Sweet pea flowers come in a wide range of colours and patterns, but not yellow. This seems strange as yellow flowers are common enough in the genus Lathyrus. Even attempts to cross the true sweet pea, Lathyrus odoratus, with other species such as Lathyrus belinensis, have failed to produce the elusive yellow flower. The lack of yellow, however, seems a minor omission when one considers the wide range of colours that are available.
Blue Sweet Peas
True clear blues are rare in sweet pea flowers. Most have a tinge of pink to them which becomes more obvious under artificial light. It also makes life difficult for the photographer. The grandiflora variety, 'Flora Norton', is one of the clearest blues available.
Blue sweet pea flowers are often among the most susceptible to weather damage. Botrytis spores, germinating on the petals under conditions of high humidity, leave white spots which are most disfiguring on dark blues.
Cream Sweet Peas
A most valuable colour among sweet peas, cream blends well with most other colours. The Spencer variety 'Jilly' has long been the mainstay of exhibitors and serious gardeners alike. Among the old grandiflora sweet peas, 'Mrs Collier' holds a similarly elevated position.
Lavender Sweet Peas
One of the most traditional sweet pea colours, there is always a wide choice of excellent lavender varieties available. Much work has gone into their breeding , and modern varieties combine large flowers with good configuration and clear bright colour. Lavender sweet peas are more weatherproof than the blues, but equally hard to photograph successfully.
Rose Pink Sweet Peas
Always popular, and available in a wide range of shades on either a white or a cream background. Generally vigorous growers, these varieties perform consistently well in the garden and on the show bench. 'Mrs Bernard Jones' remains a popular and reliable choice.
Red Sweet Peas
Really good red sweet peas are few and far between. Crimsons tend to over vigorous with coarse spikes and badly positioned flowers. Some scarlets develop a blue edge to their petals in hot weather, although this tendency has now largely been eliminated by careful breeding. Few red sweet peas can be relied upon to produce top quality exhibition flower spikes, but 'Restormel' is generally regarded as the best.
White Sweet Peas
White sweet peas have always been popular, and there have been many excellent varieties starting with the grandiflora 'Dorothy Eckford', bred in 1901. It makes a fascinating contrast to modern varieties like 'White Frills'. Older varieties tended to be "white" seeded, but most recent sorts are "black" seeded. Black seeded varieties are considered easier to grow, but have the disadvantage that flowers may develop a pink tinge in hot weather if the plants are under stress.