Do you want to start growing your favorite plants indoors without resorting to soil? Then, growing in Rockwool as the growing surface provides a structure for the rootstock of the plant, which keeps it extra moisturized.
For me, as a newbie in gardening, one of the most challenging things was to identify the best growing environment. With multiple choices, it can be intimidating, but I kept going up and found the solution to share with you.
Rockwool is a multi-purpose material that has been used for more than 40 years. Nowadays, it’s used to grow a large variety of vegetables, herbs, and flowers all over the planet. Besides, it helps the plant roots absorb nutrients provided by the farmer.
Here, I’ll guide you in the issues of how to grow in Rockwool and how you can enjoy its use in your garden.
How to Plant in Rockwool?
Rock wool is a multi-purpose growing medium that can be used as a stand-alone product or in various hydroponic systems.
For now, you’ll be introduced to essential items needed in Rockwool planting:
- A container/reservoir;
- A lid;
- pH measurement tools;
- A pH control kit;
- The seeds you need;
- Diluted nutrient solution provision;
- New media to transfer your Rockwool cubes.
As far as I’m concerned, cubes are comfortable to work with; they are packaged in plastic sleeves.
Media Alternatives for Planting
The following alternatives are only a few of the most popular and promising.
Granules of Expanse Clay
This artificial product is often referred to as growth rocks and functions extremely well as a growth medium. They are best for backflow and drainage systems or other systems that have frequent watering.
Gravel is generally inexpensive and works well. Its weight makes it difficult to manipulate, but it has the advantage that it doesn’t break into the structure and can be reused.
The primary benefit of coconut fiber is its ability to retain oxygen and water. It can maintain a higher oxygen capability than rock wool while having a higher water retention capability.
What are Rockwool Cubes?
Rock wool cubes also referred to as rock wool cubes are the best way to germinate root seeds and cuttings. They are a rock wool shape, a popular growth medium for hydroponics gardening.
Manufacturers create blocks of rock wool by rotating a combination of basalt and chalk to create an interlaced blend that looks like the consistency of cotton candy. The matter is squeezed and formed into cubes. Most rock wool cubes are one to two inches in length and come in their packages, which are the best leftovers throughout the growth process. Larger stone wool cubes can also be bought, which measure three to four inches.
Large sheets of rock wool are available as well, which can be cut to fit a planter or a customized pruning system. According to their size, rock wool cubes are intended for small plants; however, many producers simply transplant seedlings from small cubes into larger cubes. Alternatively, rock wool cubes may be transplanted directly into the ground or used in hydroponics.
How to Use Rockwool Cubes for Growing?
Here are five easy steps to follow during the rock wool trial for the first time.
1. Buy the Product
Buy a pack of 1-inch stone wool cubes to spread the seeds. They are usually sold in handy packages that fit perfectly into a standard 10” x 20” plastic tray.
2. Setting Up the pH Level
According to the rock wool brand you bought, the following instructions may vary. Set the pH of the water to 5.5 with low pH or lemon water if you have it handy.
3. Put the Seeds in
Place seeds into every cube. Depending on the seed, you can plant several seeds into each cube. Your seed supplier may provide you with additional information.
4. Addition of Nutrient-Based Solution
Water your plants as needed with a dilute nutrient solution. Usually, it’s between 1/8 and 1/4 of the nutrients recommended for the nutrient solution.
5. Transplant to the New Environment
Rock wool cubes are ready for transplantation when the swivel root is visible at the bottom of the cube. Make sure the new supports are precooked with a nutritious solution or work correctly before transplanting.
4×4 Rockwool Cubes Case
As for the transplantation, you’ll see the plants begin to germinate at the end of a few days. Once these germs reach 2-3, they may be transplanted into a 4-inch container cubic, slab, or even in the ground.
Transplanting should be done when you see roots coming out of the cube. When transplanting small 4-in cubes, make a hole just big enough to put the little cube in.
Pro Tips For Using Rockwool Cubes
When growing clones in rock wool cubes, consider the following tips to make sure they grow successfully into healthy plants:
- Use methyl alcohol to sterilize the razor blade or scissors used to cut the clones of the mother plant;
- Dry the chopping board with methylated alcohol;
- Once the roots are open, keep them in a cool place like a refrigerator;
- Eliminate excess dust from the clones if you use rooting powder;
- Don’t use rock wool cubes that collapse as a result of placing clones.
How to Prepare Rockwool?
To use rock wool cubes for hydroponic cultivation or transplantation in your garden, you must first prepare the cubes so that the seeds sprout.
