Are there different styles of Gro-Slabs? Did the names of the slabs change?

GRODAN Gro-Slabs were previously available in two different stone wool weaves; vertical fibers (previously called Expert) and horizontal fibers (previously called CLASSIC). All GRODAN Gro-Slabs in the newer platinum packaging have vertical running fibers except for the 12” Gro-Slab – which has horizontal fibers. The vertical fibers allow for faster drainage (drier slabs) than the horizontally run fibers (wet slabs). The stone wool inside the newly packaged GRODAN Gro-Slabs are the next generation Expert slabs which are up to 5% dryer. This slight adjustment in the stone wool weave has proven to improve overall yield in commercial greenhouse growing. 

Why do my plants look crappy and grow slowly?

I did seedling in AO’K plugs then transplanted directly into a Hugo block. Problem: Purple stems, yellowing, root pack much less dense. The roots barely use 25% of the Hugo block. Block stays consistently heavy and what used to be a once a day watering is now an every other day watering.

Answer: The lack of roots is the main reason your plants look the way they do. The problem started with your seedling.

About 75% of the root mass is established when the plant is young. The roots will get longer/thicker later but the all the roots hairs must be established by the young plant. This is why all our literature preaches ‘healthy baby’ is the alfa-omega to success.

Why didn’t you get the roots in the early stage: 99% sure: your cubes/blocks were too wet. The chloramine in your tap water could also have been too high and limited the root growth – but not so high that it killed the plant. Talk to your local store about a carbon filter or use bottled water.

The easy fix (without having to change too much you do): Transplant the 1.5” cube to a 3” block and then put the 3” on Hugo. Why; cause it is easier to manage the water content in the small 3” than the huge 6” block (watch our video on transplanting). Also see below notes on successful transplanting:

  • Mist the 3” twice a day but don’t water until the block feels light (half weight).
  • Use a stake to hold the 3” block to Hugo.
  • Water on the 3” (low volume twice a day) until rooted into Hugo.

Second choice: Keep your current setup – but change your watering in the early stages. The seedling in 1.5” AO’K cubes must look healthy with roots about 1” below the cubes to succeed well. After transplant to the wet Hugo; Only MIST (plain water) twice a day for the first weeks time. Do NOT water. Wait until you can feel HUGO is lighter or the upper part starts to dry out. Then water sparingly – right on the little cube – probably about ½ cup. Once you see active growing and the cubes is stuck (have rooted into Hugo) then start to increase the water volume ..but slowly. Don’t drown them!

What is the best way to wet up, and maintain moisture in the Big Mama?

Before using, ALWAYS soak the Big Mama completely with a garden hose. It’s a terrible idea to wet up a dry Big Mama using only one drip stake. Conditioning and irrigation works best when using two drip stakes per block.

Click here to see exactly why this is so.

How do you properly prepare a Big Mama block?


Keep in mind that the stone wool volume of Big Mama is a staggering 512 oz versus Hugo’s 216 oz. So although some have attempted to use the Big Mama in an Ebb & Flood system - it’s a BAD IDEA! Drip irrigation is the most effective system for the Big Mama, but any top watering will work. Placing one dripper stake into the top block, and a second one into the Big Mama should be sufficient to maintain proper moisture levels. 

  1. Use a garden hose to completely saturate the blocks with water.
  2. Insert two drippers into the block. Fill the tank with pH 5.5 water, and water each block long enough so that the block receives 2.5 gallons of water. This ensures a complete flush of the block. If you only have a few blocks, skip steps 1 and 2, and simply use the ½” hose from the pump and hand-water with pH 5.5 from top down, until completely saturated.
  3. Discard the drain water. Mix up the same nutrient solution that you have been using for the plants you are about to transplant to Big Mama.
  4. Irrigate until each block has received 2.5 gallons of nutrient solution.
  5. Adjust your tank back to pH 5.5.
  6. Place a 3” or 4” block with well-rooted plant onto Big Mama. Insert one drip stake into the right side of the plant the small block and one drip stake into the Big Mama on the left side of the small block. If the top surface of the Big Mama doesn’t feel particularly moist, it’s ok. Less surface moisture on the stone wool means less algae growth.
  7. After placing smaller plant on top of Big Mama, minimize initial watering to encourage root growth from the top block to expand into the one beneath. But keep an eye on it to make sure the top block doesn’t become too dry. The best way to achieve this; place both drip stakes immediately below the small block. Let the drip stakes stick in under the block. For the first few days after transplanting; irrigate six short cycles per day.


  • Do not piggy-back one Big Mama on top of another Big Mama - the top will be too dry, and the roots won’t need that much space.
  • Do not use Big Mama in Ebb/flood systems - the top half will be too dry.
  • Do not place a tiny plant directly into the Big Mama – it must be well-rooted into a smaller block first so that it’s mature enough to root into the larger home. You wouldn’t expect an infant to run a marathon, right? Both need time to develop first.

Click here to view an experiment that was conducted on wetting up Big Mama blocks.

How do I get my store listed on your website?

Simply click here and fill out the form. We will also make sure that you automatically receive information, fliers, and newsletters from us.

You can also e-mail us a picture of your store and employees to put with your store profile at info@grodan101.com.

I have just opened up a new store, how do I set up a wholesale account?

