Two months before the final spring frost date, fill each cell of a plastic seed tray with sterile seed-starting mix. Moisten the mix with water and place two seeds to each cell. Cover the seeds with 1/8" of starting mix and moisten the soil again. Place the clear plastic cover over the tray to keep the humidity level high.
For endive seeds to germinate well and develop into healthy seedlings, the soil temperature should be kept between 55 and 70 degrees Fahrenheit. After the seeds germinate, use a grow light for 16 hours a day to nurture the seedlings. A sunny south-facing window can also be used. When the seedlings develop their first true leaves, feed with all-purpose water-soluble fertilizer.
Seedlings that have been grown indoors need to be gradually introduced to outdoor conditions. Place the tender seedlings outside in a shady spot for a few hours and then bring them back inside. Each day for the next week, leave them outside a little bit longer and expose them to a bit more sun.
When the plants are about six weeks old and well hardened off, they are ready to be transplanted in the garden. Work a generous amount of compost into the garden before planting. Gently remove a seedling from its cell and place it in a hole at the same depth it was in the tray. Space the plants 12" apart. Water well.
Endive matures in 65 to 85 days after planting. When the endive is ready to harvest, pick off only a few outer leaves at a time to ensure a continuous harvest. Endive bolts, or goes to seed, when temperatures rise. If a heat wave is expected, harvest the remaining heads for better quality.