Best Rockwool for Hydroponics: Top Picks in 2024

Updated on:
Grow Media

Some of the links on this page are affiliate links, meaning, at no additional cost to you, I will earn a commission if you click through and make a purchase. This way I can continue to produce high-quality content and keep this site running.

As a versatile and adaptable substance, Rockwool is well-suited for a wide variety of hydroponic systems. Made primarily from basalt rock and chalk, it offers a perfect blend of features that contribute to the success of your hydroponic garden, such as excellent water retention and good drainage capabilities.

Best Rockwool for Hydroponics

When selecting the best Rockwool for hydroponics, the most critical factors to consider are its size, density, and quality. The size of the Rockwool should fit the specific requirements of your hydroponic setup, while the density determines its water retention and aeration capacities. Quality, on the other hand, is paramount to ensure the Rockwool you’re using is free from harmful substances and can enhance your plants’ growth.

With so many Rockwool products available in the market, finding the right one for your hydroponic system might seem like a daunting task. That’s why we spent considerable time researching and testing the best rockwool options, to help you make an informed decision and achieve maximum yields in your hydroponic garden.

Our Top Picks for Best Rockwool for Hydroponics

Best Rockwool Cubes

Rockwool cubes are by far the most popular among hydroponic growers who start seeds and clones. There are a few good brands and you can choose from a few different sizes, depending on your specific needs. Find out about Rockwool cube sizes here.

SKINNYBUNNY Rockwool Cubes 1 Inch

SKINNYBUNNY Rockwool Cubes 1 Inch

  • Highly porous structure (96%) allows excellent water, nutrient and air flow for healthy root development
  • Holds a lot of water (91% capacity) to keep roots hydrated while still allowing drainage
  • Increases growth rate and yield with shorter planting times
  • Ideal for starting seeds, cloning plants, and growing in hydroponics
  • Usage involves soaking the naturally alkaline hydroponic seed starter in acidic water until the pH value stabilizes between 5.5-6.5 for 24 hours before use.
  • Suitable for short and long growth cycles of different plants
  • Easy to transplant with low disruption and high survival rate
  • Allows precise control over moisture, nutrients, and root temperature
  • Promotes proper root aeration and avoids issues like continuous cropping
  • 4 Sheets of 200 1-inch Cubes with a hole in each cube
View On Amazon

SKINNYBUNNY Rockwool Cubes are perfect for hydroponics, providing excellent growth conditions for seedlings and transplants.

  • Highly porous with great water-holding capacity
  • Suitable for various growth stages and different plant types
  • Easy-to-follow usage guide for optimal results
  • Requires pH adjustment before use
  • Some users reported issues with root penetration
  • May be prone to algae growth

We recently used SKINNYBUNNY 1 Inch Rockwool Cubes for our hydroponic setup and found them to be highly effective. Thanks to their high porosity and water-holding capacity, our plants’ roots grew deeper and wider, resulting in increased growth rate and yield within a shorter planting period.

These cubes are versatile and ideal for starting seeds, cloning plants, and growing both vegetative and fruiting crops.

One thing to consider, the cube size is relatively small, measuring just 1 inch on each side. While this size works well for starting seeds and smaller plants, it might not be large enough for plants with larger root structures. It is essential to be aware of this when planning your hydroponic setup.

Some users reported issues with root penetration, but we believe that following the provided usage guide, we attained good results. You may also find that some cells are not fully formed and thus unusable. Additionally, the cubes might be prone to algae growth, so it’s essential to keep an eye on your system and take preventative measures as needed.

Overall, we recommend SKINNYBUNNY Rockwool Cubes for hydroponic gardeners looking for a versatile and effective growth medium that supports various plant growth stages and types.

The Hydroponic City 1.5" Grodan Rockwool Cubes

The Hydroponic City 1.5″ Grodan Rockwool Cubes

  • Great for starting seeds or rooting clone cuttings
  • High absorption capacity for nutrient solution while still allowing oxygen flow
  • Supports plant needs at different growth stages
  • Transplant when seedlings are rooted and robust
  • Comes with 5 THCity Stakes
View On Amazon

These 1.5″ Grodan Rockwool Cubes by The Hydroponic City are an excellent choice for hydroponic gardeners in need of a reliable seed starter and rooting medium.

