<em>Lithodora</em>: planting, cultivation and care

Botany

Lithodora are bushes or shrubs, generally with a very spreading, prostrate habit and evergreen foliage. Lithodora diffusa (or grémil diffus) is the most commonly cultivated. In wild state it occurs in scrubby habitats and woodland edges, sometimes in mountainous areas, from south‑west Europe to Turkey and North Africa. Generally, lithodora (and related genera) grow mainly in dry, arid, rocky and rather warm habitats.

Lithodora belongs to family Boraginaceae (nearly 2,700 species). This family includes borage (Borago), comfrey (Symphytum), lungworts, forget‑me‑nots, brunneras, Omphalodes, bugloss (Anchusa)… It is interesting to note that most of these plants produce small five‑petalled blue flowers, like lithodora. Most are delicate, softly coloured flowerings. Boraginaceae are generally hairy plants that bear flowers gathered in cymes, composed of five fused petals, five sepals and five stamens.

Lithodora diffusa was formerly named Lithospermum diffusum; more recently it has been renamed Glandora diffusa. It is very close to genera Lithospermum and Buglossoides. The name comes from Greek lithos (stone) and dorea (gift), because it likes to grow among stones in rocky places. The species name diffusa refers to its “diffuse”: very spreading habit. In French, lithodora is called grémil.

Lithodora diffusa and cultivars derived from it (‘Star’, ‘Heavenly Blue’…) are most widely grown. Other species are also very decorative and worth trying, for example Lithodora oleifolia, Lithodora zahnii or Lithodora fruticosa. Do not hesitate to try growing them!

Lithodora is a shrub with a compact, spreading habit, reaching up to 30 cm in height at most (often less than 20 cm), and up to about one metre in spread. Branches are highly branched and foliage is dense, making it a good groundcover that limits weed growth. Some cultivars, like ‘Heavenly Blue’, are even lower than the species type. Lithodora therefore suits the front of borders, edges, rockeries alongside other mat‑forming plants, and can also be used at the base of larger shrubs.

Flowering of Lithodora diffusa (photo KENPEI), Lithodora prostrata (photo Pancrat), Lithodora diffusa ‘Star’, and Lithodora hispidula (photo Zeynel Cebeci)

Lithodora flowers in spring, usually in May–June; sometimes flowering continues a little into summer. Cultivar ‘Peter’s Favourite’ has the advantage of flowering over a longer period through spring and summer. Flowering is more abundant when grown in full sun rather than in partial shade.

Lithodora then bears numerous star‑shaped flowers, gathered in terminal cymes. Flowers are small, 0.5–2 cm in diameter, but abundant and nicely cover the foliage. Their large numbers make the display impressive and very decorative. These flowers consist of five petals fused into a tube that opens into five spreading lobes, giving a star shape. The base of the corolla is surrounded by a five‑lobed calyx (corresponding to five fused sepals). At the centre, five stamens are inserted in the corolla tube and bear the pollen. The flower also has a style (female organ) that will receive the pollen.

Flower colour is an intense, deep blue. Flowers show small violet‑pink nuances on the corolla tube, and flower buds also have a violet tinge. Flowers are bicoloured in cultivar ‘Star’: blue in centre of petals and white at margins, which really highlights their star shape. Flowers can also be white, as in cultivar ‘Alba’. Lithodora hispidula carries pink–red flowers. In general, lithodora are prized for their soft, luminous colours that can brighten borders.

Lithodora leaves are simple and alternate, arranged one after another along the stems. They are small, narrow, elliptical and measure between 1 and 4 cm in length. The midrib is strongly marked, forming a fold along the centre of the leaf. Leaves are also villous, covered in hairs. Leaves of Lithodora rosmarinifolia are a little longer and thinner than in other varieties. Lithodora names can indicate leaf shape: Lithodora rosmarinifolia = lithodora with rosemary‑like leaves; Lithodora oleifolia = with olive‑like leaves, etc.

Leaves are dark green, which sets off the paler flowering. They are paler on the underside.

Because foliage is quite dense and covers the ground well, it restricts weed growth by leaving little room for them to develop.

Foliage of Lithodora diffusa ‘Heavenly Blue’ (photo Dinkum), Lithodora ‘Cambridge Blue’, and Lithodora oleifolia (photo Guérin Nicolas)

Lithodora is evergreen, retaining leaves through winter and therefore decorative all year round. Its roots penetrate deeply into soil, enabling it to withstand drought fairly well.

After flowering, lithodora produces achenes (dry fruits that do not open at ripeness), which contain the seeds.

Main varieties

Most popular varieties

Lithodora diffusa Star

Variety bearing small star-shaped flowers, blue at the centre of the petals and white around the edges, which nicely emphasises their shape. Valued for originality of its flowering, very delicate.

• Flowering time June, July
• Height at maturity 15 cm

See the product sheet

Lithodora diffusa Heavenly Blue

'Heavenly Blue' is a must-have variety that becomes covered in spring with a multitude of small flowers in a lovely soft yet deep blue. It has a more compact habit and is less tall than other varieties.

• Flowering time June, July
• Height at maturity 15 cm

See the product sheet

Lithodora diffusa Cambridge Blue

Variety that produces many small pale blue flowers in spring, beautifully set off by dark green foliage. Its flowering is very delicate and radiant.

• Flowering time June, July
• Height at maturity 15 cm

See the product sheet

Planting

Where to plant?

