Hi there,
I am a beginner player. Each game, after the first wave of migrants stes in, my plump helmet plot starts withering and goes empty after a while 
Does it happen because they eat the shrooms faster then my brewer can extract seeds, because I don't have bags to store the seeds, or else? Is there any possibility to prevent the dwarves from eating the helmets? I know it's possible to forbid them to cook the shrooms, but the problem happens even if I don't even set up a kitchen!
Suggestions appreciated 
3 Things come to mind :
1. Do you have enough dwarves doing the "Farmer job"
2. Do you have enough stockpiles and autoharvesting
3. Have you disabled the seeds in the kitchen tab ?
A workaround would be to dig down into the first cavern after that point every underground soil becomes a mushroom bearing soil