Edging Plants and Rock Garden Plants

Edging or Rock Garden Plants


Plants that grow up to 25cm (10in) in height.


ha = hardy annual

hha = half hardy annual

hb = hardy biennial

hhp = half hardy perennial


Ageratum (hha)

A low-growing edging or rock garden plant that rarely grows above 15cm (6in), which makes it ideal for edging, while providing excellent colour. Given regular dead-heading, it will continue to thrive until the frosts. The clusters of small, mostly blue, flowers go remarkably well with marigolds (blue and orange or yellow make a striking colour partnership). There is a white variety, and also a reddish-mauve shade.


Alyssum (ha)

Most people probably associate alyssum with lobelia. Very sweet-smelling, almost to the point of being sickly, its tiny blooms are equally ideal for the front of the bed or for filling the crevices in a rock garden. It will bloom all through the summer, and most varieties never reach above 10cm (4in). It is available in white, pink or purple. A new variety, ‘Wonderland’, has won an award for consistency of flower and is a very dark red, so dark that sometimes it is difficult to see it against the soil.


Anchusa (ha)

A mass of deep blue flowers gives a low carpet of colour. Ask for ‘Blue Angel’, otherwise you may get a perennial version that grows to six times the size.


Asperula (ha) Woodruff

One of the lesser-known edging or rock garden plants. It grows to about 15cm (6in) with clusters of scented mauve-blue flowers.


Begonia semperflorens

Begonias come in two types, tuberous and fibrous rooted, which can be rather confusing to the non-expert. The fibrous rooted begonias make up in quantity what they lack in quality, but are nonetheless delightful little flowers with excellent bronze-green foliage. Begonia semperflorens is a dwarf plant, marvellous for bedding schemes. I keep some in a trough by my front door, and almost everyone who visits us in summer remarks on their attractive colours. The leaves are a pleasure in themselves, but it is the mass of mixed colour — pinks, reds, and whites — that is the big point in their favour. Given luck, some shelter, sunshine, and not too much rain, they will flower continuously until the frosts.




Some varieties are listed as annuals and others as biennials, but all should be started in a greenhouse. It has a speckled, pouch-type flower, ranging from 15 to 30cm (6 to 12in) in height, usually yellow or orange. It is extremely useful for mixing with other plants and is good for tubs and window boxes as well. Sow in February in warmth. The seed is very fine and expensive, so don’t waste it.



There are three favourite types of dianthus, the little pinks and sweet williams, and the taller carnations. All are traditional cottage garden plants, and well beloved still, but they do challenge the cultural expertise of the new gardener. Sweet william, for instance, can be either a hardy annual or a half-hardy perennial (usually grown as a biennial), and to avoid disappointment you must know which type you want, or have. The flowers all look much alike, mostly in shades of pink, red or purple, either self-coloured or zoned, but the annuals, at 20cm (8in), are barely half the height of the perennials. Although the biennials (or perennials grown as such) retain the scent that gave them their name, I cannot recall finding an annual variety that fulfils the claim. Nevertheless, their frilled petals are so pretty and attractive that one can forgive them anything.

The pinks (some of which are white) are normally used as annuals, either hardy or half-hardy, but there is a hardy biennial strain, and even a perennial. The carnations, on the other hand, are nominally biennials or perennials, but with some of them, seed sown under glass in February and planted out towards the end of May will produce splendid blooms in time for the holiday season. You see how confusing it is!

In general the sweet williams and pinks are recommended for borders and as edging plants; indeed, some pinks are so dwarf that they excel in rockeries. ‘Persian Carpet’ at 10cm (4in), is ideal for this purpose and comes in a colour range that includes pink, scarlet, cerise and white. Among the taller versions of the pinks are two F1 (first generation) hybrids that have won previous awards in the All-America trials — ‘Magic Charms’, a dwarf 15-20cm (6-8in), and ‘Queen of Hearts’ 30-45cm (12-18in).

Carnations vary in size from about 30cm (1ft) to 75cm (2-1/2ft) and are among the grandest of our scented flowers. Weddings would not be the same without them! The perfume, usually described as clove-like, is unmistakable and makes their corner of the garden (or the room) a place in which to linger. They are white, pink, vivid red, or even purple. Additionally, there are the picotee kinds, with a band of different colour around the edge of the petals. The familiar clove scent is common to all types, but the perpetual flowering ones somewhat belie their name as they are slightly delicate and should be grown in the greenhouse. For outdoor work, specify the hardy type known as border carnations.


