I’ve used pine needles for many years as mulch, especially for pathways, and it’s my favorite mulch. Better than wood chips, it’s clean and springy and breaks down slowly. It’s slightly acid but our soil is so alkaline that it rarely alters the soil. The reason why lawns and other plants don’t grow under pines is because conifers provide dense shade. But some plants do grow and thrive under pines.
If you hike our mountain trails, you’ll see Mahonia repens, or creeping grape holly, growing under ponderosas. They’re in bloom now with bright yellow balls of aromatic blossoms. This is a terrific native plant that blooms early and provides nectar for the first bees of the season. Mahonia repens often is used as a xeric planting. It is drought tolerant but will become tattered and frayed in direct sun. Plant it in shade and it remains pristine.
Compost, with acid remnants like coffee grounds and tea leaves, is the great neutralizer for our gardens. Nearly all the vegetables we grow prefer neutral soil. Extreme acid loving plants like azaleas and blueberries need a lot more acidity than is easy for us to provide. But in the world of agriculture, potato farmers in Centre, Colorado, will add sulphur to acidify their soil. Potatoes require a somewhat acid soil, otherwise they may suffer from something called scab.
What happens in our gardens is that roses and other somewhat acid-loving plants develop chlorosis, when the leaves turn yellow but with a bright green veining. Technically this is because they can’t take up calcium into their root system. But that’s not the real cause. We have lots of calcium and other minerals in our soil. It’s really because the alkaline conditions inhibit the ability of the rose to absorb calcium. Compost will help. You also can add a rose fertilizer that has a tiny amount of sulphur. Most rosarians resort to some kind of fertilizer that has this remedy. Working directly with sulphur is tricky. I’ve known experienced rosarians who have ruined their soil by tinkering with sulphur. In contrast, native plants that evolved in our soils don’t require any help at all. It’s only when we plant European or east-of-the-Mississippi plants that we discover our garden soil is not to their liking.
No matter what we do, our soil will always revert to its alkaline state. Our water is alkaline and humus eventually dissolves and disappears. So don’t worry about pine needles. Niki Hayden