Hardiest summer bulbs

Lilies

Asiatics, martagons, Orientals, hybrids… Lilies make our heads spin and fill our noses with fragrance from June to August, depending on species. They mainly originate from temperate zones of the Northern Hemisphere, with a strong concentration in East Asia, China and Japan, but also in Europe and North America. Plant in full sun or partial shade, which suits them well, especially botanical lilies.
We love them all, starting with the Regal lily (Lilium regale), whose name does not reveal that it is a Chinese lily tolerating temperatures down to −25°C, and also many botanical lilies. These include species such as Lilium nepalense, creamy and heavily speckled with purple, Lilium speciosum, Lilium formosanum, the orange Lilium tigrinum, the white Lilium auratum freckled with yellow, Lilium pumilum, and many more.
Martagon lilies, European or Asian, are also very cold-hardy!

As for the Giant Himalayan lily, it is an extraordinary bulb, growing up to 2 metres tall, ideal in shaded situations. It tolerates down to −15°C.

Lilium henryi, Lilium regale and Lilium nepalense

Some Iris

Two groups flower in summer, to our great delight !

Repeat-flowering Iris germanica

Garden iris, also called bearded iris, are Iris germanica. They put on a show in spring, but some of them are repeat-flowering bearded irises, flowering again in late summer, between September and October, even November for some.
Rather than bulbous plants, these irises are rhizomatous, to be planted at ground level, in sandy, free-draining soil, in full sun.
Among repeat-flowering iris varieties: Iris germanica ‘Cherished’, with a delicate pale pink, or Iris germanica ‘Rosalie Figge’, a velvety purplish-violet.

Iris ensata

Iris ensata, Japanese water iris, grow as immersed plants or in very humus-bearing, cool, moist soils; flowering early in May or June, they are also very cold-hardy. They are bulbous and likewise require little maintenance.
The iris ‘Royal Banner’ and the iris ‘Pinwheel’, purple, both flower between June and July–August.

Iris germanica ‘Cherished’ (photo credit ©Hogendoorn), Iris ensata ‘Pinwheel’ and ‘Royal Banner’

Some Alliums

They too are wonders brightening borders in May or June, and a few species enliven our borders later, from July onwards. These include:

Allium millenium

This is a very late ornamental onion, flowering in July. Returning faithfully each year, it is small in stature, not exceeding 50 cm tall, but forms a handsome compact clump, laden with charming small mauve pompom flowers. The plant remains attractive for several weeks. Plant it in the border or in a pot, in full sun or partial shade, in ordinary but free-draining soil.

Allium sphaerocephalon

Another allium of summer interest, Allium sphaerocephalon is easy to recognise as it is very different: it does not form globes like the others but rather elongated spikes.

Also rely on Allium senescens, particularly late, flowering between June and August depending on variety and exposure. They are very hardy, down to -20°C. Another unusual allium, Allium amethystinum ‘Red Mohican‘, flowers in early summer, between June and July.

Allium sphaerocephalon, Allium millenium and Allium senescens ‘Bubble Bath’

Some garden orchids and hardy false orchids

Less common, yet so beautiful in partly shaded areas, several terrestrial orchids display good cold tolerance, adding an original, natural or exotic touch depending on species, in our latitudes. They generally flower between June and July, depending on exposure and region.

Count on Bletilla ochracea, tolerant of temperatures down to -18°C in open ground, Cypripedium reginae, easiest to grow and a real gem in the garden, but also on Epipactis, often orange and brown, ideal for damp areas, and Dactylorhiza, pink or mauve, capable of growing at higher altitudes, as well as Gymnadenia conopsea, also called Orchis moucheron.
Spiranthes, with upright, graceful spikes flowering in late summer, complete this selection of bulbs — a tempting selection, you’ll agree!

Roscoea, Cypripedium reginae and Bletilla

Galtonia

Galtonia candicans, also called Cape hyacinths, survive down to -15°C in well-drained soil: they are superb bulbous plants, tall, with drooping bell-shaped flowers, white, or slightly green as in Galtonia viridiflora.

Galtonia candicans and Galtonia viridiflora

Liatris

I love this small perennial, still too scarce in our gardens, especially as, once established, it copes really well with summer heat spells!

Known as Kansas blazing star, and its origin is obvious: this lovely bulbous plant (in fact it has corms) is very hardy. Strangely topped with feathery spikes that open from top to bottom, unlike many other plants, Liatris are melliferous and tolerate any well-drained soil down to -15°C. Flowering is mauve in the type species (Liatris spicata) and ranges from white to pink in some horticultural varieties.

Liatris spicata

Some wild gladioli

More common, yet very useful in the garden in summer when flowering tails off a little, some wild gladioli tolerate cold down to -15°C, such as Gladiolus papilio, delightful with its yellow, white and purple flowers, and its hybridization Gladiolus x papilio ‘Ruby’, with spikes of small ruby to garnet-red flowers.

Other gladioli can also be left in the ground, provided they are well mulched, such as Gladiolus colvillei.

Gladiolus papilio

Some Eucomis

Known colloquially as ‘pineapple plant’, it is one of the charming late-summer bulbous plants. The Eucomis flower and its small tuft crowning it do indeed evoke the exotic fruit. Their flowering period is fairly long, and the different varieties offered for sale provide flower spikes of varying heights (between 20 cm for dwarf forms such as Eucomis vandermerwei and 1.5 m for Eucomis pole-evansii). The hardiest to cold are ‘Can Can’ with white flowers and ‘Purple Reign’ with purplish-pink flowers.

Eucomis bicolor ‘Alba’

Arisaemas

To finish off these cold-hardy bulbs in style, here is the cobra lily, or in Latin Arisaema. For lovers of the exotic and of unusual perennial plants, these are remarkable, almost reminiscent of carnivorous plants.

They are distinguished by a unique inflorescence, a spathe — a thin, often striate, recurved sheath resembling a narrow hood, a peculiarity of their own. The foliage is also magnificent and varies greatly between species. Arisaema grow mainly in Asia and North America, in moist, shaded habitats, so recreate these conditions for the bulbous plants to thrive here.

Arisaema consanguineum, Arisaema ciliatum, Arisaema galeatum and Arisaema costatum flower late in gardens, in midsummer. The species candidissimum flowers a little earlier, from July.

Arisaema Ciliatum and Arisaema consanguineum