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Black-Eyed Susans (Rudbeckia)

Nigel Dunnett presents his selection of Rudbeckias.

Rudbeckia, commonly known as cone flowers or Black-Eyed Susans, is a vibrant group of summer and autumn-flowering perennials and annuals. Most gardeners are aware of the typical Rudbeckia flower: bright yellow rays around a dark central cone, yet within the group there is a surprising amount of variation, and there are even a few members that at first glance you wouldn't think were rudbeckias at all. In this article I want to take a look at some of my favourite members of this genus.

Perennials

One of the most popular perennial rudbeckias is R. fulgida 'Goldsturm'. It is one of the most dependable of all perennial plants and it has just about everything going for it: toughness, ease of cultivation, and a long flowering period. The shining clear yellow flowers, 3in (7.5cm) in diameter, have a superbly contrasting black central cone and are produced in profusion from July on into September. After the petals have fallen the seed heads remain a feature for many weeks. The plant will grow to 2-3ft (30-90cm) in height and like most rudbeckias does best in full sun and a moist, fertile soil. Having said that, I obtain good flowering in a quite heavily shaded part of my garden, although the quality and number of blooms are not as good as out in the open. 'Goldsturm' has become incredibly popular and widely planted recently in the United States, where it is being used extensively in large drifts and masses in city landscaping schemes as well as in private gardens. Two other commonly listed rudbeckias, R. hirta and R. newmannii share many of the same qualities as 'Goldsturm', being relatively low growing and having bright flowers with contrasting dark central zones.

At a higher level we have two very similar species: R. laciniata and R. nitida. Both are tall growing plants and both have green cones instead of the familiar black cones. The main distinguishing feature between the two is that R. nitida has entire leaves while the leaves of R. laciniata are divided. Of the two, it is on R. laciniata that I want to concentrate. Like the other rudbeckias it is a native of the United States and forms great drifts and patches on mountain roadsides and forest clearings in the eastern US. To walk through such an unending drift with the clear yellow flowers all around at head height and higher is a wonderful experience. In good soil R. laciniata will reach 5-7ft (1.5-2.1m) in height - its upright growth requires little support unless in a very exposed position. Flowering commences in July and continues for a month or so - the flowers are between 3-4in (7.5-l0cm) in diameter and have slightly downward drooping rays and raised yellowy green cones. But the thing I like about the plant is its foliage - unlike so many other tall members of the compositae, R. laciniata has leaves which make a good contribution to a border before the plant's flowers appear. Each leaf, 6-8in (15-20cm) in length, is deeply cut and divided. This is a big bold plant and looks good in a wide border against a dark background such as a yew or holly hedge.

Occasionally double-flowered plants of R. laciniata can be seen in wild populations, and there is a double variety available commercially called 'Golden Glow'. However, to my mind the species has a certain amount of grace while the double form appears heavy. A lower growing double variety, 'Goldquelle', is usually considered a form of R. nitida but I notice the recent RHS Encyclopedia of Plants and Flowers includes it with R. laciniata. 'Goldquelle' will grow to around 3ft (90cm) in height, making it a manageable plant, but again I miss seeing the central cone. Finally a German selection of R. nitida called 'Herbstonne' has very large flowers of a richer yellow colour - the flowers are single so the green cone is visible. The plant is very vigorous, and can get to 8ft (2.4m) in height, so obviously a great deal of thought has to go into its siting! As I have already indicated, there is some confusion in the naming of forms of R. nitida and R. laciniata and as a word of caution I have seen plants labelled as 'Herbstonne' for sale in the US which were indistinguishable from ordinary R. laciniata.

I think the best way to describe the final perennial rudbeckia I am going to look at is as a kind of cross between a cabbage and a sunflower. Perhaps that doesn't sound too encouraging, but the plant in question, R. maxima, is in fact one of the most exciting perennials I know. R. maxima forms a rosette of highly glaucous steely grey-blue foliage - individual leaves can get to around nine inches in length and are almost round. And then in mid summer the flowering stem is produced from the basal rosette. Individual flowers are held at the top of three or four foot stalks, and in full flower in rich soil the whole plant can reach 7-8ft (2.1-2.4m) in height. The flowers are around 5in (12.5cm) in diameter and the rich yellow rays droop downwards around the dark raised central cone - the cone is about 3in (7.5cm) in length. Shelter, full sun and a rich soil are necessary for successful growth.

All of these perennial rudbeckias, apart from R. maxima, can be propagated by division. Seed also germinates freely and presents no problems. R. maxima though is a bit more difficult, and so far I have not been successful with seed. New rosettes are produced at the base of the plant at the end of summer and these can be detached with care and grown on, but the usual recommended propagation technique is root cuttings.

Annuals

None of the rudbeckias grown as annuals are really annuals but are instead short-lived perennials developed mainly from R. hirta. They offer us the advantages of a long flowering season, manageable compact growth, rich flower colours, ease of cultivation, and good cut flowers. Seed sown at the end of March under glass will produce plants ready for putting out in late May, and the plants should start to flower in July and carry on into the autumn. There is a wide range of varieties to choose from, some taller, some shorter, some double, some single. Plants in the mixture 'Rustic Dwarfs' grow to 2ft (60cm) in height and have richly coloured flowers of yellow, bronze, gold and mahogany-red, all with contrasting black eyes. The same range of colours is found in 'Giant Tetraploid Mixed', usually known as the gloriosa daisies, but the plants will reach 3-4ft (90-120cm) in height and the semi-double flowers are immense - up to 7in (17.5cm) across. If you are looking for a typical black-eyes Susan with glowing yellow flowers and a black central cone, then 'Marmalade' is a good variety - it will reach around 2ft (60cm) in height. So will 'Goldilocks' with double yellow flowers. My favourite annual rudbeckia is 'Green Eyes' which has a striking green cone in place of the more usual black centre.

One of the most endearing of the rudbeckias, R. purpurea has wandered off, with two other species, into a genus all of their own and is now known as Echinacea purpurea. This is a fairly tall plant, reaching 4ft (1.2m) high with purple, flushed with crimson, petals and a large central boss of a sympathetic light brown-orange. The flowers are quite large and are extremely attractive. There are several different cultivars including a white one. Thompson & Morgan sell this seed.

I know many people who tend to regard rudbeckias as a bit coarse and rank, but I like to think of them in a different way: cheerful, dependable and fun, with among the group some basic necessities of the late summer garden, as well as some very desirable garden plants.

Nigel Dunnett is a botanist, garden designer and horticultural writer.

Source of article
Growing From Seed - Autumn 1991 Vol. 5 Number 4
© The Seed Raising Journal from Thompson & Morgan