Arugula

Sow seed a quarter inch deep and about an inch apart in rows, or broadcast it across a bed. There is no need to start it indoors - it germinates in soil as cool as 40F, so it goes straight in the ground as soon as the bed can be worked. Then sow a fresh short row every 2 to 3 weeks rather than one big planting. Arugula germinates in days in cold soil and is harvestable in about four weeks, so the whole crop finishes before summer heat arrives. Successive small sowings keep young mild leaves coming instead of giving you one flush that all bolts at once.

Keep the soil consistently moist, watering when the top inch is dry to the touch. Aim for steady moisture rather than a soaking followed by a drought, and do not let the bed sit waterlogged. Dry soil is one of the three levers, along with long days and heat, that flips arugula from making leaves to making a flower stalk. Moisture stress also intensifies the mustard oils, which is what turns a pleasantly peppery leaf acrid.

Once seedlings are up, thin gradually to 3 to 6 inches apart if you want full individual plants. If you are growing cut-and-come-again baby leaf instead, leave the planting dense and skip thinning. Every thinning is salad - do not compost them. Crowded plants compete for water and shade each other, and drought stress is one of the triggers that pushes arugula into flower. Spacing also opens the canopy so leaves dry after rain, which is what holds downy mildew back.

Look at the young leaves for tiny round shotholes and for small dark beetles that jump when you disturb them. On seedlings and transplants, act when you find more than about five flea beetles per plant or 10 to 30 percent of the leaf area is gone. The reliable fix is a floating row cover laid at sowing and sealed at the edges. Flea beetles overwinter as adults in leaf litter, hedgerows and wooded edges and move onto the first green thing in spring, and they are drawn hardest to the sharp mustard oils in arugula. A seedling has no reserves - beetles that would only freckle a mature plant can kill it outright.

Start once leaves are 2 to 3 inches long, usually 3 to 4 weeks from sowing. Rather than pulling plants, cut the stand about an inch above the ground with shears - it will regrow for another cutting in 5 to 14 days. Cut often and cut young. Cutting above the growing point leaves the crown intact to push a second and third harvest from one sowing. Frequent harvest of young leaves also delays bolting, since the plant keeps being pushed back into vegetative growth.

Once days run above about 85F, give arugula afternoon shade or run 30 to 50 percent shade cloth over the bed. Light shade will not stop bolting forever, but it slows it enough to be worth doing. Heat and long days together are what trigger the flowering stem, and reducing heat load is the only lever a grower actually controls in midsummer. Once the stalk is up, the leaves turn bitter and no amount of care brings them back.

Start sowing again once the worst summer heat breaks, and keep making plantings every 2 to 3 weeks into late fall as long as soil stays above 40F, the low end of arugula's germination range. Under a low tunnel or cold frame you can keep cutting well past your first frost. Arugula grown into shortening days and falling temperatures does not get the long-day, high-heat signal that triggers bolting, so leaves stay tender and mild far longer than a spring crop that is racing summer. A fall sowing can give you multiple harvests, running on until the plant finally bolts the following spring.

Arugula shrugs off light freezes on its own. When nights start dropping below freezing, put frost cloth, a low tunnel, or a cold frame over the bed. In a cool greenhouse or high tunnel a late-summer sowing will feed you through the winter. Arugula is hardier and faster than lettuce, so a few degrees of protection is the difference between a crop that stops in October and one that keeps producing for months. Cold also sweetens the leaves and takes the harsh edge off the pepper.