Potting soil is any substrate or medium where you grow your plants in containers or pots. Although different, it is used interchangeably with the term potting mix which is specifically a soil-less potting soil commonly used for house plants because of its light, weed-free, and less compacted properties. When your soil is good, your indoor plants can grow healthy, vibrant, and beautiful.
If you are a gardener, you should know that once you remove plants from their natural habitat and start growing them in pots, they become dependent on whatever nourishment and properties your potting soil can provide. But how can you be sure if the soil mix you have in your container is the best for your plant?
The first step is to know your plant’s original home. Can your plant be found on forest floors together with prayer plants and ferns? Does it grow on branches of trees like how orchids and air plants do? Is it similar to a cactus or other succulents which thrive well in dry and sandy deserts?
Do a quick research about it then we will guide you in selecting the best well draining potting soil for indoor plants.
Properties of a potting soil
The goal is to mimic the properties that can be provided by the natural growing medium of the plant. Forest floors that are covered heavily by shed leaves and other falling debris remain evenly moist through time and are rich in organic matter.
Branches of trees provide good support for the roots of climbing plants. Desert soil has good airflow, easily drains, and is low in nutrients. To break it down by components, good potting soil should provide you with the following:
Anchorage/Structural support
Good soil must allow enough room for roots to hold tightly so it can support a sturdy structure for the foliage or top part of your plant. This is not much of a concern for shallow-rooted plants such as ferns and other small plants that can grow on surfaces and even rock crevices.
Water retention
The roots must be able to absorb enough water to be transported to your plant’s body to keep them in shape and do their everyday activities. It also cools your plant so it will always stay refreshed during summer days.
Airflow
Roots also need oxygen below the ground so they can breathe and stay alive. These are provided by little pockets from your soil. When you overwater your plants, water fills up those spaces intended for air and drowns your roots. The same thing happens when your potting soil is too compacted.
Fertility
Like humans and animals, a plant needs nutrients to grow and develop. These nutrients are provided in both large and small quantities by your potting soil. The addition of fertilizers is often needed for potted plants as the soil does not have enough capacity to recycle nutrients the way it does in natural ecosystems.
Types of potting mix
Take note that the extent of each property varies depending on your plant species. Luckily, plants belonging to similar groups often have the same requirements. Below are the usual types of potting soil that can be bought from garden stores:
Seed-starting mix
The soil mix is used when germinating seeds or starting from leaf, stem, or root cuttings. This weed-free mix has good airflow and drainage to help stimulate the growth of strong roots. It is also sterilized to prevent the infestation from pests such as fungus and bacteria.
All-purpose potting soil
This product can be used for all kinds of potted and container plants whether grown outdoors or indoors. Enriched with fertilizers and with improved moisture-holding capacity, it is suitable for most applications including herbs, vegetables, and other ornamentals.
Indoor potting soil
Although all-purpose potting soil can be used in a wide variety of indoor plants, there is a mix designed specifically for houseplants. It is composed of peat, coir, perlite, slow-release fertilizers, and wetting agents in support of your plant’s growth and development for about 6 months. It does not contain compost or bark which can be a source of fungus gnats inside your home.
Orchid mix
Officially blended for orchids such as Dendrobiums, Phalaenopsis, Vanda, and Cattleya, it contains almost fine bark and wood chips. Other epiphytes including bromeliads also thrive well in this coarse potting mix.
Cacti and other succulents mix
This soil mix is best made for cacti, palms, citrus, and other succulents. It contains a large proportion of sand and perlite to ensure fast drainage and to prevent compaction.
See more: Soil for Growing Succulents
What Are Some Common Soil Amendments You Should Know?
A good potting soil amendment is any organic or inorganic material that you can add to improve the properties of your soil. Sold potting mixes are tested combinations of these materials with added slow-release fertilizers and hydrogels to hold a large amount of water then gradually release it into the soil. But if you want to make your own, below are the most commonly used amendments and its purpose:
Compost
This is like an all-in-one package improving your soil water holding capacity and oxygen penetration while providing enough nutrients to both indoor and outdoor plants. However, too much of it does not provide ample anchorage and can be a source of unwanted pests and insects you do not want to find in your homes.
Worm castings
As a safe and natural organic material, these “black golds” when added are a source of nutrients for your potting soil. This organic potting mix can be good for plants that are low feeders but not enough for other plants requiring a large amount of nitrogen such as your house trees.
