The biggest factor that goes into germination is simply, time. Seeds of differing plant varieties germinate at different rates and that rate can be affected by your unique environmental factors such as soil temperature and moisture level. Some other varieties require sunlight to germinate, such as lemon balm and mint.
Generally, greens like lettuces, spinach, or kale are quick to germinate at 4-6 days. Herbs, like basil and dill, sprout in about 5-10 days. Root veggies such as carrots and beets germinate in 7-10 days. Fruiting plants like tomatoes and cucumbers vary widely depending on the variety, between 4-14 days.
Some of the fastest varieties to sprout are arugula, beans, and cucumelons. Some of the slowest to germinate are peppers, parsley, and eggplant, so be patient!
Watering your seeds every day to keep the surrounding soil moist is vital to the germination process. The moisture acts as an alarm bell for your seeds to “wake up” and sprout.