Leafy Greens

I would like to know why I get only a couple of pickings off my silverbeet, then I get a big thick stem which grows up from the middle and don’t get much off it from then on. What am I doing wrong?

I grew ‘Brightlights’ Silverbeet from seed. These plants have now gone to seed. If I collect this seed, will any new plants still be ‘Brightlights’ or will they revert back to white stem ‘silver beet’?

I find whenever I grow rocket; it goes to flower quite early on. I have heard that it is possible to collect the seeds and re-sow them. What are your recommendations?