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AGM plants have been through a rigorous trial and assessment programme. They are:
Plantsman Graham Rice casts his critic's eye over recent award winners, including some classic perennials
Plants are given the prestigious RHS Award of Garden Merit (AGM) in one of three ways:
Some fine perennials have recently received the AGM accolade. The large and long-running trial of the old favourite Phlox paniculata yielded awards to an astonishing 32 cultivars. The award was also given after trials at Wisley of bellflowers (Campanula) and woodland saxifrages (Saxifraga fortunei). The trial of blue poppies (Meconopsis) was held in the more suitable growing climate of RHS Garden Harlow Carr while expert discussions added more excellent plants to the list of perennials holding the award. Here’s a selection:
One of the most dependable and prolific of columbines, Aquilegia chrysantha 'Yellow Queen' is an improved form of a species from the southwestern United States. From a blue-tinted mound of green foliage, vertical stems carry a long succession of large, two-tone yellow flowers with long nectar-filled spurs. This selection is longer-lived than most columbines and is mildew resistant. Cut back as the first flowers fade to encourage a second flush. Height to 80cm (2½ft) H5.
(H = hardiness rating)
In recent years, the Chinese woodland saxifrage, Saxifraga fortunei, and its hybrids have been increasingly valued as autumn-flowering perennials for the woodland garden. S. 'Blackberry and Apple Pie' is larger and more vigorous than many, with fresh, apple green, scalloped foliage whose red underside is glimpsed as the edges turn up. From October until the December frosts the prolific clumps are topped by clouds of starry, pale, biscuit-coloured flowers. Height to around 30cm (1ft). H4.
As new woodland saxifrages have been developed both in Britain and in Japan, plants have increasingly combined good foliage and bright flowers. Saxifraga 'Mount Nachi' has neatly-lobed leaves that are reddish-brown when young, maturing to a lovely coppery-bronze shade. In autumn, the starry, white flowers appear. As with other selections, each individual flower has two long, slender petals topped by three shorter ones - all pure white. The effect is delightful. Height to around 10cm (4in). H4.
Himalayan blue poppies are always captivating though often disappointing. Meconopsis (Infertile Blue Group) 'Mrs Jebb' is one of the award winners that gardeners with the right conditions can grow with confidence. The judges noted that it has a “strong constitution”, does not disappear after a season or two as many do, and is a little shorter than most. Finally, there is no trace of purple to taint the clarity of the saucer-shaped, 8–12cm (3–4in) blue flowers. Height to around 1m (3ft). H5.
Of the continuing succession of variegated phlox to arrive in nurseries in recent years, two were given AGMs. The old favourite Phlox paniculata ‘Nora Leigh’ was one, the other was P. 'Becky Towe' which has each leaf broadly edged in yellow. This bright margin can occupy almost half the leaf surface, but the plant is still surprisingly vigorous. The carmine flowers with their dark eyes are same as those of ‘Windsor’, from which it was derived. Heigh to around 1m (3ft). H7.
'Eva Cullum' is a compact selection of Phlox paniculata and deservedly popular not only for being self-supporting but for its prolific display of dark-eyed, pink flowers. Raised by the distinguished plantsman Alan Bloom, he described it as “fine, bright, deep pink, so free to flower and with such abundant foliage”. The judges agreed. It was introduced in 1978 and named after one of the managers at Alan Bloom’s nursery. Sometimes wrongly listed as ‘Eva Callum’. Heigh to around 1m (3ft). H7.
While ‘Eva Cullum’ was the result of a professional breeding programme, Phlox paniculata 'Monica Lynden-Bell' was spotted as a self-sown seedling in the Hampshire garden of the woman whose name it carries. Simply describing the flowers as pale, blushed white does not do justice to the subtlety of their colouring which has a penetrating silvery tone. “Fantastic plant. Reliable.” said the judges, though dead-heading is essential as the brownish, fading flowers detract from the display. Height to around 1m (3ft). H7.
Many of the most impressive recent introductions of border phlox are hybrids between the familiar P. paniculata and the shorter, more delicate woodland species, P. divaricata. P. x arendsii ‘Luc's Lilac' is one of three to receive the AGM after the Wisley trial. The magenta-centred, soft pink flowers are relatively small but come in huge clusters from July to October and are well-scented. The judges said: “Neat habit. Stands out. Very healthy and even.” Height to around 1.2m (3.5ft). H7.
The trial of campanulas at Wisley has so far yielded five AGMs in both traditional blue and in intriguingly different shades. Campanula glomerata 'Caroline' is a selection of the clustered bellflower, a British native whose main feature is its crowded heads of two-toned flowers. They are a pale, lilac-tinted white, stained in darker tones, especially towards the tips of the petals and as the buds open. Noticeably less vigorous than the usual blue-flowered form. Height to 30cm (11in). H7.
For sheer volume of flowers in a traditional border, Campanula lactiflora 'Favourite' can not be beaten. This robust plant produces upright stems clad in fresh green foliage, topped by generous clusters of widely flared, five-pointed, bell-shaped flowers in summer and autumn. Each flower is deep violet in colour with a white centre. The judges said: “Good colour. Brilliant foliage. Very floriferous.” Height to around 1m (3ft). H7.
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