the best medium for indoor growing

The Best Indoor Grow Media

Growing indoors is an extremely effective way to cultivate plants. You can control everything from the lighting to the temperature and humidity in order to ensure a prime growing environment.

But just like outdoor cultivation, indoor growing still requires you to choose a medium. There is always your run of the mill potting soil that works great in either application.

However there's a wide range of media to choose from for indoor cultivation, or even no medium at all.

Potting Soil

You can never go wrong with traditional potting soils in an indoor grow. Especially if you are coming from an outdoor setting, it is an easier transition to make using a potting soil that is familiar. But of course that isn't the only reason potting soil makes a good indoor grow medium.

Potting soil comes packed with natural nutrients and micronutrients like earthworm castings, bat guano, and other organic inputs. Having these inputs in your medium from the beginning is great for your plants that will crave a lot of nutrients for growth.

One of the downsides to growing in traditional potting soil indoors is drainage and aeration. Compared to other media, potting soil is typically more dense. For this reason potting soil may take longer to drain between feedings, and the soil can clump up more easily creating blockages that restrict oxygen to your roots.

With a proper feeding schedule and plant maintenance however these issues can easily be avoided. For growers looking to maximize growth indoors, soilless media has become a popular option, and the options are broad.

Coconut Coir/Fiber

Growing in coconuts? Not exactly. Coconut coir — more commonly just called coco coir — is a byproduct.

Not just from harvesting the coconut meat or the milk inside, but also from the textile industry. The fibers of the husk are used for making textiles on continents like Asia, but the short hairs on the coconuts are not used.

It turns out that these short hair fibers become a great medium when packed together in bulk. 

The way coconuts spread across the globe was by falling off of their tress and rolling into the ocean. After landing on a foreign beach the coconuts would shed their outer material through the journey and eventually result in the sprouting of a new tree.

The same organic, nutrient rich material that the coconut produces to sprout new trees is also in coco coir. By adding coco coir to your soil mix you get additional nutrients rich in hormones and bio-stimulants that encourage more growth. You can also grow in just coco coir and get great results thanks to its moisture holding properties and great aeration which allows for more feedings and bigger plants.

Peat Moss

Most commonly sourced from sphagnum moss, peat moss is the result of this moss dying and decaying on top of itself over millions of years. This decomposition turns what was once thriving moss communities into bogs of decayed moss, full of organic nutrients and material, similar to compost.

Peat is known for being more acidic than other mediums, making it a great addition to soil that houses acid loving plants. It is also highly absorbent, being able to hold several times its weight in water. Peat also holds onto nutrients well, so watering doesn’t rinse them out as easily.

However, while peat is a popular component in soilless mixes, peat moss is not quite as efficient as standalone medium. Unlike coco coir, it is non-renewable. Most will use it sparingly in their mixes for some added benefits.


Rockwool is volcanic rock that has been pummeled into dust and then spun into stringy fibers. When compacted, this process creates blocks of what is basically a rough wool, made from rock!

A quick google search will show more house insulation than grow medium, which can be confusing. But what shouldn't be confusing is the benefits of growing your plants in rockwool.

For starters, rockwool is completely inert. It has no nutrient content, and a neutral pH. In other words rockwool gives the grower full control over the medium, making it easier to keep feedings consistent without much adjustment.

Additionally rockwool has more drainage than any other medium. Faster drainage means the medium will dry more quickly, which requires more feedings, resulting in bigger plants and a bigger harvest!

Rockwool is very common in large scale indoor grow operations, as it is cleaner than soil, easy to train employees to use and it is efficient.


Why not ditch a medium all together? Aeroponics is the next step up from traditional hydroponics that removes the medium and feeds the plant roots directly from nutrient rich water source.

Starting in some root plugs, the plants stick through the bottom over a reservoir where they are either misted or dipped using a flood and drain system for feeding. As the roots develop and the plants grow, and the only real adjustment that will be made is changing the container that supports the plant.

Luckily there are pots specifically made for this called net pots, designed with holes throughout to resemble a net, so your plant is supported by the rigid structure of a traditional pot while allowing your roots to grow through each hole and maximize access to nutrients.

However aeroponics is not for beginners, and can even be difficult for experienced cultivators. One clog in the irrigation line can lead to dire results, as your plants have no other source to pull nutrients from like a soil. It is also easier for your plants to catch disease or develop deficiencies in an aeroponic system.

Which should you choose?

As with most aspects of growing, the medium you choose is a matter of preference. Some may like the ease of using traditional potting soil, while others want to experiment with Aeroponics.

A great option for any indoor grow is a blend of soil-based and soilless components to create a powerful mix with everything you want. The organic inputs of a potting soil with added aeration from coco coir and great moisture holding capabilities of peat. The possibilities are nearly endless.

If you want the cleanest way to grow, as in the least mess to clean up in the end, rockwool or aeroponics will be the way. No dirt, no mess, it's pretty much that simple.

Whatever you choose, Cultivate has the supplies you need to fill out a large scale operation with rockwool or create your own powerhouse medium to grow the best you can.

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