All lettuce is open-pollinated.
1 gram packet sows 25 ft; 2 grams, 50 ft; 1 oz, 500–700 ft. Varieties average 875 seeds/1g pkt, or 1,750 seeds/2g packet.
Culture: May be started indoors in March and at regular intervals thereafter, or sowed outdoors as soon as ground can be worked. Many varieties won’t germinate in soil temperatures above 75° and most shut down above 80°. Where available, we present data here from a California germination experiment at 84°.
Hardy. All save icebergs tolerate heavy frost. Grow best in cool weather with ample moisture, many kinds suffer bottom rot and tipburn in heat; select summer varieties carefully. Use shade cloth to keep summer lettuce tender and sweet longer. Sesquiterpene lactones produced in the latex render lettuce bitter when it bolts.
Sow every 2 weeks for continuous supply. Lettuce will not head unless thinned frequently and ruthlessly to final distance of 1'. Heavy nitrogen feeders.
Minimum germination soil temperature 35°, optimal range 40–80°, optimal temperatures 70–75°. Emergence takes 15 days at 41°, 7 days at 50°, 3 days at 68°, 99% normal seedlings at 77° but only 12% normal at 86°.
Days to maturity are from direct seeding.
- BOR: Bottom Rot
- DM: Downy Mildew
- LMV: Lettuce Mosaic Virus
- PM: Powdery Mildew
- SC: Sclerotinia
- TB: Tipburn
- X: Xanthemonas
Pest: Aster Leafhopper (vector for Aster Yellows disease)
Cultural controls: control perennial broadleaf weeds near lettuce plantings, plow lettuce fields immediately after harvest.
Cultural controls: avoid mulch or nearby grassy areas.
Disease: Bottom RotDiseases:
Cultural controls: rotate with grass-family green manures, plant in well-drained soil or on raised beds, more upright varieties escape infection.
Downy Mildew, Grey Mold, White Mold
Cultural controls: rotation, reduce duration of leaf wetness, plant parallel to prevailing winds, use wide spacing, control weeds, use well-drained fields in spring and fall.