Planting cannabis seeds rockwool

Planting cannabis seeds rockwool

If you’re ready to start growing and want to find out the best seedbanks that ship to the U.S. click here.

After acquiring growing equipment and cannabis seeds I now had everything I needed to start growing marijuana. The first major step in this process is germinating the seeds or getting the plant to sprout from the seed.

The Plan: Use Rockwool to Sprout and Grow

There are many numerous methods germinating seeds. Popular methods include using paper towels, solo cups or just directly inserting seeds into soil.

I decided to use rockwool cubes as my germination / sprouting medium. It seemed like many people had success using rockwool to start their homegrows. In addition, I liked how after they sprouted it’s easy to transport to soil (the cube has a solid structure) without disturbing the root structure which stresses the plant.

My plan for growing the marijuana plant using rockwool was as follows:

  • Insert the cannabis seed in the rockwool cube (1.5 inch size)
  • Let it germinate and sprout
  • Transfer the cube into a pot with soil
  • Let it grow and flower on my balcony
  • Harvest the fruits of my labor

When formulating this plan I was a little hesitant as I hadn’t seen that many people using this process. Most people if they use rockwool stay with rockwool in a hydroponic indoor growth setup. I didn’t find many people who took the rockwool cube and transferred it to soil after it sprouted and wasn’t sure if this would work.

From this Question & Answer post someone asked if you could use rockwool outside and answered:

Sure, you can grow autoflowering plants using rock wool cubes outside or inside. If you are using the large cubes you can put them into a fabric container, plastic, etc., but they do need a place for the water to run out of them when it rains and when you water.

Granted this was only one answer and didn’t mention if it’s OK to transfer rockwool directly into soil. A little further digging and I found this snippet from another guide which said:

Another method is to use 3″ rockwool cubes to start seedlings in, then put 20 of them in a litter pan, cover it with another pan, and transport this to the grow site. The cubes can be planted directly into soil.

That was good enough (I’m so trusting about stuff I read online) for me so I decided to proceed.

Below will show you what the whole process looks like in video form:

Preparing Rockwool Cubes for Germination

The downside to using rockwool is the need to prepare the cubes before you insert your seeds. Rockwool has a pH of 7.8 and plants like a pH range of 5.5 – 6.8. If you were to simply insert the seeds into rockwool soaked in regular water the pH would be too high and will cause the seed not to sprout or kill the seed.

To prevent this from happening you use an acid like pH Down (phosphoric acid) which can bring down the pH level of the water you plan to soak your cubes in. This is why it was important to buy a reliable pH meter.

Calibrating the pH Meter

The pH Meter I bought was new so even before I could start soaking my cubes I needed to calibrate it first.

Bringing Down the pH

Now I had to mix a proper pH water solution to soak the cubes in. I filled a plastic food container with Brita filtered water (don’t think this is needed, but why not?) and added 0.25ml (a few drops) of pH Down. I stopped when I got to a pH level of 6.1.

IMPORTANT NOTE: Use pH Down sparingly as it’s a strong acid and will quickly bring down the pH level if you use too much. I ended up going too low and had to add more water to bring the pH back up. Better to be more conservative with this stuff.

Soak the Rockwool Cubes

With the rockwool cubes properly pH adjusted to 6.1 I placed 5 rockwool cubes into the solution for 60 minutes. As for the exact time to soak I found conflicting advice. Some guides said to soak for a whole day while others said 15 minutes. I took a gamble with 60 minutes.

Remove Cubes and Let Drain

After 60 minutes I removed the rockwool cubes and let it drain in the sink for 10 minutes. I was surprised how little water came out and how firm the cubes still were after being soaked. I thought from pictures that rockwool would be like a sponge, but it holds its structure surprisingly well.

Another tip I learned is to not squeeze out or shake out the water from the cubes. You want the cube to be damp as the wetness is what helps trigger the germination process.

Saving Some of the pH Adjusted Water

Instead of tossing away the reduced pH water I saved some in a separate container. As you wait for your seeds to sprout you may need to re-water the rockwool cubes if they get dry. Re-using this water saves you from having to mix up another batch of reduced pH water.