Place Lithodora in full sun: flowering will be more generous than in partial shade. It will tolerate partial shade but will be less vigorous. In sun, young plant will be healthier and more vigorous, with faster growth and a more harmonious habit. Preferably it should receive at least six hours of direct sun per day.

Lithodora needs a draining substrate, and appreciates stony or sandy soils… It does not like heavy clay soils and is less winter-hardy if soil retains water. You can also plant on a mound or on a sloping site to improve water runoff. Lithodora is perfect in rockery or on an old stone wall, with other small drought-tolerant plants. As it is spreading and requires little maintenance, it can be used to cover a bank. You can also plant it in a pot or container, and place on balcony or terrace. But it can also be positioned at front of a bed of perennials, in full sun.

Lithodora diffusa (notably variety ‘Heavenly Blue’) needs a slightly acidic substrate, while other Lithodora species prefer soils tending towards alkaline. Preferably substrate should also be humus-bearing, rich in humus.

As Lithodora is a plant that spreads, allow enough space around it to develop correctly. Avoid placing in a confined spot, cramped between other plants. Leave at least 1 metre between Lithodora and other plants.

When to plant?

Plant Lithodora in spring, around May. Autumn planting remains possible if you live in an area with a fairly mild climate. Most important is to avoid periods of frost.

How to plant?

• Dig a planting hole measuring two to three times size of rootball. You can improve drainage by adding gravel or coarse sand. It may also be worthwhile to plant on a mound or slope to improve water runoff.
• Remove Lithodora from pot, loosen rootball slightly, then place it in the planting hole, top of rootball flush with soil level.
• Backfill soil around, then firm down with palm of hand.
• Water thoroughly.

Continue watering in months following planting to allow Lithodora time to develop its root system, making it more resistant to drought.

Discover our video advice on planting perennials:

Care

Lithodora tolerates drought quite well, as its roots seek water deep in the soil. However, if you grow the Lithodora diffusa, it is preferable to water it during the year of planting, and during extended droughts, while avoiding excess moisture. Other species of Lithodora (L. oleifolia, zahnii, rosmarinifolia, etc.) prefer soil to remain dry in summer.

We recommend pruning lithodora lightly once it has finished flowering (usually from late June). This helps keep a compact, dense habit. Shorten shoots and take the opportunity to remove dead or damaged branches, as well as faded flowers.

You can also add some well-rotted compost in autumn to enrich the soil. If ground is too poor, lithodora leaves may tend to yellow.

If you grow it in a pot, remember to repot it from time to time into a slightly larger pot.

Lithodora is not susceptible to diseases; the main problem you may encounter is excess moisture, which can cause the roots to rot. As for parasitic insects, Lithodora is sometimes attacked by aphids. These small insects settle on the plant and extract sap, which weakens it. To get rid of them, we recommend using black soap diluted in water, which you will spray onto the plant.

Lithodora diffusa ‘Heavenly Blue’ (photo Ghislain118)

Propagate Lithodora

Lithodora is easy to multiply through propagation by cuttings. Do it in mid-summer.

• Prepare a pot with a mix of potting compost and coarse sand (for drainage). Water until it is well moist.
• Take a cutting, preferably healthy and well-formed, without flowers, and cut it to about 5 cm long.
• Plant the base of the cutting into the substrate, then firm well all round to ensure good contact between soil and stem.
• Place the pot in a sheltered spot, out of direct sunlight, and make sure the substrate remains slightly moist.
• In first year, it is best to protect lithodora from winter cold. Keep them under cover and wait until spring before planting out in open ground.

Companion plants for Lithodora

As it favours full sun and well-draining, stony substrates, lithodora integrates very easily into a rockery. Plant it with sedums, Phlox subulata or Phlox bifida, Alyssum montanum… Enjoy white flowering of Arenaria montana or Cerastium. You can also add a few small gentians, such as Gentiana acaulis, valued for its trumpet-shaped flowers of an intense blue. Optionally integrate clumps of grasses for a sense of volume and movement. It is also possible to plant lithodora on a low wall, between stones… It will bring colour! It can be planted there with sedums, houseleeks, Cerastium tomentosum and Cymbalaria muralis.

Lithodoras integrate easily into a rockery, with other plants suited to stony, dry soil. Cerastium tomentosum (photo Krzysztof Golik), Gentiana acaulis, Lithodora diffusa ‘Heavenly Blue’ (photo Meneerke bloem), Saxifraga cotyledon ‘Southside Seedling’, and Phlox subulata (photo Meneerke bloem)

You can also plant lithodora at front of a perennial border. Pair it with taller plants that will add volume, such as large grasses and some bushes. We also recommend pairing it with other blue, mauve and white flowerings, to create a border in soft, delicate shades. Choose, for example, Anchusa azurea, Aquilegia vulgaris, centaureas… Also discover graceful pale-blue inflorescences of Veronica gentianoides! Not forgetting Iris germanica and their elegant flowering (for example varieties ‘English Cottage’ or ‘Blue Crusader’).

However, you can also play with contrasts, knowing that blue’s complementary colour is orange. These hues reinforce each other and will energise the border. You can therefore pair lithodora with Euphorbia griffithii ‘Dixter’, Geum coccineum ‘Borisii’, Iris germanica ‘Good Show’, or Papaver orientale ‘Harvest Moon’…

You can also plant lithodora as a groundcover, for example at base of your bushes. Place it in front of roses, Deutzia, mock orange, Weigelia… As lithodora covers soil effectively by forming a fairly dense tapetum, it will limit weed growth. Similarly, you can plant it on a slope to green up a corner of garden you rarely tend.