[shokkyy]

I'm growing both for the first time this year and I'm not sure how to do the harvesting bit. Should I just take individual leaves for either/both, or pull the whole plant (for cooking rather than salad leaf)? And if leaves, how big should I let them get before I start taking some?

[snowdrops]

For the swiss chard just take the outside leaves off regularly leaving the centre ones to grow on.As for the pak choi I think you can do the same or when I grew them I just thinned them out by taking alternating plants

[arugula]

Agree on the swiss chard, but for the pak choi I've resorted in the past to taking the whole plant as they can bolt so quickly and easily!

[Diddy Gardener]

*sigh... yes, that's what's happened to mine 

[oldcow]

Just harvest leaves at any time for swiss chard, it will keep producing more. For pak choy, they can be eaten at any stage (the Chinese have different names for different sizes, the smallest one being "chicken feather size"). Since they bolt easily, you can just harvest them whole once they have a flower stem (which, by the way, tastes delicious). I find they're nicer when they're around 5 or 6 inches, since I think they get a bit watery when they're big.