All across the northern hemisphere, September is a time of change. Days start getting shorter, evenings get cooler, and the leaves begin their yearly change. Not only do these hallmarks signal that Autumn is fast approaching, but they also indicate walnut season is upon us.
Although black walnut trees provide delicious nuts, an unkempt walnut tree can cause ugly black and copper stains on your patio or driveway. Since you’re here, I bet you’re experiencing that right now! So, how do you remove walnut stains from concrete?
Use Granular Chlorine for Walnut Stains
Granular chlorine is your only option to remove the walnut stains completely from your concrete. While designed and typically used for swimming pools, granular chlorine is also a heavy-duty cleaner. While this sounds hard to believe, it’s backed up by Jay Hayek, a forester at the University of Illinois.
PLEASE NOTE THAT CHLORINE IS A HARMFUL AND EXTREMELY CORROSIVE CHEMICAL. TAKE ALL PRECAUTIONS WHEN HANDLING IT. MAKE SURE TO ALWAYS USE RUBBER GLOVES, RUBBER BOOTS, AND PROTECTIVE EYE GEAR.
Okay, with that warning out of the way, let’s walk through how to actually clean the stains from your concrete.
- Garden hose
- Granulated chlorine
- Spray bottle
- Mop bucket
- Bristly scrub brush
- Dawn dish detergent
Dampen the stained area with your garden hose, making sure to cover the entire stain. Do not over-water. You’ll know you added too much if puddles develop. If this occurs, simply allow the water to dry or mop up the excess with a towel before continuing.
Apply the Chlorine
Apply the chlorine granules to the dampened area. Using a spray bottle, lightly mist the granules without over-watering them. The chlorine will immediately get to work. Set a timer for 5 minutes and leave it alone until the alarm sounds.
Scrub the Area
While you wait, fill a household mop bucket with a gallon of hot water. Add four tablespoons of Dawn dish detergent and 2/3 of a cup of Borax. Mix thoroughly.
After the alarm sounds, dunk your scrubber in the mop bucket and scrub vigorously. Add more of the liquid mixture as necessary. The longer you scrub, the more effective this step will be. Rinse thoroughly.
Examine the Area
By now, your stain should be gone (or very close to being gone). If it isn’t, let the area dry thoroughly. Repeat steps 1-4 until you reach your desired results.
Prevent It From Occurring Again
Once the area is clean, you can apply a surface sealer to prevent it from happening again. However, if walnuts are a persistent problem on your patio / outdoor space, you have two other options that may be more effective.
- Call a tree service to remove the offending walnut tree.
- Apply a growth regulator to prevent flowering altogether (link).
A Different Approach
If you’ve done everything you can and the stain still refuses to go away, consider installing carpet directly over the concrete and simply hiding the mess.
Alternative Uses For Walnut Hulls
If you want to take a “glass half full” approach with your walnut situation, you might be interested in some other uses for the black walnut tree. If you’re going to keep the three and suffer through its annoyances, you could try to extract some benefit as well.
Surprisingly, some folks claim that walnut hulls have medicinal purposes. Many herbalists swear by black walnut hulls for the treatment of constipation, diarrhea, skin diseases, fungal infections, and cold sores. I don’t personally have any experience with this and I’d recommend you check with a doctor first before trying anything crazy.
My approach has always been composting the hulls and leaves while consuming the fruit within. It’s simple and low-risk, but still gives you something useful to do with the discarded walnuts byproducts!