Although the original, wild Sweet Pea, Lathyrus odoratus, from which all Sweet Peas have been derived was summer flowering, strains have been developed that are able to flower at different times of the year. This is controlled by the length of daylight hours, which varies both by season and geographic location. As a rule of thumb, Summer Flowering strains require 12 hours daylight to initiate flowering, Spring Flowering strains require 11 hours, while Winter Flowering strains require only 10 hours.
Spring Flowering types are best sown in the autumn while Summer Flowering types are best sown from mid winter in areas with mild winters like those experienced in Northern New Zealand. Spring and Summer types produce more sturdy plants, which produce strong basal shoots that soon take over from the primary shoot. Notwithstanding both the Winter and Spring strains perform very well if sown at the same time as the Summer types.
Scent is a difficult characteristic to breed. Expression of scent is very much dependant on temperature and humidity, while different people have differing ability to detect scent. Notwithstanding, Keith's work in combining the colours of the ancestral cultivars with bigger flowers and longer stems has also resulted in strongly perfumed cultivars. His 'High Scent' is recognised as the world benchmark for scent. This has smaller flowers with a clamped keel, but new introduction 'High Society' combines a waved, crisp white ground picotee edged pink flower with strong scent.
Very frequently, home gardeners are advised to soak seed overnight before sowing. This is unnecessary and potentially harmful for any hand harvested seed obtained from this website. Because of harvesting methods, seed from field production can on occasion result in hard seed coats, which delays or prevents germination. This is why the idea that seed needs to be soaked to identify hard seed has arisen.