If you're looking for a soilless substrate for seed starting, stem rooting or hydroponics, consider using rockwool growing medium. A wool-like material, rockwool for plants is easy to use and available in cubes and blocks. Learn about rockwool in this article. Germinating seeds in rockwool cubes will be a great process for your plant’s growing experience. Rockwool is a soil-free medium or substrate used for starting seeds In this post we focus on explain the functioning of a hydroponic crop with rock-wool, pointing out the different steps to follow to get a successful c
Growing In Rockwool Cubes – Is Rockwool Safe For Plants
If you’re looking for a soilless substrate for seed starting, stem rooting or hydroponics, consider using rockwool growing medium. This wool-like material is made by melting basaltic rock and spinning it into fine fibers. Rockwool for plants is then formed into easy-to-use cubes and blocks. But is rockwool safe to use for the production of food?
Advantages and Disadvantages of Growing in Rockwool
Safety: Formed from natural materials, rockwool contains no harmful chemicals. It’s safe to use as a rooting medium and substrate material for plants. On the other hand, human exposure to rockwool represents a health issue. Due to its physical properties, rockwool growing medium can cause irritation to skin, eyes and lungs.
Sterile: Since rockwool for plants is a manufactured product, it’s contains no weed seeds, disease pathogens or pests. This also means it contains no nutrients, organic compounds or microbes. Plants growing in rockwool require a balanced and complete hydroponic solution to meet their nutritional needs.
Water Retention: Due its physical structure, rockwool drains excess water quickly. Yet, it retains small amounts of water near the bottom of the cube. This unique property allows plants to attain adequate hydration while allowing more air to circulate and oxygenate the roots. This difference in moisture levels from the top to the bottom of the cube makes rockwool ideal for hydroponics, but it can also make it difficult to determine when to irrigate the plants. This can result in over-watering.
Reusable: As a rock derivative, rockwool doesn’t break down or erode over time, thus, it can be reused many times. Boiling or steaming between uses is recommended to kill pathogens. Being non-biodegradable also means it will last forever in a landfill, making rockwool for plants a not-so environmentally friendly product.
How to Plant in Rockwool
Follow these easy instructions when using rockwool growing medium cubes or blocks:
- Preparation: Rockwool has a naturally high pH of 7 to 8. Prepare a solution of slightly acidic water (pH 5.5 to 6.5) by adding several drops of lemon juice using pH test strips to attain the correct acidity. Soak the rockwool cubes in this solution for about an hour.
- Sowing Seed: Place two or three seeds in the hole at the top of the rockwool growing medium. Water using a hydroponic nutrient solution. When the plants are 2 to 3 inches (5 to 7.6 cm.) tall, they can be transplanted into soil or placed in a hydroponic garden.
- Stem Cuttings: The night before taking the stem cutting, water the mother plant thoroughly. In the morning, remove a 4 inch (10 cm.) cutting from the mother plant. Dip the cut end of the stem in honey or rooting hormone. Place the cutting in the rockwool. Water using hydroponic nutrient solution.
Rockwool is the substrate of choice for many large hydroponic farms. But this clean, pathogen-free product is also readily available in smaller-sized packages specifically marketed for home gardeners. Whether you’re dabbling with cultivating lettuce in a hydroponic jar or you’re setting up a larger system, growing in rockwool gives your plants the advantage of superior root zone technology.
Germinating Seeds In Rockwool Cubes
Germinating seeds in rockwool cubes will be a great process for your plant’s growing experience. Rockwool is a soil-free medium or substrate used for starting seeds. They can as well be used in hydroponics or stem rooting.
Rockwool offers so many benefits in almost any type of plant which makes it popular and best-loved among most growers.
This article attempts to enlighten you on germinating seeds in rockwool cubes and more, so read on to learn.
Table of Contents
Rockwool are made from spinning chalk and basalt rock which are formed into a thick mat of natural fibers. The combinations are made to look like the consistency of cotton candy. The spun fibers are then combined with a binding agent. The materials are pressed and formed into cubes which we know as rockwool cubes. Mostly, rockwool cubes can come in one or two inches sizes: although, you can also obtain bigger rockwool cubes of about four inches.
The smallest rockwool sizes are the most appropriate for starting seeds, leaf cuttings, and stem propagation. Bigger rockwool cubes are mainly used to grow denser plants.
Guide On Germinating Seeds In Rockwool Cubes
Seed germination requirements can sometimes demand careful and precise planning or process. Take for instance moisture requirements: moisture is an essential factor when it comes to seed germination.
Therefore, rockwool cube is a great choice to use in germinating seeds because rockwool cube has the ability to retain moisture. Rockwool cubes will keep your seeds moist at the same time preventing your seeds from sitting in a waterlogged environment. They can retain just the right amount of water to keep your seeds from drying out thereby improving the germination of your seeds.
How To Start Seeds In Rockwool
- The first step to take in germinating seeds in rockwool cubes is the preparation of the rockwool cubes. Rockwool cubes need to be soaked in pH adjusted reverse osmosis water before use. They don’t require too much soaking; however, ensure the cubes are fully absorbed in water.
