The Secrets of Potting Soil: Ingredients to Look For!

Why is Soil So Important and Specific

Potting soil-its secrets are in the ingredient list on the bag! Don’t overlook them. A plant in a pot has special requirements, it is not in its natural environment. First, it needs water, oxygen, and nutrition, and to have its roots anchored. Also, a potted plant requires some special features in the soil it grows in and that medium may not be soil at all. Here is how to choose the soil and why It’s important to read the ingredients on the bag before you buy.

“Garden making, like gardening itself, concerns the relationship of the human being to his natural surroundings”

Russel Page (1906-1985) International Garden Designer

How Everyone Can Garden

Growing plants in pots serves to increase the number of people who can garden. You don’t need space, plenty of time, or vigorous good health to get in the game. In addition, gardening in pots can give us all more opportunities to interact with nature than we might otherwise have.

The Secrets of Potting Soil: Ingredients to Look For

Once you check the ingredients list when buying soil for your plants you will understand the features you need for your containers or your garden beds.

But What Is The Difference Between Garden Soil And Potting Soil?

Garden soil is topsoil (the top layer of soil on the ground below your feet). It is then enriched with organic material to make it nutritious for your plants. First. lift a bag of it; you’ll find it is much heavier than potting soil and will hold water longer. Next, look at the price tag, it should be cheaper because it does not contain the expensive materials (see the list below) that help potting soil to drain successfully and not become compacted. Now compare this to potting soil.

Try this for more detailed information: ‘Learn the Secrets of Good Soil and How to Make Your Own.’

Important Features Of Potting Soil

The best material for plants in containers is sold under these names: Potting Mix, Potting Soil, or Potting Medium. It often does not contain soil at all. In addition, the best media for planting in pots is light fluffy, offers nutrition, and preserves air spaces to give oxygen to the roots, and maintains moisture. Pots can dry out fast! This is even more important if you have a hot, dry summer.

The Limitations Of Growing Plants In Containers

Our greatest challenge in growing plants in pots or containers is that the soil we use cannot regenerate. This means that the potted plant is unable to stretch its roots out to find more nutrition, water, or oxygen further underground. The plant lives entirely on the soil we provide it.

How To Read The Labels On The Potting Mix Bag

A careful reading of the labels on the bag of potting mix will help you get better results in the planter. It’s a good idea to lift the bag. Lift a bag of nearby topsoil. Again, it should be heavy-it’s dirt! The bag of potting mix should be much lighter. It should feel fluffy. If it is weighty, it is likely waterlogged or has too much soil or sand, which are less expensive materials. Once planted and watered it will become compacted and starve the plant’s roots.

The labels tell you what you are growing your flowers or your food in, they will have instructions for use and, importantly, they offer ratings that tell you how well the product is made.

What Should Be In Your Potting Soil 

The 5 Categories of Ingredients To Look For And The Percentages Of Each You Should Find.

Material To Hold Moisture And Nutrients

Peat Moss

1. About 15%-40% of the bag should consist of something to hold moisture and nutrients. Sphagnum Peat Moss holds several times its weight in moisture and releases that moisture to the plant roots as needed. It also holds onto nutrients so they are not rinsed from the soil when watering the plant. It is brown like soil, but the texture is yielding in your fingers.

 It is a little hard to get it wet, but it holds water like a sponge when it is wet. It is slightly acidic, which is good for plants like hydrangeas. Acid-loving plants can grow in it alone.  For most plants, it is mixed with other ingredients. It is made from sphagnum moss and is harvested from bogs.

Coir

Coir pronounced “core” which is made from coconut husks, has many of the same features and serves the same purpose. It has a neutral pH, and high levels of soluble salts, and potassium.

Use only products labeled as horticultural coir, which has been aged and buffered. This can reduce the quantity of salts and potassium. Potassium can be great, but too much can cause mineral deficiencies like Magnesium deficiency.  

You will often find this sold in a brick form, which you soak in water. It will produce very small soft pieces. This is because coir is made from the fibrous husks of the inner shell of a coconut.