Insert the Seeds and Store

Now that the cubes were properly prepared it was time to insert the marijuana seeds and store them in an ideal sprouting environment.

Inserting the Cannabis Seeds

I placed the cubes into the seedling starter tray and then inserted each seed about a quarter of an inch into the 1.5 inch cube. The seeds are really tiny so to help I used tweezers to place them inside the cubes.

Here’s a video of me inserting one seed into a cube:

Place Humidity Lid and Store

With the seeds now inserted I placed the humidity dome / lid onto my starter tray (came with the set I bought). The reason for the lid is it helps keep the humidity high which assists with the germination process.

In addition to humidity in order to trigger the sprouting process experts advice to place the seeds in a dark environment. This mimics being in soil and coaxes the seed to sprout. To do this I placed the tray onto a shelf in a storage closet.

Wait for Sprouting

Once setup it could take anywhere from a few days to a week or more before the seed sprouts. Just check on it each day to see the progress. You probably won’t need to add additional water as rockwool does a good job at retaining water. However, if you touch the cube and feels dry it doesn’t hurt to add some of the pH-adjusted water you saved from earlier.

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Below you can see a time-lapse of a marijuana seed germination process.

FAQ on Cannabis Seed Germination

If you are using the rockwool cube germination method and have followed the procedure correctly it could take 2 days or up to a week for it to germinate. If it’s over a week there could be issues.

Don’t get too deep. No more than a quarter of an inch.

Find a dark place or room to store the seeds. In order to germinate the seed needs to be in darkness so avoid places where light could leak in.

You need to make sure the pH of the water you used is in the correct range, 5.5 – 6.8. Depending on your pH meter it could be off as well if not properly calibrated or if you are using a cheaper pH meter. In these cases try removing the seed and re-soaking the rockwool cube in another batch of pH-adjusted water

There are multiple ways to germinate seeds. The rockwool cube method describe here is just one method. In addition, another popular method is the “paper towel” method where you place the seeds into a water soaked paper towel.

Successful Germination, Now What?

Congrats! If you succeeded in getting your cannabis seeds to sprout you are now on your way to growing a healthy marijuana plant.

Checkout our other marijuana grow phases posts to make sure you continue to succeed.

Where to find marijuana seeds ideal for growing in rock-wool?

Here is how rockwool is used in the cultivation of hemp

Many cannabis lovers wonder where to find ideal cannabis seeds for rock-wool cultivation: but are you sure you want to grow marijuana seeds in rockwool cubes? Before you do, there are a few things you should know.

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First of all, growing cannabis in Italy is illegal: the hemp plant produces inflorescences containing THC, the active ingredient of marijuana, which is illegal in percentages above 0.5%. For this reason, the cultivation of hemp is prohibited, even if it is no longer a criminal offence in case of small cultivation for personal use: what is legal is instead to sell and buy cannabis seeds. But what is the reason?

You should know that weed seeds do not contain THC in themselves and an inactive state is therefore considered in the same way as the common seeds of other types of plants.

The legal problem arises when they are germinated, as they would give birth to a hemp plant that would produce flowers with a high THC content.

So, if you are wondering where to buy marijuana seeds, the answer is in a grow shop, physical or online, such as SensorySeeds, and if you want to germinate them, you take a significant risk. Theoretically, the uses of marijuana seeds in Italy are as follows:

The use of stone wool as a substrate for the cultivation of hemp is a very particular technique and has, like all the others, pros and cons. Let’s see what it consists of and what are the advantages and disadvantages of growing cannabis seeds in rock-wool.

Growing cannabis seeds in rockwool: what is it and what are the advantages and disadvantages of using it

You’ve probably already heard of rock-wool but didn’t know it was also used to grow cannabis seeds and it wouldn’t be so strange if you didn’t have the slightest idea what it is. Rockwool cubes are, contrary to popular belief, an artificial product, created by man to imitate a typically Hawaiian natural phenomenon.

