How to Germinate Cannabis Seeds in Rockwool, Peat, or Coco

The time has come for your cannabis seeds from ILGM to arrive in the mail. You are now ready to begin your mission to become the next big thing in the breeding world, use complex hydro systems, or find the ultimate mother plant. (Why not?) Whatever your end goal, one thing’s for certain: everything starts with a seed, and germinating that seed is the beginning of the ripple effect.

Soil is not for everyone, and with so many growers expanding into the world of hydroponics, why not consider germinating marijuana seeds in rockwool, coco coir, or peat?

This article breaks down these various mediums for germinating seeds and provides step-by-step guides to make the process easier.  Understanding the various germination methods also helps ensure 100% germination rates and encourages a thriving young seedling.

So roll one up, brew your favorite tea or coffee, and let’s learn which growing medium is best suited for you and why.

Key takeaways/TL;DR

• Cannabis germination needs air, water, heat, and darkness.
• A soilless growing medium does not contain organic matter.
• Peat is made from Sphagnum Moss and taken from the Earth.
• Coco is made from the outer shell of coconuts and is buffered.
• Rockwool is made from melted and spun volcanic rocks.
• Rockwool will need to sit in water with a pH level of 5.5 for 4–5 hours.
• Cannabis seeds require 3–7 days to germinate inside a jiffy.
• Overwatering a jiffy can cause pathogens and affect germination rates. 
• Cannabis seeds can be germinated inside tissue paper, water, or directly inside a jiffy
• An aquarium heating mat, or heater, is a good way to maintain a consistently warm environment.

The Needs of the Seeds: Air, Water, Heat, and Darkness

Cannabis seeds are simply amazing. They act as a genetic time capsule ready to be explored by growers worldwide. As a beginner grower, it is wise to understand the fundamental requirements for a seed to flourish, providing you with unforgettable memories. 

There are several ways to germinate cannabis seeds. If you tried germinating your seeds in water or with moist paper towels, you gave them a head start that encouraged the seed shell to split open and a tap root to reveal itself. Once sprouted, you now have a seed with a long, fuzzy tap root. 

However, you can also plant the seed stylar side down (pointy side) directly into a jiffy plug. If that’s your path, below are a few factors to consider.

Air

Roots will grow from a seed in search of air and space. Oxygen around the seed and inside the growing medium will promote healthy new growth and allow the tap root to grow out and firmly establish itself. 

Water

A seed must detect that there is enough water available for it to germinate and successfully grow. Water is one of the most important things you can provide a seed. However, a balance between humidity, temperature, darkness, and oxygen is key.

Heat 

Weed seeds will not want to germinate in cold conditions, as they will be under the impression it is wintertime. A warm and moist environment is optimal – meaning staying within the range of 68–85 degrees Fahrenheit (20-30 °C), with a sweet spot of 75-76 °F (24-25 °C) – is the preferred temperature range for encouraging seed germination and growth. The best way to achieve a consistently warm temperature that’s ideal for germinating seeds is an aquarium heating mat or heater.

Darkness

Before your plants can enjoy all that high-intensity indoor lighting you have lined up for them or the Spring season ahead, they need to start life in darkness. This is when the shell will begin to crack open, and the tap root will emerge.

Can I Germinate Marijuana in Peat, Rockwool, or Coco?

The short answer is yes, and with much success. Peat pellets, rockwool cubes, and coco coir jiffy all possess excellent water-retaining ability and high volumes of air, making for the ideal starting block. The question you should be asking yourself is, which one is best for me and why?

Introduction to the Soilless Growing Mediums

There are many reasons why you may germinate seeds in a soilless growing medium. Perhaps you are just fed up with working with messy soil and do not plan on making any more trips back and forth to the garden center, carrying 50-liter bags of potting soil over your shoulder while reluctantly smiling at your nosey neighbor. Below is a short and sweet introduction to the soilless growing mediums of peat, rockwool, and coco, as well as what to expect.

Matthew DeBacco is a Professor of Agronomy (MS) as well as Plant Pathology and Horticulture (BS), who teaches several courses on the Horticulture of Cannabis at the Department of Plant Science and Landscape Architecture at the University of Connecticut.

Be sure to like and subscribe to his channel: https://www.youtube.com/@DeBaccoUniversity

Peat is Made from Sphagnum Moss

Peat has a dark brown color, high water-holding capacity, and provides plenty of oxygen. Harvested out of the ground on peatlands, where the earth consists of dead organic decaying material, peat is not really a hydroponic medium for growing cannabis. Yet, it is perfect for germinating cannabis seeds. Peat is an excellent substrate for growers who need to be away from their plants for long periods without worrying about watering. 