Advocates of both products will emphasize sustainability issues with the other product. It’s a little more complicated than this. Read up on these issues and make your own decisions.

Compost

2. 20%-50% is Compost, which is decomposed organic matter.  Compost is rich in nutrients; it feeds the plants, helps the soil to hold water, and promotes soil microbes. It is the nutrients in compost that ensure the plants will grow. (Soil microorganisms digest organic matter, provide nutrients, and improve soil structure; they include bacteria, viruses, fungi, and parasites.)

Compost can be made using green materials such as lawn clippings and discarded food products. It can include brown materials, such as twigs and dry leaves. Aged manures can include animal, worm, fish, or seaweed products, and the operative word here is aged. An additional benefit is that we are reusing these waste materials.

How To Get Lightness, Aeration, and Water Retention

3. 20%-25% of potting soil is from an element used to provide lightness, aeration, and water retention. In this category, you will find the following on the list.

Perlite or Vermiculite?

Perlite: This is a form of volcanic glass which is mined all over the world. Perlite expands when heated and you see it as tiny white specks which look a lot like broken popcorn. It is naturally sterile and has a neutral pH.  You will also notice that perlite is incredibly light in weight, about 5-8 lbs. per cubic foot. It has tiny cells that absorb moisture to its exterior. This is very useful in getting moisture to the plant roots. Perlite can be dusty to handle. It will improve soil aeration, lighten the soil, improve drainage, and also provide the plant’s roots with oxygen.

Vermiculite: This product is similar but has some significant differences. It is made from silicate material and when heated, it produces little accordion-shaped chips. Vermiculite is a golden-brown color and is best used for plants that require soil that remains damp. Vermiculite will act like a sponge, absorbing more water than perlite. It does not aerate the soil as well and it provides less oxygen for the plant roots.

How To Choose Between Them?

When to use each one? If the plants like to dry out between watering, perlite is good. If they need continuous moisture, vermiculite is your choice. When shopping, look for white specks if you want perlite, and gold specks for vermiculite.

Some Potting Mixes Contain Fertilizer

4. Some potting mixes have fertilizer added to them. Read the label because there are two types and they will perform on different time schedules. The potting mix may have a starter charge of fertilizer. This will be used up after the plant has been watered about two or three times. Alternatively, there may be a slow-release fertilizer; expect this to last about a month. Begin your own fertilizer plan, after the included fertilizer is used up.

Caution: Damaged Bags

If the potting mix in the bag gets wet the fertilizer can release in the bag and burn plants with too much nitrogen. If you sense, in the store, that the product inside the bag is wet or the bag is torn, skip it.

Forest Products

5. Forest Products: These are aged and composted. The ingredients might include Pine Bark sawdust, shavings, and wood chips. What do they bring to the job? The little bits of wood in your Potting Mix are small but bigger than soil particles. This prevents compaction, it will allow air and water to penetrate. The wood itself contains microorganisms and helps feed microorganisms in your soil.

Organic Potting Soil

Organic fertilizers (those from plant and animal origins) have advantages if you are growing vegetables. They add organic material to the soil and support microbial life in the soil. These would include Blood Meal, Compost, Bat Guano, Manure, Seaweed, and Worm Castings.

How Do I Know That I Am Buying Organic Potting Soil?

Look on the bag for the ‘What’s on the Label section for OMRI certificates’ on the bag. OMRI (Organic Materials Review Institute).

Look For Local Potting Soil

Planting material is heavy to transport; you will notice that all these products tend to be locally made. This means that the same product sold in different parts of the country will have local and slightly different ingredients. Seaweed is cost-effective and sustainable in Florida, not quite so much in Iowa.

What’s on the Label:

Reading the label on the bag and the manufacturer’s instructions will provide you with valuable information. The bags, however, are usually opaque, which means you cannot see the actual product until you have opened the bag at home. (Some brands offer a refund; check the bag.)

Look for symbols on the bag. These will provide some helpful external reviews of the products inside. Check for these:

Mulch and Soil Council Certification is an industry group with a product certification program. The products have lab tests, chemical tests for CCA-treated wood contaminants, and random tests at retail locations. The focus here is to ensure that what it says on the bag is in the bag.

