How can I make really slow particles?

I am trying to make a dropping leaves particle system, and I noticed I can’t use spawn values lower than 1.0. Value 0.8 worked, but when I get to lower ones such as 0.5 or 0.1 I can only see the results on the preview window, and in the game as long as I don’t push play. If I push play the particles don’t show up at all in game. Please help!

Hello are you referring to Cascade or Niagara?

Had to look it up, it’s cascade, but what is the difference? Could it succeed if I make it Niagara?