Abstract: This study was conducted to improve late and unsynchronized germination and emergence under stressful conditions such as thermo-dormancy in lettuce seeds. Thermo-dormancy becomes especially important when the production is based on direct seeding. Lettuce seeds were treated with PEG-6000 (-5.1 bar) or K3PO4 (1%) both at 15°C either in an aerated bubble-column (BC) or in petri dishes. Standard germination and emergence tests (at 20°C), emergence under stressful conditions (at 15 and 35°C), emergence in the nurseries and in the direct seeded field have all been conducted with treated seeds in comparison with the non-treated control seeds. K3PO4 applied in BC was the most efficient method in improving germination and emergence in all tests. Emergence rate (E%) at 20°C was considerably improved (91%) and mean emergence time (E50) reduced (2.74 days) by this treatment, which was 84.2% and 3.63 days in the control seeds, respectively. E% at 15°C reached 90%, while remaining 71% in the control. E50 was also improved by 1.93 days. The most notable results were obtained in E% at 35°C, which was 64.5% in the treated seeds, while being 1.25% in the control seeds. E% was not affected in the field trials by this treatment, while E50 reduced to 6.32 days, while remaining at 11.27 days in the control. Total yield was also increased from 17.50 kg/parcel to 19.29 kg/parcel.