Top 10 plants for summer

Over 40 years in the making, the glorious town gardens of 45 Sandford Terrace in Ranelagh, Dublin have been described as a horticultural tour de force. As for their creator, the Scottish-born gardener Helen Dillon, she’s earned herself an international reputation as an outstanding plantsperson who combines a painterly understanding of design with hands-on practicality, knowledge and wit.

Last week I visited those famous gardens and asked Dillon to name 10 of her favourite plants for the midsummer garden. Here is what she chose:

Sweet Rocket/Hesperis
matronalis
Easy to cultivate, tolerant of a wide range of growing conditions and loved by pollinating insects, this hardy biennial/short-lived perennial produces a froth of deeply scented, edible, white/lilac/purple flowers throughout early summer – although you have to wait until dusk to fully enjoy those great wafts of sweet, spicy, perfume. Sow seed (seedaholic.com) from now until the end of July to flower next year. H x S of 100cm x 45cm.

Helen says . . . "This plant self-seeds so readily that it's almost a weed. I prefer the darker-coloured forms so every year I select the plant with the best flowers and then let the seed ripen before collecting it (the rest of the plants are pulled up and dumped up on the compost heap). I sow into trays, then grow the young plants on in modules before transplanting into the garden in early November."

White Foxglove/Digitalis
purpurea f. albiflora
A graceful biennial/short-lived perennial, the white foxglove produces tall spires of tubular flowers whose pale beauty brings an ethereal quality to the Dillon garden. A promiscuous self-seeder, it likes a rich, moist but well-drained soil in light shade, but will also happily grow in full sun if soil stays moist. H x S 150-200cm x 25-50cm. Sow seed now (Thompson & Morgan, from mrmiddleton.com)

Helen says . . . "I let these plants self-seed every year, but make sure to weed out any that look as if they're reverting to purple. The trick is to check the leaf petioles of the young plants – if they're flushed pink/red, pull them out. In August I gather young seedlings up, pot them on and replant in October."

Allium 'Globe Master'
The giant, violet-coloured, spherical umbels of this bulbous herbaceous perennial are one of the glories of the Dillon garden, whether grown in those famous dustbins or in its spectacular flower borders.

Plant bulbs in autumn (mrmiddleton.com). Likes full sun and a fertile, well-drained soil.
H x S of 80-100cm x 20cm.

Helen says . . . "Many gardeners grow the popular Allium 'Purple Sensation' but the great advantage of Allium 'Globe Master' is that it is far
longer-flowered – those purple drumsticks will last for anything up to seven weeks."

Delphiniums
If ever there was a flower that symbolises the beauty of the classic herbaceous border in high summer bloom, it's the delphinium with its soaring spires of peacock-blue flowers. But it's a challenge to grow, requiring a deep, rich, moist but well-drained soil in full sun, constant protection from slugs and unobtrusive support – there are few sadder sights than that of the broken flower stems, toppled by a summer gale. In other words, a plant for the diligent gardener.

Helen says . . . "Yes, delphiniums are an absolute pain, but they're worth it. In particular I like those developed by the late German breeder Karl Foerster, who selected his plants for their colour, stability and resistance to disease.

“Once flowers start to fade, I cut stems back and give a good feed for a second, smaller flush of blooms in September.”

The Foerster variety, D. ‘Finsteraarhorn’ is available from mountvenus.com.

Double Welsh Poppy/
Meconopsis cambrica 'Flore-Pleno'
The fiery, ruffled flowers of this short-lived perennial poppy are everywhere in the Dillon garden, popping up throughout the borders and even under the arching caulms of the ornamental bamboo Borinda albocerea.

A tap-rooted perennial, it likes a fertile, well-drained soil and light shade. H x S of 45 x 30cm. Seed available from secretseeds.co.uk

Helen says . . . "A great plant that flowers from May until September. While it happily self-seeds, I weed out any that produce single-flowers as otherwise they slowly take over. The only exception is a single, deep orange form that I'm very fond of – but I make sure to grow it far away from the others."

Masterwort/ Astrantia major 'Ruby Wedding'
This clump-forming herbaceous perennial produces a mass of starry, dark ruby-red flowers from June right into August. Fast growing and fully hardy, it likes a moist but free-draining soil in sun or light shade. H x S of 50cm x 90cm. From boynegardencentre.com

Helen says . . . "While there are countless different varieties of astrantia, this is one of the finest. But make sure that you get the true 'Ruby Wedding'. I got mine from Elizabeth Strangman [the English nursery-owner and author] years ago, but I've seen some for sale that are only a poor imitation of the original plant.

Avens/Geum chiloense
'Mrs Bradshaw' and
G. 'Lady Stratheden'
Ultra-hardy, long-lived and clump-forming, these herbaceous perennials produce a multitude of brightly-coloured flowers if given a fertile, moist but well-drained soil in full sun/ partial shade and regularly deadheaded. Grow from seed in late summer/early autumn (seedaholic.com) or buy pot-grown plants (boynegardencentre.com). H x S of 60cm

Helen says . . . " I grow G. "Mrs Bradshaw' (scarlet, semi-double) and G. 'Lady Stratheden' (bright yellow, semi-double) mixed together for a colourful, cheerful display that starts in May and lasts right up to July."

Peruvian Lily/Alstroemeria
These hardy, clump-forming herbaceous perennials are prized for their showy flowers, which come in a wide variety of colours and are produced on slender, upright stems throughout the summer months.

Give plants a rich, moist but well-drained soil in full sun or light shade, (they sulk in very wet soils), protect from slugs and cut back flowering stems as they fade. For a range of alstroemerias, see kilmurrynursery.com

Helen says . . . "I can't understand why alstromerias aren't more commonly grown in this country – the new cultivars in particular are great, long flowering plants. One of the very best is A. 'Red Elf'."

Lady Slipper Orchid/
Cypripedium reginae
A hardy, June-flowering orchid with rose/white pouched flowers, this clump-forming perennial prefers light shade and a moist but well-drained soil that shouldn't be allowed to dry out in summer.

Emerging foliage requires protection from frosts. H x S of 40cm x 10cm (available from lanesidehardyorchids.com)

Helen says . . . "My very favourite orchid. I once lost it – many years ago – after lifting a clump to divide it and then accidentally replanting too deeply, which it hates."

Tobacco plant/Nicotiana
mutabilis
Not your run-of-the-mill tobacco plant but a choice species with tall, graceful stems and masses of white flowers that gradually fade to deep pink. Treated as a half-hardy annual, Nicotiana mutabilis is usually grown from seed in late spring (available from avonbulbs.co.uk) and needs a fertile, moist but well-drained soil in full sun. H x S of 150 x 40cm .

Helen says . . . "I love this plant so much that I grow it from cuttings taken in early autumn and overwintered in a frost-free glasshouse. That way it's in bloom from May."

The Dillon Garden, 45 Sandford Terrace, Ranelagh, Dublin. The garden is open every day during July and August, 2-6pm (admission €5), dillongarden.com