Pele’s hair is basaltic glass filaments born from the volcanic eruption of Kilauea, in the Hawaii islands. Due to the strong wind, the lava solidifies into a filamentous form that resembles blond hair, just like that of the god Pele. Artificially, therefore, this natural process is reproduced, solidifying basalt slag in filamentous form, using air flows, to obtain rock wool cubes.

The advantage of this type of substrate for the cultivation of cannabis seeds is linked to its humidity gradient, capable of retaining and distributing all the nutrients nebulised on it homogeneously. However, rock-wool tends to dry quickly on the surface, remaining more humid on the ground, so it should be continuously monitored.

Another great advantage of rock-wool cubes for growing marijuana seeds is that they can be placed in larger cubes as the plant grows, without disturbing its roots in any way. It will avoid having to move the cannabis seedlings from one pot to another, protecting their good health.

This type of substrate is very often used in professional hydroponic marijuana crops because of the absorbing power of its filaments. However, if it goes well in professional hydroponic systems, it presents risks in the management of home growing, which is legal in some municipalities of Spain.

The absorbing power of the filaments is a double-edged sword: if poorly handled it can lead to overloading of liquids underneath or excessive dryness since in a few hours they tend to slip away. If used outside of a hydroponic system, rockwool should be followed very carefully from this point of view, both to prevent it from staying dry for too long and not to have an overload of nutrients in the plant.

Now let’s see what the main steps are for growing ganja seeds in rock-wool.

Growing cannabis seeds in rockwool – that’s how to do it

As said before, growing weed seeds is not legal in our country, as they would lead to the production of high THC flowers. However, there have been cases where the law allows the home growing of marijuana for personal use, as it happens in some cities in Spain.

If you were to choose to grow marijuana seeds in rockwool cubes, you would first need to know how to handle this type of substrate. While it has a high absorbency power, it also has a rapid “slip” of liquids underneath, which you should keep under control to avoid nasty surprises.

First of all, you should know that rockwool has an average pH of 7, which is too alkaline to grow cannabis seeds, so it needs to be treated before using it. What you need to do is to soak the rock-wool cube in a nutrient solution with pH at 4.5 and CE (electrical conductivity) at 0.4-0.5, to stabilise the PH of the cube properly.

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To be sure that you have obtained the appropriate value for growing marijuana seeds, the cube must be soaked in a nutrient solution with pH 5.5 and the PH of the runoff from the filaments measured: if it remains the same, it is ready. On the contrary, if it is still too high, it will be useful to re-immerse it in the first solution for a few hours and then redo the test until the desired PH is reached.

Once this is done, you can finally place the cannabis seed in the rockwool cube, after having previously soaked it in warm water or moistened it in the previous 24 hours using absorbent paper, all strictly in the dark. Once activated, in a few days the maria seed will hatch and the first cannabis bud will be born, which will soon open its cotyledons, the first two round leaves, and will harpoon its rootlets to the filaments of the cube.

As soon as the seed is placed in the rock-wool, it will be useful to keep it at a constant temperature of 20°-25°, which can be obtained if necessary, with a suitable lamp, lit above the cube. Maintaining humidity is very important, so unless you have created an automatic hydroponic system, you will often need to check the level of impregnation of the stone wool cube.

Once well rooted, the hemp seed can be relocated, without having to extract it from the first one, in a larger rockwool cube, previously treated as we have seen before. At this point, the hemp seedlings will be ready to be exposed to artificial light in a cultivation room.

Where to buy cannabis seeds suitable for growing in stone wool?

As you have read in this article, growing cannabis seeds in stone wool has its pros and cons. Its use is certainly more suitable for professional crops. Still, there is nothing to prevent it from being used at home, in countries where the cultivation of marijuana seeds is allowed, with adequate attention.

If you are wondering where to find marijuana seeds suitable for this type of cultivation, the answer is SensorySeeds, our online cannabis seed shop. Inside you’ll find lots of weed seeds BSF, from feminized seeds to auto flower seeds, as well as fast flowering seeds.

