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starting marijuana seeds in rockwool

Starting marijuana seeds in rockwool
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.

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.

Take 1-2 seeds and insert them carefully into the holes. Use a toothpick or similar object to push them down to the bottom, as you want them to be at the bottom of that hole. Rip or push a piece of the Rockwool over the hole (you don’t have to fill it completely), so that the seed can germinate in a dark moist environment.

How To Start From Seed With Rockwool Cubes

In this lesson, we will learn how to start your own seed with Rockwool Cubes. Below is a detailed guide to success with Rockwool, and a step-by-step video tutorial can be found at the bottom of the page.

Preparation

Items you will need:

Rockwool Cubes have a PH of roughly 7.8. This is pretty alkaline, yet our plants prefer to grow in a slightly more acidic environment (between 5.5 – 6.5). In order to prepare our Rockwell cubes for the seeds, we need to soak them in some PH adjusted water, that way they have everything the seeds need to germinate and sprout; water and a slightly acidic environment.

Step 1: Hydrate And Stabilize The Rockwool Cubes

Get a bowl or some other container that is big enough to fill with water and have room left for your Rockwool cubes. Your average salad bowl will work fine for 3 Rockwool cubes, if you are planning on doing more than you will need a larger container.

Fill the container/bowl with water from your tap. You may also choose to use water filtered through a britta or reverse osmosis (R/O) water, I’ve had success with all 3 of them so whichever you have on hand will work fine.

Using either a PH test kit or a Ph meter, determine the Ph of the water. Water comes out pretty alkaline, usually around 7.4, so you will need to acidify it a little bit to bring that Ph down to the desired level. Aim for as close to a Ph of 5.5-6 as you can get.

To accomplish this, use either Ph down chemicals, or lime juice (as it’s acidic). Add these to the water in small increments (VERY SMALL), and test the water to see where the Ph is. Continue doing this until you have a Ph of 5.5-6.

Important: Do not let the PH of the water go below 5. A Ph this low will damage the fibers of the Rockwool Cube

Now that we have the Ph adjusted water, it’s time to stabilize and hydrate the Rockwool cubes in it. Insert the Rockwool Cubes into your container and let them soak for roughly 1 hour. Once the hour is up, the cubes will be big and fat with water. Take them out of the bowl of water and put them somewhere you don’t mind getting a little wet. Save the remaining water for step 3.

DO NOT SQUEEZE THEM TO DRAIN ANY WATER

Rockwool Cubes are designed to maintain the correct water to air ratio and squeezing them may damage their structure. Some of the marijuana forums advocate doing everything from squeezing them completely dry, all the way to flinging them around like paintbrushes in order to get excess water out. None of that is necessary, leave it as it is. It will stay moist for several days without needing to be watered this way as well.

On top of that, Rockwool is like asbestos, you don’t want to be squeezing it or breathing it or generally touching it any more than you need to. Here is a good article on some of the health concerns of Rockwool. I use it because it is what works best, but be cognizant to the fact that it is a potentially dangerous substance to be making contact with so don’t do anything more than you need to with it.

Here is what it should look like:

Step 2: Plant Your Seeds

Most Rockwool cubes come with holes in them, if yours did not, than create a hole in one side that is approximately a quarter inch (0.75 cm) deep.

They should look like this:

Take 1-2 seeds and insert them carefully into the holes. Use a toothpick or similar object to push them down to the bottom, as you want them to be at the bottom of that hole. Rip or push a piece of the Rockwool over the hole (you don’t have to fill it completely), so that the seed can germinate in a dark moist environment.

Now, if you can, place them in a tray with a dome on it. This will help create a little humidity in there which seedlings like. This is not mandatory, but it helps. Whichever you choose, take your cubes and put them in a cool dark place, and leave them alone. The temperature should be roughly 68 degrees F, though my house stays at about 72 and they do fine there. I usually place them above my refrigerator and just leave them for a day or two. My lettuce seedlings sprouted with a quickness the last time I tried, and by the 3rdday they had grown so tall that I had to take the plastic dome off of my container because they were bumping up against the ceiling.

Step 3: Leave Them Alone And Let Them Grow

If you put more than one seed in your cube (just in case one didn’t make it), than you probably have several seeds sprouting up in each cube at the end of

3 days. Once the first true leaves emerge, we want to select for the strongest one (the one that grew the tallest), and cut off the tops of all other seeds that are growing next to it. Do not pluck them out, as you may uproot it’s neighbors. Simply cut it off as close to the hole as you can without messing with the stronger one that you plan on keeping alive.

Depending on how hot it is (and other factors) you may need to water your cubes 1-4 times a day. Use the Ph adjusted water when doing so (that’s why I had you save the leftovers from step 2). If you already threw that water out, go make another batch of Ph adjusted water and keep it in a separate bottle or container for watering. Note: Do not over water, in fact while some say to water 1-4 times a day, I did it only once a day when I got home after work.

Some people claim they use a diluted nutrient solution to water their Rockwool cubes with during germination. Do not do this, as my experience has always been negative. Note the picture below, where I did an experiment by adding a very diluted grow nutrient to the Rockwool cube on the far left. It died within an hour or two, and the others went on to live happy lives. In my opinion, they do not need nutrients until they get into your hydro system.

Do not add any nutrients to your Rockwool Cubes. The one on the left got nutrients, the other two did not.

Step 4: Transplant Into Their Final Destination

About 2-3 weeks after germinating, you are ready to transplant these babies into the hydroponic system of your choice. A good rule of thumb to go by is that you want to transplant them once the first roots begin poking out of the Rockwool cube. Don’t wait too long though, as eventually the roots will begin tangling around the cube since it is their only source of water. You want to catch them right as they pop out, so that when you transfer them into your hydro system the roots will grow down into the system, and not just try to feed off the Rockwool cube alone.

If you have any questions, suggestions, or comments, please leave them below and I will do my best to answer all of them.