Need a little help here. What I want to do is make a long trough, above ground, deep enough for asparagus to continue to grow for at least 10 years. Don't know a lot about the plant other than it taste good and is very good for you. They say 2 years till the first harvest.
So this is what I'm looking for:

1. Width and depth of the trough
1a.Material, i.e. what type of wood that will not be adverse to the plant

2. Soil composition, sand, clay, moss

3. Full drainage or little drainage

4. Fertilizer numbers, 1st in the beginning, then after the
foliage development stalk numbers i.e.10-5-20

5. And if someone knows where to buy the best starter plants


Thank you in advance

Location: North Texas 30 mi from Oklahoma, north of Dallas