Re: Peas - Sowing time to cropping date
Sowing to cropping times should always be taken as guidance only, because in reality peas are subject to fluctuations in temperature, which have a direct influence on the time it takes for peas to mature and crop, measured in day degrees.
In practice, what this amounts to is that the crop will mature earlier if the weather is on average warmer for the duration of the peas' growing. Common sense bears this out, but it does allow us to fairly accurately predict when a crop will mature based on the mean temperature for any particular calendar period. Peas in British seed catalogues get roughly categorised as early, intermediate and main crop, but most American seed catalogues give more precise day degree ratings for varieties. This is in acknowledgement of them selling to customers experiencing wildly different conditions across a continent.
EDIT: Kelvedon Wonder's day degree index is 65 days. So, pick a date when you would prefer to harvest your peas and work back 65 days from that and you will get a reasonable prediction as to when to sow.