With my salad crops I am doing what is called "successional sowing" - in other words sowing seeds at regular intervals (in my case about 2 - 3 weeks apart), rather than all at once, so that I will be able to have a harvest over a long period. You can see here that some of my Lettuces are ready for cutting, while others are still small.
I have some little seedlings waiting in the wings for their turn, kept in 4-inch pots.
As soon as a mature Lettuce is harvested, I stick another one in to fill the gap.
Here is the third generation, recently germinated.
I have deliberately sown seeds for lots of different types of Lettuce, not only to give me a good variety in terms of colour and texture, but also in an attempt to have them mature at different times. I tend to sow fairly liberally, because Lettuce seed is cheap, and then choose a few strong specimens to pot-up. I'm afraid this means that 9/10ths of the seeds never get to grow to maturity, but that's just the way of the world!
I have adopted the same approach with my Radishes. Here you can see fully mature Radishes at the right of the photo, then there are some Lettuces, and over on the left there are two rows of Radishes that have just germinated.
Here's another view:
You can't see it at that range, but there is also a row of Spring Onions in there - between the Lettuces and the young Radishes. They are from seeds I bought in France when visiting Fiona.
Here's a closer view:
They are very tiny at present, but hopefully they will do OK. I have never had much luck with Spring Onions. They always seem to do poorly in my garden. Maybe this time will be different...?