We don't know where you are to have an idea what your outdoors conditions might be - you might want to add your zone - ie Z8 WA Coast

'Yucca' covers a lot of territory, there are many plants - do you know which one? Of the more common types:
Clothiers - Yucca baccata, filamentosa, and glauca, Sow at 71-75F for germination in less than 2 weeks

I just collected a ton of yucca seed from my uncle's plants. I wintersowed these common yucca two winters ago and had great germination.

In Arizona collecting wild seed I had better results planting them immediately.

Thank you all very much. I'm not sure of the name of my yuccas, but they have been growing for 5 yrs now.