Rockwool Is Made From Melted And Spun Volcanic Rocks

Rockwool contains no nutrients and is notorious for producing massive yields for cannabis and commercial fruit and vegetable production. The first thing you need to know when kick-starting your indoor project using rockwool cubes is that the cubes will need soaking before use. Rockwool must sit in water with a pH level of 5.5 for 4–5 hours. Drain the rockwool cube, tray, or slabs before using; this superb hydroponic growing medium can hold up to 18 times its weight in moisture.

Coco Is Made From The Outer Shell Of Coconuts

To create coco coir, companies clean and remove the husk from coconuts; the soft and fibrous husk is used to grow cannabis and other plants and is very popular amongst indoor growers. Unlike soil, there are no microorganisms inside coco. In many cases, salts contained in the coco coir need buffering and treatment before use. Not all coco products are the same quality, so take your time to discover which brand offers the best.

What does buffering coco mean?

Buffering helps with salt levels. Due to the high salt content in some coco coir substrates, you should wash the coco coir before use. This process removes the excess salts and allows the substrate to become optimal for marijuana plant growth. It also balances calcium and magnesium levels. 

What Are the Pros and Cons of Rockwool, Peat, and Coco?

Choosing between these three excellent growing mediums and knowing how to use them for sprouting seeds can be confusing! Here’s a list of pros and cons of each medium to help you navigate through this important decision and give your plants the best start possible!

Peat: Organic and Neat but Expensive

Peat can be expensive and may not be best for a grower working off a strict budget. When buying a box of peat jiffy pellets, you may not feel the pinch; however, from an economic perspective, peat farming can affect the price of peat and even the quality of the product over the span of 5–10 years due to such high demand. Yet, peat is a more readily available medium at most gardening centers and local stores, which makes it a choice medium for many growers. 

Rockwool: Sterile, Consistent but Non-Compostable 

Did someone say sterile? That has to be music to the ears of anyone who has suffered from root rot in soil and is ready for a clinical laboratory-style approach. The only downside to rockwool is that, unlike coco or peat, it cannot be recycled or composted; therefore, eco-friendly incentivized growers may wish to find an alternative growing medium.

Coco: Holds Water, Well-Aerated but Salty!

Coco is my favorite growing medium and has many uses, from growing the best potatoes you have ever come across to growing big-yielding crops of cannabis buds. Not all coco comes treated and ready for planting, and the compressed blocks more commonly found in garden centers will tend to be full of sodium and potassium. Do not worry; a quick buffering will get the coco in optimal condition; however, germinated seeds may suffer in untreated and non-buffered coco coir.

Preparing Water with the Correct pH for Your Plants

Soaking your rockwool cubes or buffering coco coir is a necessary step to produce the ideal pH range for a cannabis plant’s roots to develop. To do this, start by preparing water with the correct pH. Then, you move onto the soaking and draining stage, which will enable the plants to access a full range of nutrients and trace elements. 

How to Germinate Cannabis Seeds in Rockwool

So you have decided to go down the rockwool route. Whether you are growing at home in a Nutrient Film System (NFT), Deep Water Culture bucket, or a commercial facility using automated dripper systems, everything starts with a rockwool cube. Here’s how to germinate cannabis seeds in rockwool for the ultimate head start in the hydro game. 

Necessary Materials and Tools For Germinating in Rockwool

• Rockwool cubes
• Tray of water
• pH up / pH down
• pH digital pen
• 1 pack of cannabis seeds
• Pair of tweezers
• Propagator

Step 1: Pre-Soak the Rockwool Cubes

Fill your tray with water, and using your digital pH pen, check the pH level of the water. Next, using a product to adjust pH levels in water, known as pH up or pH down, make sure the water in the tray reads 5.5. Then, simply place the cube, tray, or slabs inside the water and allow the dry rockwool cubes to become fully saturated.

Step 2: Drain the Excess Water

Once your rockwool cube feels full of water, remove it from the tray and drain the cubes. The excess water will slowly pour out the bottom. This can take between 4 and 5 hours. Once complete, you can insert the seeds into the cubes.

Step 3: Make a Hole for each Seed

Before you plant seeds into the rockwool, make a small entry point about ⅜ of an inch (1 cm) deep using the tweezers to make the insertion easier.

Step 4: Plant Seed in Rockwool

You must be extra delicate when inserting seeds into the rockwool. Make sure that the pointy part of the seed is facing downward. If you already have a sprouted seed, be careful of the tap root.

Step 5: Fill in Tops of the Holes

After firmly inserting your seed, cover the hole with a bit of rockwool.

