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The term “growing medium” refers to any substance that acts as a place for roots to take hold. Advances in horticulture have evolved a myriad of options to choose from when it comes to growing mediums, and some are more suited for particular situations than others. There are different benefits and drawbacks to each particular medium. Important factors include water absorption, drainage, pH balance, nutrient content, support for the plant, longevity, reusability and more. Quality grow stores like MileHydro will carry all the popular options like: rockwool, coconut fiber or “coir,” soil, soiless, peatmoss, perlite, expanded clay balls or other rock type aggregate. And of course there can be advantages to combining some grow mediums together.

Popular Choices


When it comes to convenience, reduced labor, reduced weight, sterility, cleanliness and consistency, rockwool is the champ. Of course this assumes the rockwool is produced by a reputable, established company. If the manufacturer isn’t consistent then your grow medium won’t be either. MileHydro retail’s the industry leader for all of our rockwool products so our customers always know what they’re getting. Rockwool is our recommended grow medium for all hydroponic systems except those that submerge the rootzone in water constantly, like for example, Deep Water Culture. Rockwool is composed of granite and/or limestone that has been superheated and melted down, then spun into small threads and pressed into cubes or other shapes to grow in. It’s a process no insect or pathogen could survive. It’s then packaged and shipped, so unlike many growing mediums there is no chance for contamination (unless it’s sitting around in a dirty grow store or being stored in an unkept warehouse). When the rockwool is spun and pressed, it’s done at just the right air-to-wool ratio, so the cube will hold just the right amount of water before draining off. It is very popular for starting seeds or clones, and people that otherwise never use rockwool might still employ it for this purpose. Since rockwool is just rock it’s totally fine (and often beneficial) to break up and mix-in old used rockwool with your outside garden or landscaping projects. Some drawbacks to this growing medium: it tends to grow algae, it can be a little more expensive than other options, it’s more geared toward automation and not advised for hand-watering, and it is less forgiving when it comes to watering issues like pump failures or incorrect watering intervals. Rockwool is also energy intensive to produce so it’s not the most sustainable choice.

Expanded Clay Rock

Also known as Hydroton or grow pellets or Leca… or coco puffs or dog food – I mean I’ve heard it all! Clay rock is one of the few growing mediums that doesn’t really hold water, and because of this, it is MileHydro’s recommended option for growing in hydroponic systems that are constantly wet or watering i.e. Deep Water Culture (DWC) or top-feed constant-trickle type systems, NFT and even some aeroponic systems. Unlike most growing mediums, Hydroton is heavy and can provide a much more substantial anchor for large plants. It’s common for growers to mix Hydroton with other growing mediums like coco or rockwool, or to line the bottom of their soil containers with the clay rock for extra drainage. Although Hydroton is also environmentally burdensome to produce, it can be cleaned and reused again and again. Clay pellets have a neutral pH and are great for plants in a terrarium and are safe for reptiles and amphibians. Some downsides to Hydroton: it’s difficult to work with. If you spill any they will roll everywhere – and you DO NOT want to step on these with a bare foot or try to drive a pallet jack or dolly or plant cart over them. As stated, they don’t hold much water, so if you have a system failure then you better hope to notice quickly. The hydrophobic nature of this grow medium also makes hydroton less ideal to colonize with beneficial bacteria and harder to keep a stable pH. At MileHydro, we only sell the cleanest Expanded Clay Rock, but even ours has to be rinsed repeatedly before using. If a plant in hydroton is moved haphazardly the rocks can shift and damage younger stocks. And again, it’s heavy.

Coconut Fiber or Coco Coir

Coco Coir is the picture-perfect example of a “soiless” growing medium. When the husks or shells of coconuts are ground up and processed, it has the same consistency, weight, and feel of a nice loamy soil, with much better wet to dry intervals and drainage. Coco Coir allows you to grow just like you were in soil in terms of watering frequency and container size, yet gives you complete control over all the inputs via your nutrient solution – hence the classification: soiless. This sustainable by-product of the consumer coconut industry is a popular choice for the earth-conscious grower. Allowing more oxygen while retaining more moisture, this medium allows for hydroponic gardening without requiring automation and providing more forgiveness for any kind of watering inconsistencies. It’s a great medium for establishing beneficial rhizomes and there’s something about coco that roots just love to thrive in. Good quality coco coir’s, like the ones we sell at MileHydro, are generally very sterile and always salt free. The cons of coco: it’s very similar to soil, so, it’s messy. Coco also tends to “shed off” certain nutrients (specifically calcium) so it’s recommended to supplement this growing medium with extra calcium to compensate.

Peat Moss

Peat Moss has been a staple growing medium and main component of many soils for more than a century. It’s effective for a wide range of plants and can come in variations that rage from water retentive to fast draining. Like soil and coco coir, peat moss is great for building microbial life and thriving rhizomes. Peat moss comes from old decaying forest matter that has been compressed by it’s own weight over time. It’s considered a soiless media because it doesn’t really have any nutrient content, but because of where it originates it does have some beneficial properties. And although I consider it a soiless media, it is NOT recommended for most hydroponic applications. Downsides of Peat: it usually comes in larger, heavy, hard to carry compressed bales. Since it’s compressed you have to break it up before you can use it. It’s also messy to work with like a coco or soil. It’s mined or “stripped” from bogs in northern Canada mostly, so it also has big environmental drawbacks. And because this is a finite resource, the price will continue to rise year after year.


Soil has been around for millennia, even before there were plants there was soil. It truly is the original growing medium! At MileHydro we carry a large variety of different soils. Some have a coco fiber base, some have a peat moss base or forest material base, but all of them are amended with organic ingredients like bat guano, earth worm castings, lobster compost, fish meal, crab meal, beneficial bacteria, bio char, perlite, alfalfa, and other such ingredients too numerous to mention. As opposed to all the other growing mediums mentioned up to this point, soil does not require nutrients – or at least not for the first 3 weeks or so, because everything the plant needs is already built-in by way of the ingredients just mentioned. This makes soil growing one of the easiest methods, especially in that beginning 3 weeks. However, with this ease-of-use you do sacrifice control. As a soil grower, you have to be more willing to just go-with-the-flow. Soil is cheap, especially in states with a competitive grow-store market. Bags that cost $45 dollars each in some states are around $20 in states like Colorado where MileHydro calls home. Plus, since you don’t have to use nutrients for almost the first month you’ll save even more money. You can dilute a soil by cutting it with coco coir or peat moss or strengthen it by adding even more amendments, and many of our customers like to mix two different soil brands just to get the best of both worlds. Like everything, it has downsides. Soil is soil, so it’s going to be messy. It’s also full of decaying materials and organic inputs that can tend to attract and sustain bugs. The nature of soil and all its various organic ingredients make it impossible to be exactly consistent bag to bag. Even from the same pallet, bags of soil can vary from one to another, so again, you’re not in complete control as the grower and you have to be more willing to feel things out as you go.

Hopefully this will give some insight into the different growing mediums available, and help you make an informed decision when choosing what medium will perform best in your garden. MileHydro is open six days a week if you want to stop in and talk more about growing media and how it can be maximized.

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