Grow media: What are your plants growing in

Grow media physically supports and provides nutrients for your plants. Roughly, the types of media break down into 3 broad categories:

Soil or soil-like
Non-nutritive media
Water (and generally a non-nutritive media)

Choosing the right one greatly helps you get a leg up on the grow

Soil and soil-like media

The distinction here is that the soil/dirt/potting mix has organic compounds available to be broken down by the environment and taken in by the plants.

Soil is a mixture that roughly breaks down into:

Inorganic matter – Bits of rock, clay, and sand. These make up the structure of the soil and supply some minerals when placed in acidic or alkaline environments, but are mostly inert.
Organic matter – This portion, known as “hummus”, contains the majority of the nutrients within the soil. Many of the nutrients are not available to the plants directly until soil-dwelling organisms have had time to break down long and complex organic molecules into simpler nutrients that plants can readily absorb.
Soil microorganisms – The bacteria, fungi, and other single-celled organism that can subsist on the complex nutrients in the hummus and break them down into the simpler molecules that plants need for nutrient uptake.
Soil creatures – Bugs, worms, etc. These feed from the minerals and nutrients and convert even more nutrients into plant-ready waste. Additionally, worms especially, provide valuable soil aeration, which greatly helps plants grow.

Due to the living environment, and abundance of organic matter, soil tends to forgive minor issues and provide a buffer when you aren’t as good a plant parent as you should be. While that’s great, it can also either provide water to your plant OR air, so you limit the growth potential because getting optimal nutrient uptake and root-zone aeration is impossible.

Take a look at our Grow Method: Soil article for far more details on soil.

Non-nutritive media

Non-nutritive media covers the gamut from rocks to exotic agar mixtures, but the most common ones you’ll see are:

Coco Coir or Peat – Both are organic material and look like soil to a great extent, but neither provides much nutrition for the plants. Plants potted in this are generally fed compost teas or hydroponic fertilizes, which can either pool on the bottom or leave the media (called drain to waste). These are generally amended with perlite to prevent caking and add air pockets.
Expanded clay balls – These look like pebbles but are very light and can retain a fair amount of water and air. They are commonly used as support media for plants in hydroponics, or as the media where the roots grow in flood/drain systems.
Perlite – generally used as an amendment to other grow media, but people use it in Dutch buckets as the rooting media due to its low cost. Perlite helps aerate the soil and well as aids in draining. Use it if you want to lighten your grow media
Vermiculite – Much like perlite, vermiculite is used generally as an amendment to allow better drainage. Due to its surface profile, you should not use this to help with aeration.
Rockwool cubes – Made from spun, molten rocks, people use them to generally start plants due to good capillary action, and being dense enough to support the seedlings. You can also grow many full-sized plants in them. Typically, large trays are filled with either a base of rockwool, or just nutrient solution, and you place cubes (in progressive sizes as you plant grows) in the tray and they will root to find more nutrient solution.

Water with support media: Hydroponics

In the most broad term, if you are pushing dissolved, ready-to-uptake nutrients directly into your plant’s root, and not depending on the microbes decomposing your compost fast enough, you’re doing some form of hydroponics.

That said, there is a lot of variance. So, from my point of view, there are a few major types of hydro:

Deep water – Your roots are in a mass of aerated water and can get optimal aeration and nutrient uptake. Deep water culture, and bubble buckets fit this bill. NFT, to a lesser extent, as well.
Flood/Drain – you flood the root zone with nutrient rich solution then remove it, leaving only a film of nutrients that can readily absorb air. Common techniques include coco coir pots (either recirculating or drain-to-waste), dutch buckets, and flood tables.
Kratky – Taking the best and worst of both deep water and flood drain, this method immerses the roots in the nutrient solution and coaxes the plant to grow root fibers specialized to pull oxygen from the moist air in the root zone.

Flood/Drain systems typically keep the plant in the media and flood it on a schedule. Deep water systems have a water bath on the bottom, and need a second media to support the plant. It’s best to keep the water out of the secondary media.