I suspect that too much water has created a fungal infection called anthracnose. Leaf edges turn black with some spots sometimes developing further in the middle as well. Blossoms are subject to infestation as well and can look quite ugly.

Colletotrichum gloeosporioides attacks leafs and blossoms during weather that is both hot and humid/wet. This disease is more common in plant nurseries than in homes but it does develop there too. Hard to say whether yours originated in the nursery or not though. Anthracnose overwinters in plant debris so replace your mulch and dispose of fallen leaves & plant debris in the trash (specially in the fall). Never water hydrangea leaves; instead water the soil. Improve air flow around the plant if it is crowded by other bushes. Suggested fungicides are Daconil, Cleary's 3336 or any others containing the active ingredients chlorothalonil or thiophanate-methyl.

This problem is a fungal infection and not caused by something in your soil. Alkalinity in the soil will only result in iron chlorosis spells. These are very distinct from what you have described above: the leaves turn yellow but the leaf veins remain green. No black spots there. Adding sulphur compounds will greatly assist. Nurseires also carry lots of liquid iron chelated products that can be used to ammend the soil with.

Acidification will be a process that you will have to do every year since soil has a tendency to return to its original state if left untreated. So prepare to ammend the soil yearly. Your first step should be to determine your soil's Ph Level. A soil test will supply this information. Then add appropriate amounts of aluminum sulphate (keep it away from azaleas and rhododendrons), iron sulphate, organic sulphur, flower of sulphur or elemental sulphur.

The link below takes you to a Clemson University Webpage. Table 2 will tell you how much elemental sulphur to apply per 100 square feet if you know your current Ph and know what Ph Level you want to get to. Follow any product's label directions and adjust Clemson's recommended amount downwards if your soil is sandy and up if it is clay.

Good luck, irishoney.
Luis

I have the same problem and I know it's my fault because I've been watering them almost daily since I got them a month ago. Since hydrangeas drop their leaves each year. Would it be concievable to say that if I remove all the leaves and mulch from under the plant and not mulch in the winter to allow the pathogens to overwinter will you get rid of the disease without using fungicides? The problem with fungicides I have are the fact that they remove all pathogens, as well as it really doesn't cure the problem. As mentioned management practices is what prevents the problem.

No. The fungal spores are all over by now. That includes the plant itself. Meaning stems above the ground for example as well as nearby shrubbery.

However, if you take those precaustions, you increase your chances of getting a smaller fungal event next year.

Try it and report back next year. Compare how many diseased leaves you now have versus how many in 2008.

Luis

Luis pr. This does make sense everything your saying but I will monitor and try to report back next season on what happens. The thing I was thinking about is the disease triangle that I learned taking a class on plant diseases. Though I'm not going to claim I'm an expert in anyway when it comes to plants. My specialty is disease in turf grass which I'm pretty good at dealing with.

But back to the disease triangle. What you need is for disease is first the plant which of course I do. Then you need the causal agent, which it appears I do and by the way I may have a different, less deadly disease called cercospora leaf spot which I'm going to try to get identified by my local extention service. The last part of the triangle being the enviromental conditions. Once those three parts are met you then have disease. Why I think I can fix the problem without the use of fungicides is breaking that triangle impoving watering next season by drip irrigation, cleaning dead leaves this fall and clearing old mulch out from around the plant and even thin out some of the canes to allow better air flow, that will take out the environmental conditions out of the triangle.

Do not forget that the plant can harbor the causal agent in the stems themselves over winter. When the plant leafs out in Spring, its new leaves will be exposed to those spores currently on the plant and/or nearby shrubs. Another example of this is blackspot on roses. But your measures will definitely help. I use drip on all my "part shade" plants and it has reduced the amount of fungal diseases (I have a nearby creek and neighbor's with pools, all of which provide ample moisture by themselves).

I have a pink flowering Hydrangea which has been growing in my garden for over 17years getting progresively larger each year despite some vigorous pruning. This year for the first time it it starting to show leaves with black tips which then start to wither and die. While the majority of the plant is fine and the flowers are superb, do you have any advice on getting rid of this for next year?