  • High-quality rockwool material
  • Great absorption and oxygen retention
  • Can be easily transplanted once roots are established
  • Smaller size might not suit all growers
  • Plastic stakes not always included
  • Risk of size discrepancies

Grodan 1.5″ A-OK Rockwool starter plugs are the best rockwool for seedlings – starting seeds and rooting clone cuttings for your hydroponic system. We found that the Rockwool material used in these cubes is of excellent quality, durable, and holds its shape well during usage.

These cubes have a significant ability to absorb the nutrient solution and retain oxygen, which is crucial for rapid plant growth. As we used these cubes, we appreciated how well they supported our plants in various growth stages. Once our seedlings were well-established and the rooting cube was full of vigorous roots, we found transplanting was a breeze.

However, some potential drawbacks should be considered. The smaller 1.5″ size of these cubes may not suit all hydroponic growers’ preferences. Additionally, they don’t always come with the advertised five THCity Stakes. Lastly, there have been some instances where the received product’s size didn’t match the description perfectly.

Overall, we believe these 1.5″ Grodan Rockwool Cubes from The Hydroponic City are an excellent option for hydroponic gardeners, providing reliable quality and easy transplanting. Just be sure to double-check the size before purchasing.

MI0512 1.5" Rockwool Starter Plugs for Hydroponics

MI0512 1.5″ Rockwool Starter Plugs for Hydroponics

  • Inorganic and sterile growing medium
  • Ideal for rooting cuttings, cloning, germinating seeds
  • Encourages fast initial rooting and has a firm structure
  • Easier than soil – predrilled holes for planting
  • 20% air space when saturated for oxygen and growth
  • Made of natural rocks, neutral pH, and sterile
  • Cubes are 1.5″ x 1.5″ x 1.5″ in size
View On Amazon

MI0512 1.5″ Rockwool Starter Plugs are a reliable choice for hydroponic growers seeking an effective and easy-to-use inorganic growing medium.

  • Inorganic and sterile, promoting faster initial rooting
  • Easy to plant seeds and propagate plants
  • Impressive water and nutrient retention while preserving oxygen for rapid growth
  • Need precise pH adjustment during soaking
  • Transplanting to a larger block may need additional care

We recently tried out MI0512’s 1.5″ Rockwool Starter Plugs in our hydroponic setup and found them to be a versatile and efficient growing medium. The plugs held their shape well and retained plenty of water and nutrients, which allowed our plants to root quickly and experience impressive growth.

To achieve the best results, make sure to properly adjust the pH of your soaking solution and avoid squeezing the plugs when soaking.

In our experience, transplanting the seedlings into a larger 3″ or 4″ block worked well in maintaining moisture levels and encouraging even growth throughout the block. Overall, we recommend MI0512’s 1.5″ Rockwool Starter Plugs for hydroponic enthusiasts seeking a dependable and user-friendly growing medium.

Stacky Cubes 49 1.5" Rockwool Grow Cubes

Stacky Cubes 49 1.5″ Rockwool Grow Cubes

  • Inorganic and sterile growing medium
  • Superior for rooting cuttings
  • Encourages fast initial rooting and firm structure
  • 20% air space when saturated allows oxygen and growth
  • Absorbs nutrients while retaining oxygen
  • Cubes are 1.5″ x 1.5″ x 1.5″ in size
View On Amazon

These Stacky Cubes Rockwool Grow Cubes are a solid choice for hydroponic growers, offering excellent water retention and strong root growth.

  • Inorganic and sterile growing medium
  • Encourages faster initial rooting
  • Provides optimal air-to-water ratio
  • Small cube size (1.5″ x 1.5″ x 1.5″)
  • May require pH correction soak
  • Not suitable for larger plants

We recently used Stacky Cubes’ 49 1.5″ Rockwool Grow Cubes in our hydroponic setup and found them to be an excellent growing medium for starting seedlings. Coming from a reputable manufacturer in the Netherlands, these Rockwool cubes have an inorganic and sterile growing environment that encourages rapid rooting and healthy plant growth.

