Arugula is a fast leafy green in the brassica family, grown for its peppery leaves. It matures in 30 to 40 days, tolerates light frost, and is one of the earliest and latest crops of the season. Gardeners value it for quick returns and repeated cut-and-come-again picking.
Direct sow a quarter inch deep as soon as the soil can be worked, a few weeks before last frost, and every two or three weeks after that until the weather turns hot; start again in late summer for a fall crop that holds into frost. Broadcast and cut at 3 to 4 inches for baby leaf, or thin to 4 to 6 inches for full plants. It takes part shade, which extends the season in heat, and wants steady water, since a dry spell makes the leaves hot and tough.
It bolts quickly in heat and long days, and the leaves turn bitter once it flowers, but the white four-petalled flowers are edible and peppery and the bees like them. Flea beetles pit the leaves in spring; a row cover at sowing is the fix. The wild rocket sold as arugula (Diplotaxis tenuifolia) is a different plant, slower, stronger and perennial.
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.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
Bacterial Soft Rot
Rhizomes turn mushy and foul-smelling; foliage yellows and pulls away easily at the base. Often follows borer damage or overly wet soil.
Cut away all soft tissue back to firm rhizome, let it dry, and dust the cut with sulfur. Improve drainage and avoid burying rhizomes. Destroy badly infected plants.
Flea Beetle
Alticini →Small round shot-holes scattered across leaves; tiny dark beetles that jump when disturbed. Heavy feeding stunts young plants.
Use floating row covers on seedlings. Remove crop debris and weeds that harbor beetles. Apply kaolin clay or spinosad if damage is severe.