The soil for arugula need only be moderately fertile, friable and reasonably well-drained; in many gardens, little or no amendment may be necessary. Plant seeds in either a band about a hand-span wide, or a small rectangular or square patch, and let your taste for arugula determine the space you give it. As always, careful seeding saves a lot of tedious thinning later on. Scatter or drop seeds singly over the area, aiming for roughly 2.5 centimetres between them, then cover lightly with no more than a half-centimetre of soil. Soil moisture or spring rains should be enough to push them through, but a gentle watering or two, especially on the morning of a warm sunny spring day, may speed germination.
How to thin
As arugula grows, there are several ways to proceed. For baby arugula, thin seedlings just a little, leaving four to six centimetres between them, and then harvest young leaves with scissors. Cut just above the crown, the young plants will grow new leaves that can be cut again. For full-sized plants and leaves, thin eventually to 10 centimetres and pluck individual leaves from the sides of each plant. A weekly soaking promotes lush growth and milder flavour, while a mid-growth drink of dilute fish emulsion will spur plants on.
Quick growing arugula is useable as small leaves in as little as three weeks. After 40 days the plants are full grown, and the window of harvest lasts another couple of weeks. The tastebuds know when the leaves are beyond eating. A small seeding every 10 days or so, until about the first of June, keeps a fresh supply coming along, and just after Labour Day is the time to sow again. Arugula revels in the cool damp days of fall, growing slowly and standing fresh and fine long after most of the rest of the garden has called it a season.