All these food plants at Age UK Resource Centre in Eltham (pictured from left to right: rocket, sorrel and kale) are now flowering but each will have a different fate.
Generally, food plants grown for their leaves should have their flowers removed because as soon as that happens all the energy of the plant is being directed into flowering to produce seeds for the next generation. This usually affects the taste of the leaves, making them more bitter. This is why you should take off the flowers of your basil growing on the windowsill. The same goes for rhubarb in the garden - directly it starts sending up a flower spike, decorative as it is, chop it off. Note, it is the stalk of the leaves we eat on rhubarb, not the leaves themselves, which are poisonous.
The rocket (left) has produced flowers which will be left for the benefit of pollinating insects and for their decorative appeal. Flowering doesn't affect the taste of rocket as much as some plants so it is OK to let them flower.
The sorrel (centre) will have its flowers removed. They are not particularly decorative and if they are allowed to flower the leaves will become smaller and less productive. Better to let them grow minus any flowers as they make a good soup very popular in France for generations, 'Soupe à la Bonne Femme'.
Finally, the kale (right) - a decorative one with pink stripes along the leaves, is being allowed to keep growing until the seedheads have ripened after the yellow flowers have benefited any pollinating insects. Once they are dry, the seeds will be carefully collected for sowing at this site and elsewhere. It is possible that some will self-seed in the vicinity, providing free plants. Seeds that have been collected from a plant in the garden tend to germinate much more readily than ones from a packet as anyone will know who has had forget-me-nots in their garden. The other developing flower spikes (not pictured) on the kale plants nearby can be cooked and eaten."