Q.Onions fold over and die
The onions are small and seem to have stopped growing. The tops fold over and die. The onion begins to grow a black mold on. What is going on?
Also, potato plants die. The potatos are fine, just the plant dies. What is going on here?
The beans continue to blossom but not produce. Help!

Certified GKH Gardening Expert
When the tops fold over, that means the onions are done growing. If the onions do not have everything they need to grow well, the bulbs will not form well and the onion tops will fall over anyway. For next year, see what you can improve for their care. Perhaps they did not get enough water or the soil may need to be ammended more.
As to the potatoes, the plants dying is a sign that the potato is also done growing and that the tubers are ready for harvest. With potatoes, if the tubers are fine, then there is likely not a disease. But if you did not get a good harvest, it may also be an issue of too little water or nutrients.
Both potato tubers and onion bulbs are energy storage systems for the plants. When people have excess energy (i.e. food) we get fat because our bodies are storing it. The same thing happens with potatoes and onions. The more excess energy they get from the soil and sun (helped along by water), the "fatter" they get. You get lots of nice big potatoes and onions.
As to the beans, it was likely a pollination issue. You should try to attract more pollinators to your garden. This article will help:
https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm