What part is best to eat?

One of the more perplexing issues is determining when to harvest your food and what part is the most nutritious part.

From memory lettuce leaves on the outside of the plant have higher nutrition. This is thought to be in response to the higher sunlight. However other plants (which I can't remember now) have higher nutrition when they are sprouts.

Then comes the next question, let us say broccoli is highest nutrient level when small. However it is the smallest by mass then, so when would be the best time to pick broccoli when you want to feed your family, but still feed high nutrient levels.

This is no simple answer for these questions. But there are pointers that hint at solutions.

One of these studies looked at two different grasses for their nutrient levels of the various parts, with relation to their usefulness for cattle feeding. One grass is commonly called "Timothy-grass" the other Switchgrass. Unfortunately the study didn't look at vitamin levels, but did look at minor metal concentrations. In the same soil Timothy grass had much high mineral levels across all minerals measured. This is shown graphically below:

So it would seem clear if you were going to sew grass for your cow you would choose Switch grass. On the other hand Aluminum which we would all agree is not a mineral you should eat if you can avoid it, had much higher Aluminum levels, so maybe it wouldn't be as good.

They also broke down the mineral level by different plant areas, however I couldn't draw any conclusions as the data became to complex.

As an aside here we have the classic issue of food tables. If you were to look up grass in a food table - what level would you get told?

Reference: Smith & Greenfield Distribution of chemical constituents among shoot parts of timothy and switchgrass at anthesis Journal of Plant Nutrition, Volume 1, Issue 1 1979 , pages 81 - 99