You’ll be spoilt for choice, and you’ll be able to receive the best cannabis seeds directly to your home in a few days and in totally anonymous packaging to preserve your privacy.

So, what are you waiting for? Click here and enter SensorySeeds, the online shop with the best cannabis seeds on the market!

Best way starting seeds in rockwool?

Hey i really do need a BEST advice how to start my uniq seeds in high success rate! Some of my seeds may be damaged over years, but i need to try to save them!

Strains,
Whitewidow x Euforia x “Mindfuck”.
Ghost of Ghana 100% equatorial sativa. (special).
Food of Gods secret strain from village of south Africa! (special).

Professional advice = reputation+

Charlie Green
Well-Known Member
Humboldt14
Well-Known Member

germinate them them move them to the rock wool cubes

Charlie Green
Well-Known Member

germinate them them move them to the rock wool cubes

Humboldt14
Well-Known Member

germinate them what ever method you prefer to use,

I use the paper towel method 100 percent success rate for me, then once the little white tail pops out of the seed, then move the seeds to the 1 inch rock wool with the tail facing down in the hole then lightly put a little piece of rock wool over the hole that the seed is in.

Dirty Harry
Well-Known Member

Soak the rock wool in 5.5 PH water for an hour or so. Squeeze out a little water from each piece. Put a seed 1/4- 1/2 inch in each one and put a cover or humidity dome to prevent from drying out. When they pop, keep them moist and under cover until they get a good start.
Any seed that doesn’t pop just didn’t pop. Pre-germination is just a say to see what seeds pop before you put them in what ever. Some of those will die before they pop out after being put into what ever.
I find it is less stressful on the seeds to just start them in what your going to grow in as they can be damage when moving them when they are just a sprouted root. but that is just MHO and it works for me. Your mileage may differ.

Humboldt14
Well-Known Member

you dont use a humidity dome for starting seeds and second rockwool cubes will not dry out. they retain allot of water, and with

seedlings in them you would not have to water for about a week maybe longer.

i have a Hydro set up also so i have been starting seedlings in rockwool for years.

Dirty Harry
Well-Known Member

you dont use a humidity dome for starting seeds and second rockwool cubes will not dry out. they retain allot of water, and with

seedlings in them you would not have to water for about a week maybe longer.

i have a Hydro set up also so i have been starting seedlings in rockwool for years.

Just stating my opinion and am not going to argue about it. But trust me, rock wool dries faster than you think when it has seeds/sprouts in it. Cost me some $ to learn that lesson.

Charlie Green
Well-Known Member

Well i putted them in wet toilet paper and inside 2 saucers holding them locked inside. I didnt soak it with water i just made the paper wet. Now im waiting them to crack that shell open, then i will fast plant them into rockwool carefully (becouse later when the root is too long its more danger them to put in rockwool). So lets see what happens! I will start posting some pics also.

ganicsarebetter
Well-Known Member

germinate in paper towl folded up, leave a littel pocket, and moisten the paper towe, and keep moist. leave it in a tupperware contaier in the dark for 3-7 days, keeping the towel moist, and you should see the embryo.

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another ethod that ive HEARD works is just to put in a shotglass over night, see what happens ins the seed absorbs the moisture until it pops. thats what ya want..

the paper towel method ALWAYS works. IMO

Dwezelitsame
Well-Known Member

i would have soaked mine over night first 75 percent of time is split the next day

from there go to paper towel all in dark on heating pad at about 80 degrees

once split i transfer to cup with holes in bottom covered with a baggie and rubber band for a little greenhouse effect once soil break i remove plastic once again all heating pad .. i normally use heating pad until first transplant at 3 or 4 weeks old

Fuzzbutter
Active Member

Pre-sprout your seeds in a moist paper towel and then plant in the rock wool once the spouts are over 1/2″ I did this and got 14/20 sprouted from which I had to pick 7 and they are all doing AMAZING.

