Great balls of seed!
Lettuce seeds are ripening now, the small yellow flowers becoming balls of seed with white fluff on the ends. Each plant can give more than 1,000 seeds and these last up to three years in cool, dry conditions.
Either pull plants on a dry afternoon to rub out the seeds straight away. Or pull plants and hang them upside down in an airy, undercover space to rub out seeds when you have time. This is best done when the weather is damp, and it allows the plants to dry before deseeding.
I have found that rubbing the seedheads between two pieces of wood serves to loosen most of them. Do it over a sheet to ensure that you catch all of them. At this stage there is also a lot of fluff and other plant debris that accompanies the seeds, so do a careful winnowing in any light breeze from bucket to bucket to help the chaff blow away.
Broad beans and peas should have come dry to harvest in July or early August, while runner and French beans are drying now if you have left some unpicked for that purpose. Runner beans may have cross pollinated if you are growing two varieties in the same garden, whereas French beans do not cross pollinate and always stay true.
Many vegetables require cross pollination from several of the same plants to maintain genetic diversity and prevent inbreeding. Real Seeds website has information on this, but last autumn I struggled to find out whether basil needs cross pollination. I risked saving seed from one plant in the greenhouse and have grown it this summer with fair results. However, the Bingenheim plants (its parents) are stronger.