Cat Pee

I am excavating an area in front of my house where I had several Boxwood for many years....They started dying little by little and a local landscaper came over to help me figure out what was going on....We eventually realized that my two cats were going behind the shrubs and peeing in the dirt which was killing the plants....So, the Boxwood are now gone and I am excavating that area in prep for planting several beautiful "Quick Fire" hydrangeas that I recently purchased to put there....I am concerned about the condition of the dirt there and about putting the new shrubs into dirt that has been contaminated by significant amounts of cat pee....Is there anything that I can mix into the soil to neutralize the urine before putting the plant in????....I don't want to go to all this trouble of re-landscaping the area only to find the urine in the soil harming the new shrubs.....
FYI: I am going to spread "Cat Scram" all around the area once we are done to repel the cats from going there but I want to do what I can to fix the soil that has already been contaminated before I put new plants there....Any suggestions?????

This message was edited Jul 13, 2015 10:45 AM

I see this as a several part process:

1) remove the most contaminated soil. Dig a couple of inches or more into the worst areas.

2) Flood the area with lots of water to try to wash the remaining material deeper into the soil. If you can run a hose or sprinkler very slowly for several hours it may flush out a lot of the urine and salts from the waste.

3) Go to a pet store and ask for zeolite. This is a mineral used in aquarium filters to remove ammonia. Also, ask about activated carbon (they might also call it activated charcoal- either is fine) Try to figure out the most economical way to get a fair amount. I would spread it in the area, perhaps 1" deep or deeper and blend it with about 6" of existing soil. Another option is kitty litter. This is usually montmorillonite clay that has a high affinity for things like ammonia. An inch or 2 of this would probably help, too. Oil Dri is the same, or Safe-T-Sorb. If you use kitty litter, get the unscented, non clumping kind. Oil Dri and Safe-T-Sorb are automotive things.
Other sources: When companies install synthetic turf in a pet yard they put down zeolite to soak up the odor of the urine. This might be a cheaper source of a larger volume.
Montmorillonite clay is also used in ball fields, sold under the name Turface.
These materials act really fast. Give them perhaps a week just to be sure.

If you have more time, then I would do this:
Steps 1 and 2 above are optional.
Add lots of organic matter that is more brown material, not much green. When you are making compost the microorganisms need both carbon and nitrogen. The ammonia (urine) is a good source of nitrogen, and you are adding a fair amount of dried, woody based materials such as sawdust. Allow the microorganisms to work on the material for a couple of months. They will use up the ammonia and some of the minerals, and start making the soil really rich and ready for the new plants.
By then it will probably be too late to plant (winter coming on) so let it all rest through the winter, and plan on planting next spring.