Why do my herbs go to flower eg dill coriander and parsley

There is a special horticultural term for that - Bolting. Environmental factors such as high temperature, drought or lack of nutrients can all cause the internal hormone change and trigger bolting which reduce the life cycle and leaf tastes. For some herbs, you can cut off any flower stock to help postpone bolting and encourage leafy growth. Also, try the following cultural methods to help to prevent herbs from bolting: 

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Hope this helps and please do not hesitate to contact us again should you have any other query.