- Soaking is required because rockwool cubes usually have a high pH of about 7.8 but your seeds will require a pH of 5.5 which is a slightly acidic medium. This way, your seeds will have an optimal chance of germinating and sprouting appropriately.
- Remove the rockwool cubes from the soaked water and give them a gentle shake to take off excess water. However, don’t squeeze them. Now your cubes are ready to be seated in your germinating tray.
- Most rockwool cubes have holes in them, so get your seeds and drop them into the holes of the rockwool seeds. With a toothpick or other identical objects, gently bring down the seeds to the bottom holes.
- Now squeeze the rockwool hole to close them or simply break off a little piece of the rockwool from the sides to cover the top. The seeds need to be placed in a dark environment.
- Now cover with a humidity dome so that they can maintain a humid environment. Keep them at 70 to 80 degrees. Now you can place them in a gentle grow light.
- You can maintain a moist environment by misting with a spray bottle whenever you notice them drying out. Sprouting should be noticed after a couple of days.
- When the plantlets are about 2 to 3 inches, they are ready to be transplanted into your hydroponics or traditional soil.
Benefits Of Start Seeds In Rockwool
- Water Retention: rockwool cubes have an excellent water retention property which is very essential for the germination of your seeds. At the same time, rockwool will not waterlog your system. It has the ability to drain excess water, retaining just the right amount of water needed by your seeds to germinate.
- Air Circulation: rockwool cubes will provide good air circulation and oxygenation of the root system.
- Clean: rockwool is a clean or sterile medium and it doesn’t have any weeds, pathogens, or pests.
- Reusable: rockwool cubes doesn’t decompose over time. Therefore, it can be reused over again.
- Safe: they are made from natural materials. Thus, it is very safe to use for your germinating seeds because it doesn’t contain any toxic substances.
Why won’t my seeds germinate in rockwool?
The problem might be that they are not getting enough light. Rockwool is a great product for growing plants and it has been used for centuries. It’s made from ground-up volcanic rock so it provides nutrients and structure for plants to grow. It also helps maintain moisture in the growing medium. There are many different types of rockwool, each with its own unique properties.
Rockwool is like a sponge and absorbs all moisture from the air. It’s great for storing seeds but if you put them in it they won’t get a chance to germinate. You need to keep your seed starting containers dry and make sure you water the soil before you cover the seeds with the rockwool. I would use vermiculite for a seed starting medium because it’s a bit drier than the rockwool.
Do seedlings need nutrients in rockwool?
As long as they are not sitting in wet rockwool, yes. If you do not want to water them, use a bulb planter and keep them in a shaded area. If you’re going to be transplanting them to larger containers, you can add some nutrients to the potting mix if you want to. If you have the fertilizer that comes with the plant, that will be fine. You could also use a diluted liquid fertilizer such as a 10-10-10.
How often should you water seedlings in rockwool?
Rockwool needs more frequent watering than soil because it does not absorb water as well. It is best to water your Rockwool when the top inch or so of the material is wet, which usually happens within 24 hours. It is important to keep the surface of the material damp, but not wet. If the Rockwool dries out too much, it will crack and become brittle. If you see a rockwool plant that appears to be drying out, cut off the top few inches and let it dry out again before re-watering. Once you have cut back on the water supply, wait for the top inch or so of the material to be wet again, and then re-water. You can also use a spray bottle with a fine mist setting to apply water directly to the Rockwool.
Can I start seeds in rockwool cubes?
It would be fine as long as you keep it moist enough. I think it should be fine to use sand or even peat moss as long as it’s not very wet. As far as keeping it moist, I have a few suggestions:
1. You can put a humidifier in the room where the cubes are.
2. You can put a small fan in the room with the cubes and blow on them.
3. You can use a misting system (like a misting bottle). I’ve heard of people putting plastic bags over their plants and then cutting holes in the bags to spray water into. That way the plant doesn’t dry out.
Rockwool cubes are a great substrate for seed starters. They are safe and will provide your seed with good moisture and oxygen for optimal germination.
They come in various sizes and shapes and they can blend into different growing systems. So, give your seeds an excellent germinating chance with rockwool.
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Growing cannabis in Rockwool
Rockwool is a product that was first conceived during the 20th century in Hawaii by observing natural volcanic action there. Upon this discovery, a Danish company named Rockwool began to investigate and develop ways to commercialise this technique, and in the late 1930’s released the first standardised stone wool product as we know it today.
To manufacture Rockwool, the raw material of basalt rock must go through several industrial processes, the first of which is melting of the rock in furnaces at extreme temperatures, up to 1600ºC, emulating the action of a volcano and leaving the rock in a natural state of liquid lava.
To obtain the fibres, an organic binder is added to the lava and the mixture is subjected to a mechanical process using centrifugal force, resulting in something resembling a woollen mattress. This wool is then compressed to varying degrees, the density and amount of air between the fibres depending on the projected end use, whether for acoustic or thermal insulation, fire-protection and, of course for it’s use in agriculture.
