8 Great Late Bloomers

The waning days of summer present a plethora of gorgeous blooms, including these eight delightful choices suitable for a wide range of garden conditions.

Credit: John Glover

David Tarrant’s eight favourite late-summer blooming plants

There is something quite magical about the warm lazy days of late summer, especially as evening approaches and the light turns golden and soft, highlighting the intensely coloured blooms of the season. At this time of the year, all colours mysteriously seem to harmonize with one other – whether it’s orange, purple, blue or pink, every flower finds its place in the garden.

Although I am often asked if I have a favourite flower, my answer usually depends on which season we are in. With the lovely days of fall in mind then, I present eight of my favourite late-summer bloomers.

Aconitum napellus
The first is monkshood (formerly Aconitum autumnale, now reclassified as Aconitum napellus), which is variable in its form and colour and comes to us from northern and central Europe, rendering a hardiness of zones 5 to 8. In cultivation for centuries, monkshood was widely used by herbalists. However, a word of warning here – all parts of the plant are toxic if ingested. And whenever I mention toxic plants, I must add that the danger shouldn’t prevent us from growing them in our gardens, but rather we should teach our children not to eat the seeds or leaves. I grew up in a garden where we had a laburnum tree whose seeds are toxic. I was taught by my parents not to eat them. And hence, I am still around today!

A. napellus reaches a height of up to 1.5 m (5 ft.). Its foliage is attractive, rounded, deeply lobed and even before the plant blooms, it adds textural pleasure to a border. Its flowers occur in dense racemes of gorgeous indigo-blue flowers, each cowled exactly like a monk’s hood, hence the plant’s common name.

Its flower-bearing stems are strong and do not require the same careful staking that delphiniums do. Once the initial raceme has faded to form seed, prune it off and many side shoots will appear with smaller but equally showy racemes that will continue giving good colour right into the fall. Monkshood also makes an excellent cut flower.

Monkshood likes cool, semi-shaded spots, making it an ideal candidate for the back or centre of a border where other perennials will afford shade to the roots. Such a location will also keep toxic leaves away from the reach of children. Like all perennials, it enjoys a top dressing of compost or well-rotted manure each spring.

Schizostylis coccinea
Another of my all-time favourites for this time of year, Schizostylis coccinea is in the iris family and comes to us from South Africa, which, sadly doesn’t make it hardy for all our readers, just those in zones 7 to 9.

A rhizomatous perennial with iris-or freesia-like leaves, S. coccinea features flower spikes that reach anywhere from 30 to 60 cm (12 to 24 in.) in height, somewhat like miniature gladioli. These bear from four to 14 brilliant cup-shaped, scarlet flowers, each about 3 cm (1 in.) in size. This plant is underused here but so valuable as it starts blooming in September and continues through December. It also makes a wonderful container plant.

In the wild in South Africa, this plant flourishes in damp soils. Here at the UBC Botanical Garden, however, it thrives in the well-drained soil of the Alpine Garden. In a home garden, tuck it in a prominent, somewhat sheltered spot protected from early frost. Add some compost to the planting hole. Look for pot-grown specimens in specialty nurseries and garden shops in late summer.

While the wild-type S. coccinea is perhaps the showiest of the group, there are also some fine white and pink forms available.

Tricyrtis formosana
Tricyrtis formosana is extremely appealing at this time of year and again, underused. It comes from Taiwan where it grows in forest clearings at about 3,000 m (9,840 ft.).

This one is, again, sadly not hardy for all readers, but it is invaluable for semi-shaded gardens in zones 6 to 9. This stoloniferous perennial likes moist but well-drained soil conditions and reaches an overall height of 80 cm (2.5 ft.). Its stems zigzag ever so slightly and are a bit hairy with beautiful pointed, ovate leaves all the way up the stems. The leaves themselves are very glossy with dark purplish blotches and attractive veining. They look absolutely beautiful when moistened by late summer rains.

At the top of each stem, branched terminal cymes produce several upward-facing, star-shaped orchid-pink blooms about 3 cm (1 in.) in size. These flowers are spotted with deeper purplish-red spots inside their petals. And while the flowers aren’t large and showy, the plant is very pleasing nevertheless.

Aster thomsonii
Aster thomsonii is possibly my favourite Michaelmas daisy (a name commonly used in the U.K. to identify fall-blooming perennial asters). It comes from cooler regions on the slopes of the western Himalayas, making it hardy to a wider range of zones (4 to 9).

