When your herbs (parsley) and vegetables (leafy greens, spring onions and leeks) start going to seed, is it best to remove the whole plant, or can you cut the central seeding stalk and keep harvesting as and when you need them?
Unfortunately once the plants you have listed start flowering and then produce seed, the optimum time for picking and eating has passed. The plants are then entering their reproductive stage which signals that they are near the end of their productive life.
However, with parsley you can seriously cut back the plant which should then produce side shoots of edible parsley. You will notice that they will have a distinctive taste, unlike the main parsley plant.
For a small investment we would recommend planting new specimens in your garden. For leafy and spring onions, radishes, etc use successive planting e.g. every 2-3 weeks to ensure continuous harvesting of young fresh veggies.
With all plantings ensure there is adequate organic matter in the soil. Add in Daltons Compost and work it well into existing soil before you plant out. This is particularly important if you have a heavy clay or light sandy soil.