2. How to stabilise Rockwool
Rockwool Cubes and Slabs
Rockwool substrate is a product that needs to be treated before it’s use. Given that its initial pH level is quite alkaline, nearly 7 points, we should stabilize it to enable us to grow without mishaps from the very beginning.
We must immerse the slabs for 24 hours in a nutrient solution that contains a pH level of 4.5 with EC levels of 0.5-0.6 – ideal to start growing with seeds without worrying about nutrient deficiencies.
When we start to grow the pH level of the slabs should be at 5.5, if that isn’t the case, we should immerse them again during a few more hours checking the pH regularly until it is stabilised. An easy way to know if the pH of the slab is stabilised is to irrigate with water of 5.5 pH and measure the run-off with a pH meter. If the run-off is at 5.5 we can proceed to plant the seeds.
3. How to germinate cannabis seeds in Rockwool
Germination in rockwool
Once the Rockwool cubes have a stable pH as described above, we can proceed with the germination of the seeds we intend to use in our grow.
We will start the germination in two wet paper towels, placed between two dishes in order to maintain a constant humidity and facilitate the germination of the cannabis seeds. Once we see that the seed casing has cracked open and the root appears, we can very carefully transplant them into the stabilised Rockwool cubes and, once established, we can perform the transplant to the slabs.
To transplant the seedlings, we insert the small 3 x 3cm cubes into the 7.5 x 7.5cm Rockwool blocks taped to the slabs. As we do this, we must push gently and slowly until the small cube is well inserted into the larger block, taking great care not to break or damage any roots in the process.
4. How to root cuttings in Rockwool
The process of rooting cuttings in Rockwool is very similar to other cloning methods using jiffies or coco-coir (see how to take cuttings).
After the process of preparing the cuttings for cloning them, we place them in the Rockwool cubes (previously stabilised to pH 5.5) which should be moistened but not soaking wet, to avoid any problems with stems rotting.
Once the cuttings are placed in the cubes we can treat them exactly as if they were in jiffies or coco, monitoring the humidity every day and spraying the cubes to keep a constant moisture on them to ease the rooting. As time goes by it will be necessary to lower the relative humidity until we can finally remove the cover of the mini-greenhouse and start to acclimatise the cuttings so that they don’t suffer when transplanted.
Cuttings in Rockwool cubes
5. How to grow in Rockwool
As previously outlined, the growing medium must be stabilized at pH 5.5 with an initial EC of 0.5-0.6 during this first week of growth, not exceeding two waterings of 1 minute each, with a solution of around 60-70 ml per plant. In this way we will avoid water-logging and facilitate the root growth of plants in this highly absorbent and water-retentive substrate.
To ease the task of watering, using an automatic irrigation system will help enormously and is simple to assemble and use, as you can read in our post on how to install a hydroponic system.
We can maintain this irrigation schedule, varying according to conditions and demand, until the first week of flowering when we will start to gradually increase pH from the initial level of 5.5 , raising it slowly over the course of the week to a level of 5.8-5.9 suitable for this stage of flowering.
Hydroponic crop in Rockwool
From the second until the end of the third week of flowering, we will need to increase the frequency and duration of the irrigations, watering three times a day. The first watering should be of 2 minutes duration when the lights turn on, ensuring the plants start the day with energy. The second watering should be six hours later and 1 minute in duration, with an EC of 0.8-0.9 and a pH of 6.0.
Over the 4th week and until the end of the 5th week of flowering we will again have to increase the frequency of irrigation to 4 waterings at day. The first and the last irrigation should each last 2 minutes, and the remaining two waterings should be 1 minute, distributed evenly through the day. EC levels should remain at 1.0 to 1.2, always taking into account the condition of the plants. We should keep the pH at 6.0 allowing it to fluctuate up to 6.2 to lower it again to 6.0 with pH down.
During the 6th week of flowering it will once again be necessary to increase the frequency of waterings from 4 to 6 per day. The first and last irrigation should last 2 minutes each and the four remaining waterings will each be 1 minute. The EC should still be at 1.4 and the pH continues fluctuating between 6.0 to 6.2 as in the previous week.
In the 7th week of flowering period we will have to keep the same frequency and duration of irrigations; however, in this week, depending on the condition of the plants, we can increase the EC from 1.4 up to 1.6-1.7 and we can also let the pH fluctuate from 6.0 up to 6.3.
In the 8th week of flowering, plants will receive the same number of irrigations, at the same duration as in the previous week, although we can raise the EC to 1.8 depending on the condition of the plants.
In the 9th and last week of flowering phase we will have to increase the duration of all the waterings to 2 minutes, with the pH adjusted to 6.2 and with EC levels as low as possible. We can take advantage of this last week to apply a flush product to help us wash the roots, leaving the plants’ metabolism free of any remaining salts and nutrients and ensuring a far better, cleaner aroma and flavour in the end product.
Hydroponic cannabis grow using Rockwool
6. Recycling Rockwool
Rockwool can be a complicated product to dispose of, given that it isn’t biodegradable. However, today the technology is available to recycle surplus and used material and help to avoid the potential contamination caused by sending it to landfill sites.
The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.