1. Do Cuttings
Cut the block into chunks of rock wool to facilitate the preparation of the cubes.
2. Soak Rockwool
Immerse your rock wool cubes in a vessel of distilled water. If you prepare the cubes for hydroponics, let only the lower half of the cubes go below the water surface for a while to avoid oversaturation. If you plan to plant the seedlings in the soil or another container later, let the whole cube soak in water.
3. Compress Cubes
Gently press the rock wool cubes in the same direction as the fiber grain if you use the cubes for hydroponics.
4. Put Seed in Cubes
Insert your seeds into the slots on the top of the individual cubes with a toothpick or other small tool to squeeze the seed into the cube.
BONUS: What Can You Grow in Rockwool? What Plants Grow Best in Rockwool?
The base vegetables grown in rock wool are tomatoes, cucumbers, peppers, and leafy vegetables. Commercially grown lettuce is often planted in stone wool cubes before being transplanted to an NFT (The Nutrient Film Technique) system in the hydroponics greenhouse. Aubergines, melons, and various herbs behave equally well when grown out of rock wool, and many cut flowers are grown out of rock wool, the first two being roses and gerberas.
Once new farmers see the benefits of rock wool, they begin to look at how they can take advantage of it in their backyard. Many of these uses are limited to seed germination or cloning of new plants. However, bigger blocks are more versatile than simply using Rockwool start caps for this purpose.
How to Grow Lettuce from Seed Rockwool Cubes?
Now, you’ll learn how to cultivate lettuce from seeds in rock wool as a culture medium. This is a simple, straightforward process.
1. Soak Lettuce
It’s best to start the lettuce with starting plugs made of rock wool. Before planting, rock wool stoppers should be soaked in a conditioning solution with a pH of approximately 5.5.
After processing the rock wool, the excess solution is evacuated, and the lettuce seeds are placed in each plug.
2. Cover It
Cover the starting plate with a plastic moisture dome and place it close to a window or under cold fluorescent light. In a few days, it’s going to sprout.
3. Wait to Transplant
Once the roots begin to come out from the bottom of the cubes, they can be transplanted into your hydroponic culture environment.
How to Grow Tomato Seed in Rockwool?
Hydroponic tomato farming is simpler than you think, and it creates healthy living plants. This simple and inexpensive method will give excellent results without too much hassle or expense.
1. Select the Right Hydroponic Nutrients for Tomatoes
Several hydroponic mixtures exist. I use the MasterBlend blend from Morgan County Seeds, paired with a little Epsom salt and calcium nitrate.
2. Stick the Tomato Seeds in the Rockwool
Add your hydroponic solution to the pot with the Rockwool. Place the saucepan under cultivation lamps or in full sunlight.
3. Find a Small and Reusable Plastic Container and Drill a Hole
Any container containing a liquid that is reasonably opaque and has a plastic lid should be operational. Start with something much smaller than the hole you intend to pierce and move to bigger pieces until you finally have a hole the size you need.
How to Start Cucumber Seeds in Rockwool?
It’s possible to start cucumber seeds in rock wool, but it’s important to check out some points.
1. Mind Temperature and Humidity
Cucumbers enjoy temperatures a little higher than tomatoes. They are expected to have a minimum night temperature of around 68 F, and a maximum day temperature of 75-78 F is ideal. The relative humidity must be kept at around 75%.
Make sure the seed is positioned deep in the hole of the cube. In this way, it won’t dry, and at the same time, it will help the layer of the seed to detach itself while it germinates.
If you use stone wool slabs as a growth system, soak the slabs for a day before transplantation. Transplant one cucumber per pot with two draining transmitters per pot. Place one at the end of the rock wool block and another next to the plant.
How to Start Lettuce Seeds in Rockwool?
If you are looking for an easy way to start your lettuce seeds, I recommend giving rock wool cubes a try!
Choose a Small Size Cubes
You should choose 1.5 inches cubes. This size would be perfect for these seeds.
Mind Growing Conditions
The pH of Rockwool is naturally elevated, about 8. Before planting, dip the cubes in a pH solution of 5.5 to prepare them.
From the beginning, 2 or 4 seeds per cube would be okay. Thin later if needed.
Put the Seed Container beside the Window
Over the next 2-4 days, you’re expected to see tiny shoots emerge.
Germinating Autoflower Seeds in Rockwool
Since auto-flowering seeds have a shorter time to build roots, stems, stems, and other structures before it begins flowering, your auto-flowering plants do better when you use the following strategies.
