Sandy,
Dirt is a difficult one, unless it is sort of craggy. Dirt tends to be more 'rounded'. If you decide to use this also add pebbles or some crushed rock if you have it. Your stairs will likely be rustic and may not be durable for the long run, but fun for a little while.
Now about the rounded versus craggy. Cement is a 'dry glue' it does better if it has nooks and crags and sharp edges, as sand does to allow for it to adhere to all of the surfaces. After you have thoroughly mixed the dry ingredients, sand/cement/dirt etc then add water it hydrates the cement and bonds all the areas together. Dirt, dependent on where the area is tends to have more composted leaf and needle, and other organic material, bat, worm, slug, snake digested materials that as they decompose do not have sharp surfaces. The other difficulty with dirt is dependent on your area and either water run off or natural minerals in the soil you may find some area in your mix that 'harden' better than other, which could be decieiving.
But if you have a little extra dirt and some cement you can always try, if you have some saw dust and glue (Elmers, white, wood, or other) try adding that to your sample mix. If things are not anywhere set up in hmmm, say 6 hours, then I would not venture further with the stair idea.
Be creative,
Dena

Certain types of "dirt" have been used successfully in making concrete, but unless you have an analysis done by a lab to confirm the usability, odds are it will fail. It all comes down to the chemical content and unfortumately most dirt does not measure up. Even if you run a test batch that looks good initially, you could encounter serious deterioration over a fairly short span of time simply due to the chemistry being wrong. Commercial concrete production is a highly controlled affair and even then contaminants (often from the surrounding soil) can wreck the mix.

Graded sand is cheap & reliable. Personally, I'd stick with known quantities...especially for something like stairs.

Best of luck --- Tango

I would make a small batch and test it out. They made adobe for years so who knows. Make a few bricks with it, let them cure real good and then try soaking them in some water and see if they stay together.

good luck and let us know how it goes.

I have a whirly gig for drying washing i wanted to set it in cement on grass is this possible