The initial rooting in these cubes was significantly faster than other products we’ve tried, which can be attributed to their superior medium structure and firmness. On top of that, Stacky Cubes’ Rockwool allows for a 20% air space when saturated, which means that the roots receive sufficient oxygen while maintaining optimal nutrient absorption.

Another point worth mentioning is that the Rockwool cubes may require a pH correction soak before use. This step ensures that the cubes don’t negatively impact your nutrient solution balance. We found that other users had success soaking the cubes in lemon water.

Overall, we recommend Stacky Cubes 49 Rockwool Grow Cubes for hydroponic enthusiasts who want a versatile, reliable, and effective growing medium. The product may have its limitations, but the pros outweigh the cons, making it one of the top choices for starting hydroponic plants.

Best Rockwool Blocks For Plants

4 Inch Redrock Rockwool PRO Grow Block for Hydroponics

4 Inch Redrock Rockwool PRO Grow Block for Hydroponics

  • Made in the USA, priced for commercial agriculture
  • Allows growing more with less water, nutrients, and space
  • Ensures uniform water and nutrient distribution due to high fiber density
  • Promotes predictable wet/dry cycles for crop steering
  • Blend of fibers prevents channeling and dry zones
  • Water moves horizontally then vertically for full saturation
  • Tightly wrapped in co-extruded white/black film
  • White exterior keeps root zone cool, black interior prevents light/algae
  • Improves water management and reduces evaporation
  • Blocks are 4” x 4” x 4” with 42/40 hole
  • Comes with Twin Canaries Chart
View On Amazon

We highly recommend the 4 Inch Redrock Rockwool PRO Grow Block for hydroponics due to its exceptional performance and quality.

  • Made in the USA
  • Priced for commercial agriculture production
  • High fiber density for better water and fertilizer management
  • 42/40 hole size may require some modification for specific plants
  • No pre-drilled holes for seeds
  • Not suitable for all types of growth systems

We recently used the 4 Inch Redrock Rockwool PRO Grow Blocks for our hydroponic garden, and we have been delighted with their performance. The fact that they’re made in the USA is a significant advantage, as we’re confident in their quality, manufacturing, and ethical standards. These grow blocks are designed and priced for commercial agriculture production, so we had no concerns about their ability to meet our needs.

One of the standout features of these grow blocks is their high fiber density, which effectively manages water and fertilizer usage. This allowed us to conserve resources, without compromising our plants’ health. The 42/40 hole size is suitable for most plants, but we encountered some issues when trying to use them with specific plants. We had to modify the holes slightly, which is perhaps something to bear in mind depending on your intended use.

We didn’t find this to be a huge drawback overall, as it was quite simple to do this modification. However, it’s important to note that there are no pre-drilled holes for seeds in these grow blocks, so we had to create them ourselves. This minor inconvenience was easy to overlook given all the other advantages that came with using Redrock Rockwool PRO Grow Blocks.

While these grow blocks were perfect for our hydroponic setup, they may not be suitable for all types of growth systems. It’s essential to research and ensure these blocks are the best fit for your specific needs before committing to them. That said, we couldn’t be happier with our decision to use the Redrock Rockwool PRO Grow Blocks, and we’re confident in recommending them to others looking for a reliable, high-quality solution for their hydroponic setups.

If you require a larger size, 6 Inch Redrock Rockwool PRO Grow Blocks are also available for purchase.

Grodan Rockwool Delta GRO Blocks 6 Pack with Twin Canaries Chart

Grodan Rockwool Delta GRO Blocks 6 Pack with Twin Canaries Chart

  • Blocks are 4″ x 4″ x 4″ with a top hole
  • Hole size fits 1.5″ starter plugs or macroplugs
  • Plants can fully grow in the blocks
  • Grooved bases promote drainage and prevent wet feet
  • Comes with volume conversion chart
  • Enhanced wetting agent improves water distribution and nutrient use
  • Faster rooting-in and nutrient replenishment
  • Maintains structure, firmness, and rigidity throughout growing
View On Amazon

These Grodan Rockwool Delta GRO Blocks are a fantastic choice for hydroponic gardeners seeking a reliable and effective growing medium.

