Potting soil for herbs – buy or mix your own?

I plant a lot of seeds and always have pots on the go.

And as I transplant lots of seedlings, I spend a fair bit on potting soil mixes for my herbs.

It gets expensive.

And there are so many different types of soil available. You have the vegetable and herb soils. Then there are the starting potting mixes, and the list goes on.

I have talked to a lot of gardeners and specialists.

And I have come to a conclusion: You need to use soil that provides your herbs with a healthy balance and structure.

This can be achieved in two different ways.

  1. Purchase soil with the needed qualities for your herbs and vegetables
  2. Mix your soil based on the needs of your herbs and vegetables

If you prefer to make it easy on yourself, you should buy quality soil from your local garden center. You will need a couple of different soil types, depending on how much of a nerd you want to be.

But I have chosen a different path. 

You see, no one has convinced me that I must buy special soil for any particular herb.

All I need to do is to ensure that I provide the qualities any given herb needs to thrive.

Challenge accepted.

Buying affordable soil and making it fit

What works well for me is to start with good quality but affordable soil.

And to make it special, I add what is needed.

Oregano and rosemary like to dry out a bit between watering. Here I add sand, perlite, peat moss, or compost to create a looser structured soil with better drainage. I also use a terracotta pot that breathes to help the soil stay moist but not wet.

Basil likes even soil moisture, does not like to dry out, and is a hungry feeder needing more nutrients than many other herbs. Here I make sure to use a richer blend and add slow-release fertilizers that will break down and release over time. 

You can probably see where I am going with this.

Peat moss is controversial as it is a non-renewable resource leaving an undesirable carbon footprint when harvested from peat bogs. I buy all soil amendments in bulk. But when my current supply of peat moss runs out, I will stop using peat moss for sustainable and more environmentally friendly alternatives.

Buying the needed components as and when needed and adding them to my affordable soil saves me a lot of money.

And – even more important – making my mix of potting soil for herbs and vegetables helps me understand the role soil plays for my plants.

So let’s take a few minutes to understand the wonderful growing medium we call soil.

Purpose of soil (and any other medium)

Soil is of course just one of many available mediums to grow plants.

Hydroponics use water as the growing medium while some plants may prefer sandy mixes of gravel and sand.

So lets backup and look at the role soil and any other medium plays in the growth and development of a plant

  1. Provide structure for root system to anchor and develop
  2. Access to water
  3. Access to nutrition
  4. Access to oxygen

When we grow herbs or vegetables in pots, containers or vegetable gardens we are creating a closed system.

In nature plants are free to spread as needed to anchor themselves and seek out the needed water, nutrition and oxygen. Nature cleverly provides nutrition through organic materials from plants and animals that die and are broken down. 

In our closed environment we as gardeners have to provide all the necessary components to help our plants thrive.

And more importantly, we need to provide the plants with a soil with a healthy balance of water, oxygen and nutrition.

Provide structure for root system to anchor and develop

The potting soil for herbs and vegetables needs to provide the necessary structure for the root system to develop.

If the soil is too compact the root system will find it hard to spread and develop. 

A shallow undeveloped root system will make the plant susceptible to dry outs and unable to absorb moisture and nutrients from the soil.

Access to water

Plants cannot survive without water. Period. 

And when we grow plants in closed ecosystems like pots, containers and vegetable gardens we have to add water to the system.

Water is necessary for photosynthesis, cooling as well as helps to transport or move minerals and nutrients from the soil into the plant. 

Still we need to water with moderation. Overwatering will create a compact and dense solid soil with no room for oxygen.

Your soil is too compact if water forms puddles on the surface of the soil when you water.

Access to nutrition

In nature- plants and other organisms coexist and interact with each other through their life cycles and help maintain a healthy flow of energy and nutrients. 

In our closed system we need to ensure that nutrients are added to the soil.

I mostly work with slow-release nutrients that I mix into the soil. 

You need to add nutrients to your soil as your plants develop continuously. During the most intensive growing periods, I recommend liquid nutrients added to the water every 4-6 weeks. 

Access to oxygen

Both oxygen, or simply put air, and water, are necessary components of healthy soil. But they are inversely related. 

When we water our plants we displace the air content in the soil. 

Potting soil for herbs and vegetables must contain healthy levels of air for your plants to grow and thrive. 

