My native soil is pretty acidic, but some of the plants I want to grow prefer a soil a little closer to neutral. So I try to make them a bit more comfortable by slightly adjusting the soil pH just around the particular plant.
What is the big deal with soil pH anyway? pH is a measure of acidity. Something that is neutral is a pH of 7. A pH below 7 means something is acidic, above 7 is basic. How acidic or basic a soil is influences how much of any given soil component is available for a plant to use – and different plants have adapted to different soil conditions. Some plants can adapt to a wide pH range and thrive, while others have more specific pH needs and tend to pout when they are not met.
An example of this is turf grass used in lawns. Many people in my area add lime to their lawns because the grass likes a higher pH than many of our native weeds. They are trying to give the non-native turf grass a “competitive edge”.
[I should mention that I do not do this because:
- I don’t care enough about turf grass to bother – it’s just way too much surface area, life’s too short and turf grass is too boring.
- I don’t want to douse my native acid loving plants with a bunch of lime they don’t want.
- My property slopes towards a storm drain that empties directly into our local creek system – I don’t want to add a high pH slug of water to the creek after it rains. (I don’t fertilize or treat my “grass” either for the same reason – plus #1 above.)
Consequently, I don’t have a “lawn” so much as a collection of green stuff that we mow. But I’m OK with that.]
I do have a few perennials I’m willing to fuss a bit for though.
I’ll be the first to admit that my approach is not based on a meticulous analysis. I have had my soil tested in the past and I know it is acidic. My approach is to try to nudge the soil closer to the plant’s preference just around particular plants. I can’t give you a detailed scientific analysis that proves what I do helps – all I have is my own observations of increased bloom, growth and winter hardiness.
I simply sprinkle a bit of horticultural lime around the base of my targeted, higher pH loving perennials. A good sized peony might get about 2 tablespoons. Then just work it in a bit, keeping it off the leaves. I generally add a bit of lime to:
Hellebore – they prefer a pH around 7.
Peony – their pH preference is 6.5 to 7
Lavender – they also prefer 6.5 to 7
Of course, the vegetable garden is another area that may need lime, but I need to have a bit of care there. Some of the organic matter I add (like cow manure and mushroom compost) can be a bit alkaline so you don't want to go too far adding lime.
I almost always add a bit of lime to my Cole crops (cabbage, broccoli, kale) because they like a higher pH and it helps prevent some disease. But I don’t lime my whole vegetable garden unless I get a soil test done to determine what is needed. It’s also important not to lime any beds that will be growing potatoes since in can contribute to potato scab.
Remember, it’s important to have some idea what your native soil pH is before you start adding lime. I’ll be putting up a post on soil testing soon.
If you'd like to know more about managing soils in your garden, Penn State Extension has a free publication called Soil Management in Home Gardens and Landscapes.