Peat moss
These are partially decomposed materials harvested from sphagnum moss that lightens up your potting soil and improves its overall structure. It is also good for holding much water and nutrients. Some drawbacks are it is naturally acidic and the process of harvesting it from wetlands is not sustainable.
Coco coir
Similar to peat moss but more sustainable and inexpensive. Coconut coir is pH neutral and does not require the addition of lime to balance the pH. It also decomposes slower than peat moss so you are saved more time from repotting. However, it contains high salt and must be leached properly before use.
Wood chips
Can be used as mulch to prevent the growth of weeds while slowly providing organic potting soil matter as it decomposes. It also helps conserve water and in maintaining a relatively cool soil temperature especially for outdoor plants. Cons are it makes the soil acidic and consumes nitrogen as it breaks down through time.
Perlite
The process of creating perlite is like cooking popcorn. You get a volcanic glass and heat it until it pops. When added to potting soil, it provides good drainage and aeration. But handling these lightweight and white granules is a bit irking as it tends to float on water and the dust is toxic when inhaled.
Vermiculite
Overall improve the water and nutrient retention of the soil since it contains a lot of pores in its body. It also improves drainage and aeration but is not as effective as perlite. A little heavier than perlite, this brown-beige and sponge-like material does not contain asbestos and is safe for your lungs.
Sand
Coarse sand, although a bit heavy, is your cheapest soil amendment if you want to have a well-aerated and loosened potting mix. But don’t use fine sand as it gives you the opposite which is dense and heavy soil.
Selecting an ideal potting soil should not be that complicated once you get to know your plants fully. Aside from thinking about your plant and its preferred conditions, you can also try a lot of combinations that serve different purposes such as your watering habit.
If you water more often, then you can increase the percentage of coarse materials to improve drainage and to avoid rotting. But if you tend to water less, then you can add more materials that can retain moisture well.
Problems with potting mix
Decomposition
Although your soil does not tell you of its expiry date, all materials found in it decompose through time. As an effect, it reduces the available amount of nutrients, compacts your soil, and obstructs drainage. Slowly, roots are becoming suffocated due to lack of oxygen and your plants get sick under waterlogged conditions. Your plant is also becoming deprived of nutrients needed for its metabolic processes.
Acidity
One fact is that all potting mix becomes acidic with time, and the fertilizers you add speed up the process. Although some plants may thrive more in acidic conditions, levels that are too much can be harmful.
Nutrients such as nitrogen, calcium, and phosphorus are unavailable for plants’ uptake resulting in stunted growth, curling, and discoloration of leaves. On the other hand, aluminum and manganese become available in toxic quantities which impede root growth.
Salt deposit
Do you know what happens to the excess minerals you provide when you apply fertilizers? When water evaporates, white crystals or build-ups can be found along with your pots or sometimes on the leaves of your plant itself.
These are minerals like sulfates, nitrates, sodium, and iron which are added extra when you apply fertilizers or when you water your plants using tap water. Too much of it disrupts the flow of water in the plant’s system, adjusts the soil pH leading to unavailability of other nutrients and minerals, and of course, you do not want to see your plants with white build-ups. Using soil test kits can be very beneficial for your plants and garden.
Maintaining your potting soil
Replace your soil at least once a year
Changing your container to a larger one or simply replacing it with a new and fresh potting mix is needed by plants at least once a year. When your roots have grown through the bottom holes of your pot or you just noticed that your plants are growing slower than normal, your little companion might be sending you a message that it needs repotting.
Follow directions carefully when adding fertilizers
Not all fertilizers are the same. Some products contain high amounts of nutrients that are dissolved in water so that effects are immediately seen a day or two after application. Other kinds are formulated for slow-feeder plants like ferns which slowly release a small and steady amount of nutrients over time. The manner of application also differs from one another, and doing it the wrong way may deem your fertilizer ineffective.
Excessive application can bring more damage while too little application can deprive your plants of essential nutrients. Therefore, you must always consider the kind of fertilizer to be used, the timing of application, mode of application, and the amount to be applied when you feed your plants.
Flush regularly to remove excess salt
Your potting soil may harbor a lot of excess salt due to fertilizer application and frequent watering. This can be removed by flushing or leaching your potting soil with water every two or three months. Simply bring your plants to a sink or bathtub then give it a generous pour of water. Be careful not to let your soil mix overflow while allowing water to drain through the bottom holes. The initial watering should dissolve the salt, and the subsequent washes will remove the salt out of the pot.
FAQs
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