If you have an ailing houseplant and have done everything you can possibly think of to help the plant, but it still looks sick, suspect improper soil pH. Referring to the soil’s degree of acidity or alkalinity, a proper pH balance is vital to healthy plant growth. Many houseplant problems aren’t affected by diseases or insects or insufficient fertilizer. It’s actually soil pH problems—to acidic or too alkaline—that can cause plant demise. When pH is too low or too high in the soil, nutrients can’t release to the plants. So you could be fertilizing, but the plants aren’t getting anything to eat.

Soil pH in houseplants critical to plant health

Phosphorus is commonly hard for houseplants to pull out of soil. This nutrient requires a neutral pH in order to become available to plant roots. Plants won’t photosynthesize without sufficient phosphorus, which means they won’t root or flower. Chlorosis is another common pH problem. It is particularly a problem on citrus trees growing indoors. It’s actually caused by an iron deficiency, but often there is iron in the soil. The pH isn’t acidic enough to release the iron for the plant. Other nutrients that can become stuck in soil and cause imbalances and resulting symptoms include calcium, nitrogen and magnesium. Soil pH imbalance can also cause problems with soil microorganisms—all those little guys that help out and create a self-sustaining environment for your houseplants. Tip burn is another problem that can be caused by improper soil pH.

How to fix improper soil pH

So what do you do about improper soil pH in your houseplants? First, it helps to understand how soil pH works. It runs on a scale of acidity to alkalinity. The range is 0 to 14. Most soil pH comes in between 4 and 8. Neutral with soil pH is 7. Any readings above that are alkaline, and any readings below are acidic. Many houseplants thrive in the 6-6.5 range. Citrus and strawberries like it even more acidic—under 6. Some houseplants like the soil on the alkaline side. So it pays to find out what your houseplant requires. A point on the scale may not sound like much, but it is. It turns out that each point is exponential.

Test houseplant soil pH

Most potting soils start out at 7—neutral. But over time with fertilizing and watering, the pH will shift. Your best bet is to test your houseplant soil to see what you’re dealing with. Do this with a soil test kit or with a pH meter. To test, take a few samples from a pot so that you get a good overall representative reading. When using a soil test kit, always use distilled water, which is neutral.

Adjust houseplant soil pH

If you find after testing that your soil pH is too high (alkaline), use soil sulfur to bring the pH down. For soil that is too acidic, use horticultural lime. Follow directions when applying. Wait a week and retest to make sure that the pH is ideal.