There is nothing like the light, sweet, ethereal fragrance of sweet peas. Unlike roses and so many other floral fragrances, the scent of sweet peas has not been captured in perfumes or body creams.
Last year Kirchhoff’s seed introduced a range of heirloom sweet peas and according to Marlaen Straathof if you think normal sweet peas smell good, they don’t come even close to the heirloom varieties. The intense perfume was lost when hybridisers (the English in the 1700s) decided to sacrifice fragrance for fewer larger flowers with longer stems, instead of the many, smaller flowers.
Fortunately some plant lovers kept the faith and the seed descendants are now available with names like “Cupani”, “Old Spice” and “Painted Lady. Besides their intense fragrance the Heirloom range of some 20 varieties has a wide range of colours with many striped, bicolour and multi-colour mixes in shades from deep pink to mahogany red and pale to deep blue, mauve and purple.
Most are climbers but “Cupid” is a bush variety that doesn’t need staking and can be grown in a large container. Seed is available in single colours of cherry, pink, lavender, white and mahogany or in a mix.
Whether you plant modern or heirloom varieties, all sweet peas have the same basic requirements, says Straathof.
Sweet peas do best in full sun and with plenty of space and air around them. That is often why sweet peas do so well in a veggie garden, that is open and with better prepared soil. Growing on a slight slope assists drainage and is particularly appropriate for gardens that receive winter rainfall.
If the plan is to grow them next to the house make sure that they don’t get too much shade or get too hot if planted directly against a wall that reflects heat. It may also be that the soil next to the house is not as fertile, or as deep because of the foundations.
Soil preparation is the most important part of growing sweet peas. Because they are such vigorous growers, sweet peas need fertile soil that also drains well. For climbing varieties the soil should be prepared to a depth of 50cm (either a hole or trench) with lots of additional compost, well rotted manure, and a handful of agricultural lime per square metre.
A tip from Straathof is to sprinkle iron chelate at the bottom of the hole and add superphosphate or bonemeal for root development. Set up the support (trellis, stakes, etc) before planting so that the plants tendrils can cling to it as they grow. Putting in support later could damage the stems. Unsupported plants are easily damaged by strong wind. For bush sweet peas the same soil preparation only needs to be done to a depth of 30cm.
When plants are about 18cm high, pinch off the top leaves. This encourages strong basal shoots. Never let the roots dry out, but also make sure that the soil does not get waterlogged. Picking the blooms also encourages the plant to flower.