Arurra wrote:Yes It would be nice to know if one shold keep the crop in the ground a little longer

As far as WIKI goes - the only crop that can be harvested before its final stage is carrots?
Stage 2 (before they flower) will only give you one carrot. When they flower, stage 3, they give seeds, and final stage they give 2? carrots (is it 2? I got full nature right off the bat so I don't remember). You can also harvest hemp before it's fully grown, when it's orange, but yeah, you won't get plant fibres or seeds and instead a hemp bud. Waiting until it goes again from orange back to full green and you'll receive the seeds and the fibres. I like to grab a couple buds if I can catch them, to smoke to increase FEP gain when I grind, but I keep at least 2/3 for seeds and fibres.
Otherwise, it doesn't matter when you harvest them. Quality will always be -5/+5 the original seeds and depending on your farming skill. When you harvest your crops is really only important for producing more crops, or if you're producing wax/honey. If you leave them at their final stage too long when you're farming wax, the quality will lower and you also won't be producing any, as beehives production is dependent on whether there are crops growing within radius.