  • Optimal hole size for 1.5″ starter plugs or macroplugs
  • Capable of supporting full plant growth
  • Grooved bases for better drainage and prevention of “wet feet”
  • Requires moderate watering
  • Limited to six blocks in a pack
  • Sandy soil type may not suit every plant variety

We recently tried the Grodan Rockwool Delta GRO Blocks in our hydroponic setup and were genuinely impressed. The 4″ x 4″ x 4″ size of each block, along with the perfectly sized hole at the top, made it easy to transplant our starter plugs. Novice and experienced gardeners alike would appreciate the convenience of these blocks, as the included Twin Canaries Liquid Volume Conversion Chart is a helpful tool for watering and nutrient management.

The base of these Rockwool blocks is grooved, promoting drainage and preventing our plants from experiencing “wet feet.” This design choice results in healthier plants and better growth overall. Additionally, the blocks are versatile, as plants can be fully grown in them without needing any additional support.

However, it’s worth noting that these blocks require only moderate watering. Furthermore, some gardeners might prefer a larger package size, as this pack only comes with six blocks. Nevertheless, if you need reliable Rockwool blocks for hydroponics, these Grodan Rockwool Delta GRO Blocks are definitely worth considering.

Grodan Pargro 36 x 12 x 3 in. Classic Grow Slab

Grodan Pargro 36 x 12 x 3 in. Classic Grow Slab

  • Based on NG2.0 technology which enables extremely uniform water distribution throughout the substrate, allowing the crop to fully utilize the entire volume of the growing medium.
  • Reliable substrate for simple and frequent irrigation and drainage
  • Quick EC refreshment and promotes root growth
  • Guarantees good yield with consistent fruit quality
  • Horizontal root development and vertical fiber structure
  • Single-year slab
View On Amazon

Grodan Pargro Classic Grow Slab is a solid choice for hydroponic growers looking for a reliable and effective stonewool solution for plants with extensive root systems.

  • Excellent absorption of nutrient solution
  • Retains ample oxygen for rapid plant growth
  • Graduated sizes for seamless transplantation of plants
  • Oversized item and may not qualify for free shipping
  • Comes in a UV-resistant poly sleeve, which might not be durable
  • Some users reported damaged packaging

The Grodan Pargro 36 x 12 x 3 in. Classic Grow Slab has proved to be a game-changer for us. The stonewool fibers make it efficient in absorbing nutrient solutions and retaining oxygen, leading to rapid plant growth. We particularly appreciate the graduated sizing of the product that allows for a hassle-free transfer of plants from cubes to blocks and then to slabs. It’s perfect for long-term crops with extensive roots like peppers, tomatoes, or cucumbers.

The slab is made using vertical fibers, creating better drainage and fast-growing plants. And, since it’s packed in a UV-resistant poly sleeve marked with clear instructions, it’s super easy to use. We have, however, discovered that the poly sleeve might not always be durable enough for the product’s lifespan.

While Grodan Pargro Classic Grow Slab does have its perks, it comes with a few drawbacks. First, this item may not qualify for free shipping due to its oversized nature. Also, some users have reported receiving the package in damaged condition, which could potentially expose the stonewool to contaminants.

Despite these cons, we firmly believe that the benefits provided by the Grodan Pargro Classic Grow Slab in hydroponic gardening are worth considering. It caters to the needs of various plant stages and provides optimum support for rapid growth and healthy plants.

Rockwool Starter Plugs

YBB Round Rockwool Starter Plugs

YBB Round Rockwool Starter Plugs

  • Superior inorganic growing medium for cuttings, cloning, germination, propagation, and starting seeds
  • Made from safe, environmentally-friendly rock fibers
  • High absorption capacity retains nutrients and oxygen for rapid growth
  • Faster initial seed growth for increased productivity and quality
  • Easy to transplant from plugs to blocks to slabs
  • Suitable for hobby or commercial growing
  • Plugs are 0.79” x 0.79” x 1” in size
  • Fits seedling trays, net cups, and basket pots
View On Amazon

We highly recommend the YBB Round Rockwool Starter Plugs for a superior hydroponic growing experience.

