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growing cannabis in rockwool

Rockwool For Hydroponic Marijuana Growing

Rockwool is a great medium for growing marijuana. You can take your strain of choice through the whole cannabis life cycle with rockwool. Growers of all levels, using a variety of hydroponic setups are harvesting heavier yields a whole lot sooner. It’s about time you tried rockwool too.

WHAT IS ROCKWOOL?

Well, originally this wonderful medium was exclusively used as insulation. Mineral wool, stone wool, or rockwool, it’s all the same. Interestingly, this material just so happened to have all the properties essential to a thriving hydroponic root zone by accident, rather than by design. Of course, modern horticulture-grade rockwool substrates have been refined and packaged specifically for cannabis cultivation. Nevertheless, rockwool is still a cotton candy-like fibre spun from basalt rock. Blocks, cubes, and slabs of rockwool come in a variety of shapes and sizes. These products are staples of any decent hydroponics store.

HOW TO USE ROCKWOOL IN HYDROPONICS

Before you can get growing in rockwool, you must first adjust the pH. Rockwool is naturally alkaline. Too alkaline for cannabis. It’s best to soak your cube or block in 5.8–6.3pH water for 24 hours in advance. Going forward, you will need to invest in either a pH pen or pH-perfect nutrients to maintain optimal pH levels.

CUBES FOR CLONES AND SEEDLINGS

Clones and seedlings will readily root in rockwool cubes. You can get a tray of 12–24 small rooting cubes cut to size for about €5. Tiny rockwool blocks are great for getting started, especially for those new to hydroponics. Seedlings and clones can tell you it’s time to transplant when roots start to poke out. All you really need to watch out for is algae. Keep the cubes covered with some plastic if they start turning green. Without light, the algae will die.

BLOCKS AND SLABS FOR BIGGER PLANTS

Transplanting couldn’t be simpler with rockwool. Simply cut a hole to size in the slab or larger block you plan to use. Then, sit the smaller block in place and let the roots do the rest. This is really handy if you are tight on space and/or working with large numbers of seedlings or clones. If a plant should ever get root bound, you can always get a bigger block of rockwool. Heavier mediums like soil can be awkward, and you risk doing more harm than good stressing the plants with transplant shock.

THE BEST HYDRO SYSTEMS FOR ROCKWOOL

Rockwool is commonly associated with advanced hydroponics like flood and drain, NFT, and DWC. However, it’s a pretty versatile substrate and works well with top feeding from drip irrigation to hand-watering. Rockwool slabs are preferred by high-volume cultivators, but you can also grow a monster plant in an oversized 50l+ rockwool block.

BEST FERTILISERS FOR ROCKWOOL

Brand name, cannabis-specific hydroponic nutrients, ideally formulated in a pH perfect solution are the smart choice. As rockwool is inert, the grower is in complete control of plant nutrition. This can be a double-edged sword. You can potentially pump-up bud production to the max with a high-quality chemical fertiliser regime. At the same time, it’s all too easy to over-fertilise. Feeding must be controlled. Unfortunately, most organic nutrients are too thick and often can become difficult to flush from the medium. Organic fertilisers are also notorious for causing blockages in water lines.

DISADVANTAGES OF ROCKWOOL

Take care to maintain optimal pH with each and every watering. The biggest downside of using rockwool is also its unique selling point: total control over nutrients. Unlike soil, this medium is sterile and very unforgiving. Being in charge of plant nutrition is a full-time job for the duration of the grow. Soil acts more like a buffer and doesn’t require the same kind of precision.

Organic growers will have the hardest time with rockwool. But to be honest, if you really want to grow organic cannabis, you should just use soil.

Rockwool is not really a natural product, so it won’t biodegrade. When you’re done with rockwool, it’s garbage. Old soil you can dispose of in the back garden or reuse. We can’t recommend either for this hydroponic substrate. Reused rockwool has a tendency to have a shifting pH that requires extra monitoring to keep in check. Play it safe and buy some fresh, clean media for the next crop.