Step 6: Place Inside Propagator

After following the previous steps, you’re ready to put your Rockwool cube in the propagator. This propagator provides the perfect conditions for your seed to start growing and sprouting properly.

How to Germinate Marijuana Seeds in Peat Pellets

Some garden centers may have small propagation kits with a lid, a base, and a small tray of peat pellets. This is all you need! This guide explains how to use those kits alongside your pack of feminized seeds for an exciting first-time grow. 

Necessary Materials and Tools For Germinating in Peat Pellets

• Peat pellets
• Tray of water
• 1 pack of cannabis seeds
• Pair of tweezers
• Propagator

Step 1: Place the Jiffy Peat Pellets in Water

First, remove the dry and compressed peat pellets, determine how many you will need, and place them into the tray of water. The peat pellets are already close to 5.5 pH levels, so unlike rockwool cubes, there is no need to pre-soak them in a pH-adjusted solution.

Step 2: Shake the Excess Water and Prepare the Pellet 

As the pellets expand and become thick and rigid, you can pick them up and gently shake them until there is no more dripping water. Now, use tweezers to make a 1 cm-deep hole for the seed.

Step 3: Make a Hole for Each Seed

Make sure that the seed is facing pointed side downwards. Using the tweezers, make a hole for each seed.

Step 4: Plant seed in Peat pellet

Carefully place the seed into the hole until there is a firm fit.

Step 5: Fill in tops of the holes

Cover the hole with Peat. Make sure to put enough peat on the hole so that it’s all covered up.

Step 6: Place inside propagator

Sit the pellet inside the propagator. You are now officially a grower! 

How to Germinate Cannabis Seeds in Coco Coir

Coco coir is my favorite hydroponic growing medium, and, in my opinion, germinating seeds in coco always produce the best seedlings. Coco jiffy pellets are small, compact, and dry pellets that rapidly expand once in contact with water and, just like rockwool and peat, are lightweight until soaked.

Necessary Materials and Tools For Germinating in Coco Pellets

• Coco jiffy pellets
• Tray of water
• 1 pack of cannabis seeds
• Pair of tweezers
• Propagator

Step 1: Place the Coco Jiffy Pellets in Water

Since coco and peat are so similar, you can pretty much replicate the step-by-step guide to peat pellets. Once you have determined the number of coco pellets, sit them in the tray of pH 5.5 adjusted water and let them soak up the water and expand.

Step 2: Shake the Excess Water and Prepare the Pellet 

Gently shake the wet jiffy and let the excess water drip out the bottom. Never squeeze the jiffy to get water out; doing so will ruin the structure of the jiffy.  Use tweezers to make a 1 cm-deep hole for the seeds. 

Step 3: Place the Seed

Place the seed, making sure the pointed side of the seed is facing downwards before firmly pressing down and covering the hole up. Seeds germinate well in this moist environment. All that’s left is placing the coco jiffy pellet inside a propagator and patiently waiting for the magic to happen! 

Step 4: Place Seed in Coco Pellet

Place the seed, making sure the pointed side of the seed is facing downwards before firmly pressing down.

Step 5: Fill in Tops of the Holes

Fill the tops of the holes by covering them up. Seeds germinate well in this moist environment.

Step 6: Place Inside Propagator

All that’s left is placing the coco jiffy pellet inside a propagator and patiently waiting for the magic to happen! 

What is The Expected Germination Time?

If anyone has spent hours staring at their propagator, waiting for seeds to pop up magically, it was me. Overzealous and obsessed, there is nothing more exciting than seeing your first-ever seedling come to life and emerge out of the pot, proud and ready for the marathon ahead. 

If you are a first-time grower, know that seeds can take 3–7 days to germinate inside rockwool, coco coir, or peat. Of course, if you have already opted to germinate them in water or tissue paper, you can shave a couple of days off. This makes the germination time in that scenario around 3–5 days before the first sighting. The following section will guide you through your next steps.

How to Transplant Marijuana Seedlings? 

Transplanting Jiffys into soil

To successfully transplant your jiffy and seedling into soil, make a hole the same size as the jiffy plug and gently insert it into the soil. The top of the jiffy should be above the soil.

Transplanting into coco coir

Growers using coco coir can transplant a jiffy plug into a coco slab (100 cm x 15 cm) or a larger pot of coco. In the event you are using a coco slab, then cut an X into the slab cover, insert your finger to make the right size insertion, and then gently place the jiffy inside.

