This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
These are charming little Alpine plants, distinguished, as the name implies, by the inflorescence being gathered together into compact globular heads. Some of the species are not hardy in all parts of the country, and the following should be avoided in making selections for cultivation in the open air north of London, unless the climate of the locality is mild in winter and the soil light and warm: - Globularia Alypum, integrifolia, longifolia, and spinosa. These are likely to succeed well in the southern parts of England and in many parts of Ireland, but, except in the more favoured parts of the west of Scotland, they are likely to succumb to the bad effects of our winter climate in the north. The majority of the hardy species are best adapted for the rockwork in most parts of the country, and most of them succeed well in the open border in light rich naturally well-drained soil, where a little shade can be given them. They are pretty things in pots, and in wet cold localities they will not live for any length of time, unless kept in pots for handiness for winter protection. Rich peat and loam forms the best compost for them in pots, and it should be well sharpened up with rough gritty sand.
They are easily increased by division, which is best done in spring as growth commences, and attention to watering will be necessary for some time afterwards till the plants are fairly established.
Globularia Cordifolia is of somewhat creeping habit, rooting at the joints as it extends. The root-leaves are wedge-shaped on longish stalks, blunt and toothed at the points. The flower-stems are about 6 or 8 inches high, clothed at the base with leaves, similar in form to, but smaller than, those of the roots. The flowers are blue, and appear in June and July; suitable for the mixed border as well as for the rockwork, but a somewhat shady situation should be chosen for it. Native of Germany.
This is rather a stronger-growing species than the last named. The root-leaves are lanceolate, on short footstalks, and the flower-stems are nearly naked, having only a small lanceolate bract or two under the flower-heads. The flower-heads are large, dark blue, and appear in June and July. Native of Germany, and adapted alike well to the rockwork or mixed border, in partial shade.
Globularia Nana is a very diminutive species, forming dwarf carpet-like patches of small, bright-green leaves. The flower-heads rise only an inch or two above the foliage, are not large, but profuse, are pale-blue or lilac, and appear in June and July. Native of the mountains of France, and suitable only for cultivation on rockwork, or in pots in gritty peat and loam.
Globularia Vulgaris grows about 6 or 8 inches high. The lower leaves are stalked and lanceolate, the upper ones stalkless and smaller, but of the same form. The flower-heads are dense and bright-blue, appearing in May, June, and July. Common on the mountains of Europe generally. Adapted for cultivation on rockwork or in the open border where a little shade can be secured.