Roses will uptake maximum nutrients when the soil pH is between 6.0 and 6.5. This reading changes in different locations of the garden. Other factors that change pH include use of chemical fertilizer and when the pH is tested, before, during or after the rainy season. West of the Cascades, the native soil tends to be acidic. (East of the Cascades the soil is alkaline) My Kitsap garden beds have had readings on October 2, 2016 between ph 4.5, pH 5.0 and pH 6.2. I applied granulated lime according to directions on the bag after these readings. You may have heard that lime is a slow acting soil amendment. I waited three months, until late December, to find pH in all rose beds to be pH 6.3 and pH 6.6.
I did not think this chart would project very well in the Rainier Room and even if it were projected, it seems to me to be something to study to fully understand.
I was moved to action this summer after reading a blog entry by my Minnesota friend Jack Falker pH of your garden soil is not uniform. pH is the amount of acid (H+) or base (OH-) in the material. Numbers 0 to 6.9 are acidic, with 0 being extremely acidic. 7 is neutral (deionized water). Numbers 7.1 to 14 are basic, with 14 being extremely basic (caustic and alkaline are also commonly used terms for basic). Although most references differ, roses generally enjoy a pH of 6.0 through 6.9, with about 6.5 being ideal. In other words, the soil should be just slightly acidic. For pH outside this range, the availability of nutrients to the plant is greatly affected. For example, at a pH of 5.0 or less, phosphorous is ‘trapped’ by aluminum ions and rendered insoluble which cannot be absorbed by the plant. In the 6.0 to 6.9 range, all nutrients are in a form that is available to the plant. The more basic the soil, the less nutrients, such as iron, nitrogen, and manganese, can be absorbed.
pH of the Native soil in my rose garden is within recpmmended range.