Winter Sunshine™ Sweet Peas – Cultivation.
The Winter Sunshine™ strain of sweet peas have different growth characteristics from later flowering types, and require somewhat different cultivation.
Early growth is vigorous, and this continues throughout the winter even in the UK where low light levels normally severely restrict plant development for many weeks. As a consequence, soil fertility levels need to be higher, and early sowing can lead to excessive vegetative growth before flowering commences. This latter problem is restricted to high latitudes where the winter daylength is insufficient for floral initiation. In the UK, mid September is a suitable time for sowing. In Holland these varieties are also sown in May to produce autumn flower.
With most types of sweet pea, excessive early growth is not a major problem as the plants can be cut back to a short basal growth. This, however, is not an option with the Winter Sunshine™ strain as the production of side shoots very limited until flower production starts. Pinching out the tip of the seed growth in the usual way will give one strong side shoot, but cutting this back may kill the plant, or result in a long delay before any further growth is produced.
The factors which determine the onset of flowering are daylength, temperature and light intensity. Floral initiation is reputed to occur at a day length of around 8 hours, but I have not seen any experimental data to confirm this. In the UK flower can be expected from early March under glass, in California cut flower can easily be produced in time for the Christmas market. Attempts to produce flower too early under low light conditions can lead to bud drop.
This strain is more vigorous than other winter strains of sweet pea and should perform extremely well in the warm temperate regions of Australia, New Zealand and southern Africa. Yields of up to 400 stems per square meter have been reported from Holland.
© 2018 P. E. M. Rowland