Seed in the huge bed

Hello, my name is Enrica I live in North Italy, I am new here and I am new to permaculture, it means that I am still learning, reading and understanding how to do a huge bed for my vegetable garden. The spring raining here in Italy is becoming more and more extreme, with heavy rainfalls, and I wonder how to saw seed in the sloping sides of the Hugelkultur bed if the rain is a mass of sudden water that remove the seeds up to the base of the bed. Have you suggestions on this matter? Or is the huge bed used for transplanting only? Thank you .....ciao

Heavy mulch and/or transplants!