Mind Growing Conditions
Maintain the culture chamber temperatures to 75F when the lights are on and 68F when the lights are off. Cultivate the relative humidity of the room in the 54-60% vegetative phase. For the flowering phase, 52-57%.
Start the auto-flowering seeds with the appropriate pH level of Rockwool cubes. It should be 6.0.
Transplant sprouted seedlings into a deep-sea crop, hydroponic, or a similar pure hydroponic system for better yields and growth rate.
Growing Basil in Rockwool
I tried to grow basil inside with rock wool. I found out that the most successful cultivation method to date is the Mason Jar hydroponic culture. It’s effective and looks good.
1. Make the Nutritious Solution
To prepare the nutrient solution, transfer the distilled water to a clean pail or large bowl. Next, mix small amounts of nutrients and measure electrical conductivity (EC) with your CE measuring device (range is 1.0 to 1.6).
2. Dip Your Rockwool
Then, place a nutritional solution in a small bowl and place a cube of rock wool into the liquid. Let rock wool dip in nutritional solution for 10 to 20 minutes.
3. Soak in the Rooting Hormone
When soaking rock wool, dip basil in the rooting hormone.
4. Flush Out LECA
The next step involves rinsing the LECA. Place the LECA in a colander and rinse the patties in the sink. Shake the rollers, gently stirring the colander.
5. Mount the System
Remove the stone wool from the bowl it soaks in, and use a sharp knife to cut a slot in the cube. Insert your cut into the slot and reserve.
Fill the masonry pot with the nutritional solution you prepared. The water level should be approximately halfway up the fillet cup.
How to Grow Microgreens on Rockwool?
Microvegetables are among the easiest plants to cultivate at home. Cultivating from seeds could be a new and different experience, but once you hold on to it, you’ll be addicted!
1. Growth Solution
Before sowing, the plugs must be supplied with a solution; for this, use a container of suitable dimensions, in which the entire cassette can be immersed.
2. Growing Conditions
After placing the seed in the hollow, spread it with vermiculite or perlite.
The temperature and moisture conditions are different for each plant species. If they can be seen, seeding will be more friendly. I got every crop in one place.
Cubes are placed on a smooth, homogenous surface or on a film (to improve lighting – on a white surface).
4. Developing Seedlings
Weigh the cube right after harvesting. Wait for it to lose half its weight, pour 50-70g of solution and keep the weight within these limits. When transferred to the soil, rock wool rapidly loses moisture (because there is less moisture in the soil).
Bonus: How to Grow Clones Indoor With Rockwool Step by Step
Cultivating rock wool clones is easier than ever. Follow these steps to successfully cultivate your clones using rock wool cubes.
1. Buy the Perfect Cube of Rockwool
You must obtain the right rock wool cube for the process. Choose the appropriate size of rock wool, for example, 1.5″ x 1.5″ x 1.5″.
2. Preparing the Rockwool Cube
As mentioned earlier, use the highest quality water to process stone wool cubes. Rinse cubes with distilled or treated water. Dip rinsed cubes in a solution of water overnight. It must have a pH of 4.5. Then, it should be 5.5.
3. Prepare Cutting
To obtain the cut, cut approximately one-quarter of an inch transversely under the mother plant to remove the knots. Alternatively, cut about an inch and a quarter under the original knot.
4. Place the Clones within the Rockwool Cubes
After soaking your cup in a rooting gel, connect it to the culture medium. Make sure the cube keeps the clone in place. Place your cubs in an appropriate growing pond in a temperature range of 80-85 degrees Fahrenheit. The best choice is to choose a solid culture tray with a dome.
A faulty tag often results in the death of innumerable clones. You can make mistakes sometimes, irrespective of the quality of your memory. So labeling each Rockwool cube is important.
How to Care for Seedlings in Rockwool?
The best growth performance can be obtained with rock wool, but as with most high-performance things, some details should be right for the utmost result.
Fertilize Your Rockwool at All Times
Any nutrients present in the block will be in the solution for the disposal of the plant or ready to drain the bottom. It means that the nutrients you use will have an immediate effect on the plant, and any feeding error can be corrected immediately, allowing you to improve your fertilizer usage.
Allow Enough Flow
Plants always absorb more water than nutrients, so expect an increase in the concentration of fertilizing salts in the environment between waterings.
No Excessive Watering
Always fertilize the rock wool when you irrigate and leave a bit of drainage whenever you wash the excess fertilizer.
