Choosing Compost for Indoor Plants
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Plants rely on the right compost for growth. Learn about alkaline and acid composts and their impact on plant health.
TL;DR
Plants depend on the correct compost for growth. Alkaline composts contain lime, while acid composts are deficient in lime.
- Plants depend on the correct compost for growth.
- Alkaline composts contain lime.
- Acid composts are deficient in lime.
Plants depend largely on 1 the mixture they are potted in for the nutrients they need for growth. If they are not given the correct compost they will either fail to grow well or not grow at all. Plants that do not thrive may be growing in a compost that is too acid for them, or too alkaline.
Alkaline composts
In general, alkaline composts are those that contain large amounts of lime (also know as chalk). Chalk or limestone soils occur naturally in many parts of Britain, and chalk is one of the minerals added to both peat- and soil-based composts.
Acid composts
Acid composts are the opposite of alkaline ones, as they are deficient in lime. While most plants that prefer an alkaline compost will also do well in any fertile mixture, there are certain plants, known as lime-haters, that cannot grow in anything but acid composts. Ericas and camellias are good examples.
Testing compost
The acidity or alkalinity of compost is measured on a pH scale, which ranges from 0 to 14. A pH of 7 indicates that the compost is neutral — that is, it is neither acid nor alkaline. Composts with a pH below 7 are acid, and the lower the pH number, the more acid they are. Similarly, those above 7 are alkaline.
Most plants grow best in compost with pH of 6.5-7. Those plants that are lime-haters will eventually die in alkaline composts.
Using a soil tester
A pH meter is very easy to use. Simply push it into moist soil and the pH number is shown on the scale. Cheaper soil-testing kits are litmus paper. A little soil is shaken up in water litmus paper dipped in the solution turns either red (acid soil) or blue (alkaline soil).
Acid-loving plants
- Calluna (Ling, or heather)
- Camellia
- Erica (varieties of heathers and heaths)
- Gentiana (gentians)
- Kalmia (Calico Bush)
- Lapageria
- Lilium (lilies)
- Magnolia
- Menziesia
- Pernettya
- Rhododendrons (including azaleas)
Special composts
Some house plants cannot grow in ordinary soil- or peat-based composts, but need one with added materials such as leaf mold. They include cacti, bromeliads, orchids and insect-eating plants.
Bromeliads such as the Urn Plant (Aechmea fasdata) need a compost that drains freely and is also free of lime. They will thrive in a compost made of equal parts leaf mold and peat. Insect-eating plants such as the Venus Fly Trap should be grown in a compost with plenty of organic material such as sphagnum moss, or equal parts moss and peat.
Cacti
Cacti and many succulents need a well-drained compost of 1 part coarse sand to 2 parts soil- or peat-based compost. Commercial cactus composts are available.
Orchids
Orchids, like cacti, also need a porous compost and you can buy commercial orchid composts. A good orchid compost should consist of equal parts peat, sphagnum moss and osmunda fiber.
Plants depend largely on 1 the mixture they are potted in for the nutrients they need for growth.
More Information on Choosing Compost For Indoor Plants
Choosing the right compost is crucial for the growth and well-being of indoor plants. The composition of the potting mixture directly affects the availability of nutrients to plants. Failure to provide the correct compost can result in stunted growth or even plant death. It is important to understand the pH level of the compost, as it plays a significant role in plant health. Alkaline composts, which contain lime or chalk, are beneficial for certain plants. Lime helps to neutralize acidic soil and provide essential minerals. On the other hand, acid composts are necessary for plants that thrive in acidic conditions. These composts lack lime and are preferred by lime-hating plants like ericas and camellias. To determine the acidity or alkalinity of the compost, a pH scale is used. The scale ranges from 0 to 14, with a pH of 7 being neutral. Composts with a pH below 7 are considered acidic, while those above 7 are alkaline. Most plants prefer a slightly acidic to neutral compost, with a pH range of 6.5-7. It is essential to test the soil using a pH meter or soil-testing kits, such as litmus paper, to ensure that the compost meets the specific needs of the plants. Acid-loving plants like rhododendrons and azaleas thrive in acidic composts, while plants like calluna and camellias prefer neutral composts. Some house plants, such as cacti, bromeliads, orchids, and insect-eating plants, require special composts. These plants have specific drainage and nutrient requirements that ordinary soil- or peat-based composts may not fulfill. For example, bromeliads thrive in compost made of equal parts leaf mould and peat, while cacti need a well-drained compost with coarse sand. By understanding the importance of compost selection and pH levels, indoor gardeners can provide their plants with the optimal conditions for growth, ensuring healthy and thriving greenery in their homes.
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About the author
Rupert Foxton-Smythe is a seasoned horticulturist and avid plant enthusiast with over three decades of experience in the field of botany. As a leading expert at Houseplant Guru, Rupert brings a wealth of knowledge and a deep passion for all things green.
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