This time of year, my garden has lost it’s charm and beauty, but it’s filled with thousands of seeds from my hundreds of plants. While you could save the seeds in bags for spring planting or plant them in pots outside (see cold stratification), the easiest method I’ve found for my varieties is to just scatter the seeds in the garden this fall. This even works for some annual species. I frequently find zinnia, marigold, and salvia sprouting up from previous year's seeds.

First off, put on gloves – many of the seeds are very sharp and spiny. I then either gather the seeds by hand or use some hand pruners and cut them off. I then put all the seeds in a five gallon bucket. When I’ve gathered as many seeds as I want (always leave some for the birds) I go to the kitchen and borrow the blender and bring it out to the garage. (This process can be a little messy.) Then it’s a matter of putting small batches of seeds into the blender to break up the seed heads. As I take out the seeds from the blender I also strain them over a fish tank with a wire mesh. This way the seeds fall through and the large pieces can be picked out and put in the blender again.
(Also see Fish Tank - Other Uses)

At this point I’ve got thousand of useable seeds and can start spreading them around the garden by hand. You can also mix them with some top soil so they won’t blow away as readily.

For a couple of hours of work, you have the potential of hundreds of new seedlings for zero cost on your part. It doesn’t get any cheaper or easier than this method.