Which vegetable spearheads the writing of a poem?

Asparagus.
Steamed or roasted. Plain or in the the company of --

asparagus salad with shrimp & almonds & olive oil & black pepper & lemon & tomatoes (if they be ripe) & depending upon the season either fuyu persimmons or manila mangoes

What connection between asparagus and the unwritten poem?

Anticipation. Looking forward with glee to the advent of plentiful asparagus in the markets. Knowing it won't be long and the waiting, rewarded. The mouth knows such things.

Sometimes there's a specific moment when you know the next poem will be begun. Sometimes with glee. Always with a sense of expectation.

For sure, dread in either asparagus or poem-making.

Asparagus. How does roasted asparagus mimic lines of poetry?

By form, asparagus is linear. Line-like. Roasted asparagus is sweet and soft -- unexpected. Poetry frequents the unexpected even when it looks mild on the page.