Lettuce
Authority: University Extension Horticultural Research Tables
Lettuce germinates in cool soil, optimally 65-70 degrees F, sprouting quickly in just 4-7 days, and unlike most vegetables it tolerates partial shade well, needing only 3-4 hours of direct sun. Depending on the variety, from loose-leaf to head lettuce, maturity ranges widely from 40-80 days.
| Parameter / Specification | Standard Value | Unit |
|---|---|---|
| Optimal Germination Soil Temp | 65-70 | °F |
| Days to Germinate | 4-7 | days |
| Sun Exposure Needed | 3-4 | hours partial sun |
| Days to Maturity | 40-80 | days |
History & Origin
Lettuce is one of the oldest domesticated leaf vegetables, bred from the wild, bitter, prickly-stemmed weed Lactuca serriola an estimated 6,000 years ago. Egypt and the Middle East are the two recognized centers of its domestication, and the earliest evidence of lettuce as food comes from Egyptian tomb art dated to around 4500 BC.
Egyptian growers appear to have first cultivated lettuce for its seed oil, with leaf lettuce grown as a vegetable documented as early as 2500 BC. Over centuries of selection, Egyptian farmers bred the plant's natural bitterness down and its leaf texture up, producing the ancestor of the sweeter, softer lettuces grown today.
Varieties & Bolting
Not all lettuce types handle heat the same way. Ranked roughly from most to least resistant to bolting -- the process where rising heat and long daylight hours trigger a flowering stalk -- loose-leaf varieties hold out longest, followed by romaine, then butterhead/bibb types, with crisphead (iceberg-style) lettuce the quickest to bolt.
Once a lettuce plant bolts, it diverts its energy from leaf growth into the flower stalk, and the leaves turn bitter as a result -- there's no reversing it. Gardeners growing in warm climates typically favor loose-leaf and romaine varieties, or simply harvest lettuce young as baby greens before summer heat sets in.