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The ultimate border flower guide: what to buy, when to plant, and how to provide year-round care

The double herbaceous borders at Mottisfont Abbey, Hampshire (National Trust), are full of plants that provide interest for months - Marianne Majerus
The double herbaceous borders at Mottisfont Abbey, Hampshire (National Trust), are full of plants that provide interest for months - Marianne Majerus

Spring brings a hectic round of planting and sowing, but summer is a gentler season. The gardening doesn’t stop, though; this is the time to keep the show on the road.

Experienced gardeners have a few tricks up their sleeves, managing plants so that they flower when needed and tweaking borders like a hairdresser with a longhandled comb. They eradicate the shabby – and are not afraid to cheat and bed in a new addition or two from the garden centre, either.

As well as tips on how to squeeze flower power out of your borders, I have this advice: don’t attempt the year-long border – it’s fraught with ­difficulty. You’ll end up with a fading peony going dormant in August, spoiling an aster gearing up for September glory. Create borders that concentrate on one season and make careful additions.

For example, a spring woodland border will shine again in September if Hydrangea paniculata is woven through. And I favour H. ‘Limelight’ for its neater panicles that eventually age to green jade and rose quartz.

Summer borders linger on until November with the aid of penstemons, Gaura lindheimeri and annual cosmos. Autumn borders, set to blaze from August on, can be livened up in April-May with a blend of Triumph and late tulips.

Don’t concentrate wholly on flower. Echinacea buds look like fairy coronets long before the daisies appear. The silvery parchment scales on the buds of Catananche caerulea (Cupid’s dart), are works of art for weeks before the flowers unfurl.

Japanese anemone buds hang like grey seed pearls strung on garlands. And foliage, well, that’s the most important long-term benefit of all. Just snip away the odd shabby leaf.

Delaying tactics for long flowering

The Chelsea chop

Plant Sedum 'Matrona' - The Garden Collection
Plant Sedum 'Matrona' - The Garden Collection

Cutting a whole plant back by a third in the last week of May is a well-known tactic, known as the Chelsea chop. You can use this on achilleas, sedums, phloxes and heleniums.

However, not all sedums respond well. They may not flower, although that may not matter if you’re after sumptuous foliage. ‘Matrona’, iridescent like a pigeon’s breast, and ‘Karfunkelstein’, a smouldering pink-brown, have the best foliage.

The front third only

Helenium 'Sahin's Early Flowerer' - Marianne Majerus
Helenium 'Sahin's Early Flowerer' - Marianne Majerus

Extend the flowering season of phloxes and heleniums by cutting their front few stems by a third. You can do this with all heleniums, but the precociously early and sterile hybrid ‘Sahin’s Early Flowerer’, in shimmering orange and brown, starts up in June or early July and is willing to rebloom.

The pale-pink phlox ‘Monica Lynden-Bell’ is the most drought-tolerant of border phloxes, along with the airy, white ‘Alba Grandiflora’. If you’ve failed with phloxes and heleniums, give these three a try.

Extend the roses

Roses are glorious in June, but you need to fill the gap between the main summer and autumn flushes. It’s possible to use the full Chelsea chop on English lavenders, such as Lavandula angustifolia ‘Hidcote’, ‘Melissa Lilac, ‘Imperial Gem’ and ‘Munstead’. These are the short, bushy lavenders, with stubby flower spikes and needlelike foliage.

They normally coincide with the roses, but if cut back by a third in May, they perform in July instead. Lavender ‘Melissa Lilac’ is in a class of its own, with far larger lavender florets, although ‘Hidcote’ is a striking purple-mauve. Downderry Nursery sells the widest range (downderry-nursery.co.uk; 01732 810081).

Rich blues make for long summer evenings

 Campanula lactiflora 'Prichard's Variety' - Marianne Majerus
Campanula lactiflora 'Prichard's Variety' - Marianne Majerus

Campanula lactiflora ‘Prichard’s Variety’, one of the best partners for roses of any colour, has flowers the colour of Cadbury’s milk chocolate foil. The metre-high heads consist of a pyramid of small recurved bells produced just as the roses begin to fade.

Cutting back by a third in May allows the entire blue wave to shine after the roses have taken their first curtain call. Or you can let the top flowers do their thing and then deadhead to promote more flower lower down the stem.

Aconitum ‘Sparks Variety’ also provides glimmers of deep blue, via side shoots that radiate out at 45 degrees. You get the same rich blue from an easy summer bulb, Triteleia laxa ‘Queen Fabiola’, an agapanthus-like native of California. This cheap as chips bulb is superb on sunny edges, especially when set against clear yellow flowers – such as Hemerocallis ‘Whichford’.

Halfway houses

The best late-summer hardy geranium is ‘Rozanne’, but it’s a sprawler that needs at least a quarter of a square metre of space. When cut back by half in May however, it will produce later flowers.

In soft blue, exquisitely veined in purple-pink, with a central white zone framing dark stamens, they shine in clear autumn light and the foliage looks fresher. ‘Rozanne’ should stay more compact too, in the front of an autumn border – try it with purple asters such as ‘Helen Picton’.

Second flushes

Geranium psilostemon "Patricia" - Dieter Schinner
Geranium psilostemon "Patricia" - Dieter Schinner

Getting a second bite of the cherry is a real bonus, particularly when plants bounce back quickly and produce leaf and then flower. Two obvious candidates are nepeta (catmint) and hardy geranium – a scalping back to nothing prompts them into miraculous regrowth within days. The smaller-leaved aromatic nepetas work best.