It’s easy:
get 2 paper towels
fold them in half together
place the seeds in-between the folded area
dampen the paper towel (damp, not dripping, but not too dry either)
place the damp paper towel with seeds in a ziploc bag
put them somewhere dark for a couple days
ta-da!

Also, rock wool is naturally alkaline, so you’ll need to soak it in PH balanced water over night first before putting ANYTHING in it. My plants are currently in rock wool and doing great

Fuzzbutter
Active Member

you dont use a humidity dome for starting seeds and second rockwool cubes will not dry out. they retain allot of water, and with

seedlings in them you would not have to water for about a week maybe longer.

i have a Hydro set up also so i have been starting seedlings in rockwool for years.

Just stating my opinion and am not going to argue about it. But trust me, rock wool dries faster than you think when it has seeds/sprouts in it. Cost me some $ to learn that lesson.

He’s right, rock wool can and does dry out very fast. I had to work with professional hydroponics in my horticulture classes and we ended up losing a whole crop from a tard forgetting to properly set the water timer and the cubes dried up.

Serapis
Well-Known Member

I don’t know where the paper towel method started, I only know that it has been around far too long. I first learned of it over 30 years ago. It’s hogwash. does it work? Most of the time, but why risk handling a delicate seed and it’s new born tap root when you can simply place the seed in any moist medium and have it germinate? If the seed germinates in a paper towel, which surely can’t sustain the seed, won’t it surely germinate in moist rockwool?

Please don’t tell me God created weed that needed man’s assistance to sustain it’s self because there is no paper towels laying around in mother nature. LOL I’m sorry, but I have to laugh at the though of all the extra work towlies have to go through. Just plant the seed already, if it’s viable, it will grow, because amazingly, it is a weed. It’s hardy. The only time the plant has troubles is when we try to care for them.

Serapis
Well-Known Member

He’s right, rock wool can and does dry out very fast. I had to work with professional hydroponics in my horticulture classes and we ended up losing a whole crop from a tard forgetting to properly set the water timer and the cubes dried up.

Yep, you can skip the dome ONLY if you are flooding the tray and watering from bottom up, which is actually recommended. I understand Humboldt’s concern too, because moist seedlings in a cold environment run the risk of damping-off disease. Those trying to avoid damping-off disease, usually the same one’s who have lost crops to it, do not use dome tops unless absolutely necessary. So it’s not that one guy is more right than the other, it is just 2 different methods. Pick the one that best suits you or develop a 3rd.

Well-Known Member
Serapis
Well-Known Member

No, I sense a debate/argument brewing with this one. lol Also, we haven’t heard the other 27 ways to do it yet.

Well-Known Member

i know, i know. i think you nailed it pretty much with the viability aspect. i personally use root riot plugs but i have also had 100% success rate with striaght into coco and water. i don’t know why people make a big deal out of germinating seeds, it couldn’t be much simpler.

Serapis
Well-Known Member
Fuzzbutter
Active Member

I don’t know where the paper towel method started, I only know that it has been around far too long. I first learned of it over 30 years ago. It’s hogwash. does it work? Most of the time, but why risk handling a delicate seed and it’s new born tap root when you can simply place the seed in any moist medium and have it germinate? If the seed germinates in a paper towel, which surely can’t sustain the seed, won’t it surely germinate in moist rockwool?

It’s done because it gives a higher growth yield. This is a fact. In my horticulture class we were taught this by having to germinate seeds in different ways. Some were just dropped in soil, some rock wool, and others were pre-germinated like the above mentioned method. You get a higher yield because you are supposed to germ more seeds than you expect to sprout, once sprouted, so long as they are properly taken care of, you’re all set to go and you already know that your plants are started vs waiting to see it the seeds ever sprout. It’s very rare to lose a sprout from transplanting long as you know what you’re doing. Also, germinating with the paper towel method let’s you already see which plants are growing fastest and strongest so you can do an initial picking of stronger genetics to start with and possibly end up with better plants. I’m a wee bit stoned, so i hope this makes sense. I’ll re-read it later and edit if necessary. but I think that conveys what I’m trying to get at.