. In addition, our compost contains some lime fertiliser, which is needed for good growth. If your garden or pot soil is too heavy, add sand or expanded clay to ensure optimal drainage as waterlogging harms the plant. If the soil is rather acidic, apply lime fertiliser to the chosen site to improve growing conditions.

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Restharrow can be grown in your garden by either sowing seeds or planting pre-grown plants. Sow the seeds directly in the chosen location in autumn. It is better to sow too much than too little, because the chances of successful germination the following spring are not particularly high. It is possible that some seeds will not germinate until the following year. Keep the seeds evenly moist in a semi-shady location at first. As sowing requires a little patience and tact, it is more common to plant pre-grown restharrow from March to October. Plant the young perennials 50 cm apart. One square metre can accommodate up to four plants.

Tip: The spiny restharrow is ideal for planting on dry south-facing slopes.

Just like other perennials, cut back the restharrow to a few centimetres above the ground after the growing season. This can be done in winter after flowering, however, it is best to wait until the beginning of March, because the small legumes of the Ononis spinosa are a winter food source for many birds.

Tip: Restharrow, like all other leguminous plants, forms a symbiotic relationship with nodule bacteria and can thus absorb nitrogen from the air. As a result, it does not need any additional fertilisation. However, make sure that there is a sufficient supply of lime in the soil.

Harvesting, uses and benefits of restharrow

The spiny restharrow has been used as a medicinal plant since the Romans. The majority of the nutrients are contained in the strong taproot. The valuable taproot can be dug up from late summer to autumn and then hung up to dry. The root is a diuretic, which means that water excretion via the kidneys is increased, and harmful germs are eliminated from the urinary system more quickly. For example, tea made from restharrow root is used to treat bladder infections. To make the tea, finely chop the root and brew in boiling water. To prevent the medicinally active ingredients from evaporating, cover the infusion while brewing i.e., in a tea pot.

The kidney purifies our blood by filtering toxins and stimulating the formation of new red blood cells. Restharrow is used to improve kidney function. Blood cleansing and purification are said to have many benefits in naturopathy, including stimulating digestion and improving overall health.

The young green shoots of the restharrow can be harvested from April to June, and the leaves until October. The plant’s green is mild in taste and can be used in salads, for example.

Caution: People who suffer from oedema (water retention) caused by cardiac insufficiency should avoid products made from spiny restharrow!