Growers of blueberries, azaleas, rhododendrons, potatoes and conifers know their plants need more acidic soil, while artichokes, asparagus, broccoli, parsnips and sunflowers prefer more alkaline soil. But why? The “pHact” is, it’s not that plants crave or detest acid. It’s all about the microbes (as usual). The acidity of the soil dictates which soil microbes thrive there, which impacts the availability of nutrients to the plants. High pH levels limit the availability of iron, manganese, boron, copper and zinc. Potassium, phosphorus, calcium, magnesium and molybdenum are less available in low-pH acidic soils.

The microbes that gravitate to acidic or alkaline soil also produce secretions that keep their environment optimal. Most bacteria, especially the ones that enable nitrogen-fixing, prefer alkaline soil – they need pH levels of 7 or above. These bacteria secrete a slime that has an alkaline pH to help keep the pH high. Fungi, on the other hand, prefer acidic conditions, and they produce acidic enzymes that keep soil pH lower.

To help manage soil pH, consider adding one of our pH-adjusting ingredients to your custom fertilizer blend. Our Organic Limestone can help raise pH over time. For the opposite effect, our Organic Iron Sulfate can help lower the pH of alkaline soil. Optimizing your composting ratios can also help manage soil pH. If your plants favor acidic soil, you want more bacterial activity in your compost and should increase the proportion of nitrogen-rich “greens” in your bin. But if your crops prefer higher pH soil, you’ll want to feed the fungal population of the pile with more carbon-rich “browns.”

Don’t expect immediate and drastic results from any of these efforts, though – it takes time to make adjustments to soil pH, because all those microbial secretions try to keep pH in the range the microbes want, even if it’s not what you want. Of course, if you’re using natural and organic fertilizers and compost at all, you’re already ahead of the pH game. Organic matter in general encourages diverse microbial life, and diverse microbial life encourages amazing plant growth!