Growing marijuana hydroponically simply means that you grow the plants in an inert, sterile growing medium instead of in soil. All of the plants’ nutrient requirements are supplied when you mix water with the nutrient solution
Perlite is mainly composed of minerals that are subjected to very high heat, which then expand it like popcorn so it becomes very light weight, porous and absorbent. Perlite has a neutral pH, excellent wicking action, and is very porous. Perlite can by used by itself, or mixed with other types of growing media’s. However because perlite is so light that it floats, depending on how you designed your hydroponic system, perlite by itself may not be the best choice of growing media for flood and drain systems.
Perlite is widely used in potting soils, and any nursery should carry bags of it.
Soilless mixtures are sphagnum-, peat- or coco-based blends that look, act and feel extremely similar to regular topsoil. These mediums are better suited for indoor gardens than outdoor topsoil because they carry less pests, diseases, bacteria and mold. Standard topsoil is rarely used indoors anymore.
Soilless mediums generally come pre-mixed with beneficial amendments like perlite, wood chips and, at times, mild nutrient additives. Many advanced growers will mix their own ratios of base medium (most often coco coir) with additives that absorb and retain moisture as well as others that help aerate the medium.
Soilless mixtures are most commonly used in top-feed drip- or spray-emitter systems, which are able to saturate the medium evenly (especially when spray emitters are used). This type of medium doesn’t perform as well in flood-and-drain or DWC systems, as soilless mixtures are composed of small particles of matter.
Growstones are manufactured from recycled glass. The growstones are lightweight, reusable and porous like grow rocks but are unevenly shaped. They provide good moisture and aeration to the root zone. With good wicking ability, they can retain the water up to 3-4 inches above the grow media. So good drainage or depth is important to ensure that it doesn’t wick the water all the way to the top. Otherwise it can cause stem rot if the surface of the growing medium is continually wet. Although manufactured from recycled glass, they’re not sharp and will not cut you, even if they break.
Hardened expanded clay
HEC, or pop clay, has the look of small brown marbles. It offers a number of benefits, including being inexpensive, reusable and sterile. It’s also very sturdy and great for stabilizing plants in flood-and-drain systems, though it can very easily be used in DWC and nutrient-film technique (NFT) setups as well.
The downside with HEC is that it offers little to no buffering, rendering it useless as a safeguard against overfeeding (i.e., nutrient burn). Growers who choose HEC need to be well versed in the nutrients and doses they’re using. Additionally, top-feed setups like drip-emitter systems tend to leave too many dry areas in the medium, making it harder for the HEC to become saturated and deliver adequate moisture to the roots.
Lava rocks have a long history of being used as a hydroponics growing medium. Why? Because they provide beneficial drainage, aeration, water retention, and are pH neutral. Lava rocks are also light-weight, porous, and provide trace elements (magnesium, zinc, copper, calcium, aluminum, cadmium, manganese) to plants grown in this hydroponic grow medium. A notable disadvantage is the fact that the inherent sharp edges of lava rocks have the potential to damage the root systems of hydroponically-grown plants. However, lava rocks have many beneficial hydroponic grow medium properties, and are worthy of consideration.
Mineral wool—or rockwool, as it’s most commonly known—is a medium made from spun molten limestone, with a look and feel similar to fiberglass. Rockwool is extremely absorbent, with an ability to stay firm while holding moisture for hours at a time. However, rockwool is a tough medium to understand and is not recommended for beginners.
Rockwool offers only limited buffering for roots, making nutrient dosing a precarious endeavor for those new to the medium. Salt buildup is another common issue, requiring rockwool growers to do pure-water flushes at least once a week. Keep the rockwool at a pH between 5.5 and 5.9 for best results, and be sure to cover it from light to prevent algae growth around the root zone. Rockwool is best suited for use with flood-table systems or flood-and-drain setups.
Pine shavings are an inexpensive hydroponic growing media, and a lot of commercial growers use it. Generally for large scale hydroponic drip irrigation systems. Don’t confuse pine shavings with saw dust. Saw dust will become compact and water logged easily. You’ll want to make sure your pine shavings were made from kiln dried wood, and does “NOT” contain any chemical fungicides. Kiln dried to burn off all the sap in the wood that is bad for the plants. Most pine shaving products would be kiln dried to begin with.
Good source to find pine shavings are pet supply stores. Its used for bedding for hamsters and rabbits . Just make sure to read the package to be sure it doesn’t have any chemical additives like fungicides or odor inhibitors. You should be fine if it states it’s organic. Another good cheep source for pine shavings is at feed stores, it’s also used as bedding in horse stalls and they sell it by cubic yard. If you have a choice get the largest partial size you can. The larger the air pockets between the shavings, the better aeration to your roots.
Pine shavings are a wood product, so they absorb water easily, thus can become water logged easily. So make sure you have good drainage so the shavings don’t sit in water. If there is a possibility of it sitting in water, a layer of rocks at the bottom will aid drainage greatly.
There are a lot of things to consider when choosing what to use as a growing media. The type of system your growing in, and how you design and build that system is the biggest factor. While there is no one best growing media for all situations, some growing media’s work better than others in different systems.
[Updated, originally published 25.2.2017]