The plant is clump-forming with erect, slender 60- to 75-cm (2- to 3-ft.) stems covered with coarsely toothed, mid-green leaves that reach 10 cm (4 in.) in length. The flowers grow up to 5 cm (2 in.) across, single lilac-blue with a bright-yellow centre occurring in free-forming sprays. They are absolutely gorgeous and a must-have for a late-summer border. If this sounds too tall and rangy for you, then seek out A. thomsonii ‘Nanus,’ which has long-lasting flowers and only reaches 45 cm (18 in.).

All perennial asters like a sunny spot with reasonably rich soil. Because of their clump-forming habit, they must be lifted and divided every third season or so in the spring. Add some well-rotted manure or compost at this time.

Kniphofia triangularis is a charming smaller member of the red hot poker genus, and one of those plants subject to some confusion about its correct name. For years we called it Kniphofia galpinii here at UBC, and according to the Reader’s Digest A-Z Encyclopedia of Garden Plants it often gets confused with Kniphofia nelsonii.

K. triangularis comes from high elevations in the eastern Cape of South Africa and is said to be hardy in zones 4 to 9. It truly is the most charming plant with delicate arching linear grass-like leaves that reach about 60 cm (24 in.) in length and late-summer flowers of a warm orange borne on wiry yet strong stems in dense racemes. Each tubular flower grows to 4 cm (11⁄2 in.) in length. I am absolutely taken by the amount of flower spikes this plant produces. They also last well as cut flowers.

Based on our plant here in the garden, I would suggest this to be drought tolerant. And because of its less rambunctious growth habit, it is ideal for all home gardens, even doing well in large patio pots.

Kniphofia nelsonii on the other hand blooms a little earlier and has dense racemes of deeper orange tubular flowers that have a slightly yellowish base to them, giving the impression that they are illuminated from within.

Phlox paniculata ‘Fujiyama’
This erect herbaceous perennial is a wonderful late-summer bloomer native to the eastern United States (which makes it suited for zones 4 to 8), reaching up to a metre (or yard) in height on strong wiry stems. Its foliage is elliptic and toothed up to 30 cm (12 in.) in length, all the way up the stems. The panicles of sweetly scented, pure-white flowers on this one are outstanding, a good 20 cm (8 in.) across and somewhat mounded (hence the resemblance to Mount Fuji). Each floret is 2 cm (3⁄4 in.) across.

I know some people dismiss the idea of a white garden being viewed on a moonlit night, but this plant is perfect for this purpose. All P. paniculata are quite drought-tolerant, but enjoy an annual spring top dressing of compost.

Sometimes when phlox are mentioned, people throw their hands up and complain that they get “so much mildew.” While this cultivar is actually touted to be mildew resistant, when the problem is widespread and conditions right, it will still get it. However, mildew hasn’t wiped out our plant yet, and this is its 10th season in the border.

Sedum spectabile
This is probably one of the best known and most widely adored late-summer plants, and I love it myself because it has been around for many years and brings back such happy childhood memories.

A clump-forming deciduous perennial, Sedum spectabile is very hardy, coming originally from higher elevations in China and Korea. This showy succulent stonecrop is entirely drought resistant, with upright unbranched stems reaching 45 cm (18 in.) in height carrying whorls of obovate, glaucous, grey-green leaves slightly toothed all the way up.

Its tiny flowers are pink and star shaped, borne in dense flat cymes 15 cm (6 in.) across. Apart from being eye-catching, the blooms also attract bees and late-summer butterflies.

Penstemon ‘Andenken an Friedrich Hahn’

Last but not least is Penstemon ‘Garnet,’ or as it was originally named ‘Andenken an Friedrich Hahn,’ an amazing cultivar obviously hybridized in Europe. Hardy to zones 7 to 10, it flowers over a long period of time starting in June and continuing through until frost.

The plant reaches 75 cm (30 in.) in height and is quite bushy, with linear dark-green leaves to 12 cm (4.5 in.) in length. The flower spikes bear masses of bell-shaped, deep wine-red flowers. It is a resilient grower and again, extremely drought tolerant.

The following plants are hardy to the zone number indicated:
Aconitum napellus – zone 5
Aster thomsonii – zone 4
Kniphofia triangularis – zone 4
Penstemon ‘Andenken an Friedrich Hahn’- zone 7
Phlox paniculata ‘Fujiyama’ – zone 4
Schizostylis coccinea – zone 7
Sedum spectabile – zone 4
Tricyrtis formosana – zone 6

David Tarrant of the UBC Botanical Garden is a well-known gardening expert, author, and host of Spring on HGTV.