OMRI (Organic Materials Review Institute), Potting Soils, fertilizers, pesticides, and herbicides are not certified organic.  They can be “approved for organic production”. This is marked by a logo on the bag and you can also search the OMRI website for a specific product.

Potting Mixes for Specific Purposes:

African Violet Soil

African Violets are sensitive to changes in soil content and ingredients. They perform best in bright, warm, and humid conditions but will not accept poor drainage. A German explorer in eastern tropical African forests discovered the plant. The climate in which each plant originates is a good indicator of its requirements. An ideal combination of ingredients for African Violets is as follows:

• 50% Peat moss
• 25% Vermiculite
• 25% Perlite

This will fulfill the plant’s need for well-drained and aerated soil that retains water and oxygen.

Indoor Plants

Mixes for Indoor Plants: A good indoor mix needs to absorb moisture very well and resist compaction. Look for ingredients composed of peat moss, vermiculite, and perlite. The downside is that this medium tends to dry out more quickly and, unless compost is included, provides no nutrition. You will need to provide a steady supply of fertilizer as well as regular water.

Starting Seeds

Mixes for Seed Starting material must be very light and have a high capacity to hold water and air. The mix must be free of disease and weed seed and, therefore will be soilless. You will see coir, perlite, and perhaps compost on the label.

As seeds contain their own nutrition, seed starting mixes are customarily soilless. They are often sterilized, which is desirable as it will ensure no contaminants or pathogens in the mix. Seed starting is rewarding but has risks and sterilized mixes reduce the odds of failure.

Cactus And Succulents

Mixes for Cactus and Succulents mix will include elements like coir, perlite, pumice, sand, and stalite.  Sand is important for free-draining soil. Stalite and pumice rock also improve drainage.

Orchids-Aerial vs Terrestrial

Orchids need a medium that produces aeration and drainage.

Aerial Orchids grow on the surface of trees, and media for them are made from materials such as chopped bark, stone, and peat.

Specific varieties have needs that can be adjusted for. Phalaenopsis Orchids can be potted in bark with a material to provide moisture in the ratio of 5:1

Terrestrial Orchids are forest ground plants and grow in soil like other terrestrial ground plants. Use them as bedding plants and in containers. Root rot is the most damaging disease, and superior drainage for your planting medium is paramount. Use a wide but not necessarily deep container to accommodate their spreading but not long roots. Water when the top of the soil is dry.

How To Choose Potting Soil-So Many Choices

Go to your local garden center or any of your big box stores. Loads of choices, lots of bags! How should I choose the right soil?

There are a lot of “best potting mix” lists, and they are not the same. How to decide?

Try This When You Shop

When I go to the store I try to think of standards I would like to meet. Here they are:

• Brands may be national and have quality standards, but the actual materials in my bag will be pretty local. What I bought for my garden near Philadelphia is not what I get today in South Florida from the same company. Local materials are usually best.
• Use the certifications on the labels. Mulch and Soil and OMRI, The bags are usually opaque. You need information to rely on.
• Check quality. Reject torn, wet, or heavy bags, anything without a clean smell.
• What am I planting? In container planting, drainage is usually the big issue so, perlite helps. But if the plant needs steadily moist soil choose vermiculite instead.
• Look for brands you know, national or regional.

How To Store Potting Soil

• Store unopened, sealed bags in tight containers with lids.
• Reseal partially used bags; some brands come with resealable tops. Otherwise, use tape.
• Check the expiration dates if available, compost materials over 1-2 years old or beyond expiration dates.
• Store in clean tubs in dry conditions.
• Don’t use materials, that are wet or with bugs, bacteria or fungi.

Brands of Soil To Consider

Here is my list of major brands. In each case, I have linked to the maker’s website. You will find product specifications and where to buy information. If there is a handy tool or shortcut on a website I have linked to it also.

Do you have other products to add? I’d love to know, Here is how to contact me.

Summary

The soil we use is our most important tool. Careful selection will pay off, in healthier plants, brighter flowers, and more abundant food crops. I hope this information is useful to you.