Echium (ha) Viper’s bugloss


A short, bushy-growing plant. The bell-shaped flowers are prolific, mostly in deep blue, but there is a mixture of white, pink, lavender, blue and purple.


Lobelia (hhp)

Though a perennial, the universal lobelia is best grown as a half-hardy annual. Very low-growing, it seldom reaches more than 15cm (6in). It is a great favourite, and its appearance in partnership with alyssum marks the start of the spring and summer display in thousands of gardens. It is mainly purplish or blue, but there are some red and white versions. Use in borders, on rocks, in walls, or hanging or trailing from baskets. One perennial strain rises to approximately 1.5m (5ft) so be careful which you choose!


Marigold (hha)

See Tagetes


Mimulus – Monkey flower mimulus

This is a plant, nominally half-hardy perennial, which is best treated as a half-hardy annual, and is excellent for the rock garden where this edges a pool. Mostly it grows to a height of only 10 — 15cm (4-6in), though there is at least one taller variety. It is also known as the musk flower, but has long since lost its famous scent and consequently is not now so popular as it once was. Nevertheless, it shows an abundance of tiny antirrhinum-like flowers, and is well worth a place.


Myosotis (hb) Forget-me-not

The ideal accompaniment for almost every spring flower or bulb. Its dreamy, wispy, tiny blue flowers are seen as though through a haze, and this ‘shyness’ is the perfect foil to the strong colours of some of the other border plants. Mix it with marigolds or wallflowers or interplant with tulips, half close your eyes, and it would not be difficult to imagine them as ships sailing on a calm sea of blue.


Nemesia (hha)

If you want a massively impressive dwarf bed of just one plant showing almost every colour there is, this is the one to choose. The Carnival Mixture is famous, but nemesia is also available in a number of individual colours.


Pansy (hhp)

See Viola below.


Phlox (hha)


Phlox drummondii is one of our most popular bedding plants, and understandably so. It packs a mass of colour into a low-growing flower stem, is quick to germinate and remains in sweetly scented flower a long time. The seeds come in mixtures; fill a window box with them and you will have a wonderful perfumed view from that window all through the latter half of summer. Most of them grow to no more than 25cm ( 10in) but there is one strain that grows to about 40cm ( 6in) and is excellent for cutting.


Verbena (hha)

This was a favourite of the Victorians and Edwardians: a delicate-looking little plant that is nevertheless remarkably robust, even in poor weather.

Although grown as an annual, for propagation purposes it is best treated as a perennial by taking cuttings, as it is not very good at reproducing true from seed. Low-growing, excellent for edging or boxes (again, there is a perennial version growing much taller and making excellent cut flowers). The white eye serves to accentuate the brilliant colours in which verbena is obtainable — yellow, gold, pink, blue, scarlet and purple.

A very old favourite, fairly difficult to get (but also easy to propagate from cuttings) is lemon verbena, which, although a member of the family, is a shrub or pot plant for the greenhouse or a warm room and is known as Lippia citriodora. On its own the plant has very little perfume, but brush against it or squeeze one of its pale green leaves and you are enveloped in a delicious lemony perfume that makes the taste buds work overtime. Keep it free from frost and it will ‘perform’ for you at Christmas.


Viola (hhp) – Viola and Pansy

This is yet another of the many perennials that are mainly used as annuals or biennials. Most are low-growing, seldom above 20cm (8in). Few people can resist the quaintly marked frilled-edge petals of the pansies, their faces looking not unlike a cheerful little pug dog. They have the common factor of a yellow eye and a generally violet shading around it, but this colour is in turn affected by the other shades —yellow, rose, pink or purple — on the same petal. Some are scented, but in this they cannot match the specialist of the family, the sweet violet, Viola odorata, which incidentally is a true perennial and somewhat temperamental as to when or how it will grow.

The viola proper, which can be grown like the pansy, has become somewhat rare in recent years but seems to be heading for a revival. Probably one reason for its lack of popularity is the fact that it does need fairly constant attention. As soon as the flowers start to go to seed they must be removed, for once the plant sets seed it does not bloom again. Although listed as hardy perennial, the viola will flower in the same year if sowing is done by February in a warm greenhouse, so it has the instinctive compulsion of the annual (and its tendencies) to produce as much seed as possible.


28. April 2011 by admin
Categories: Annuals, Biennials and Perennials, Plants | Tags: , , , , , | Comments Off on Edging Plants and Rock Garden Plants


Get every new post delivered to your Inbox

Join other followers: