Posted: 12/01/2014 at 10:08
There are so many variables Tom, e.g. weather, soil condition, aspect, variety ........ I don't want to pour cold water on your idea but I don't think I'd find software helpful in gardening - so much depends on experience and judgement. I hope that's not discouraging - I find that reading books and magazines on the subject gives me background knowledge that I'm then able to draw on when gardening - I see the theory that I've read about spread out in front of me and recognise it.
I've found that a helpful and inexpensive book on veg gardening is the one in the River Cottage series.
I'm sorry that's not really the sort of answer you're looking for but I hope it's a practical suggestion.