Answer: The acceptable pH range for all-around gardening is 6.2-7.2, slightly acidic to barely alkaline. This range provides the best mix of nutrients for most plants. A pH of less than 5.5 renders many plant minerals (nitrogen, calcium, potassium) required for healthy growth unavailable. Other nutrients (the same minerals that pose toxicity problems in humans?zinc, iron, copper, aluminum) become toxic when the pH approaches 5.0.
The only way to know with certainty whether your soil is too acidic is to test the soil. Soil tests measure the exact chemical composition of the soil. At a minimum, test pH levels when a garden underperforms and before preparing a new garden bed. Professionals recommend routine testing every two to three years, in either the fall or the early spring. Testing in the fall allows plenty of time to adjust the pH before blooming season.
Most Cooperative Extensions offer inexpensive soil testing and provide recommendations as well as personalized help. Soil types vary according to locality, and Cooperative Extension scientists are the theoretical and practical experts on local soil properties. They offer a wide variety of free and inexpensive community services--one of the best-kept secrets of the universe.
I'd recommend having your soil tested before adding lime. You may not need it.
You didn't provide too many clues on the fuzzy mold on the undersides of your camellia leaves. If it is a black mold that you can scrape off with your fingernail, it is sooty mold, which is quite common on camellias. It indicates the plant is hosting insects such as scale or aphids or even mealybugs. If the fuzzy mold is gray, it could be botrytis, which is common under conditions of high humidity and poor air circulation. I'd simply remove the affected leaves, not only to get rid of the disease pathogens but to open the plant up to better air circulation, as well.
Best wishes with your landscape!
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