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The Best Potting Soil for Your Indoor Herb Garden

You have to choose the best soil for indoor herbs if you want to start an indoor herb garden. Soil is essential for a successful garden. If you plant your garden in poor soil, you won't get the best results. Let's learn more about the best herb potting soil.

Healthy herbs in pot and potting soil.

If you are getting started on growing herbs indoors, one of the first decisions that you have to make is which kind of dirt to buy to fill your herb pots. You can just go to the garden center and buy a bag of potting soil, but if you are the type to wonder what is in that big plastic bag, read on to get all of the dirt on your potting soil. 

It’s All Dirt Right?

Dirt is all around us in the natural environment. All you have to do is use a shovel to cut through the grass in a park or on your front lawn and you will find a layer of dirt below the grass roots. However, not all dirt is equal.

Dirt can vary in fertility, with some places being richer in nutrients than others. Dirt can also vary in drainage, either allowing water to seep out easily, as in sandy soils, or allowing water to seep out slowly like in clay soils. Dirt that is full of loam or compost holds water like a sponge but still allows excess to drain away.

A gardener's hand with black soil.

Dirt can also vary in compaction. Compaction is how well the dirt particles press together and stay pressed together. Soils that have a lot of clay stay compressed together easily. Soils that are high in compost have particles that stay light and fluffy, allowing plenty of water, nutrients, and air to get to plants’ roots. 

When builders create a structure, one of the first things that they do is scrape away the topsoil and level the building site. When you look at the dirt in places that have experienced disturbance, like in urban or suburban places and around buildings, you never know what kind of dirt will be underneath the buildings and grass. 

Sometimes the builders will add a layer of topsoil to the building site as a final step before planting grass, but sometimes, sod is just rolled out over the top of the poor subsoil that was exposed during construction. Just because there is dirt under the roots of your front lawn doesn’t necessarily mean that the dirt will be good for your indoor plants.

When you grow an indoor herb garden, your herb plants are limited to the dirt that is in the pots that you provide. This means that if you want your herbs to grow well, you have to give them the best possible soil.

This soil should be light and fluffy to allow plenty of air to circulate around the roots of the plants as well as hold some moisture without getting boggy and wet. The soil should have plenty of nutrients to provide for healthy growth of your herbs.

Why You Should Never Use Outdoor Dirt for Your Indoor Herb Garden?

When you need soil for your indoor herb garden, it may be tempting to go out into the backyard with a shovel and start digging holes and filling your pots with the soil in the yard.

However, this is always a bad idea. Generally, lawn soil can be too heavy if it has too much clay, or too sandy if it has too much sand. The soil can compact in the pots and this means that water will not be able to drain out, leaving your herbs in a soggy mess. 

There is no way of knowing the general fertility of your lawn soil either. Your plants will need fertile soil to grow healthily and beautifully.

Another reason to avoid using lawn soil is that it can be packed with seeds from other plants. Biologists call the seeds present in the soil a seed bank.  The seed bank can consist of seeds from plants that grew in the area in the past as well as seeds that were recently shed from plants that are currently growing.  Some of these seeds have been in the dirt so long that they will not grow, but other seeds can remain viable for decades.

A shovel in backyard soil.

Why does this matter? Because if you are growing herbs in dirt with other seeds, you can’t be certain that what is sprouting in the soil in the pots is your herb seed or some other plant.

As soon as you start watering and fertilizing the lawn soil in your pots, all kinds of seeds can germinate and start growing, competing with your herb plants for nutrients and water.  Many people prefer indoor herb gardening to avoid chores like weeding their plants, and if you use lawn soil, you will be right back to yanking out weeds from your herb pots.

Components of Good Soil

So what makes good soil for your herb plants?  Healthy soil consists of water, air, plant material that has decayed, organic materials, and minerals like sand, clay, and silt. Healthy soils are porous, allowing air and water to move freely through the dirt as well as allowing the roots of your plants to easily penetrate the dirt.

Most commercial potting soil mixes have three basic ingredients–peat moss, pine bark, compost, and vermiculite or perlite.

Peat moss is an absorbent moss that grows in boggy ground. The lower parts of the moss decay to create peat deposits which are harvested for use in growing plants. Peat moss is spongy and helps the soil hold moisture. Peat moss is acidic and does not compact, improving the structure and drainage of the soil. 

In potting soil, pine bark is ground very finely. It helps create a light, fluffy potting mixture, and it degrades slowly. It does not have much nutrient value in the potting soil, but does help maintain good aeration in potting mixtures. 

Compost is the decayed remnants of plant materials. This is very nutrient dense and holds water well. You can create your own compost at home in your backyard if you like. This is a great way of eliminating food waste, since any unused food items can go to the compost pile where they will be broken down into nourishing food for your plants. 

Vermiculite and perlite are lightweight additions to potting mixes. Perilte is a volcanic rock that increases drainage and aeration in potting mixes. Both of these additions help create a light and fluffy mixture. 

Buying Commercial Potting Soils

Miracle-Gro Potting Mix, 8 qt. (2 Pack)

The easiest way to fill your herb pots is to buy commercially created potting soil at your local garden center or hardware store. When you are shopping for these mixtures, be sure that you read the labels carefully. You want potting soil, not topsoil or compost.

Some commercial potting soils have added granular fertilizer. If you purchase this kind of potting soil, you will not have to fertilize your plants once or twice a month. Do not use extra fertilizer if you’ve bought this kind of potting soil or you will burn your plants and they can die. 

Mixing Your Own Potting Soil for Herbs

Gardener making potting mixed soil.

Most herbs are grown for their foliage and they need excellent drainage. For this reason, most of the recipes for these herbs contain sand to help with drainage. Often, these mixtures are calculated fractionally. This means that you can generate whatever quantity of potting mix that you want, simply by measuring equal parts of each component. 

For growing indoor herbs, you can use any of the following mixtures. You can alter the components depending on what is available in your area and what is most economical for you. For instance, if you can’t find perlite, you can substitute vermiculite, or the other way around. 

Here are a few potting soil recipes for you to try:

2 parts peat moss + 1 part perlite + 1 part coarse sand + 1 part compost

or 

1 part peat moss + 1 part finely chopped pine bark + 1 part coarse sand + 1 part compost + 1 part perlite

If you are growing seedlings, you may want to try the following recipe since the seeds will need a lighter mixture:

2 parts compost + 2 parts peat moss + 1 part of pre-wetted perlite or vermiculite 

You can mix these recipes in a large wheelbarrow or, if you are making smaller quantities, you can use a dishpan or shallow tray to thoroughly blend the components before you fill your pots. Just use a shovel or trowel to blend them well, but be sure to keep your face away from the tray to avoid inhaling the dust of the mixture.  

Managing Fertility With Your Indoor Herb Garden

Healthy herbs plant in pot near windowsill.

All the plants in your indoor herb garden need additional fertility. Even if you are using liberal amounts of compost in your potting mixtures, you should still fertilize your indoor herbs once every two or three weeks. Water soluble fertilizers like Miracle Grow or similar fertilizers can be used to feed your plants and keep them healthy and strong. 

When you understand how potting soil is created, you may want to create your own. However, its just as good to just buy commercially created potting soil and fill your pots with that. Whatever choice you make, your herbs will grow healthy and strong and beautiful.