Which edible crop has the fastest growing time from seed until something you can eat? (And yes, I know the human digestive system can eat seeds themselves, but that’s not what I’m asking about)
Sprouts?
ETA: for example: Sprouting - Wikipedia
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That most likely would be microbial, such as yeast or bacteria, though that is not seeds as you speak of.
Going larger scale you have sprouts which are just germinated seeds (and using the stored energy on the seeds for that), and really not much more the the seeds you wish to disqualify.
A few AT thru hikers actually carry sprout with them (in the growing form) as nutrition.
Radishes go from seed to fully mature in 3-4 weeks.
Greens
Maybe sprouted grains.
In the gardens I used to tend, radishes and leaf lettuce, about 3 weeks.
Dennis
Certainly some kind of sprouted seed - I think it might be mustard or cress - a bit quicker than beansprouts in my experience - and they form a small plant with actual green leaves, so I can’t think of any way they wouldn’t qualify as a ‘crop’
You can eat lettuce a few days after it sprouts. Vegetable know-it-alls suggest saving the plantlets removed to thin the row and eating them, which is possible, but it’s a pain to remove the roots and clean them for such a tiny amount of food.
I did it when I had a garden because I don’t like to waste things, along with adding tender new dandelion greens. But I agree, the cleaning part can be a pain. If I only had a few I’d add the thinned plants to a salad made with grown up lettuce.
It’s a bit of a trendy food thing right now: microgreens. I suppose it sounds cooler than sprouts. They’re harvested with scissors, too, so you’re not eating the root end. They’re grown from all kinds of seeds, from common greens to herbs. Microbasil is particularly nice, IMHO. Takes about a week.
So no eating the seeds, but does it have to have more energy than the seeds themselves? You can have pre-photosynthesizing sprouts in a few hours or days, depending on the seed, but it’s just as dead end an approach as eating the seeds if you’re looking for something sustainable.
Or to put it another way: “Grows the fastest” is a vague question. Do you want quickest increase in calories? Quickest increase in gross weight? Quickest increase in volume? Do you want a sustainable process where growth has to continue until new seeds are produced?