First, it is extremely unusual for the same disease problems to affect a whole range of different plants - they are typically very plant-specific (the exception being powdery mildew). Therefore, it is highly unlikely that the same problem is affecting all your plants and so the same blanket treatment will not help. It is of primary importance to get an accurate diagnosis of the specific problem for each plant in question and then utilize the appropriate remedy. Hopefully someone on staff at a better garden center can help or check out a Master Gardener clinic or your local extension service. Often, the incidence of a lot of plant problems is more culturally related than an actual disease issue - fix the growing condition and the problem disappears. Fungal issues like leaf spot are often related to weather, overwatering, watering at the wrong time of day (leaving water on foliage overnight), poor drainage, lack of air circulation or even proper garden clean-up and sanitation. And mulching in winter can help a lot - a good layer of mulch smothers fungal spores that can overwinter on the soil surface and prevent them from splashing up with rains and reinfecting. Your hydrangea issue is most likely cercospora leaf spot, a very common problem with a number of hydrangea types. If you read the attached info sheet, you'll notice that the condition is primarily due to cultural issues. Correct those and you will correct the problem. Here is a link that might be useful: Cercospora leaf spot.

Thanks to everyone here for all the great advise! Here's a company called Woodworker's Supply (woodworkers.com) website I found to purchase three types food-safe finishes. I also checked the John Boos Company which manufactures both residential and commercial butcher block and wood countertops and cutting boards for prices on their Mystery Oil and Boos Cream which combines mineral oil and beeswax, which is rather expensive, but the website has a lot of helpful information in their FAQ section. GENERAL FINISHES AND BEHLEN Salad Bowl Finish are formulated to create a non-toxic, food safe finish coating. Apply to raw wood, allow 6 hours dry time before recoating, then wait 72 hours prior to use. Pint, quart or gallon cans. Preserve™ contains a blend of oils from the meats of exotic nuts. Immediately safe upon application (made without toxic driers or solvents). 8 oz. squeeze bottle. Clapham's Beeswax Salad Bowl Finish is made with natural beeswax with oil and is perfect for use on cutting boards, cheese boards, fruit or salad bowls, toys, utensils and more. Ready for use immediately after application. Buffs to an elegant shine once it dries. 8 oz. container. http://woodworker.com/gen-fin-salad-bowl-finish-mssu-107-279.asp

The morning after I oil my counters (Black Venata), they always have that "mottled" look you describe. I just go over them one more time with a dry paper towel, rubbing fairly vigorously, and it smooths everything right out. Occasionally, I'll have to do this one more time in spots, but after that, it looks great for months. I'm honestly not a huge fan of the beeswax-oil combo, even though it does keep the stone looking darker longer. I have used it a couple of times, but I found it far more difficult to apply (even following all the softening suggestions here), and I didn't really like the feel of it afterward. I want to feel my stone, not a wax coating on it. Going over it with an oily rag is just so much easier. I just keep the rags in a ziplock bag and hardly even have to add oil any more. And, after a year and a half, I only need to oil every four or five months to keep it looking good.

Thanks, looks like the mineral oil used may be ultrafiltered and have things like dewaxing done, so it might be different from cosmetic grade mineral oil.