House plants are an important addition to the home, both because they add aesthetic beauty and because they have some positive effects on health. Several house plants thrive in imperfect indoor conditions and prefer a slightly acidic soil -- one with a pH which is less than 7 -- rather than a neutral or alkaline variety.
Increasing Soil Acidity
Acid-loving plants are those that thrive in acidic soil, a condition that often results in limited soil nutrition. Selecting plants that tolerate acidic soil is key to growing a healthy indoor plant. A number of additions can aid in creating an acidic soil, ideal for certain plant types. These products should be added carefully and adhere to manufacturer's instructions as closely as possible for best results. Granular sulfur is the least costly and safest product to reduce soil acidity, and is available from most gardening or home improvement stores. Sphagnum peat, aluminum sulfate, iron sulfate, nitrogen and organic mulch are all excellent additions to decrease soil pH. The amount required for use will vary greatly depending on the size and type of the soil sample and how much reduction in pH is required.
Houseplants for 4.5 to 5.5 pH
There are more than two dozen plants ideal for indoor growing in a soil pH of 4.5 to 5.5, according to Colorado State University. Among the most familiar are hydrangeas, a plant which is widely used in landscaping with large, clumping flowers common in the cut flower industry. These flowers are notable because of their occasional color change, due largely in part to the acid content of the soil. White flower might turn green, while pink flowers will occasionally change blue. Additional options for growing indoors include the azalea, begonia, amaryllis, zygocactus (Schlumbergera bridgessii) and African violet (Saintpaulia ionantha) among several others. Each has its own growing, watering and sun exposure needs.
Houseplants for 5.5 to 6.5 pH
The 5.5 to 6.5 range is an ideal option for a number of plants thatl thrive indoors or out. Among them are the daffodil (Narcissus), a spring-blooming bulb which is part of the Amaryllis family. It is a hardy flower that is fairly easy to grow and a good choice for novice gardeners. These flowers prefer partial sun or shade, and have moderate water needs and do best in moderate temperatures with a loam soil. Additional options include the gladiolus, iris, tulip and hyacinth (hyacinthus).
There is a very wide range of soil acidity, and a wide variety of indoor plants which will thrive at different levels. It is important to make a selection based on the soil that is available, or be able to work the soil until it is an appropriate pH. There is a wide variety to choose from since several whole families of plants, dozens of species in some cases, each favor acidic soils. Several members of the Platycerium fern family as well as the coffee fern (Pellaea andromedifolia) all thrive in acidic soil and will each grow to feature a different size, shape and overall look. The Vanda plant genus, which features a number of brightly colored orchids, as well as several members of the saxifrage genus are all ideal choices for growing indoors with an acidic soil.