Frankenia thymifolia looks like a tiny cross between creeping thyme and heather. Its wiry stems are clothed in minute grey-green leaves that knit into a tight, cushiony carpet, and from late spring the whole mat is sprinkled with small rose-pink flowers that sit right on the foliage.
It grows wild on dry, often salty ground in Spain and North Africa, which makes it a natural fit for a gritty alpine trough, a scree bed or a breezy garden near the coast. Read on for where it grows best, how to plant and water it, how to trim it, how to get it through a soggy winter and which plants keep it good company.
Frankenia thymifolia at a glance
- Botanical name Frankenia thymifolia
- Common name Thyme-leaved sea heath
- Plant type Evergreen, mat-forming alpine sub-shrub
- Hardiness Around RHS H4 (about -10C) in sharply drained soil
- Height and spread 5 to 10cm tall, spreading 20 to 40cm
- Flowering Tiny stemless rose-pink flowers from late spring into early summer
- Foliage Minute grey-green leaves on wiry stems, often picking up reddish tints in cold weather
- Position Full sun, open and airy
- Soil Sandy or gritty, low fertility, tolerates salt and alkaline ground
- Good for Troughs, scree, paving cracks, seaside gardens and alpine beds
Not quite a heather
Despite the common name, sea heath has nothing to do with Calluna or Erica. It belongs to the Frankeniaceae, a small family of plants adapted to salt flats and coastal sand. The tiny, rolled leaves cut down water loss, which is how it copes with sea spray, wind and blazing sun.
Britain has a native relative, Frankenia laevis, found on the drier upper edges of salt marshes in south-east England. Frankenia thymifolia is the Mediterranean species, with greyer, finer foliage and a neater habit that suits a rock garden or trough.
Picking the sunniest spot
Give sea heath an open position in full sun with good air movement around it. Shade makes the stems lanky and cuts flowering dramatically, while a hot, bright spot keeps the cushion dense and the leaves silvery.
It shrugs off wind and salt, so it is a valuable plant for exposed seaside gardens on the Lincolnshire and Norfolk coasts where many alpines struggle. Inland, try it on a raised scree bed, along a sunny path edge or in the cracks of a gravel terrace.
Planting in grit and sand
Like most alpines, Frankenia judges a home by its drainage. Spring is the best time to plant, giving roots a full season before winter, though early autumn works on light soils.
- For troughs and pots, use two parts horticultural grit to one part peat-free compost.
- On clay, build a mound or raised bed of grit-rich soil at least 20cm deep.
- Plant with the base of the stems at or slightly above the surface.
- Finish with a collar of fine gravel or crushed stone right up to the stems.
- Leave 20 to 30cm between plants if you want them to meet as a carpet.
A light hand with the watering can
Water young plants whenever the top few centimetres dry out during their first summer. After that, plants in open ground rarely need extra water, even in a dry East Anglian or Lincolnshire summer.
Troughs and pans dry faster, so check them weekly in hot weather and water thoroughly when the grit below the surface feels dry. Fertiliser is unnecessary in the ground. A pinch of slow-release alpine feed scratched into a trough every second spring is plenty, as rich conditions make the mat loose.
Winter wet and how to beat it
Cold is rarely the problem for sea heath in a free-draining bed. Trouble comes when rain sits around the crown for weeks, which can blacken the stems from the centre outwards.
Lift troughs onto bricks or pot feet so water escapes freely, and slide small pans under a cold frame lid or the eaves of a house from November to February. Reddish tints on the leaves during frosty weather are normal and fade as spring growth begins.
Clipping after the flowers fade
Once flowering finishes in summer, give the cushion a light trim with sharp scissors or small shears, removing the faded flower shoots and any stray stems. This keeps the mat tight and stops it opening up in the middle.
Avoid cutting back into old, leafless wood, which often fails to regrow. If an older plant has gone sparse and woody after several years, it is better to replace it with a fresh young plant raised from cuttings.
Raising new plants
Take 3 to 4cm cuttings from non-flowering shoots in late spring or early summer. Strip the lowest leaves, insert the cuttings around the edge of a pot of very gritty compost and keep them in bright light out of fierce sun.
Water sparingly and expect roots in four to six weeks. Alternatively, look for stems that have rooted where they touch the ground, sever them from the parent in spring and replant them straight into their new position.
Trough companions and seaside schemes
In a stone trough, the fine grey texture looks lovely beside small sempervivums, silver saxifrages, Dianthus alpinus and Erinus alpinus. For a pink and silver theme, add Armeria juniperifolia and Raoulia australis.
In a coastal gravel garden, grow it beneath sea holly, Crambe maritima and thrift for a planting that echoes a shingle beach. Our guide to the best drought-tolerant plants for UK gardens has more ideas for dry, sunny schemes.
Questions about Frankenia thymifolia
Is Frankenia thymifolia hardy in the UK?
Yes, it is hardy outdoors in most of Britain when grown in sharply drained soil, and comfortably takes frosts to around -10C. Long spells of cold, wet ground are the real risk. A gritty trough or raised scree bed gives it the best chance of thriving for years.
Is sea heath evergreen?
Yes, Frankenia thymifolia keeps its leaves all year. The grey-green foliage often takes on red or bronze tints in frosty weather and turns greener again with spring growth. It keeps the trough or rock garden furnished through winter.
Does Frankenia tolerate salt spray?
It is one of the most salt-tolerant alpines you can grow, coming from salty coastal and inland flats in its native range. It copes with spray, wind and sandy soil, which makes it a good choice for seaside gardens where many plants scorch.
When does Frankenia thymifolia flower?
Flowering usually starts in late spring and runs into early summer, depending on the season and how sunny the spot is. The tiny rose-pink flowers sit almost flat on the foliage and can cover the whole mat. A light trim afterwards keeps the plant compact.
Sea heath is a small, tough plant that rewards a sunny, gritty spot with year-round texture and a carpet of pink each spring. You will find Frankenia thymifolia among the trough-sized treasures in our Alpines collection, grown on our Lincolnshire farm.