Scallions are the quickest, most forgiving allium in the patch, ready to pull as slim green wands long before a bulb onion has even sized up. They tolerate crowding and cool soil with equanimity, and a pinch of leaves can be snipped without pulling the whole plant. The one rule: keep the row weeded, since the grass-like seedlings compete poorly early on.
The oniony scent of scallions confuses carrot fly and aphids hunting neighboring crops by smell.