Lavender and Spring Onion

I was told by my mum that when my lavender went a bit woody and the buds were drying up to cut the plant right back to prevent the plant growing back woody. Whilst doing this today, it occurred to me that I may be able to get seeds from the drying buds that are on it, so I asked my mum about my plans and she said to put them in an envelope and the seeds will come out themselves. I have done this now and am storing them in a box with other envelopes of seeds I have been collecting (peppers etc), so hopefully I'll have lavender seeds soon!

I noticed a spring onion that I planted last year but didn't come up had been growing this year, so I left it to it's own devices as it seemed a bit woody to eat. It's flowering at the moment, and I'm wondering if I should be getting seeds from that (the flowers) too? If anybody knows, feel free to comment and let me know.