How to choose rudbeckias

Image: Rudbeckia hirta 'Cherry Brandy' seeds from T&M

Rudbeckias (Black Eyed Susans) are a vibrant group of summer and autumn-flowering annuals and perennials. The typical rudbeckia flower has bright yellow rays around a dark central cone, yet, within this group there is a surprising amount of variation and even a few members that, at first glance, you wouldn't think were rudbeckias at all. Here, we asked botanist, garden designer and horticultural writer Nigel Dunnett to tell us about his favourite varieties.

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My favourite perennial rudbeckias

Rudbeckia 'Goldsturm' looks wonderful when planted in swathes
Image: Rudbeckia fulgida var sullivantii 'Goldsturm' from T&M

One of the most popular perennial rudbeckias is R. fulgida 'Goldsturm'. It's 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 -rowing 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's 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.

All of these perennial rudbeckias can be propagated by division. Seed also germinates freely and presents no problems.

My favourite annual rudbeckias

'Rustic Dwarfs Mixed' contains a blend of yellow, gold, bronze and mahogany blooms
Image: Rudbeckia hirta 'Rustic Dwarfs Mixed' seeds from T&M (© T&M)

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 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're looking for a typical black-eyed 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 called Echinacea purpurea 'Alba'.

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 additions to the late summer garden, as well as very desirable garden plants.

For more helpful tips, read our article on how to sow seeds successfully and check our guide for what to sow and grow each month. Our selection of hardy annual flower seeds will fill any temporary gaps until your perennials get established.

About the author:

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