If planted from seed, the required "wait" before harvesting is 3 years.
However, it IS possible to buy "crowns" that are already 2 years old.
If you plant these crowns, you may take a few spears the following next year, but the suggestion is to wait 2 years.
After that, the harvesting is progressive, allowing for a longer harvesting season.
A good bed can produce for many, many years.
After harvesting is over, we just let it stand, water it occasionally,
cut it off at ground level in the Fall,
top dress with compost & mulch,
and wait for next year.
It had proved to be surprisingly easy with no pests, diseases, or special needs.
Our primary bed (shown in the photos) is 4 years old, and we started it with crowns that were two years old,
so we are at the maximum allowable harvest season of between 4 weeks - 6 weeks.
We are two weeks into that span, and are eating fresh cut Asparagus nightly.
We started with 10 crowns evenly spaced in a 10' X 4' raised bed, and that is now more than sufficient for 2 Asparagus Lovers who plan to eat it daily for a solid month.
Asparagus has proved to be very hardy, and self propagating through its own seeds.
We now have Asparagus seedlings popping up all over the garden.
Last year, we moved the seedlings to another dedicated bed that is doing well.
We also bought 15 more crowns (at WalMart!) of another variety (M. Washington) and started another bed along a fence line.
We are hoping to reach a point where we can look at each other and say, "Please, No more Asparagus tonight,"
but , so far, we haven't reached that point.
The only real problem we have with Asparagus is that we haven't found a really good way to preserve it for the rest of the year.