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starting cannabis seeds in rockwool cubes

starting cannabis seeds in rockwool

They should look like this:

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.

Starting cannabis seeds in rockwool
Germinating with starter plugs or cubes is easy and the most reliable method on this list.

Best Way To Germinate Weed Seeds

You’ve probably noticed by now that there are a few different methods you can choose to germinate your cannabis seeds.

Not all of these methods have the same success rate, and your precious cannabis seeds are expensive to buy.

Therefore, you really want to choose the germination method that’s going to give your seeds the best chance to become beautiful, bud producing plants.

So what is the best way to germinate weed seeds? Read on to find out…

Related posts from GreenBudGuru

Best Way To Germinate Weed Seeds

First, take a look at the comparison table below to get an idea of some general success rates for each germination method.

We’ll explore each method in more detail below.

Germination Method Success Rating
1. Starter plugs & Seedling Cubes 5/5
2. Planting directly into soil 3/5
3. Soaking seeds in water 4/5
4. Paper towel method 3/5

1. Starter Cubes & Seedling Plugs

This is by far the best method to germinate weed seeds.

Germinating with starter plugs or cubes is easy and the most reliable method on this list.

What Plugs Should You Use?

Options for starter cubes are seemingly endless, but the majority are made of either rockwool or peat.

The differences are subtle, but very important depending on how you plan to grow your plants after germination.

Peat plugs are an organic option, and sometimes contain a small starter nutrient charge which helps young seedlings after germination.

Rockwool cubes, composed of fibrous wool-like material provide great water and air exchange, which is ideal in hydroponics.

Peat plugs hold more water than air compared to rockwool cubes, so they aren’t ideal for hydroponic grows.

So, rockwool or peat? The primary difference comes down to how you will grow the plant after germination.

For hydroponics, rockwool is the better choice.

For soil/coco/etc., peat plugs generally fare better, but ultimately germination will be nearly identical for these two germination mediums.

How To Germinate With Plugs:

Step 1: After buying your plugs or cubes, soak them in water until they are fully saturated.

Step 2: Place your seed(s) into the pre-cut holes in the plugs. Use some of the plug material to gently cover the opening.

Step 3: Put the plugs into a square box or tray and cover with a plastic dome. This ensures a high humidity environment, which increases germination success, and helps seedlings along after germination.

2. Planting Directly Into Soil

This method is as old-school as it gets, drop your seeds in some dirt, add water, and you’re done.

If only it were that easy!

Unfortunately, it’s not quite so simple.

There are lots of factors that go into this method, and each must be nearly perfect for germination to occur.

How to germinate seeds directly in soil:

Step 1: Purchase quality soil from a reputable source. You want soil with good drainage, this allows for air exchange; seeds need moisture but you don’t want to drown them.

Step 2: Now, you need to plant your seeds at the right depth. A good rule of thumb is to plant seeds 2 times deeper than the width of the seed.

Step 3: Provide water for your seeds by soaking your container in a tray containing about an inch of water. This allows the soil to be moistened uniformly, preventing over-watering. This also keeps the seed in the perfect place for germination to occur.

Check out this method in action:

This method allows you to start your seed directly in your planting medium, but if you aren’t careful with this technique, you can run into trouble.

Seeds need air and water to germinate, if there’s too much of one, the other falls short, preventing germination.

If planted too deep, the energy available to the seedling won’t be enough for it to break the surface.

This will essentially starve and kill your seedling.

If you don’t plant deep enough, the seedling may dry out, or never become moist enough to germinate.

3. Soaking Seeds in Water

This method is not so much a way to fully germinate your seeds, but rather ensures rapid and reliable germination.

As mentioned in the previous methods, seeds need water to germinate.

This method involves placing seeds in a container filled with water rather than into a plug or the soil.

How to start germination with water:

Step 1: Place your seeds in a container of clean water and allow to soak overnight, or for at least 12 hours.

Step 2: After soaking at least 12 hours, use sterilized tweezers or clean hands to remove the seeds. Immediately place the seeds into your medium, such as a plug or soil.

Check out this method in action:

Why does this work?

This method increases germination rates because the seed is primed, it’s already absorbed water and broken dormancy, so is ready to push out it’s first roots.

4. Paper Towel Method

The paper towel method is similar to soaking seeds in water, but this method will germinate your seeds to the point where the taproot has emerged.

How to germinate seeds with paper towels:

Step 1: Place a folded wet paper towel into a plastic container, or on a plate.

Step 2: Place your seeds on the paper towel with adequate space between them. Cover the seeds with another folded wet paper towel.

Step 3: Put a lid or plastic wrap on the container, or another plate on the plate. Seal the container but leave a small hole for air exchange.

Step 4: Place your plates or container in a warm (70-80F / 21-26C) and dark environment

Like soaking the seeds in water, this method provides lots of water to the seeds to start germination.

But it also allows enough air exchange for the seed to produce a taproot and begin growing into a seedling.

Check out this method in action:

This method helps to increase the chances of germination and seedling success, but can introduce some extra issues.

  • Once seeds have germinated, they may grow into the paper towel, making removal difficult and potentially damaging the fragile seedlings.
  • The paper towels and the container you use for germination must be sterile. This is nearly impossible, so you are likely to grow more than seedlings (i.e. fungus) with this method.
  • The extra handling of sprouted seedlings is the biggest issue with this method. Even if you’re very clean and careful with your seedlings, it is extremely easy to damage or contaminate them. Contamination and early damage can ultimately stunt or kill your baby plants.

Verdict

So what is the best way to germinate weed seeds?

After examining each method, if you absolutely had to pick one, it would be starter cubes and seedling plugs.

If you consider everything that can go wrong when germinating seeds, this method does the most to remove potential pitfalls.

Why Plugs?

  • It’s relatively fool-proof because the cubes can only hold so much water, so no overwatering.
  • The pre-drilled holes are not too deep or too shallow for cannabis seeds.
  • The cubes/plugs hold moisture for long enough time to allow for the seeds to take up water. They also won’t dry out too quickly.
  • They provide a soft medium for young roots to push through.

But the best way to germinate weed seeds would really be a combination of these methods.

Use either the paper towel or water soaking method to get your seeds to uptake water.

Next, transition them to either soil or plugs.

This gives you the advantages of each method, with the least downside of each.

Germination Tips

Here are a few extra tips to follow when trying to germinate your cannabis seeds:

  • Keep temperatures in the area you are germinating seeds between 70-80F (21-26C)
  • Germinate seeds in total darkness
  • Don’t use hard tap water (ppm above 120), it can damage the seed
  • Avoid using chlorinated tap water, it can damage or kill microbes that help young seedlings develop
  • Don’t add nutrients to the water when germinating seeds, the seeds already contain all the nutrients they need
  • When seeds germinate, don’t put them under intense light (HID or sunlight), the seedlings will burn and/or dry out
  • Provide non-intense light (i.e. T-5 fluorescent light) for seedlings as soon as they emerge, this will prevent stretching

Related posts from GreenBudGuru

They should look like this: How To Start From Seed With Rockwool Cubes In this lesson, we will learn how to start your own seed with Rockwool Cubes. Below

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