Carpets are a magnet -- for red wine, ketchup, juice and, of course, dirt. Although a potting soil spill will take time to remove, you should be able to lift the stain. Potting soil should be easier to lift than mud because it has a loose, large texture and contains bits of perlite, a natural soil additive designed to keep the soil from becoming compacted and dense. Before you get started, allow the soil to dry. Surround the spill with a baby gate, an upturned laundry basket or some other barrier and allow it to dry for several hours or overnight.
Vacuum the area as soon as the potting soil is dry. Run the vacuum cleaner over the carpet several times to make sure you have removed as much as possible.
Mix a solution of 1/4 teaspoon of liquid dishwashing detergent with 1 cup of warm water in a spray bottle.
Spray the solution on an inconspicuous spot of carpet and leave it for an hour. Check the spot carefully to make sure the solution hasn't changed the color of your carpet. You can also use a commercial cleaner, but some carpet cleaning solutions may cause bleaching or discoloration. When in doubt, use plain warm water.
Mist the potting soil stain area lightly with the detergent solution. Allow it to sit for 10 minutes.
Blot the spot gently with a clean, white cloth. Spray and repeat until the stain is gone and your cloth comes back clean. Never scrub a carpet. Scrubbing makes the carpet fibers fray and unravel.
Wet a clean cloth with warm water and blot the spot gently to remove the soap residue. Repeat this several times to remove all the soap.