When it comes to growing plants in containers, the growing medium is one of the most important factors that determines success. The two main options for container gardening are potting mix and potting soil. But what exactly are the differences between potting mix and potting soil? And which one is better for growing healthy container plants?
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What is Potting Mix?
Potting mix, also known as potting compost, is a soilless blend of various ingredients that is specially formulated for growing plants in containers. The key characteristics of a quality potting mix include:
- Good drainage and aeration – Potting mixes contain porous ingredients like peat moss, perlite, vermiculite, and/or coconut coir to prevent soil compaction and provide good drainage and air circulation to plant roots.
- Moisture retention – Ingredients like peat moss and coconut coir help potting mix retain moisture while still draining well.
- Nutrient-poor – Unlike potting soil, potting mixes do not contain rich compost or fertilizers. This allows control over nutrient levels for plants.
- Lightweight – The soilless ingredients make potting mixes lighter than potting soils, an advantage for container gardening.
- Soilless – Potting mixes provide a sterile, soilless growing environment ideal for containers.
By tailoring the blend of ingredients, potting mixes can be created for different types of plants. A good general purpose mix provides an optimal balance of drainage and moisture retention for most container plants.
What is Potting Soil?
Potting soil is exactly what the name implies – soil that is prepared and optimized for growing plants in pots and containers. Here are the key features of potting soil:
- Contains soil – Unlike soilless potting mixes, potting soil contains garden soil or topsoil as a main ingredient.
- Holds nutrients – Potting soils usually contain compost, manure, worm castings, or fertilizers to provide nutrients for plants.
- Can lack drainage – Garden soils tend to compact and may not drain sufficiently in containers.
- Heavier – All that soil makes potting soil much heavier than soilless potting mix.
- Not sterile – Potting soils are not sterile and can contain weed seeds, insects, or plant pathogens.
With added compost or fertilizer, potting soil can provide nutrients for plants. However, the drawback is potting soil lacks the aeration and drainage of soilless potting mixes.
Comparing Key Properties
Let’s compare some of the key properties between potting mix and potting soil:
| Property | Potting Mix | Potting Soil |
|---|---|---|
| Ingredients | Peat moss, perlite, vermiculite, coconut coir | Garden soil, compost, fertilizers |
| Drainage | Excellent | Can be poor |
| Aeration | Excellent | Moderate |
| Moisture retention | Good | Moderate to high |
| Nutrient content | Low | Can be high |
| Weight | Lightweight | Heavy |
| Sterile | Yes | No |
Benefits of Potting Mix
Here are some of the reasons why potting mix is better than potting soil for most container gardening:
- Excellent drainage and aeration – The porous ingredients in potting mixes provide the air pockets and drainage that plant roots need in containers.
- Lightweight – The lower weight compared to soil makes potting mixes easier to handle and move around.
- Less compressible – Potting mixes resist compaction in containers better than soil does.
- Fewer weeds and pests – The sterile soilless ingredients prevent weed seeds, insects, and pathogens.
- Better moisture control – Potting mixes strike the right balance of holding moisture while still draining excess water.
- Easier to re-wet – Potting mix absorbs water easily after drying out whereas soil can become hydrophobic.
- pH neutral – Most potting mixes come buffered close to neutral pH, ideal for most plants.
With these favorable properties, potting mixes create an optimal growing environment for container plants. The excellent drainage prevents overwatering issues while still providing moisture and nutrients to plant roots.
Benefits of Potting Soil
Potting soil does have some advantages over potting mix in certain situations:
- Holds more nutrients – The compost and fertilizers in potting soil provide nutrients for plants.
- Can retain more moisture – Potting soil has higher water holding capacity, good for drought-tolerant plants.
- Usually cheaper – Potting soil is more affordable than quality potting mixes.
- Easier to find – Potting soil is readily available at most garden centers.
- Good for temporary pots – Potting soil can be used for very short term container gardening.
The main disadvantages of potting soil – poor drainage, heavy weight, and lack of sterility – are less problematic when only using containers very short term. But for growing most plants for longer than a few weeks, a proper potting mix gives better results.
How to Improve Potting Soil
To improve potting soil and overcome some of its drawbacks for container gardening, here are a few strategies:
- Add perlite or vermiculite to improve drainage and aeration.
- Use lightweight potting soil instead of dense topsoil.
- Avoid compressing potting soil when filling containers.
- Add fertilizer to potting soil to provide nutrients.
- Test and amend pH to an optimal range for plants.
- Sterilize potting soil prior to use to kill pathogens.
- Add coconut coir to increase moisture retention.
With enough amendments, potting soil can approach the properties of a potting mix. But starting with a proper potting mix prevents having to heavily modify poor quality soil.
Conclusion
In most situations, potting mix is superior to potting soil for growing plants in containers. The tailored blend of ingredients like peat moss, perlite, vermiculite, and coconut coir gives potting mixes excellent drainage, moisture retention, and aeration for healthy plant root growth. Potting mixes also tend to be lightweight, sterile, and pH neutral out of the bag.
Potting soil can work for very short term container gardening thanks to its high nutrient content and ability to retain moisture. But poor drainage and aeration quickly causes problems when using potting soil long term. Heavy weight, lack of sterility, and potential for compacting are other disadvantages.
While potting soil can be amended to improve its properties for containers, starting with a high quality potting mix avoids the need for excessive modifications. For container gardeners looking for the easiest path to success, an appropriate potting mix designed for optimal drainage, moisture retention, and aeration is the best choice for growing thriving container plants.