Garden plants are rather like members of a choir. There are always one or two divas that take centre stage for a brief period, outshining everything – I’m thinking of peonies and oriental poppies.
Then there are some that will only perform properly if conditions are perfect. This summer – with the recent sunny weather and upcoming heatwave – my Solomon’s seals (aka polygonatum), are more toothpick than walking stick.
The late summer combination of Helianthus ‘Lemon Queen’ and the moody puffs of Eupatorium maculatum Atropurpureum Group is also far from guaranteed. Sometimes it happens… sometimes not!
Luckily, some ‘crème de la crème’ perennials never let you down, whatever happens. Most form pleasing clumps, without roaming far and wide, and flower for weeks without producing copious seeds. Better still, they’re all readily available, because they’re outstanding performers.
For quicker results, plant three of the same together, if possible. Eventual heights of each plant are given at the end of the descriptions.
Below I have chosen my top 10 pristine plants that don’t demand special treatment or soil, yet they shine for weeks.
Best perennial plants and how to grow them - even during a heatwave
1. Nepeta grandiflora ‘Summer Magic’ AGM*
This bumblebee-pleasing catmint, a star of the recent nepeta trial held at RHS Wisley, provides willowy mid-blue spires of flower that don’t flop about. A chance seedling, it was spotted by the late Malcolm Spencer of the long-gone Croftway Nursery and was then launched at Chelsea 2013 by Hardy’s Cottage Garden Plants. The sage green foliage bounces back quickly after winter, so you get a haze of blue from May until September. Cats won’t attempt to roll on it either. Soft blue and orange work well together, so I use it with Paul Lewis’s July-flowering Fire Series crocosmia ‘Scorchio’. This year I’ve added a new gingery Bressingham red hot poker named ‘David Blake’, after Bressingham head gardener Jaime Blake’s father. 40cm
* AGM stands for Award of Garden Merit. This is the Royal Horticultural Society seal of approval that the plant performs reliably in the garden.
2. Amsonia tabernaemontana
Although listed as widely available, amsonias are underused by British gardeners. Admittedly they are slow-fuse plants, taking two to three years to look magnificent, but they shine at every stage. This one is the best for me, so ignore the shorter ‘Blue Ice’. The show begins in late spring, when blue-black, asparagus-like spears of foliage rise up quickly. By late May a tight dome of grey-blue starry flowers tops neat, oval foliage, mid-ribbed in paler green. Dark finger-like seedpods follow on, so no dead-heading please, and then the foliage turns butter yellow. Mine mingles with the tissue-paper flowers of Geum ‘Totally Tangerine’ and the stately spires of moody purple Dictamnus albus var. ‘Purpureaus’. 60cm
3. Hemerocallis ‘Whichford’
These drought-tolerant plants provide arching foliage and lots of flower. However, this Jekyll and Hyde genus contains plenty of monstrous modern cultivars, largely bred for the American climate. I still rate this British-bred classic of 1960, for its excellent foliage and fragrant, elegant pallid-yellow flowers, cooled with a hint of lime-green. There’s a pleasing touch of midnight-blue at the base of the green foliage and the leaves stay neat, before dying down. I also rate another Brit called ‘Red Precious’ (Coe 1968) for its late summer tomato-red flowers. Use ‘Whichford’ with blues and purples, including the easy self-seeding summer bulb, Tritelia laxa ‘Queen Fabiola’ and garnet penstemon ‘Andenken an Friedrich Hahn’. 90cm
4. Geranium ‘Orion’ AGM
Large, cobalt-blue saucers of flower, veined in reddish purple, float above divided light green foliage on this clump-forming hardy geranium. Shearing it back to nothing in July will promote later flowers and, although this sounds drastic, new leaves will appear within days to be followed by more blue saucers. ‘Orion’, a seedling discovered by Dutch nurseryman Brian Kabbes in the 1990s, stunned the experienced judges on the RHS Wisley Hardy Geranium Trial held in the early 2000s, because it was previously unknown. Its secret weapons are hybrid vigour and sterile flowers that keep-on-a-coming. It’s thought to be a hybrid between ‘Brookside’ and G. himalayense ‘Gravetye’ and it’s fabulous in front of, or among roses, or along a path. Anywhere in fact. 70cm
5. Phlox paniculata ‘Monica Lynden-Bell’ AGM
