Guest Author - Charity Armstrong
Whether you’re just a rose gardener or you have other types of plants in your garden as well, knowing your soil ph is very important. Soil that is too acidic can cause problems for your roses as well as soil that is too alkaline. In order to help you better understand how soil ph works, I’ve covered some basics below.
The ph scale ranges anywhere from 0-14, with 0 being the most acidic and 14 being the most alkaline. The middle number or 7 is considered neutral. Most plants like a somewhat acidic soil and generally need a ph between 5.5 and 7 for healthy growth. The best ph for roses is around 6.5, but anywhere between 5.5 and 7 is acceptable.
What do those ph numbers mean? Ph is measured on a Logarithmic Scale. This means that each whole number in the ph scale is ten times higher or lower than the whole number above or below it. An example would be that a ph of 5.5 is ten times more acidic than a ph of 6.5. While a ph of 5 is 100 times more acidic than a ph of 7.
Every gardener needs to be aware of their soil ph. Nothing is worse than putting in a bunch of expensive plants and having them die or become ill due to soil ph. If your soil is outside of the preferred range your roses will have difficulty taking up phosphorous and other nutrients. This will cause yellowing of leaves, then browning and can eventually lead to death.
So how does one test for soil ph? You can do one of two things. Your first choice would be to take samples from the area you want to have tested. Scoop soil up from three different areas of the bed and place it all into a clear zipper bag. You could then take it to your local Master Gardener office or a garden center that offers soil ph testing. Generally soil testing is free. Master Gardener offices have high tech equipment that gives a very accurate reading.
The second option is to purchase a home soil ph test kit or soil ph testing strips from a local garden center. The tests you perform won’t be as accurate as the results from your Master Gardener office, but they’ll still give you a good enough idea of your soil ph. I inquired as to the price of my county’s Master Gardener soil ph testing equipment, thinking I’d purchase a model to use at home, and was told the machine was about $800! I then decided the test strips, which usually cost around $10, would be good enough for at home use.
Now one way or another you’ve tested your soil. Once you have a ph number, unless it’s more than .2 points off the 5.5 – 7.0 range, I would attempt to bring my soil closer to neutral by adding organic matter. This could mean anything from compost or shredded leaves to using mulch. If your ph is very far from desirable you should apply either elemental sulfur to lower your ph or lime to raise your ph. This will generally need to be done for several years on a consistent basis each spring.
Once you know your current ph and where you want your ph to be, you can either call your Master Garden office or find a table on-line that will tell you the exact amount of sulfur or lime to apply per sq ft to raise or lower your ph. Make sure you know the exact amount to apply. Simply throwing down sulfur or lime, without knowing the exact amount you need, is likely to make your plants ill.
Changing your soil ph permanently is a slow process, the effects of sulfur and lime only last about a year. The best way to change your soil’s ph permanently is by adding lots of organic matter, along with sulfur or lime each spring. Eventually the organic matter will change your soil’s ph so the sulfur and lime become unnecessary. If excellent soil with the correct ph is a goal for your rose garden, it can be achieved, simply incorporate organic matter season after season.