  • High water absorption for nutrient solution
  • Encourages faster seed growth
  • Easy transfer and transplant process
  • May require protective gear while handling
  • Care needed when cutting, use scissors

We recently used the YBB Round Rockwool Starter Plugs for our hydroponic setup, and we were impressed by their performance. Made from ground rock fibers, these plugs are environmentally friendly and offer a superb capacity for absorbing nutrient solution while still retaining plenty of oxygen for rapid plant growth.

When using these plugs, we noticed faster seed growth, which ultimately helped us increase productivity and improve our crop quality while reducing production cost. One of the most significant advantages of these plugs is their streamlined transfer and transplant process. Seedlings started in these Rockwool plugs can be effortlessly moved to blocks, slabs, and eventually more traditional planters.

It is essential to use scissors for cutting and avoid tearing the plugs.

Overall, the YBB Round Rockwool Starter Plugs provide an exceptional growing medium for hydroponic enthusiasts, whether you’re a hobbyist or a commercial grower. Their excellent water absorption, faster growth rate, and ease of transplant make these plugs well worth considering for your hydroponic system.

Buying Guide

When it comes to choosing the best Rockwool for hydroponics, there are a few key factors that we should consider. These include the size and shape of the cubes, their water retention capacity, and their pH levels. We’re here to help guide you through these considerations to make an informed decision. You should also read up on the different types of hydroponic Rockwool available.

Size and Shape

Rockwool cubes come in various sizes, ranging from small starter plugs for seedlings to larger cubes for more established plants. It’s important to select the appropriate size for your hydroponic system and the stage of growth your plants are in. In addition, some Rockwool cubes have grooves or channels for better nutrient distribution, which can be beneficial depending on your system’s design.

Water Retention Capacity

An essential feature of Rockwool is its ability to retain water while still providing adequate oxygen to the plant roots. This balance is crucial for the health of your hydroponic plants. Look for Rockwool that offers a good balance between water retention and aeration. A quality product will effectively absorb water, promote root growth, and prevent root rot.

pH Levels

The pH level of Rockwool is an essential factor to consider, as it affects nutrient availability for plants. Rockwool typically has a natural pH level of 7.0 to 8.0, which might not be ideal for some plants. It’s important to choose Rockwool that has been treated and balanced to a level closer to the optimal pH range for your specific plant needs. You can also adjust the pH level yourself using water and pH-adjusting solutions.


Rockwool comes in various densities, each offering different levels of support for plant roots. Higher density rockwool provides more support for larger plants, while lower density rockwool is better suited for seedlings and cuttings. Choose the appropriate density based on your plant’s growth stage and the type of hydroponic system you’re using.

How do Grodan Blocks Compare to Other Rockwool Brands?

Grodan blocks are a popular choice for hydroponic growers due to their quality and consistency. They are made from high-quality basalt, which ensures that they maintain the right balance of water retention and air circulation.

One advantage that sets Grodan blocks apart from some other Rockwool brands is their use of advanced manufacturing techniques like Delta Technology. This technology helps create a more uniform structure within the blocks, providing better control of the water and nutrient distribution.

In terms of price, Grodan blocks are generally competitive with other brands in the market. It’s important to remember that the overall cost of your hydroponic system can vary depending on factors like the size of your setup and the exact type of Rockwool you choose.

When selecting a Rockwool brand, it’s crucial to consider your specific hydroponic setup and growing needs. In general, we find that Grodan blocks offer a reliable and effective solution for many hydroponic growers.

Buying Guide

Claudia Lewis
About the author

I’m Claudia, a hydroponic gardening enthusiast with years of experience in this exciting and rewarding hobby. Over the years, I’ve experimented with different hydroponic systems, nutrient solutions, and plant varieties. 

On this website, I share everything I know about growing plants without soil. You’ll find everything you need to know to start your own hydroponic garden, from choosing the right system to selecting the best plants and nutrients.