Border phloxes vary enormously in vigour and their ability to return year after year. However, this mid-season pale pink border phlox occurred as seedling in a chalky Hampshire garden in the 1970s. As a result, it doesn’t demand the same level of moisture as others do. It was the only phlox that grew for me in my previous garden, on dry ironstone soil, along with ‘Alba Grandiflora’, an airy white. The blush-pink flowers of ‘Monica Lynden-Bell’, which appear from darker buds, remind me of faded apple-blossom and it forms good clumps with pleasing foliage. It cuts well and, like all border phloxes, the flowers follow June roses. Cutting the front stems down by a third will delay some of the flowers. Deadheading also produces more flower. Mine are backed by a purple-leaved cotinus, named ‘Royal Purple’ but the darker purple-pink eye on the the flowers will allow you to mix and match. 75-80cm
6. Verbascum chaixii ‘Album’
Uprights are vital in a border, because so many perennials form hummocks. Verbascums join heaven to earth wonderfully well, but many of them seem to have a death wish. This truly perennial mullein endures for years, sending up several slender tapers, each containing hundreds of damson-blushed white flowers, studded with bright orange anthers. The insect-friendly flowers, which appear to break free from square satin buds, give weeks of interest as the graceful stems straighten and break into flower, starting off in the middle. This, a favourite of designer Arne Maynard, is best threaded through a summer border to provide continuity. Mine follow earlier herbaceous peonies and pre-empt the dark-stemmed Japanese anemone ‘Pallida’. 90cm
7. Anemone hupehensis var. japonica ‘Pamina’ AGM
This is the only roamer on my list of ten, but all Japanese anemones travel: it’s the nature of the beast. However, you must forgive ‘Pamina’ her wandering tendency, because the semi-double, bright pink flowers light up the lacklustre month of August unlike any other plant. It isn’t the flowers alone though, lovely as they are. The pliable stems are dark and willowy, rising above a low frill of foliage. The buds hang there for weeks, like grey seed pearls left over from one of Coco Chanel’s necklaces, and the flowers eventually turn to kapok and cotton. It’s the perennial equivalent of an annual self-seeder, popping up in gaps, yet willowy enough to allow you to gaze through the stems and flowers. 1m
8. Rudbeckia fulgida var. deamii AGM
Deam’s sunflower is the Rolls Royce, or should that be Tesla, of well-behaved dark-coned golden-yellow daisies. This knee-high daisy stays pin neat for at least two months and the hairy foliage is equally handsome. It should not be confused with the inferior (and often seed-raised) ‘Goldsturm’, which doesn’t flower for as long or as tidily. Deam’s sunflower will bridge late summer and autumn, staying in a clump for many a year. It’s superb planted with two exceptional lavender-tinted perennials, the drought-tolerant Aster x frikartii ‘Mönch’ and Succisella inflexa ‘Frosted Pearls’. The lavender daisies of Mönch and the small bobbles of succisella (a scabious relative) will probably appear before this crisp yellow daisy stirs. 80cm
9. Veronicastrum virginicum ‘Fascination’
I love a plant pun and I often wonder if ‘Fascination’, a tall long-flowering veronicastrum with lavender flowers, is a play on the botanical word ‘fasciation’ because some flower spikes distort and flatten into mermaid’s tails. This architectural star, faintly damned by the common name of Culver’s root, has dark stems clothed in foliage and then a candelabra whorl of flowering stems beneath a main spike. Good winter structure and durability also feature and ‘Fascination’ came from the garden of the Dutch artist Ton ter Linden, an exponent of the Dutch Wave and no-dig flower gardening. Veronicastrums are definitely underused in British gardens, possibly because taller, later-flowering plants always look ragged on garden centre benches. 120 cm
10. Symphyotrichum novae-angliae ‘Helen Picton’ AGM
September-flowering New England asters are undemanding and willing perennials. This purple-flowered form, named after Helen Picton of Old Court Nurseries, has a stand-out quality inherited from its excellent New England parents – the bright pink ‘Andenken an Alma Pötschke’ and ‘Purple Dome’. These butterfly catching plants need a middle-of-border position because their lower stems tend to develop ragged foliage, but this is their only bad habit. Plant with a bright companion, because darker flowers can get lost visually. The yellow-banded, vivid-green sheath of Miscanthus sinensis ‘Zebrinus’ is a good foil, or you could use that Afghan hound of a plant, the willow-leaved sunflower Helianthus salicifolius. Another good combination with the aster is Korean feather reed grass (Calamagrostis brachytricha), and the pigeon-breast-grey sedum ‘Matrona’. 1.2m
This article is kept updated with the latest advice.