Cochliasanthus caracalla

Flowers in September: the best plants this month

Head gardener Tom Brown chooses plants that will respond well to the warm days and cooler evenings of September

A sophisticated Spanish flag and an unusual vine are among Tom’s choices for plants this month. Read our piece on where to catch them in bloom here.

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1

Ageratina altissima ‘Braunlaub’

Ageratina altissima ‘Braunlaub’
© Jason Ingram

Less common than the popular cultivar ‘Chocolate’, but equally as useful in a mixed border, this tall, herbaceous perennial is a wonderful late-summer plant. As it grows, it forms a shrub-like habit that works well as a filler among other plants, but it comes into its own as the summer begins to draw to an end, and masses of white flowers appear throughout the branched stems, illuminating the plant as the evening light starts to recede. It also works well as a cut flower.

Height 1.5-2.5m.
Origin Garden origin (species from North America).
Conditions Moisture-retentive soil; partial shade.
Hardiness RHS H5, USDA 3a-8b.
Season of interest Late summer into autumn.


2

Malus x robusta ‘Red Sentinel’

Malus x robusta
 ‘Red Sentinel’
© Jason Ingram

If you’re still searching for the perfect tree for a small garden then it’s worth considering a crab apple. They tick a lot of boxes, not least because they offer a long period of interest. ‘Red Sentinel’ blooms incredibly well in April and May, with a tremendous show of white flowers that are blushed pink. Then from September bauble-like, shiny, red fruits are produced in abundance all over the tree’s canopy. To my amazement, in a wildlife-filled garden, the fruits persist on the branches until Christmas. AGM.

Height 4-8m.
Origin Garden origin.
Conditions Moist but well-drained soil; full sun or part shade.
Hardiness RHS H6, USDA 4a-8b.
Season of interest Fruiting in September/October.


3

Gladiolus ‘Violetta’

Gladiolus ‘Violetta’
© Jason Ingram

If I had to choose just one gladioli, it would be this one. It makes a great cut flower and has rich, sophisticated flowers, of the deepest purple, that are produced from corms in late summer. The delicacy of these dwarf cultivars allows them to grow in borders without the need for staking and clumsy supports, and I adore the way this cultivar’s flowers work well with so many other garden plants in a border or vase without dominating it. Plant from May until July for continuous colour during late summer and autumn.

Height 1.5m.
Origin Garden hybrid (species from South Africa).
Conditions Fertile, free-draining soil; full sun.
Hardiness RHS H3, USDA 7a-10b.
Season of interest Mid to late summer.


4

Euonymus alatus ‘Compactus’

Euonymus alatus ‘Compactus’
© Jason Ingram

In spring and early summer this is an unassuming plant, but once late-summer evenings start to have a nip of cold about them, this glorious shrub becomes a real attention grabber. Its dense, green foliage turns a rich, claret colour, and this autumn foliage is equally attractive when admired up close or from a distance. Few shrubs can rival this neat cultivar for colour when it is in its autumnal glory. AGM.

Height Up to 2m.
Origin Garden origin (species China, Japan, Korea).
Conditions Tolerant of clay and most moisture-retentive soils; part shade or full sun.
Hardiness RHS H6, USDA 4a-8b.
Season of interest Late summer to autumn.


5

Symphyotrichum novae-angliae ‘Rubinschatz’

Symphyotrichum novae-angliae ‘Rubinschatz’
© Jason Ingram

New England asters have a robust nature that I find greatly appealing and admirable. They generally suffer very little from powdery mildew that can affect other asters and produce a reliable show of flowers each year. ‘Rubinschatz’ requires little fuss and attention, I fell in love with the rich, rosy, claret-coloured flowers, which are most unusual and attractive. Divide every few years to maintain vigour and if cutting, treat the end of the stems with hot water to improve water uptake.