Hydroponics is all about getting bigger, more potent buds, faster than a typical soil grow. We take a closer look at cannabis cultivation with rockwool.

Have Fun Using Grodan Rockwool for Marijuana Growing!

Looking for a sterile, easy-to-use root zone media your marijuana roots will love in indoor grow ops? Then you need to look at rockwool.

Rockwool is one of the most useful hydroponics growing media ever invented. It’s made from basalt, a volcanic rock composed mostly of silica, and also contains smaller amounts of titanium, iron and other elements. Basalt starts out as lava, then hardens into rock.

To make rockwool (which is sometimes called “stonewool”), manufacturers temporarily turn basalt back into lava and spin it at high speeds to create an end-product of porous, wool-like material with the texture of cotton candy.

The only rockwool I recommend is made by the Grodan horticultural products company, which is based in The Netherlands. Grodan is by far the world leader in quality horticultural rockwool.

Rockwool is a manufactured commodity, and like cheese or bread, it can be fabricated into a variety of shapes and sizes. Grodan rockwool comes in slabs, cubes, chunks and loose material.

Be aware that you can get confused by Grodan product terminology because there are two types of Grodan cubes: one type are various sizes of cubes used to germinate seedlings and/or root clones, as well as to provide a platform for plants sitting on rockwool slabs. The other types are little cubes, a quarter inch square, used to fill pots in root zones.

Explained another way, the very smallest rockwool cubes are used as loose root zone material. The next largest cube sizes are used for professional marijuana cloning or seed germination, cloning, early grow phase, and for platform drip irrigation systems in which the cubes sit on top of rockwool slabs, which are long, thick pieces of rockwool for use in ebb-and-flow systems.

You see Grodan rockwool systems in the largest commercial greenhouses and glasshouses in The Netherlands where a significant portion of Europe’s tomatoes, peppers, lettuce and other vegetables are grown. You also see rockwool in plenty of cannabis gardens worldwide.

Grodan rockwool comes in specialized types including Grotop Master, Grotop Master dry, and Grotop Expert, all of which have slightly different properties and horticultural uses. Grotop Master Dry, for example, maintains a slightly drier root zone and is used by growers in high-humidity areas. Grotop Expert is designed for rapid root growth and development.

Rockwool = Total Control Over Hydroponics Nutrients & PH

Why is rockwool so useful for marijuana growers? It gives you total control over nutrient elements and other compounds plants absorb through their root zone. Rockwool is 100% sterile and inert—it has no nutritional component unless the grower adds nutrition to the media.

That makes it an inert blank slate, a neutral carrier material that holds water, nutrients put in the water, and oxygen. Cannabis roots must have easy access to water, oxygen and nutrients, and rockwool provides this very efficiently, especially compared to soil and coco coir.

When growers use rockwool along with reverse osmosis water and high-quality hydroponics nutrients, plants get exactly what they need, and nothing else. This gives the grower power to control exactly what plants feed on and how much of it. It also allows precision control of root zone pH, which is a crucial factor in roots’ nutrients absorption. These benefits increase growth rate, harvest weight and potency.

Contrast this with soil and coco coir, which contain on-board nutrient elements that complicate and interfere with your feed program. Coco coir and soil can play havoc with root zone pH as well.

Pre-Soak Rockwool Before Using

Growers must adjust rockwool pH before they put plants in it. This is done via a pre-soaking process. You can’t just take rockwool out of its package and use it immediately. In its native state, it has a glitchy pH and must be presoaked with solution that has a pH of 5.5. That’s why you do a presoak with reverse osmosis water adjusted to pH 5.5. The grower has to have pH adjusting solution and a reliable pH meter such as the Bluelab series of meters to make this happen.

When I pre-soak rockwool, I place it in a clean bathtub filled with reverse osmosis water adjusted to 5.5 and allow it to soak overnight. Then I drain the water and place the rockwool on racks over a drain so excess water can leak out. I capture the excess water and measure its pH. If the pH of the excess water is 5.5-6.2, I’m satisfied that the pre-soak has worked well enough. If it’s not within that range, I contact Grodan and ask for their advice.

