How long into the summer can you harvest it?
I can usually harvest asparagus for the entire month of May up here in Southern Wisconsin. Depends upon the Spring weather and warm up. It’s important to leave some so it can go to frond and put nutrients back into the root stock for the next year.
A top dressing of compost in the fall is all I’ve ever done for it, then some corn gluten in the spring to stop weed seeds from germinating. NOTHING gets weedier faster than an asparagus or strawberry patch!
My red Rhubarb is already peeking through! So, 4-7” of snow is on it’s way starting tonight, LOL! That’ll teach it! (Snow won’t hurt rhubarb.)