Sweet Peas are beautiful and fragrant, but they last only a season. By collecting their plentiful seeds you will be able to keep enjoying them every year.
In August Sweet Peas produce their seeds within pods, these pods start off green and then grow brown and brittle, eventually breaking open. The trick is to time it right, harvesting the pods too soon, whilst they are still green will mean the seeds will not germinate. Alternatively, if you wait too long the pods will become brittle and the seeds will split out from them. If your intent is to grow next year’s plants in the same place then simply let the pods splits open and the seeds will self-sow.
If you want to relocate the plants, let the flowers die back, the pods will not grow if you dead-head them. The process of the pods growing and turning brown can take a couple of weeks so ensure you check regularly as the pods start to split, harvest them immediately. Take them indoors, remove seeds from the pods and let them dry out for two to three days. Once dry keeps them in a dry place such as sealed bag or airtight pot until planting time.