Types Of Soil For Container Gardening

In this post I would like to talk about the different types of soils, where they are best used.  I am no expert in soil, in fact I have recently learnt that I have never used soil in my gardening.  I decided to investigate online and the results were slightly confusing, so I will mention all definitions here, and then you can decide what is best.  I will mention three types of scenarios, container plants, raised beds and gardens.  I will not go into farming, and large plots of land as it is beyond the scope here.

I used to think that soil is soil, you can find it in fields, buy it from nurseries, or get some from generous relatives.  One visit to the nurseries, and I suddenly found myself with a dozen different types of compost, peat, fertilizer  for vegetables, for herbs, for plants; the combinations were endless.

Nursery Selection

Plants in hand, I asked the person at the nursery what type of "soil" was best for my plants.  He got a packet of multi-purpose substratum (even though he called it compost, and really it's the same thing), and I never looked back since.

One day a relative of ours gave us  a bucket full of soil from his garden.  It was reddish in color (soil in Malta is called 'Terra Rossa' or red earth), and was full of weeds, and bits of pottery!    I had just planted half of my basil seeds in my substratum, so I decided to plant the rest of the seeds in this soil to see if it made any difference.  The basil that I planted in the multi-purpose compost grew and flourished, the basil that I planted in the soil never even sprouted.  I was gutted, thinking, we have some of the best soil in the world, and I can't even grow basil in it.  I decided to do some research to understand why this happened, and I now realize that my basil never had a chance.

I would like to mention some types of soil/compost/mix as I found them to be the most commonly used.  I hope this helps the humble beginners like myself, experienced gardeners feel free to contribute.

In the Garden

Garden Soil - Image Source

Garden soil is made up of topsoil and subsoil.  Topsoil is normally the first few inches of soil and is where all plants grow.  This soil is rich in organic matter as all sorts of insects, plants, weeds have lived and died there.  Plant roots normally do not go deeper than topsoil and therefore all plants get their nutrition from this soil.  

On the other hand, I have also read that topsoil is considered of little quality and referred to as dirt.  The lack of nutrition can be rectified by adding compost or other fertilizer to it.

Beneath topsoil is subsoil.  This is the soil that is the most dense and compacted, and little plant life  can survive or grow in this type of soil.  This type of soil does not contain the organic material found in top soil since plant roots do not reach this far down.  As a result this type of soil contains little nutrients and makes it unsuitable for growing plants on its own.

Loam:

The amount of praise I saw online for this type of soil makes it necessary to give it special attention.  This week was the first time I heard about this soil so pardon my ignorance.  It is however, apparently the best soil you can use for gardens and farming, being an ideal mixture of sand, clay and silt, contains lots of nutrients, and retains the perfect amount of water.  You couldn't manufacture something like that!

All these types of soil are not ideal to be used in containers for the following reasons:

1. They are full of bacteria, bits of rock and dead organic matter that you don't want in a container.

2. The soil is dense and compacted and does not allow for proper air and water flow.

3. The soil retains a lot of moisture causing possible root rot for plants in a container.

Raised Beds - Somewhere in between

Raised Beds - Image Source

Raised beds are neither gardens nor containers, but something in between.  They can have a large surface area and are too big to  be considered containers, however they are in a container so they are not a garden!  The soil used in raised beds is also a mixture of topsoil and potting mix, or compost.  

The compost or potting mix helps to aerate the topsoil, so it is not as dense.  This helps the water to flow more easily and drain better in the beds.  Due to their large surface area, however it is also desirable that the soil retains some of its moisture.  The sun plays a big part in moisture loss, so in large volumes it is best that the soil is not too well draining, or the beds will dry out too quickly.

Containers and Small Environments

Containers - Image Source

In my experience I am beginning to see how container gardening can be more challenging that owning a normal garden. You need to create a small world in a container for your plant to live in and flourish.  Soil is the basic medium in which the plants will grow so it is important to get it right, especially in a container.

Potting Soil vs Potting Mix

I have seen the terms potting soil and potting mix used interchangeably to mean the same thing.  I found, however, a distinction between the two, in Tennille's very informative blog post Potting Soil vs Potting Mix.

Potting soil is a mixture of topsoil and compost as mentioned above used in raised beds.  In large containers this type of soil can also be used for the same reasons.  

Potting mix is a mix of peat moss, perlite and vermiculite among other things, and does not contain any soil.  Vermiculite and perlite are two interesting minerals used in areas such as construction and insulation.  When mixed with soil however, they add certain desirable properties.  

Vermiculite retains air, moisture and plant food and has a slow release system, so the plant will get the right amount when required.  Perlite, on the other hand, retains very little moisture, and is used to prevent the soil from becoming compact, encouraging air and water flow.

Potting mix is what we generally buy from nurseries and use in containers.  The 'soil' is normally sterilized to kill off all bacteria, and prevent the chance of disease.  It is not recommended to re-use this type of soil for plants after other plants have died in it, although I have done this on occasion, and I did not run into any trouble.  

The nutrients in potting mix tend to be absorbed quickly by the plants, and the soil should be replaced once a year, or mixed with fertilizer to replace them.

Compost

Compost is made up of decomposed organic material such as leaves, greens and food if made at home.  This material is very rich in nutrients, and is normally used as a fertilizer, so it should not be used on its own when planting container plants.  It can however be mixed in with other types of soil to increase the nutritional value, such as mixing with top soil to make potting soil.  Compost is not dense, and can be mixed with other soils to create water and air flow in containers or raised beds.  In gardens, compost can be placed directly on the ground, and mixed in with the top soil before planting the seeds, or plants.  

So there they are, the basics of soil!    Many things can go wrong in container gardening. Too much water, too little, lack of food, too much sunlight etc.  The wrong type of soil can also prevent the plants from reaching their full potential, so it's a good idea to have at least some basic knowledge of what there is out there.  Hopefully this post will help achieve that.