Not all houseplants like the same kind of soil. Along with moisture control and nutrient content, soil pH is important for keeping your houseplants healthy. Now, a lot of people use the recommended potting mix for that houseplant, never think about the pH, and have a ton of success. Many standard potting soil mixes for houseplants tend to have a pH of about 6.0, just slightly acidic. This is just acidic enough for most acid-loving houseplants and just neutral enough for houseplants that prefer a higher pH.
The Best Soil and Houseplant Care Practices
Most people who cultivate houseplants know about the differences between regular potting soil, fast-draining soil for succulents, and specialized mixes for orchids. To review this type of information, check out our main resource page for choosing the best soil for your houseplants.
You should also know that some houseplants like acidic, neutral, or even slightly alkaline soil. A mild deviation from the ideal pH will rarely kill a houseplant directly. It may result in lackluster growth, or it may be why a houseplant isn’t flowering. It can also make a houseplant more susceptible to pests and disease. Severe deviations can lead to serious disruptions in delivering nutrients or damage to root systems. Especially for long-term houseplant care, it’s important to have a soil meter that can measure pH and help you monitor the acidity or alkalinity of your potting soil.
How to Make Alkaline Potting Soil More Acidic
Depending on where you live, the mineral deposits in hard tap water can gradually turn the soil alkaline. (Water softener can be even worse as the salts that comprise these softeners are also harmful to plant roots.) Composting is another common cause. You can make your own potting mix at home, but composting can create a more alkaline potting mix. A simple solution is to add peat moss which will increase the aeration, drainage, and acidity level of the soil.
Another creative way to gradually increase acidity is to collect and use rainwater for your houseplants. Rainwater tends to be slightly to moderately acidic in most places. Finally, you can look for fertilizers and soil amendments that have been specially formulated for greater acidity.
How to Make Houseplant Potting Soil More Alkaline
It’s more common for tap water to increase alkalinity, but the composition of some tap water may instead leach more of the calcium and magnesium than other nutrients, slowly causing the soil to become overly acidic. Using rainwater with higher acidity levels is another possibility. Overuse of peat moss and other alkaline soil amendments could also be a contributing cause.
One quick way to increase the alkalinity of your potting soil is to add dolomite lime. However, some gardeners suggest looking for other types of rock dust with minerals that are more likely to benefit your houseplant. The benefits of rock dust may depend on how quickly the dust decomposes into nutrients that the houseplant can access. Seaweed is another popular choice to add nutrients and reduce acidity level.
Perlite and vermiculite are two soil amendments with pH 7-7.5 that can help maintain a growing medium with more neutral pH. The perlite is a kind of volcanic rock glass that is a superior aerator for fast-draining potting mixes. Vermiculite is a kind of clay that is also an aerator, but which retains more moisture than perlite.
Houseplants that Like Acidic vs. Alkaline Soil
Some finicky houseplants may need to stay within a narrow range for soil pH, but many popular types of houseplants are fine with slightly acidic soil and have a high tolerance for soil pH in general. Some exotic houseplants may also need unusually acidic or alkaline soil.
Houseplants that are known for liking more acidic potting soil include the azalea, hydrangea, parlor palm, camillia, amaryllis, and most varieties of orchids and cacti. Few houseplants prefer truly alkaline potting soil, but some plant types like neutral to very mildly alkaline potting mixes including the asparagus and maidenhair ferns, hyacinth, oxalis, and canna lily plants. There is no definitive chart for ideal pH soil conditions for every type of houseplant, but here are some of the useful lists we’ve found online.