Transplanting into rockwool

Usually, after germinating your cannabis seeds in rockwool, you’d transplant them into 4-inch rockwool cubes or meter-long rockwool slabs. There will already be a space for the rockwool, coco coir, or peat pellet to go inside. Simply make an X and insert the cube 2 inches deep when using slabs.

What Else to Consider When Germinating Seeds in A Soilless Medium

There is nothing really complex about transplanting cannabis seeds into a growing medium, regardless of whether they are fresh out of a pack or have a long tap root ready to go! There are, however, some basic things to remember:

Place the Seed Pointed Side Facing Down

When you ponder in amazement at how tiny but magnificent a cannabis seed truly is, you will notice, upon closer inspection, that there are two clear sides. One will be pointed (called the Stylar end), and the other will be round and smooth with a circle imprint. It is essential to make sure the pointed side is always facing down and in contact with the growing medium.

Be Delicate

Even though many growers are heavy-handed, you must be as graceful and delicate as possible when transplanting seeds, especially if the tap root is out. You do not want to damage the seedling in any way, shape, or form. You also do not want to lose the seed (it’s easily done!).

Use Tweezers

I find the best way to provide a delicate touch is to use a pair of clean tweezers. This approach will allow you to place the seed exactly where it needs to be. Using your fingers and thumb can work just fine, but do not expect the clinical finish that tweezers can provide. 

Sterile is Best

Whether you are using tweezers, scissors, razor blades, or scalpels, it is extremely important that all of them are kept clean and sterile. The same applies to using coco coir, rockwool, and peat; use hydrogen peroxide to ensure your starting substrate is pathogen-free. 

Mistakes to Avoid when Germinating Cannabis in Rockwool, Peat, or Coco

Overwatering Starves Your Seedlings of Oxygen

Coco, peat, and rockwool can hold tremendous amounts of water, which has many advantages for a mature cannabis plant. However, weed seedlings need all the tender, loving care they can get and a perfectly aligned environment. Remember, oxygen is a seed’s best friend, and overwatering your growing medium early on can cause germination rates to drop and seeds to develop slowly. 

Constantly checking and Being Impatient

When you cannot sit tight any longer (after 48 of the longest hours of your life), you may want to check if the cannabis seedling is coming out. You may think digging around in the jiffy is harmless, but you will do much more damage than good by constantly checking the state of the seed. Be patient, and good things come to those who wait!

Jiffy Pellets Should Never Be Cold

Cold temperatures can be a real problem for cannabis plants, especially during the earliest stages of development. Cold jiffy cubes generally mean the environment you have the propagator in is not where it needs to be. Your jiffy cubes should never be cold to the touch; they should always be warm and moist. 

Algae Growth

Noticing algae growing on your rockwool, peat, or coco pellets in the propagator can be a disturbing experience for a first-time grower. Algae will grow on jiffy pellets if there are nutrients present, and even though it is not the end of the world, it is still something you would prefer to avoid. Have some hydrogen peroxide on hand in the case of algae development and make sure to get our plant protector as well, just to be sure!

Bergman’s Plant Protector

• Protect your plants from diseases and harmful pests.
• Consists of three 20 ml bottles
• Enough plant protection system supplies for up to 20 plants
• Suitable for soil, hydroponic and all other grow mediums

GET YOUR PLANT PROTECTOR

Foul Smells are a Good Indicator of Bad News

When I say a bad smell, I mean a foul, rotten egg smell coming from the growing medium. The main culprits of a smelly growing medium are poor aeration, over-watering, and early signs of root rot. Beware of pathogens, and be prepared to try organic solutions such as effective microbes (EM1), trichoderma, mycorrhizal fungi, probiotic bacteria, and other beneficial inoculants. 

My Final Thoughts

There are many advantages to using a hydroponic growing medium for germinating cannabis seeds. From a logistics standpoint, each of these substrates is light in weight and can be transported more easily than loose soil. As a grower, ordering 50–250 jiffys online is easy, won’t weigh much, and is extremely discreet. Unlike soil, you can store dry rockwool, coco, and peat for years without worrying about their longevity or lifespan.

Thanks to rockwool, coco, and peat’s ability to hold a huge amount of water, a beginner grower doesn’t really need to do much after the growing medium is well saturated and the seeds have been planted. My main advice when it comes to germinating seeds is: read  Robert Bergman’s Grow Bible, be patient, leave the jiffy plugs alone, and always check to make sure the temperature of the propagator is as close to 75.2 degrees Fahrenheit (24 °C) as possible. (An aquarium heating mat or heater is a good way to maintain a consistently warm environment.) Beware of pathogens, root rot, bad aromas, and signs of algae when germinating cannabis seeds; otherwise, good luck getting your foot on the big green ladder.