There are several explanations why seeds don’t germinate once they are planted.
1. Insufficient soil moisture. The seeds did not have enough moisture to germinate, or shortly after, there was insufficient water to continue their sprouting.
2. The top layer of soil is crusted thus preventing the seedlings from emerging.
3. Incorrect planting depth.
4. Heavy rains that will wash the seeds away.
5. Seed are eaten by insects. Or, in the case of larger seeds like corn, they may be eaten by birds or even domestic chickens.
6. Old seed.
7. Damping off – this is a fungal disease which arises when the fungus is present in the soil and conditions are suitable for its growth – mainly over watering.
The problem also occurs when seeds are started in pots or flats, and the potting soil is contaminated with the fungus. Apply less water, keeping the soil moist not soaked and
use only a sterile potting mix and clean pots. The second planting of this seed should not be in the same location, since the fungus is still there; plant in a new area. Transplant vegetables that are well established and preferably from a different plant family, in the old location.
