Growing Ashwagandha

2 years ago I bought some ashwagandha seeds from Richters and planting them indoors in early spring and then transplanted the seedlings to a fairly large pot ( 1ft. diameter, 2ft deep ), putting it on the balcony for the remaining summer and early fall. the plants were watered well only a few times caught them wilting, recovering easily once watered again. The plants grew fairly bushy ( 3 ft. round ). However when I harvested the roots in the fall I noticed how shallow the roots and thin they seemed ( about 1/4" at top tapering to fine thread about 5" long altogether. The roots also seemed to have many very fine thread runners from the main. I am planning on growing more for this season on the balcony knowing the conditions are good, but am wondering what I might be able to do to make the roots much thicker and longer. Perhaps I did not thin out the initial seedlings well enough or even need larger pots?

I have a suspicion that you are a northern grower and not situated in the subtropical climate preferred by ashwagandha. It needs 8 months of growing to achieve its maximum size. It will show that it is mature by having the leaves start to turn yellow and the fruits will turn red.
To make sure that the plants do as well as is possible in your perhaps less than optimum climate, make sure that the soil you grow it in is a sandy loam with a pH of 7.5 to 8. Give the plants full sun if possible, but half shade will still get good growth, just not optimal growth. Keep the plants just barely moist, since they get lush tops and poor roots if grown too wet or in soil that is too rich. To try to get as close to 8 months growing period, you should start the plants indoors and maybe finish them off indoors as well. In the subtropics direct seeding in the second week of July gets an optimal crop, but not here in the temperate regions of the world. Planting them too close could also be a problem. Plant no closer than 15cm (6inches), since the plants will get to be 30cm (one foot) wide at maturity.