Bunching onions, or scallions, are perennial alliums grown for their mild green stalks rather than a swollen bulb. They mature faster than bulb onions, tolerate cold, and can be picked over a long window, which makes them a reliable cut-and-come-again crop for a small garden. Pulled young they are the scallions of the market; left to thicken they make a leek-like white stalk.
Sow directly a few weeks before last frost, a quarter inch deep and an inch or two apart in rich, loose soil, and again every few weeks until late summer for a steady supply. They are shallow-rooted, so keep the bed weeded and the soil evenly moist. Pull plants as needed from the time they reach pencil thickness, or cut the tops an inch above the ground and let them regrow.
Established clumps can be left in the ground for years; they divide themselves into bunches, and you can lift and split them in spring or fall to multiply the planting. They overwinter through zone 3 and are often the first green thing in the garden. Let a clump flower and the white globes feed bees and hoverflies. Deer and rabbits leave onions alone.
Downy mildew
Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.
Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.
White Rust
Raised white to cream-colored pustules on leaf undersides, with yellow blotches on upper surfaces. Infected tissue may swell or distort.
Remove and destroy infected leaves. Improve air circulation and avoid overhead watering. Rotate brassicas and avoid planting in previously infected soil.
Onion White Rot
Yellowing and dieback of leaves, soft rotting at the base, and a fluffy white fungal growth with small black sclerotia on roots and lower stems.
Remove and destroy infected plants. Do not compost. Avoid replanting alliums in affected soil for several years and rotate crops. There is no chemical cure once established.
Onion Thrips
Thrips tabaci →Silvery streaks and stippling on leaves, distorted growth, and tiny pale insects hiding in leaf bases during hot, dry weather.
Spray plants with water to dislodge thrips, encourage predatory insects, and apply insecticidal soap if populations build. Keep plants watered to reduce stress.