Arugula, a popular leafy green, sometimes sends up a tall, woody stalk topped with small flowers. This common phenomenon, known as bolting, is a natural part of the plant’s life cycle. It signals a shift from producing tender, edible leaves to reproducing itself through seed. Understanding why your arugula is flowering helps determine what to do with the current harvest and how to prevent it next time.
What is Bolting and Why Does it Happen
Bolting is the plant’s transition from vegetative growth (producing leaves) to reproductive growth (forming a flower stalk, flowers, and seeds). This physiological switch is a survival mechanism designed to ensure the plant reproduces before environmental conditions become unfavorable. The process is rapid, often causing the central stem to elongate quickly, sometimes seemingly overnight.
The primary environmental triggers for bolting in arugula, a cool-season crop, are rising temperatures and increasing day length. When the average temperature rises consistently above the plant’s preferred range, which is generally between 45°F and 65°F, it induces thermal stress.
Arugula is sensitive to photoperiod, measuring the duration of light in a 24-hour cycle. As days lengthen toward the summer solstice, the plant perceives extended daylight as a cue to flower. This combination of heat and longer days overrides the vegetative state, prioritizing seed production. Stressors like insufficient or inconsistent watering can also accelerate bolting, convincing the plant that reproduction is necessary for survival.
The Impact on Flavor and Texture
The transition to flowering brings noticeable and undesirable changes in the leaves’ quality. The most significant change is an increase in the bitterness and spiciness of the leaves. This is a direct result of the plant concentrating defensive chemical compounds called glucosinolates.
Glucosinolates are naturally occurring compounds in all plants of the Brassicaceae family, including arugula. When the plant is stressed, it rapidly increases the production of these compounds. When the leaf is chewed or cut, glucosinolates break down into pungent isothiocyanates. This chemical defense mechanism deters pests but makes the leaves far less palatable due to increased bitterness and spiciness.
The texture of the leaves and stems also degrades. The central stem becomes tough and woody, and the remaining leaves grow smaller, thicker, and more deeply lobed. These leaves are less tender and feel fibrous, making them unpleasant in a salad. If a small, newer leaf tastes overwhelmingly bitter, the plant is past its prime for fresh consumption.
Salvaging the Harvest and Future Prevention
When your arugula bolts, you still have a few immediate options before pulling the plant entirely. Pinching off the flower stalk as soon as it appears can temporarily slow the process, forcing the plant to focus on new leaf growth for a short period. Harvest any remaining, smaller leaves that still have an acceptable flavor for immediate use. The small, white flowers are edible and possess a milder, peppery flavor, making them a suitable garnish. If you let the plant fully mature, it will form seed pods called siliques, which contain seeds you can collect to replant or allow to drop naturally.
Future Prevention
To ensure a continuous supply of tender leaves in the future, employ a strategy called succession planting. This involves sowing a small batch of seeds every two to three weeks, rather than planting everything at once. This practice ensures that even if one batch bolts, another young crop is always ready for harvest.
You can also take steps to mitigate the environmental triggers that cause the plant to bolt. When temperatures begin to climb, use a shade cloth to cover your arugula during the hottest part of the day. This can reduce the ground temperature and delay bolting by several weeks.
Consistent watering is also important to avoid moisture stress, which is a significant factor in triggering the reproductive phase. Planting heat-tolerant varieties, or planting earlier in the spring or later in the fall when temperatures are naturally cooler, will also help to prolong the harvest.