When arugula sends up a tall stalk and produces small white or yellow flowers, it is undergoing bolting—a natural shift from leafy growth to reproductive growth. This signals the end of the prime harvest period. While the quality is affected, you can still harvest the leaves, though they will taste and feel significantly different. Bolting is often triggered by rising temperatures and longer daylight hours.
Why Arugula Quality Changes After Flowering
The change in leaf flavor and texture results from the plant redirecting energy away from generating tender foliage. As the arugula concentrates on developing the flower stalk and seeds, it mobilizes resources from the leaves. This causes the leaves to become thinner and substantially tougher, making them less desirable for fresh consumption.
The plant also increases its production of glucosinolates, the compounds responsible for arugula’s peppery flavor. After bolting, the concentration of these compounds rises sharply, leading to a much stronger and often unpleasant bitterness. This intense flavor is a chemical defense mechanism to protect the developing seeds. The resultant leaves are dramatically different from the mild, tender leaves harvested earlier.
Harvesting and Using Edible Components of the Bolted Plant
Even after bolting, the entire arugula plant remains edible, requiring only a change in harvesting technique and culinary preparation. The leaves closest to the base of the plant, or the smaller, newly grown leaves lower on the stem, retain a milder flavor profile than the large leaves higher up. Harvest these less-bitter leaves and use them quickly, as their quality will diminish as the plant matures its seeds.
For the older, more bitter leaves, cooking is the most effective way to mellow the intense flavor. Heat helps break down the glucosinolates, reducing the sharpness and bitterness. These leaves are suitable for cooked applications, such as being finely chopped and added to soups, stews, or sautéed with other greens.
Other Edible Parts
The flowers are entirely edible and offer a milder, slightly sweet, peppery flavor than the leaves, making them an excellent garnish. They can be sprinkled over salads or used to decorate savory dishes. After the flowers fade, the plant develops small, immature seed pods, called siliques. These siliques are often harvested when still green and tender and can be pickled to substitute for capers, providing a sharp, intense flavor.
Strategies for Preventing Arugula Bolting
To extend your harvest and delay bolting, focus on mitigating the environmental stressors that trigger the reproductive phase. Arugula is a cool-season crop that thrives in temperatures below 75°F, so planting in early spring or late summer for a fall harvest is recommended.
Stress from heat is a primary trigger, so providing partial shade during the hottest part of the day can significantly slow the process. Consistent and deep watering is another way to reduce stress, as the shallow roots of arugula are prone to drying out quickly. Applying a layer of mulch around the plants helps keep the soil cooler and conserve moisture, delaying the bolting signal. Finally, using succession planting—sowing a small batch of seeds every two to three weeks—ensures you always have young, non-bolted plants ready for harvest.