Lettuce bolting

Cited bolting and bitterness notes (pattern comparison only)

Separate source assertions — not a BioArva average.

• Clemson (South Carolina): their sheet links high summer temperatures with seed-stalk formation and bitter flavor. Pattern comparison only—not a confirmed cause for a given planting.
• Maryland Extension (Maryland): their sheet notes Bibb lettuce can become bitter in high temperatures. Pattern comparison only—not a confirmed cause.
• Clemson (South Carolina): their sheet distinguishes slow-bolting or heat-resistant variety categories. Type note only—no cultivar ranking, product, or promise.
• Maryland Extension (Maryland): their sheet lists slow-bolting, heat-resistant types, including oak-leaf types. Their sheet lists that category in the context of extending the lettuce-growing season. Type note only—no cultivar ranking, product, or promise.
• Maryland Extension (Maryland): their spring succession note describes using tall crops and trellises to shade late-spring lettuce plantings. Source-specific planning note—not a companion ranking or a BioArva calendar.
• Maryland Extension (Maryland): their sheet links increasing day-length and high summer temperatures with seedstalk formation and bitter flavor. Pattern comparison only — not a confirmed cause for a given planting.
• Maryland Extension (Maryland): their sheet notes crisphead (iceberg) requires a long, cool season and goes to seed as temperatures rise. Type note only—not a cultivar ranking, product, or confirmed cause.
• Clemson HGIC 1312 (South Carolina): lettuce does not tolerate hot weather on their sheet. Pattern comparison only — not a confirmed cause for a given planting.
• Purdue PPDL (Indiana): annual cool-season vegetables including lettuce will bolt as days grow longer in summer; their sheet links bolting with bitter flavors in the foliage and with hot temperatures. Pattern comparison only — not a confirmed cause.
• UMN Extension (Minnesota): when bolting, the plant sends up a flowering stalk and stops growing. Pattern comparison only — not a confirmed cause for a given planting.
• UMN Extension (Minnesota): these plants may bolt in response to long days, high light intensity, and heat; bolting causes extreme bitter flavor. Pattern comparison only — not a confirmed cause.
• UMN Extension (Minnesota): heat will slow growth and the leaves will become tough and bitter as the plant bolts. Pattern comparison only — not a confirmed cause.
• UMN Extension (Minnesota): multiple days of high temperatures (greater than 75°F) can cause lettuce plants to flower; this is often called bolting. Pattern comparison only — not a confirmed cause.
• Illinois Extension (Illinois): at high temperatures, growth is stunted, the leaves may be bitter and the seedstalk forms and elongates rapidly. Pattern comparison only — not a confirmed cause for a given planting.
• Illinois Extension (Illinois): some types and varieties of lettuce withstand heat better than others. Type note only — no cultivar ranking, product, or promise.
• University of Delaware Extension (Delaware): bolting is the term used for flower stalk formation in vegetables; bolting response may be related to temperature, daylength, or a combination. Pattern comparison only — not a confirmed cause for a given planting.
• University of Delaware Extension (Delaware): bolting in spinach, lettuce, and some radishes will occur naturally as days get longer (daylength effect). Pattern comparison only — not a confirmed cause.
• University of Delaware Extension (Delaware): high temperatures will accelerate bolting in spinach and lettuce; lettuce may also be induced to bolt just by high temperature stress. Pattern comparison only — not a confirmed cause.
• University of Delaware Extension (Delaware): late planting in others (such as lettuce) will contribute to bolting. Pattern comparison only — not a confirmed cause or a national calendar.
• University of Delaware Extension (Delaware): choose slow bolting varieties of spinach and lettuce. Type note only — no cultivar ranking, product, or promise.
• Clemson HGIC 1312 (South Carolina): many South Carolina gardeners find crisphead (iceberg) difficult to grow due to its lack of heat tolerance. Type note only — no cultivar ranking, product, or confirmed cause.
• Illinois Extension (Illinois): their sheet notes seedstalk formation is caused by a combination of long days, warm temperatures and age. Pattern comparison only — not a confirmed cause for a given planting.
• Maryland Extension (Maryland): their sheet notes leaf lettuce can be grown from March to December with a break in July and August. Type/season note only — not a national calendar or a confirmed cause.
• UMN Extension (Minnesota): even types described as slow to bolt may flower. Type note only — no cultivar ranking, product, or promise.