How much rain do you have right now? If there is more than 1 inch of rain per week, roses in pots will blackspot since there's not enough buffer to neutralize acidic rain. Rain pH here is 4.5, same with the East coast. To raise the pH by 1 point for a square foot (the surface of a pot), one needs 2 TBS of Garden lime (dolomite lime with 22% calcium and 12% magnesium). So to raise the pH from 4.5 by 2 points to 6.5, one needs 4 TBS of Garden lime per pot.

Calcium is best applied in small doses frequently (prior to a heavy rain), rather than a bunch at once. When the pH drops, all the major nutrients are NOT available, so no matter how much nitrogen is given, it won't be available. Granular Espoma products (Rose Tone, Tomato Tone, Plant Tone) are more alkaline fertilizers than SOLUBLE fertilizer. I always apply a few TBS of organic fertilizer with a few TBS of garden lime prior to a heavy rain. See below chart on how all the major nutrients are less available below pH 5. Click on pic. to enlarge:

Thank you for this tip. It hasn’t rained in over a week here in central NJ, so if overwatering is the culprit, I am the guilty one . . . I was shocked that the rose has been attacked so badly because it had very little disease last year.

Agree, overwatering can leach out nutrients. I elevated pots on wooden-planks, and found 1/8 cup of whitish powder oozing out from the bottom-holes. Nitrogen gets leached out 1st with frequent watering, then calcium & potassium & magnesium. Topping pots with slow-released organic fertilizer like alfalfa meal NPK 2-1-2 (has calcium & trace elements) help. I do that weekly if we have rain.

After 10 years of growing own-root roses in pots, I learn to be stingy in watering, just enough to wet the pot but not too much as to leach out nutrients.

Thank you again! I love the look of potted roses mixed in with plants in the ground and climbing roses and clematis. I also love that they’re elevated so they make a bolder statement and of course, they can be moved, which also makes me happy!

But I see that I have to be more careful with them.

Have you applied a fugicide?

Black spot for sure. Remove all the infecte leaves and canes, you can apply a fungicide or the baking soda mixture. I had iceberg in a pot last year, she would black spot all the time bc she was getting the harsh afternoon sun only.

I would move the pot to morning sun and afternoon shade so she is less stressed. Water well, fertilize and she will come back. stresse roses usually can’t fight disease as well as happy roses

My iceberg rose now in a happy morning sun space. No longer in pot! Good luck!

Forgot to say, remo all the dead leaves on pot and mulch! I always use compost to mulch...