Jasione - Attractive blue flowers on these bulbous perennials - Fully Hardy. The Jasione laevis group are the most widely available.
Jeffersonia - Slightly unusual foliage in the bi-pinnate leaves - hence its common name of 'Twin Leaf'! Cupped flowers of pale blue - sometimes white. Good for damp shaded areas.
Jovibarba - Very similar in all respects to the Sempervivum - houseleek - plants. Easy to grow ground-hugger, for troughs, rock garden or gravel areas.
Juncus - Rush or Reed - Rushes for a damp area. Of interest is the twisted and contorted stems of the Juncus effusus 'Spiralis'.
Kirengeshoma - Herbaceous perennila foming a clump of attractive foliage, with tubular, yellow flowers nodding on dark coloured stems. Fully hardy and does well in perennial or shrub border, or in wooded areas.
Kitaibela - Mallow family herbaceous perennials, with typical mallow flowers. Not bothered as to full sun or partial shade. Damp areas ok, but need to be well drained for the winter months.
Knautia - Not the showiest of herbaceous perennials,
but with flowers that are unusual in colour, being dark maroon or red.
Sometimes classed as Scabious - incorrectly!
Kniphofia - There are many new cultivars of the old fashioned Red Hot Poker, so most gardens can find enough space for one. They now come in a wide range of colours, borsering cream, yellow and orange. Some are evn bi-coloured. well worth inclusion.
Koeleria - Ornamental Grass - Blue Hair Grass. Good
clump forming evergreen grasses with distinct blue foliage (Koeleria
glauca). A larger version of the Festuca glauca, growing to around