Don’t Squeeze the Cube
A common myth is that excess water in rock wool should be removed by tightening the block or stoppers. The structure of the fibers in the rock wool contains beneficial properties of water retention and air porosity, which allow the root systems to grow.
Rockwool Hydroponics Bunnings
At Bunnings Australia, you can buy Cultilene 75 x 75 x 65mm Rockwool Hydroponic Substrate Block. Grow everything suitable for a small pot on the top of your bench for easy access when preparing your meals.
Natural raw materials are used in stone wool. At the same time, the substrate solutions are the result of a completely controlled and advanced process. This means that they provide maximum control and can be fully tailored to the client’s circumstances and needs.
In the development of their slabs, plugs, and blocks, they always concentrate on constant quality and maximum forecasting so that producers can control their production process as precisely as possible.
Rockwool Sheets for Hydroponics
I bought Grodan Rockwool sheets. Each sheet contains 200 rock wool cubes. Grodan rock wool cubes are ideal for rooting cuttings or sprouting seeds. I recommend dipping them in water at pH 5.5 at night and adding seeds or cuttings the following day. Store under a dome to retain moisture and mist when required.
From there, you can transplant to any growing environment, soil or hydroelectricity. If you want to transplant in larger blocks of stone wool later, do not use these cubes, they are too small – use the 1.5 x 1.5 x 1.5 cubes.
Grodan Stonewool is made from melted rock spun from cotton candy fibers and then compressed into cubes, blocks, or plaques. Grodan has an enormous capacity to absorb the nutrient solution while retaining a lot of oxygen for fast-growing plants.
So, this is the guide for you to follow when you grow in Rockwool. I’ve made it since I’m fond of gardening, and already gained some experience in it. I guess it’s my mission to share my ideas and help you. Let me know if you liked the article in the comments right below and share it, if so!
Is Rockwool Safe for Plants?
Consisting of natural materials, rock wool contains no harmful chemicals. You can use it as rooting support and as a substrate for plants. Given that rock wool for plants is a manufactured product, it doesn’t contain pathogens or pests. It also means that it doesn’t contain nutrients, organic compounds, or microorganisms. Plants that grow in rock wool require a balanced and comprehensive hydroponics solution to meet their nutritional requirements.
When to Transplant Rockwool Seedlings?
When your seedlings are about three inches high and have roots sticking out of the bottom of rock wool cubes, it’s time to transplant. But a week earlier, you'd have to toughen your plants.
What Size Rockwool Cubes to Use?
Cubes (1.5, non-packaged) are recommended for housing starts and cuttings. They fit into a standard 1020 propagation plate and can be transferred to traditional growing blocks or media as needed. The mini-blocks (1.5 & 2.0, packaged) are used for seed propagation and cutting.
How Many Rockwool Can You Fit In a 3x3 Grow Tent?
In this grow operation, it takes 2 square feet of space to grow a plant. Therefore, the answer to the question, “How many plants can you get into a 3x3 cultivation tent under this method?” would be 4 plants!
How Long Does It Take for Roots to Grow through a Rockwool Cube?
The majority takes 10 days. Hard-rooted stumps took 3 weeks. They all end up taking root. Don’t allow the cubes to become too moist until the roots appear.
How Often Should I Water Rockwool?
Rock wool retains approximately 80% water and 20% air when saturated and must dry out (as in a soil-based environment) before re-watering. In a perfect environment, rock wool blocks generally need to be watered once a day at the vegetative growth stage and twice a day at the flowering stage.
Can You Overwater Rockwool?
If you are watering, and there is more than 30% drainage, you are probably over-watering. It can result in algal growth. The plant can tilt because the block is too lightweight before you have to water it again.
How Do You Stabilize Rockwool?
Rock wool has a naturally high pH range from 7-8. Prepare a slightly acidic water solution (pH 5.5 to 6.5) by adding several drops of lemon juice with pH test strips to achieve good acidity. Dip the rock wool cubes into this solution for approximately one hour.
Is Rockwool Good For Starting Seeds?
Rock wool cubes are popular for seed germination because they retain excellent moisture. They’re excellent to help prevent seeds or seedlings from drying out, but don’t let them sit in water-drenched environments.
Why Are My Seeds Not Sprouting in Rockwool?
If the soil is too humid, anaerobic conditions persist and the seeds may not be able to germinate. Don't let your rock wool fully immerse in the water! If your rock wool is too cold or too hot, your seeds may not germinate.