This famous diarist wrote some seminal gardening books, including Aceteria: A Discourse of Sallets, 1699.
This demonstrates that growing a wide range of salad leaves is nothing new - he lists lettuce, chervil, myrrh, fennell, wood sorrel, spinach, purslane, orrach, nasturtium, corn salad, rocket, tansy, alexanders etc ...
Here are some excerpts:
"In the choice of sallets, observe,
First, that the kinds are young and delicate.
Secondly, that they are picked very clean from imperfect, slimy leaves.
Thirdly, that each kind be washed separately in two clean waters.
Fourthly, that they are well drain'd in a cullender, and afterwards swing'd dry in a clean Napkin.
Fifthly and lastly, that every sort be proportion'd as directed in the preceding sections, and laid singly in the dish, in such a manner, as to form a pyramidical, or other agreeable figure."
He also advises picking salads in the morning during hot weather.
Other tips include inter-cropping:
"One may sow raddish and carrots together in the same bed: so as the first may be drawn whilst the other is ready: or sow lettuce, purselan, parnsips, carrots, raddish on the same beds and gather each kind in their season, leving parsnips to winter."
Also, he's a fan of edging beds with chervil.