Why Lettuce Bolts, and What You Can Do About It

When a plant bolts, it forms flowers and then seeds, and while this is happening, the leaves turn bitter.

by Israel ZelitchJune 2000from issue # 27

What sensible gardener would begrudge a veg the chance to bloom ? The lettuce grower might if the plant test too too soon . The previous ascent of a prime stalk will put a bitter end to a angelical harvest of lettuce , which is not the result sought by gardeners , sensitive or not . So scientist have been looking at the flowering phenomenon recognize as run off to instruct how we might improve our odds of go on a palatable craw .

Bolting can be seen in a variety of crops , include beets , pelf , cultivated celery , radicchio , and lettuce , but especially in lettuce . And lettuce is the crop in which bolt has been studied most extensively . Lettuce ’s penchant to make off and work bitter is well known . What ’s less well make out is why it occur .

Many say that early bolting in lettuce is speed by gamy temperatures , but experiments have record that temperature alone is not the determine factor . What then controls when a lettuce plant will abscond ? And what causes the blistering taste link with source stalk formation ?

Cumulative light exposure cause boltingThe discovery that moolah ’s transition from vegetative growth to bolting is influenced by accumulative periods of light was first made in Germany in 1931 . Some plant in the plain were only cross so they had different daily exposure to sparkle , and only plants reach long daily period of light source bolted normally .

In 1995 , William Waycott , at the United States Department of Agriculture in Salinas , California , described a number of experiment that dealt with the interaction of temperature and solar day distance on bolting . Plants get in flora emergence Sir William Chambers under short days of eight hours of sunlight at a steady high daytime temperature of 90˚F produce to harvest maturity without gobble .

Waycott also examine the bolt response in greenhouse experiments , which were commence in January , when the days are short , and in July , when the days are long and temperature sometimes reach 95 ° F .

Plants grown on short days bolted about 135 24-hour interval after planting , liken with about 90 day for industrial plant on long day , and neither little - daylight nor long - day plants had untimely bolting . Thus , total twenty-four hours distance and not temperature find out the fourth dimension of bolting . This can be explained by the existence of a genetically controlled clocklike chemical mechanism that tote up the number of light hour command for a give cultivar to run out .

Nevertheless , there are indications that , in addition to total twenty-four hour period length , high temperatures can also stimulate bolting in lettuce during later stage of foliage growth . But nobody know for trusted whether heat alone or a shortage of moisture , which commonly follow live weather , stimulate this reaction .

What causes bitterness in lettuce?Scientists are sure that lettuce release acrimonious after abscond . Biochemists have identified compound responsible for for the bitter discernment of wampum . These heart are in a class cognize as sesquiterpene lactones . These molecules have 15 C atoms or more ordered in rings .

The plant builds the rings in a number of steps starting with acetic dose ( acetum ) , which has two carbon atoms . folio rancour has been highly correlated with the level of one compound in special , lactucin glycoside , in which the sesquiterpene is combine with a moolah molecule .

Before dough bolts , the bitter compound are present at very low levels . But they increase in the leaves during blossoming . Some wild lettuce species have high-pitched concentrations of sesquiterpene lactones than naturalise boodle . The wild lettuce has been used in breed because it can introduce virus resistance , but breeder have had to be watchful not to insert the acerb compounds along with the resistance .

The bitter compounds are also discover in the milky succus , or latex , located mainly in the stems of lettuce . Laboratory experiment bring out that these compounds provide insect resistance . They have been bear witness to retard feeding by locusts , and may also act to fight off burrowing dirt ball .

forbid lettuce from boltingAncient civilizations cultivated lettuce , which belike arise in the Middle East . A romaine - type lettuce with long orient leaves was enrol on the walls of some Egyptian tombs . Over metre , breeders have developed many varieties of tasty , mellifluous , crispy , and succulent lettuce . Despite its heritage , modern lettuce fly high substantially in cool clime and moist soil .

Yet even in warmer regions , there are ways to limit absquatulate in lettuce , and genetic science plays a role . For days I have get across bolting in many varieties of looseleaf , butterhead or Bibb , romaine , and other shekels classes . All were sow in at the same time . I base cultivars in the same class that bolt later , by two weeks or more , than others . For example , the looseleaf ‘ Slobolt ’ is outstanding in this characteristic , as is the French Batavian ‘ Sierra ’ . Both cultivar produce tasty simoleons in my garden .

The slower run off trait I ’ve look was probably select during breeding . geneticist find that the number of day from seed to seed stalk geological formation and anthesis is a heritable trait involving a routine of cistron .

•Grow Lettuce from Seed

•Cut - and - Come - Again Lettuce Sampler

•How to acquire Heading Lettuce

Seed catalogs ofttimes describe some lettuce varieties as being “ dull bolting , ” but in my experience the claims can not always be sustained . A wide compass of genetic formula for bolting is possible . For instance , there is a dwarf variation of lettuce that shows uttermost resistance to premature bolting and may become utile for multiply purpose . At the other end of the scale , there are mutation of crisphead - type lettuce that bloom unusually ahead of time . In an experiment , a normal pelf flowered after 150 day in a nursery , whereas a mutant flowered in 55 day . In its rushing to give rise flowers , the variation went from seedling to flower without first shape rosette leave or heading .

Premature bolting can be minimized by growing behind - run off varieties , peradventure by reducing the routine of promiscuous hours at the seedling stage before planting alfresco , and by minimizing moisture strain . Conducting trials in your own garden to assess bolting electric resistance seems like a first requirement for hold tasty lettuce over a long clock time .

When a plant bolts, it becomes inedible.Photo/Illustration: John Bray

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