The oldest in there was planted 7 years ago this fall, and I went back in a couple years after that. Yesterday, I discovered that the patch is now self seeding also, as there are some babies here and there.
I dug a couple roots yesterday to get pictures, and even the huge three prongs are not yet ready to dig for market.
Both of those roots are three prongs and both the same age. The best indicator on size is the thickness of the stem, though that doesn't always predict accurately. That larger root will dry to about a medium size and the smaller one to a small. Neither are big enough to be especially beneficial to a collection of dry roots yet.
These plants were within ten feet of one another, both were three prongs and would be legal to harvest this fall. However, clearly, they need more time to mature before they are going to be ready to harvest.
I'm going to give you some simple math that hopefully you can use in your growing plans.
The average ten year old plant will cover an area of lets say 2 square feet. We all agree?? OK there then.
If you use the skatter method or any other uncontrolled seed dispersing method you will plant as close as one or two square inches if your lucky 3 square inches.
Now I never finished grade school and math is not my thing but if one seed grows to cover two square feet
then at a seeding of every 4 inches in two square feet that will equal 36, sorry 35 plants that will die. That equals about 97% plant lose!!!$$$$
Now lets try three inches, thats 63 plants that die and that one that covers the two square feet and thats 98% lose.!!!$$$$
If you listen to the majority here, they say that they have huge lose and don't want to waste their money growing wild simulated like. They want to add fertilizers and fumigate the soil then spray the plants every time they think there is a disease present. This up keep is costly never mind the natural fact that the plant require at least two square feet to survive on, and 98% of their seed is fungal food after a few years.
Now... I got that out about right.
Listen it's childs play look at a ten year old plant, check out the soil and growing conditions ,take a soil sample of where the root grows. Go find a wild stand make note of the soil growing conditions and spacing of the mature plants then take a soil sample.
Now go and duplicate what you saw, or learned. You will get a sore back and maybe grow some callous, and in the end you'll spend less for a better return.