No summer garden is complete without the scent of sweet peas.

Robinson described the sweet pea (Lathyrus odoratus) as ‘Perhaps the most precious annual plant grown’ and who could disagree. There is something joyful about sniffing the first sweet pea flower of summer and it is a wonderful treat to pick the first bunch.

I have written loads about sweet peas in the past including a series that take you through the growing of them, starting here. I will not repeat myself since it a long and complicated process, riddled with options. Suffice to say that the best sweet peas are sown in autumn but you can sow them in spring too. They are hardy annuals and, as I write, my old plants from last summer, which I should have pulled up, are still green and looking healthy.

The wild sweet pea is native to south Italy, Sicily and environs but for many years it was thought to come from South America. ‘Quito’ (an area of Peru) is the name of an old variety with purple flowers and ‘Painted Lady’ (above) is an ancient type with red and white blooms. Both have intense fragrance. At the turn of the last century the Eckford sweet peas were produced with larger flowers and were called Grandifloras. But then the Spencer type spontaneously evolved, with larger flowers, four or five to a stem, with frilly petals. These are the sweet peas we think of today.

To repeat what I have said before:

The origin of sweet peas was, for some time, confused but it is thought that they were first noted in the wild and written about by the Franciscan monk Francisco Cupani in 1695 in Sicily. He gave seed to Casper Commelin, a botanist in Amsterdam in 1699. The plants produced small blue and purple flowers with intense fragrance. Amazingly this is still available today as ‘Cupani’. It is thought that seeds were also sent to Dr Robert Uvedale in Enfield, Middlesex. The plant progressed slowly with little variation in colour until Henry Eckford, at the end of the 19th century hybridized existing varieties and introduced the Grandifloras.

Grandiflora. These had larger flowers than the wild sweet peas with a wide variety of colours. They were very popular. They have two or three flowers per stem and 20 or more of his varieties are still available. However, the real rise of sweet peas began in 1901.

Spencer. In 1901 Silas Cole, Head Gardener to the Earl of Spencer found a natural mutation among the Grandifloras with larger, wavy petals and these were named Spencers. They flower slightly later than the Grandifloras and have three to five flowers per stem – four or five for showing. Most are sweetly scented but it varies: the red cultivars are often only slightly scented.

Multiflora. These are developed from the Spencers and have slightly smaller flowers with less ruffled petals but have at least five flowers per stem. They are not so good for exhibition

There is a big difference between these but a bigger difference is shown by cultivation. Talking purely about the Spencers, the plants can top out at 1m, with flowers for a month and on stems 15cm long or, the same variety, with good cultivation, can bloom for three months with 40cm long stems and grow to 3m or more tall.

The Spencers and Multifloras are the best for cutting, with long stems and showy flowers but the Grandifloras have the best perfume and are becoming increasingly popular. The Spencers and Multifloras also have longer internodes and, for garden decoration, are rangy and not as successful as the Grandifloras. The exception is the Solway Series (below), which is the best ‘dwarf’ sweet pea, perfect for pots, reaching about 1m high and pleasantly bushy and compact. There are also very dwarf varieties such as ‘Cupid’ but I personally don’t rate these very highly.

The failing of sweet peas is that, once they set some seed pods, they give up flowering so you need to deadhead very frequently. If growing for cutting this is not an issue. And never feel guilty about cutting the stems. Twice a week, cut all the flowers for the home but do not cut off unopened buds because they will not open in water. The more you cut, the more you get.

Sweet peas like moist, rich soil. If the soil is too dry or the weather too hot, plants will get mildew, flower buds will drop and the flowering period will be severely reduced. As the season progresses, aphids will spread virus diseases and you may see streaked flower colour. It is not a huge issue because it is then time to pull up the plants and if you save seeds these will not carry on the disease.

Sweet peas are easy to grow, but a challenge to grow well. That should be seen as a challenge and not a reason not to grow them!