Normally you start cutting in the third year for a full harvest. That means you can cut all spears for about 6 weeks. Then you stop and let them grow.

I've grown asparagus for 35 years.
I've always picked every spear that was bigger than the diameter of a pencil. Some years, I can pick right through Sept. I don't ever let a spear go to fern during the time I harvest. It's a drain on the rest of the plant. The energy goes into the fern, making the plant think it's needing to store energy for winter, when in fact, there's a WHOLE lotta good eatin' left.
Asparagus has it's own mind. When a spear gets picked, the roots say to themselves..."WOW! Sumpin' happened, we better make another spear."
Experiment with one of your plants.

Thank you Forpityssake and laceyvail,

I already let mine grow into a rather tall and dense fern and have started putting small yellow flowers. Should I cut them back now or let the flowers finish and then cut them ? The variety is martha washington. I am thinking of cutting back at least 2 of the ferns.

thank you again for your input.

If they were mine...I'd be cuttin' 'em ALL off at ground level,now.

How big around are the stalks? How big around are the new spears coming on?

The stalks are(were) very good size. some of them bigger than the ones they sell in the store. I thought I should let the first one grow into fern so it feeds the later ones but reading your post, I realize I was wrong.

This morning I saw another one that was the size of a pencil - pretty thin compared to the ones that came out last month but I cut it off and ate it and it was delicious.

I think I will do what you suggested forpityssake and cut down the grown fern. They are the largest I have seen. More than 5 feet tall and still growing. My asparagus plants are righgt next to compost area and gets mostly indirect sun because of the fence on two sides except during summer it gets may be 2 hours of direct sun.

Good for you! I'm not one to TELL folks what to do with the asparagus, but...I do suggest things that I know work. They really do need more sun than what they're gettin', but...as long as they're alive...that's all that matters.

Glad ya liked that spear. You'll get more, once the roots get used to not having those nutient hogs attached.

Remember to leave the skinny-minnies for wintering over.

Suggestion...Pick the edible spears while the tip is still pretty tight... try to pick in the mornings...rinse in COLD water...and refrigerate for up to 2 weeks...in a loosely closed plastic bag.

ENJOY!

I've grown asparagus since 1979. What I was told and what I have done all these years is to either cut them off barely under the ground surface (about 1/2") with a thin, sharp knife, once they get about 8" high or so. I'm very careful not to cut any underground plants growing next to the one I'm cutting. Use a "stabbing" motion, rather than a "side swipe". Some break their spears off. Either works for me, unless the spears are "flexible" and hard to break off. I quit cutting June 1st and let the fern grow then. I was told it needed that to replenish itself for the next year.