From now through to the autumn is a good time to collect and save seed. As we move to wards autumn, on a dry day its nice to walk around the garden looking at the flowers and veg to see where the seeds are forming.
A good tip when saving seed to ensure it's completely dry before you packet it. Seeds need to be stored in an environment more or less the opposite of that required for germination, which means the seeds need to be very dry, cool and dark. On the left are Viola seeds which are ripe but not dry, they will go brown and dry out in the pods, at this stage the seeds can be carefully taken out ready for storage.
The other photo shows a pod open with Nigella seeds which are drying and will soon be ready to pick out, tweezers are good for small seeds as they help to ensure you get just the seeds and no other plant matter. Then put into packets and label. Another plant easy to save and germinate is Digitalis, foxgloves, I often leave some seeds on the plant to scatter where they grow, pick some spires and distribute the seed and dry some so I can sow the seed and variety precisely where I want it, at least that's the theory. As with so much of gardening, its trial and error. Some plant seed stores well, germinates and produces just what you want, good cheap plants; other seed sulks and refused to perform; but it's always worth a try. Easy to collect and grow are nigella, sweet peas, viola, Calendula, Nasturtium , and in the veg plot rocket seed and the bean family are easy to save and germinate.
Make sure that all other matter is cleaned off the seed and it's just the actual seeds which are saved. I stick most seeds in the fridge in old tins and containers, anything which comes to hand really. Unfortunately, not everyone is happy with a fridge full of seeds but keeping seeds cool does help so if not the fridge, in a garage, especially over winter and dark is best.
Saving your own seed is environmentally friendly and cheap. Not all plants come true from seeds, any plants which are hybrids will not but it's often interesting to see what comes from seeds. If you really want to reproduce from a hybrid take a cutting....more about cuttings later in the month.