I use city water on my roses; I know rainwater is preferred. Every so often I like to add some Lipton instant tea to the water(1/2 tablespoon to 1 quart of water-a weaker mix than I drink). This tends to keep my roses green and happy between fertilizer treatments. I think the makes the water more acidic and the sugar is a boost for the roses. This is only my opinion. Best yet the tea the roses do not drink is for me.

I've heard that Chamomile tea is excellent for preventing damping off in seedlings. It is also a concentrated form of Calcium potash and sulphur. I guess the sulphur would act as a fungicide. The calcium and potash would promote growth.

I wonder if it would have any effect against rose canker?

I don't think it would hurt to try it.

Im going to start tomorrow. I'll let you know how it goes

If you put tea on the rose leaves make sure not to use any sugar(sweeteners). Sugar will crystallize on the leaves. I only use tea(with sugar) at the roots and rinse off any foliage that gets wet.

I never water the leaves as Ive been told that this can promote fungus and other nasties. have I been told wrong?

I'm not afraid to spray the leaves on my roses when I think they need it. Today we enjoyed full sun all day. This evening I gave them a refreshing shower.

Never spray leaves in the full sun, that they don't like.

I will spray the leaves with a strong spray from the hose to knock off any insects such as aphids. I only spray in the morning though as leaving the leaves wet overnight can promote PM and BS. So long as you don't spray in full sun as cuyahogakid says.