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Hardiness Zone: 9b
Gayle from Queen Creek, AZ
The stress of late summer heat can certainly take a toll on roses, especially in your part of the country. You didn't mention exactly what was happening with your roses before adding coffee grounds and Epsom salt.
What often happens when the summer heat sets in is that some of the lower leaves on the bush turn yellow and drop off. This is actually normal, providing the discoloration is uniform and the affected leaves are confined to the lower part of the canes that are closest to the ground. These leaves are older and their loss shouldn't be cause for concern.
If the yellowing of the lower leaves becomes more widespread and the yellowing discoloration extends to canes beyond ground level, then you may be looking at a magnesium deficiency (often corrected by adding Epsom salt).
I'm not certain if your roses are suffering from Black Spot or not. Because the leaves started to turn brown AFTER you added the Epsom salt and coffee grounds, you may have temporarily tipped the pH balance too far in the other direction.
Most soils in Arizona tend toward the alkaline side of the pH scale. I would have yours tested before you add any more soil amendments.
For now, carefully flush the soil with water to dilute possible salts (water from the ground). If you think your bush has Black Spot, remove any affected leaves (dispose of in the garbage) and spray the remaining leaves with baking soda or a fungicidal soap every 7 to 10 days.
Browning leaves can also be caused by salt burn, sun and windburn. Constant drip irrigation may be causing a build up of the salts left behind as the water evaporates. Try giving your roses a long deep drink at least once per month to help flush away salts from the root zone. Applications of gypsum will also help to remove the salt from the root zone.
Would it be possible to offer your roses some afternoon shade during peak summer heat? (e.g. a potted tree, a sun umbrella or a temporary shade screen?) Avoid applying too much fertilizer during the hottest weather (1/2 strength is best in your summer climate) and apply 3 to 4 inches of mulch around the base to help keep moisture in and keep plants cool. Be sure to rake up all dropped leaves in the fall to prevent the possibility of Black Spot spores overwintering in the soil.
Here in SE Idaho, I put coffee grounds on my roses with no problems - they LOVE the acid in these leftovers. I wonder if the epsom salts are what is causing the browning? I hope you can figure it out and salvage the roses.
I should have posted this all together, but here's a link I found about this very issue: forums.gardenweb.com/
Read down a bit and get into the part about how much to use. GL!
Roses need to be watered from the bottom and take care the leaves are not gotten wet. This will cause the black spots.
my brother was keeping his onion sets in coffee grounds and they kept dying & he couldn't figure out why until it dawned on him that, they always put table salt in their coffee before brewing. After they quit that they quit dying. If you do the same that might explain why your roses are dying. Table salt & epsom salts are not the same.