Artichoke from seed

I get one central flower and then lots of smaller flowering side shoots. Last year's best doer (violet de provence) gave over 30 heads, but I pick small so maybe it would be less productive if you were letting them grow on?
I plant about 75cm apart, 2 rows in a 1.5m wide bed. My neighbour replants from off shoots each year but mine have always died, so I just leave the plants to get huge. I've replaced them once in 10 years, but that was because the voles eventually ate the lot