Height 1.5-2.5m.
Origin Garden origin (species from Eastern North America).
Conditions Moist but well-drained soil; full sun or part shade.
Hardiness RHS H7, USDA 4a-8b.
Season of interest August – September.


6

Lophospermum erubescens ‘Bridal Bouquet’

Lophospermum erubescens 
‘Bridal Bouquet’
Maurandya ‘Bridal Bouquet’
© Jason Ingram

By September, some garden plants are starting to show signs of fatigue after a long summer. Lophospermum, on the other hand, builds as the summer progresses and comes into its own in late summer. Its unusual, pure-white flowers drip from the twining stems and persist until first frosts. It’s happy in a container, where you can manage the feeding regime more closely, and a fortnightly tomato feed is of great benefit for colour.

Height 2.5-4m.
Origin Garden origin (species from Mexico).
Conditions Moist, fertile, free-draining soil; full sun.
Hardiness RHS H2, USDA 9a-10b.
Season of interest Late summer until the frosts.


7

Ipomoea lobata ‘Citrina’

Ipomoea lobata ‘Citrina’
© Jason Ingram

Affectionately known as the Spanish flag, this annual climber is easy to grow and gives beds and borders a much-needed boost of colour at this time of year. Ipomoeas have flame-like flowers that cover twining stems from midsummer, and this cultivar has more subtle, pale-lemon flowers, compared to the species. Like most annual climbers, ipomoeas dislike the cold, so don’t plant out until the warmth of June is fully felt and harvest the ripened seed for next year as the frosts loom.

Height 4-8m.
Origin Species from Mexico and Brazil.
Conditions Reasonable garden soil with good moisture retention; full sun.
Hardiness RHS H1C, USDA 11a-12.
Season of interest Midsummer until the first frosts.

8

Cochliasanthus caracalla

Vigna caracalla

Although I grow this vine each year, from seed, it can be perennial if given a little protection from frosts. Often sold under its previous name of Vigna caracalla it is commonly known as the corkscrew vine on account of its exquisite flowers that are tightly coiled like a corkscrew. Their emergence at the end of the summer always causes great excitement. You can successfully grow it in a container or in a conservatory or in a border, provided you apply a potash-based liquid feed throughout the growing period to encourage a strong flowering.

Height 3m.
Origin Tropical South America.
Conditions Moist, free-draining soil; full sun.
Hardiness RHS H2, USDA 10b-12.
Season of interest July – October.


9

Symphyotrichum ‘Little Carlow’

Symphyotrichum 'Little Carlow'
© Jason Ingram

Some Symphyotrichum can be difficult to harmonise with other perennials and shrubs in naturalistic plantings but this much-admired cultivar, with its sprays of soft-blue flowers that appear in abundance in late summer, provides an elegant charm in a number of garden situations, making it one of my favourite plants. I’d recommend a little birch or hazel to support the plant when it’s in full bloom as the sheer weight of the flowers can overwhelm the wiry stems. AGM.

Height 50cm-1m.
Origin Garden origin (species from North America).
Conditions Moist, fertile, free-draining soil; full sun or partial shade.
Hardiness RHS H7, USDA 3a-8b.
Season of interest August – September.

 

Salvia splendens ‘Yvonne’s Giant’

 

Salvia splendens ‘Yvonne’s Giant’
© Jason Ingram
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Salvia splendens has been a bedding plant staple for many years, often surrounding manicured gardens in parks – but don’t let that deter you from using ‘Yvonne’s Giant’ in more contemporary plantings. It is easy to grow as an annual from seed offering non-stop, bright-red flowers from June to first frosts, at a height that works incredibly well with perennials, such as rudbeckias and sedums. If you take cuttings in midsummer you will have more established plants ready to plant out once all risk of frosts has passed, and so be able to achieve a greater height in a shorter period of time.

Height 1.5m.
Origin Garden origin (species from Brazil).
Conditions Fertile soil; full sun.
Hardiness RHS H3, USDA 11a-12.
Season of interest June until first frosts.