Perennial plant: Every thing you need to know

Perennial plant

Perennials are plants that can live for several years. Follow the advice of Terre Vivante and Aymeric Lazarin who give you lots of advice on how to cultivate mertensia, also called oyster plant, in a book ” My perennial vegetable garden “, full of tips for taking care of your vegetable garden. Here is an excerpt from the book that explains everything about this perennial plant.

ID card :

Mertensia maritima (Borraginaceae)

Other vernacular names: vegetable oyster, maritime mertensie, vegetable oyster, Virginia lungwort, sea blood

Part eaten: the leaves

Exposure: full sun

Hardiness: –30°C

Harvest: April to November


Mertensia is a creeping perennial plant. Its leaves are oval and slightly pointed. The whole plant has a bluish color, sometimes close to turquoise, very aesthetic! Its foliage is persistent, but can disappear completely depending on the severity of the frosts. In fact, the young leaves do not tolerate low temperatures well and the adult leaves can also disappear if the frosts are severe. By the sea, when the plants are exposed to sea spray, small light spots appear on the leaves.

These are salt glands, thanks to which the plant excretes the salt it has absorbed, present in a significant way in its natural environment. In spring and early summer, blue-colored flowers are formed in loose panicles, which turn pink when fertilized.

History and origin

Mertensia originates from the Atlantic coastal beaches. It was thus found in the natural environment, on the Breton or Norman seafront. But following decades of irrational picking, it has almost disappeared, although it still grows on some beaches of the English Channel and the Baltic Sea. It is undoubtedly its growing popularity with gardeners that saved it from extinction, since it is now planted in many vegetable gardens . In addition, it is sometimes sold by knowledgeable fishmongers, in the same way as glasswort ( Salicornia spp. ).


Very easy to grow, this is a plant that will surely surprise all your guests!


Type of soil: keep in mind that mertensia is a plant that comes from the beach. Prepare a light substrate for it, two-thirds of which is sand. If it is fresh and rich, the conditions will be optimal!

Watering: a few punctual and light waterings will do it the greatest good during hot and dry periods.

Maintenance: in the spring, it is possible to clean the stump of all the dead leaves. Some hoeing is also welcome.

Time before the first harvest: about 2 to 3 months.

Multiplication: the simplest and fastest is sowing. To do this, collect seeds at the end of summer and sow them in spring, in groups of three, preferably in pots. It is also possible to take cuttings from this plant, but the production of new roots from a leaf is very slow, and depending on the conditions, it is not uncommon for the leaf to rot before it even roots.

Diseases and parasites: watch out for snails and slugs! I happened to see adult mertensia plants disappear overnight under the appetite of these gastropod ogres…


The leaves can be cut regularly, preferably on the outside of the plant.


Thanks to its strongly iodized flavor evoking the taste of oysters, mertensie finds its place in salads and with many raw vegetables. A leaf simply placed on a buttered slice of bread is enough to appreciate all its flavor and all its freshness. It’s also a fun nod if you have friends over expecting a plate of oysters…



Once cut, mertensia leaves do not keep for more than a few days in the refrigerator. No reliable technique today makes it possible to keep them longer. Some keep them in vinegar, but the results seem unsatisfactory to me…














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