Many of the microorganisms that provide nutrients to the plant need the air to survive.

Is there a difference between types of potting soil?

There are of course differences between different types and brands of soils. 

Instead of throwing percentage and pH-values around I will focus on the main differences. 

  1. Structure – Soils can be airy and loose or more dense and compact. 
  2. Nutrition – Soils with added fertilizer or nutrition for fast or slow release.

Here you simply choose the soil that suits your herbs or vegetables. You want loose structured soil for plants needing a well drained growing environment. 

For plants needing a more moist environment with no dry outs a more compact soil will help retain moisture better between watering. 

As for nutrition, it can of course be helpful if it is added to the soil. But the nutrition added will not last forever. You will still need to add nutrition later on. But you do not need to add it from day one.

Mix your own Potting soil for herbs and vegetables

It is actually quite simple and dare I say fun to mix your own soil. I work with two different recipes or mixes.

I often use my standard mix as I always have the 3 needed components at home. And it works really well.

But with larger seeding projects I use a recipe with 5 components. Why you may ask?

The main reason is that my 5 component soil mix does a better job at retaining moisture without hurting drainage.

And when you are juggling 50+ pots in hot weather I find this little extra help quite useful. Especially when planting herbs where seeds are placed on the surface like basil, oregano, sage and even parsley.

My standard go to mix for potting soil

There are many soil mix recipes on the internet and after testing I have arrived at my ideal mix. I say ideal as it is economical and works really well for preparing a soil mix for any given herb or vegetable.

Mix soil to save money and get the right properties
Mixing our own soil for a well balanced growing environment

The base mix is comprised of equal parts of 

  • standard garden or potting soil 
  • peat moss
  • sand or Perlite

Mix the components together and feel the texture. If you need a looser soil you add peat moss and sand/Perlite. For a firmer potting soil for herbs or vegetables you simply add soil.

It is all about making you potting soil meet the needs of the herbs or vegetables you are planting. And it is truly not rocket science and there is no need for exact measuring or weighing the different components.

Read the information on the seed packet or check out my how to grow tutorials. Focus on how deep you should plant the seed and whether the plant wants a moist or dry growing environment.

When I am happy with the structure of the potting mix I sometimes add a slow-release fertilizer as needed. But most of the time I wait 4-6 weeks before adding any additional nutrition or fertilizer.

Learn the role of soil and how to mix your own potting soil

My 5 component soil mix

My 5 component soil mix takes my standard recipe a bit further. You can see an image of all five components in the image above.

You can see the recipe for the 5 component soil mix below. Please note that the last component, vermiculite, is only added when needed – see below.

  • Standard garden soil (2 parts)
  • Composted cow manure (2 parts)
  • Peat moss (2 parts)
  • Perlite (1 part)
  • Vermiculite (1 part as needed)

Garden soil and composted cow manure are self-explanatory. If you use fertilized garden soil, you should decrease the proportion of cow manure and increase the proportion of garden soil.

Peat moss holds onto moisture and nutrients and disperses them to the root system when needed. Peat moss also helps with drainage and aeration.

I buy peat moss in blocks and it needs to be soaked before use. In its dry for it it hard and will initially repel water. As we soak the peat moss we tear it apart into smaller pieces to speed up the process.

Perlite (white) and vermiculite are often mistaken for having the same properties. And while they do share some features they are also different.

I use perlite as it loosens the soil by improvising aeration allowing the root system to grow and spread. Perlite will also retain water and nutrients for slow release as needed by the root system.

And as all herbs and vegetables benefit from a growing environment with improved aeration and drainage I always use perlite.

Vermiculite (grey) is however the master of water retention and absorbs water like a sponge. Vermiculite is looser than soil but does not improve aeration like perlite.

If you are planting herbs or vegetables that like to dry out between watering like oregano and rosemary you may find that adding vermiculite will add too much constant moisture for the root system to thrive and develop.

Again, read the information on the seed packet to learn if the plant wants a moist or dry growing environment. Then proceed to mix your soil to match the needs and create the ideal growing environment for your plant.

Mattias Magnusson: Hello, I'm Mattias, a passionate and experienced gardening enthusiast. I am the creator of MattMagnusson.com, your guide to year-round herb and veggie growing. Let's simplify green living, no matter your space or location.