Some growers pre-soak rockwool cubes and slabs by putting them into horticultural trays and using an ebb-and-flow hydroponics to circulate treatment water. When using loose rockwool (which is sold as shredded loose pieces), growers place the material into a large bucket and pour in the pre-soak solution. After the rockwool is drenched and soaked for several hours, the grower transfers it to a bucket that has holes in the bottom, and place that bucket in a place where excess water can drain and not create a mess.

Before I put seeds, clones or older plants into presoaked rockwool, I dry it out a little so it’s moderately moist but not soaking wet. Overwatering is one of the most common problems for novice rockwool users. Although some types of high-quality horticultural rockwool are made porous and aerated so they have unusually efficient drainage, if you water too often and too much, or if your grow-op drainage system isn’t set up for proper drainage, the rockwool may become waterlogged.

On the other hand, growers with extremely low humidity in their grow ops might find that Grodan rockwool dries out too fast, so you have to send a tremendous amount of nutrients water through your root zone. Grodan has professional, timely technical support. I suggest you contact them to tell them what type of garden you run and your environmental factors (especially humidity), before you purchase specific Grodan products.

Growers must also note that rockwool should be watered from above. Rockwool isn’t good at wicking water from bottom irrigation to transfer up into the root zone.

In the best rockwool marijuana growing systems I’ve seen, the grower is using drip irrigation from a reservoir with a pump timer that delivers very small amounts of nutrients water on an hourly basis.

Professional growers use sophisticated rockwool sensor system made by Grodan, the world leader in horticultural rockwool and rockwool management technology. Grodan has had an edge in developing horticultural rockwool because it has been able to test its products in Holland’s thriving indoor hydroponics agriculture industry.

This has helped Grodan develop and improve many types of rockwool to suit a wide variety of grow conditions. The company provides excellent technical support. I’ve always been very pleased with detailed tech support I get from Grodan when I’ve asked for help choosing and using rockwool products.

Nutrients Dosing in Rockwool

Because Grodan rockwool is so efficient in its ability to optimally release, store and transfer water, oxygen and nutrient elements into plants, growers save money on nutrients by under-dosing. For example, if the nutrients manufacturer calls for 4ml per litre, a grower would use 3ml per litre or even less, depending on how well the plants are handling the nutrients load.

Rockwool is much easier to flush than coco coir, soil or soilless mix, Flushing is useful because it clears plants of nutrients elements, producing cleaner buds that burn and taste better.

The rapidity with which nutrients salts can be totally purged out of rockwool is a benefit at the end of bloom phase, and any time during the growing season if the root zone has been overfertilized.

The main thing to remember is that in the world of hydroponics marijuana growing, one of the purest, most productive gardening methods is to use rockwool and synthetic hydroponics nutrients. Only deep water culture and aeroponics provide better nutrients control and more oxygenation in the root zone.

Please note: I don’t recommend using organic nutrients in rockwool, as organics are likely to clog the medium and foul it, creating habitat for harmful fungus gnats and root rot.

Also note: a two cubic-foot bag of Grodan cubes or chunks has instructions printed on it claiming that one bag will fill 23 1-gallon pots. It won’t. I can only fill between 12-14 gallons of pot space total from two cubic feet of cubes or chunks.

For growers who’ve been using soil, coco coir, lava rocks, or soilless mix and have been experiencing problems with nutrients and/or root zone pH, Grodan rockwool is a great alternative. For anyone with more questions about whether rockwool is right for their garden, contact Grodan directly.

Looking for a sterile, easy-to-use root zone media your marijuana roots will love in indoor grow ops? Then you need to look at rockwool. Rockwool is one of the most useful hydroponics growing media ever invented. It’s made from basalt, a volcanic rock composed mostly of silica, and also contains smaller amounts of titanium, iron…