Gentiana thunbergii

Seed - best sown as soon as it is ripe in a light position in a cold frame^[2]. It can also be sown in late winter or early spring but the seed germinates best if given a period of cold stratification and quickly loses viability when stored, with older seed germinating slowly and erratically^[2][3]. It is advantageous to keep the seed at about 10°c for a few days after sowing, to enable the seed to imbibe moisture^[3]. Following this with a period of at least 5 - 6 weeks with temperatures falling to between 0 and -5°c will usually produce reasonable germination^[3]. It is best to use clay pots, since plastic ones do not drain so freely and the moister conditions encourage the growth of moss, which will prevent germination of the seed^[3]. The seed should be surface-sown, or only covered with a very light dressing of compost. The seed requires dark for germination, so the pots should be covered with something like newspaper or be kept in the dark^[3]. Pot up the seedlings into individual pots as soon as they are large enough to handle and grow on in light shade in the greenhouse for at least their first winter. The seedlings grow on very slowly, taking 2 - 7 years to reach flowering size^[3]. When the plants are of sufficient size, place them out into their permanent positions in late spring or early summer.

Division in March^[4]. Most members of this genus have either a single tap-root, or a compact root system united in a single root head, and are thus unsuitable for division^[3].

Cuttings of basal shoots in late spring^[5].

In general, gentians require a moist well-drained soil in a sheltered position, a certain minimum of atmospheric humidity, high light intensity but a site where temperatures are not too high^[3]. They are therefore more difficult to grow in areas with hot summers and in such a region they appreciate some protection from the strongest sunlight^[2][3]. Most species will grow well in the rock garden^[2].

A moisture loving plant, preferring to grow with full exposure to the sun but with plenty of underground moisture in the summer, it grows better in the north and west of Britain^[6].

Plants are intolerant of root disturbance^[2].