Last week I decided that I should probably start a few more to grow inside through the fall and into the winter.
Here's how it's done.
Take a whole celery stalk and cut it about an inch from the base.
Now take the base that you cut off and place it in a dish with a little water in the bottom.
Watch over the next few days and you will see it start to grow from the center of the base.
Next, you can plant your celery in either a pot of soil inside, or in your garden.
As for how long to wait to plant it in the soil, I have heard you can plant it after only a couple days of letting it sit in water. I waited a week before planting mine.