How to choose Potting Soil-what should be in it!

December 20, 2021

Why is Soil So Important and Specific

A plant in a pot has special requirements. It needs its roots anchored, and it requires water, oxygen, and nutrition. A pot is not a natural place for a plant to live. A potted plant requires some special features in the soil it grows in and it 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. Gardening in pots can give us all more opportunities to interact with nature than we might otherwise have.

the front porch is a place for plants in containers with the best potting soil.

At our house, the front yard is in full sun all day! But the covered front porch is a place to grow some shade lovers in pots. And there are good, science-based reasons why those pots need to be filled with the right mix of healthy materials.

The gardenia trees behind the railing have morning sun, around the corner to the right are croton, hibiscus, and canna lily, they revel in the sun. But the potted plants are happy with much less.

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. Lift a bag of it, it is much heavier than potting soil and will hold water longer. Look at the price tag, it should be cheaper because it does not contain more 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 informationWhat is Good Soi For Planting-l And How Do I Get It”

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. 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! If you have a hot dry summer this is even more important. In our dry Florida winters and unpredictable summers, it’s also an issue.

The Limitations Of Growing Plants In Containers

Our greatest challenge in growing plants in pots or any container is that the soil we are using cannot regenerate. Our potted plant is unable to reach its roots out to find more nutrition, or 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 yield better results in the planter. It’s a good idea to lift the bag. Lift a bag of nearby topsoil. 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

  1. About 15%-40% of the bag should be 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 out of the soil when you water 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 when it is wet it holds water like a sponge. It is slightly acid 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 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 as well as potassium.

Use a product 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 a Magnesium deficiency.  

You will often find this sold in a brick form which you soak in water. It will produce very small soft pieces. 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. It’s good to 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; it helps the soil to hold water and it promotes soil microbes. This helps the plants to grow. (Soil microorganisms digest organic matter and 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. Aged is the operative word here. An additional benefit is that we are reusing these waste materials.

How To Get Lightness, Aeration and Water Retention

3. 20%-25% 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. It 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.  It is incredibly light in weight; it is 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. It can be dusty to handle. It will improve soil aeration; it lightens the soil and improves drainage and provides 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. It is a golden-brown color. It is best used for plants that require soil to stay damp. It acts like a sponge, absorbing more water than perlite. It does not aerate the soil as well. It provides less oxygen for the plant roots.

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, gold specks for vermiculite.

Some Potting Mixes Have Fertilizer

4. Some potting mixes have fertilizer added to them. Read the label because there are two types. It may have a starter charge of fertilizer. This will be used up after the plant has been watered about two or three times. There may also be a slow-release fertilizer, expect this to last about a month. Fertilize after that.

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. They 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 very small but they are 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

If you are growing vegetables, organic fertilizers (those from plant and animal origins) have advantages. 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 below 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 valuable information. The bags, however, are usually opaque. 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. There are some helpful reviews of potting products. 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. The plant was discovered by a German explorer in eastern tropical African forests. An ideal combination of ingredients is

  • 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-this material needs to be very light and have a high capacity to hold water and air. It 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 get most of their nutrition from the seed itself seed starting mixes are customarily soilless. They are often sterilized which can be desirable as it will ensure that there are no contaminants or pathogens in the mix. Seed starting is rewarding but has risk and sterilized mixes reduce the odds of failure.

Cactus And Succulents

Mixes for Cactus and Succulents-this 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, media for them are made from materials such as chopped bark, stone, and peat.

Phalaenopsis orchid

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. In containers 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 wet materials, 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 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.

flowers in a pot

Better Gro Products Starting life as Sun Bulb products, in 1956 in a Florida garage, Better Gro makes products for orchid growing and care. Located in Arcadia Florida, the company operates in the heart of America’s orchid country.

If you grow orchids and bromeliads here are the specialized products.

flowers in a pot

Black Gold Potting Soil

This company is part of Sun Gro Horticulture, a provider of horticultural products to the top 100 commercial growers. Black Gold provides potting mixes, specialty mixes, amendments, and soil conditioners, You will find certified products, and the website provides detail on each product.

flowers in a pot

Espoma Potting Soil

Espoma has been producing fertilizer since 1929. In the 1940’s they produced the well-loved Holly Tone products. Today the company produces a variety of potting soils, fertilizer, and planting ingredients.

Click for potting mix specs: Use this little online chart for product information.

flowers in a pot

Fox Farm Soil and Fertilizer

Soil mix, fertilizer, potting soil, and liquid plant food since 1984. It is a choice of healthy microbe-filled soil and avoids sterilized products.

This page lists the specific soil products.

flowers in a pot

Good Earth Organics manufactures Hoffman products, as well as Country Cottage, and Pioneer Southern. The company emphasizes organic products.

There are a lot of products, this link will take you to Hoffman potting soils.

flowers in a pot

Kellogg Garden Organics, founded in 1925, Kellogg has been a family business for 90 years. The potting soil product, Amend is designed for improved soil. It does not contain fertilizer. You add your own.

flowers in a pot

Michigan Peat has been making retail and commercial grower products for 50 years

This link will take you to three categories of products for home gardeners.

flowers in a pot

Miracle Gro, With 2 billion in worldwide sales Scotts Miracle-Gro is the world’s largest marketer of branded lawn and garden products. Miracle-Gro potting mix provides a solid basis for plants to grow indoors or out and it contains a slow-release fertilizer lasting about 6 months.

flowers in a pot

Proven Winners provides a wide range of plants and garden products including soil and growing media.

Potting Soil products.

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.