A good potting soil will provide your plants with nutrients and allow water to drain away to prevent overwatering. Use this guide to learn more about the different types of soil to find the best potting soil for your plants.
Potting Soil Ingredients
Different types of potting soils contain different ingredients. Most potting soils are a combination of pine bark, peat moss, perlite and vermiculite. Most are sterilized to kill microorganisms that could cause plant disease.
Potting soil is not really soil, as it does not contain humus or minerals. Some of the best potting soils contain fertilizer, but if your soil does not contain fertilizer, it is easy to add it.
Vermiculite is made from compressed minerals that expand when they absorb water. When vermiculite is dry, it looks like spongy flakes. When added to potting soil and the soil is watered, the flakes help retain water. Vermiculite also helps to aerate the soil so that it does not settle. Potting soils containing vermiculite work well for water-loving plants and for growing seeds.
Sphagnum peat moss comes from peat bogs. It is dried and often mixed with other organic materials. Sphagnum peat moss is mixed into sandy soils to retain moisture and into clay soils to loosen the soil and improve drainage. Sphagnum moss is also used as a base for hanging plant baskets.
Perlite helps aerate the soil, hold water and keep the soil from settling. It is made from superheated volcanic glass and looks like small white popcorn pieces. It is not recommended for cacti and most succulents or other plants that require relatively dry soil. Perlite is good for rooting cuttings because it increases the moisture around them by releasing water. It is also good for epiphytes, moisture-loving plants that need to dry quickly after watering.
Homemade compost can be made from brown leaves, untreated grass clippings, eggshells, coffee grounds, fruit and vegetable scraps and other organic materials. As these materials decompose, they add nutrients to the soil. They also help retain moisture and promote good soil microbes that help plants grow. Although compost contains nutrients, plants usually need fertilizer as well, depending on what you are growing.
You can buy compost, which is often made from wood scraps, such as fir bark. Commercial compost may also contain coconut fiber, pumice, sand, bone meal, feather meal, worm droppings, manure, and other organic materials.
What to Look For in Potting Soil
Potting mixes are often called potting soils. We will use both terms here, but they are not exactly the same thing. Some potting soils are actually soils, not mixtures of materials. They are not recommended for plants in pots or other containers. If you are growing potted plants, choose a product that is suitable for container or potted plants.
Also, look for potting soil that is loose and crumbly in texture. Heavy, dense potting soil can hold too much moisture, which means oxygen cannot reach the plant’s roots. This can lead to root rot and give mold the opportunity to grow. Avoid potting soils that contain large pieces of bark or wood.
Different Types of Potting Soil
Some potting soil mixtures are designed for specific types of plants, such as orchids or succulents. They differ in the type of materials they contain and their density.
All-purpose potting soil: This product is suitable for most indoor and outdoor container plants. It is generally the best potting soil for new container plants or those that need repotting. It may or may not have slow-release fertilizer (fertilizer that releases plant nutrition slowly over a period of time) and moisture control granules (granules that prevent overwatering).
Organic potting soil mixes: These are made from carbon-based materials such as worm droppings, manure, compost, bone meal, fish meal, and other previously inhabited items. If you grow organic vegetables or herbs in pots, you can add organic fertilizers to get the best organic soil for your edible plants.
Seedling Mix: This very fine, sterile, soil-free mix helps seeds germinate and cuttings establish roots. It is low in nutrients, which encourages roots to grow and branch out in search of food. Once seedlings and cuttings have a good root system, they should be repotted into a mixture that provides nutrients. Plugs and pellets are also available for growing.
Orchid potting mix: most orchids need good air circulation. They also need a substrate that holds moisture but drains quickly so the roots don’t get wet. Orchid mixes may contain fir bark, sphagnum moss, charcoal, coir fiber (sometimes called coconut fiber), perlite, or a mixture of these materials. Some orchid mixes are designed for different types of orchids, such as dendrobiums or phalaenopsis, also known as butterfly orchids.
Potting soil for cacti, palms, and citrus plants: The best potting soil for containers of cacti, palms, citrus plants, and succulents is a mix that drains quickly. Some potting mixes for cacti, palms, and citrus plants contain fertilizer. Some also contain sand, which improves drainage and adds weight so containers with large or heavy plants won’t tip over as easily.
Moisture-regulating potting soil: some potting soils contain moisture-regulating pellets without slow-release fertilizers. They usually contain more sphagnum peat, coconut fiber, and wetting agents than general-purpose potting soils to prevent over-and under-watering.
Outdoor potting soil: some of these mixes are labeled for use in indoor and outdoor container plants. They often contain aged wood fiber and provide plants with the same basic benefits they would receive under trees in a forest. Some have added fertilizers and moisture control granules.
Eventually, the nutrients in the soil will be depleted, causing your plants to “starve.” So replace your potting soil regularly or mix half of the old soil with fresh potting soil when repotting. You can also freshen up old potting soil with compost, vermiculite, and a slow-release fertilizer. Do not reuse potting soil if your plant has been sick or had pests.
Some soils are designed for specific types of plants. Others are designed for seed starting or rooting cuttings. Potting soil mixes are available with or without slow-release fertilizers and moisture control granules. You can add additives such as composted manure to freshen or enrich your potting soil mix.