These begin in May, but generally look tired by early to mid July. Sheared off then, they will be back to their best four weeks later – whether it’s ‘Six Hills Giant’, ‘Walker’s Low’ or ‘Junior Walker’. They all respond. This year I’m growing two new stunners, ‘Hill Grounds’ and ‘Summer Magic’. They’ll be chopped back imminently but will rise again.

A cautionary tale

Some plants do not appreciate being scalped. I have been caught out with lupins and a rather invasive red scabious, Knautia macedonica. They resolutely stayed underground afterwards and sulked for the rest of the year. Learn from your failures and fill the gap using penstemons instead.

Second helpings

Some species of tall beard Iris, pictured, will bloom again and again - GAP PHOTOS
Some species of tall beard Iris, pictured, will bloom again and again - GAP PHOTOS

Some flowers are remontant. That is, they flower again when prompted by autumn dew. Certain heritage tall bearded irises will perform again, when truly happy; they include ‘Golden Encore’, ‘Lovely Again’ and ‘Red Revival’.

Dark-red astrantias, such as ‘Gill Richardson’, ‘Hadspen Blood’ and ‘Claret’, look magnificent in May, but will also throw some September flowers after a wet summer (all the above varieties need good soil).

The candy-pink ‘Roma’ and the pale-pink ‘Buckland’, both sterile, produce no nuisance seedlings, flower for months and they’re not so fussy about soil – just cut them back as the flowers brown.

Claire Austin (01686 670342) has a remontant iris list and many perennials, including red astrantias.

Follow-ups and repeat peformers

Sterile keeps on giving

 yellow deam's coneflower (Rudbeckia fulgida var. deamii) - Michael Gray
yellow deam's coneflower (Rudbeckia fulgida var. deamii) - Michael Gray

One way to get more flower is to grow sterile plants that can’t set seed (owing to pollen incompatibilities between parents). They flower for months, but still attract bees. Geraniums ‘Patricia’, ‘Orion’, ‘Nimbus’, ‘Spinners’, ‘Blue Cloud’, ‘Ivan’, ‘Nicola’ and ‘Joy’ all flower for many weeks.

The Plantsman’s Preference (01379 710810) has a great range. Other excellent sterile perennials include Geum ‘Totally Tangerine’ and the crisp Rudbeckia fulgida var. deamii, which produces brown-centred yellow daisies from August. The latter is a perfect partner with Aster x frikartii ‘Mönch’. All easy and effective.

Deadheading

A plant doesn’t have to be sterile in order to perform for many months, because deadheading has the same effect – it prevents seeds from being formed. A pair of kitchen scissors, or pinching between finger and thumb, is faster and easier than secateurs.

Annual cornflowers, Scabiosa atropurpurea, tall French marigolds, cosmos and calendulas just keep going. Red valerian (Centranthus ruber and the mauve C. lecoqii) can also give you months of flower when deadheaded. If your valerian gets shabby, shear it back to base in July for later flowers.

A rose tip or two

Deadheading roses (Rosa 'Lady of Shalott') with secateurs - Andrea Jones
Deadheading roses (Rosa 'Lady of Shalott') with secateurs - Andrea Jones

Deadhead repeat-flowering roses to promote more flower. Simply grasp the top of the flower and twist it, right under the bud, with your fingers.

Any thick stems that need secateurs, make a slanting cut down and away from you, rather than a straight one, and then you only see the tip. The shake test is invaluable here, because sometimes it’s difficult to tell which flowers are over. It’s the same with peonies.

Exceptions to the rule

There are some seed heads you’ll want to keep: herbaceous clematis, such as C. integrifolia ‘Ozawa’s Blue’, creep through summer borders and their thickly tepalled, blue pagoda-like flowers eventually metamorphosise into pale, silken spiders.

Deciduous eryngium flower heads can fade beautifully too, although in wet summers they have to go because they turn to rust-brown. Go by instinct.

Generous self-seeders

Self-seeders like foxglove will need to be culled - GAP 
Self-seeders like foxglove will need to be culled - GAP

Always cull the generous self-seeders, like foxgloves, annual poppies and the biennial Eryngium giganteum, leaving about one tenth standing.

Last year I created a trail to the compost heap with Miss Willmott’s ghost (E. giganteum), so careful removal is advised. The remainers can be left to self-seed and will often place themselves to advantage.

Gapping up

August is a dire month that needs all the help it can get, so be prepared to gap up with well-grown late performers from the garden centre – preferably in bud, not full flower. You’ll find good-looking dahlias, asters, sedums, crocosmias and asters. Look out for a dark-leaved, pink verbena called ‘Bampton’ – it’s a great, late addition.

Face the front

Bear in mind that every plant has a front and a back, so twirl it around before you plant to get its best profile. Water the spot well and then dig the hole, a little larger than the pot if possible, although we’re talking shoehorn here.

Fill the hole with water, drop in the plant quickly and then backfill – an ancient technique known as puddling in. It will give your plant a damp base.

Use the southern hemisphere

Eschscholzia Californica (orange) and Penstemon Barbatus (red) -  Rii Schroer
Eschscholzia Californica (orange) and Penstemon Barbatus (red) - Rii Schroer

Plants from the southern hemisphere (e.g. South Africa) have lots of pigment in their rain-resistant flowers and are fond of longer nights because they evolved close to the equator. Penstemons, salvias, gauras and fuchsias will flower until November. Diascias carry on, too.

The hardy D. personata rises to around a metre high. Alstroemeria ‘Indian Summer’ provides near-black foliage and sunshine red and yellow flowers and lasts year to year. Pluck fading flower stems on alstroemerias to encourage more. Thompson & Morgan (0333 400 0033).

If all else fails – cheat

Place a colourful container in the foreground to draw the eye in dull corners with not much flower, or place it in the border on a couple of bricks.