First of all, welcome to the hydro industry! GRODAN retail products are sold exclusively through four master wholesale distributors in the USA, and four in Canada. To set up an account to purchase our products, simply contact one of our distributors. To find one who services your area, use the Store Locator feature on grodan101.com. Select the distributor tab, input your state and zip code and hit search. From there, you can click directly to their Websites where you can contact them directly.

Your GRODAN retail team wants you to succeed and we’re here to support you via:

  • Free technical service
  • Educational/marketing literature
  • GRODAN Posters and banners  - when available
  • FREE online store listing. Add your store name to our online database by completing the “New retail store” form. Don’t forget to check subscribe, under the “Primary email Subscription Preference” so we can be sure to include you when we send out GRODAN news.
  • A FREE, counter top holder with 6-pockets to display our complete set of our tri-fold (user guides). Just add these to your GRODAN order when you place it. These brochures help educate growers on proper usage so they have success and return to you to purchase more. You can order more FREE at any time.

Maximum Yield (www.maximumyield.com) and Garden Culture (www.gardenculture.net) are industry publications that are popular.  Ask your GRODAN suppliers for free copies to hand out to your customers. Max Yield also hosts multiple industry expos that you may wish to plan to attend one in your area to help keep you updated on new industry trends and products.

GRODAN wishes you much success and look forward to hearing from you if we can be of any further assistance.

Does GRODAN sell directly to consumers?

GRODAN does not sell anything on our website, we are just here to provide technical support. Our products are available through retailers, just click on the “Look for Shops” drop down menu on the top right of this screen to find a local retailer near you. We appreciate your interest in our products.

Why does the GRODAN Stater tray not come with 98 cells to suit the package of plugs? What about inserts for your other plugs 50/pkg and 200/pkg?

The inserts we make must fit into the standard 10 x 20" flat black tray that everyone uses. For that reason there is only room for 66 individual cells If you want to use the full package of 98 plugs - then you simply place the package directly into the 10 x 20" flat. Most of our commercial growers will start plants that way.

The advantage of using the insert is one that the roots from each cube do not get entangled. And secondly by having the tray hang on the 10x20 flat you can have water underneath that helps creates the necessary humidity. The 98-count packages is by far the most popular starter plug so we started with an insert for those.

The number of packages used of the 50 plugs or the 200 plugs is low. The mold to make an insert is very expensive - so if we made an insert now it would probably costs us about $40 per insert- which no one will pay. - but thanks for your suggestion - keep them coming!

How do I transplant from stone wool into coco coir?

The most important thing with Coco is to get it from a reputable company. I have used CocoCanTM coco products and they have served me well. You have to make sure that the coco fibers are not too old (if the shelf life of the coco is over two years, there will be problems with wetting the coco). Also, bad companies will sell coco that have high salt content in them, so you would need to soak and flush with water to get rid of the salts before use. CocoCan is OMRI certified (organic), so it has not been buffered with chemical fertilizers. So if you decide to use an OMRI certified coco, it is important to flush through with some nutrient mix that contains either calcium or magnesium nitrate before planting, or the equivalent organic nutrient of your choice. So the steps are:

  1. If using a compressed block, soak in water (around pH 6.0) and fluff it up to get loose coco. If using a ready bag of growing mix, then just take out what you need.
  2. If the above is organic (has not been nutrient buffered), then flush through with a nutrient solution that contains higher levels of calcium and magnesium. A mix with calcium nitrate in it would work well. Keep pH again around 6.0, depending on type of plant.
  3. Transplant into the coco the plant that you started. I have successfully transplanted flower and veggies that I started in GRODAN A-Ok plugs and Gro-Blocks™, just make sure to cover the top of the stone wool with coco. Also maintain the coco right around the stone wool moist because you don't want the coco to dry quicker and wick out water from the stone wool.
  4. Then feed with a grow, and eventually bloom nutrient solution.

There are some companies that make specific nutrients for growing in coco. Ask your local hydroponic shop and they will be more than happy to help (you can find a list of stores on our website). One other hint, I have mixed in GRODAN Grow-Cubes™ in with the coco at about 1/3 Grow-Cubes to 2/3 coco, and I have had great success. The stone wool seems to add a little more aeration.

What to use instead of GreenMix and how to condition Gro-Wool

I have decided to use some Grow-Cubes™ in the bottom with some Gro-Wool™ and a few Grow-Cubes on top in place of the discontinued GreenMix, as you suggested. Do you suggest using the Europonic stone wool conditioner from hydrodynamics?  How long must Gro-Wool be soaked overnight?

Answer: The purpose of 'conditioning' is to dissolve and wash out the lime stone from the wool. Lime stone is pH 8 - thus anything under pH 8 will dissolve the lime stone. Lime stone is vital when we produce stone wool, but getting the lime stone into your stock tank makes it the pH too high for the plants - so we like to wash it out. Gro-Wool typically takes a little extra work to wash out well. However if you have the Grow-Cubes and Gro-Wool in your mix - it does make it easier.

  • Take tap water and adjust to pH 5.5. You can use the suggested product as long as you achieve a pH of 5.5 Keep pouring the solution onto the Gro-Wool until you have a lot of run off.  Use at least twice as much water as your container of wool can hold.
  • Leave it for 30 min or so.
  • Mix up your balanced nutrient solution.
  • Water your Gro-Wool from the top - using as much water volume as before.
  • Drain to waste (not to your tank, as the lime then will end up there).
  • Now you are ready to place the container in your system and pot up your plant.

I've run out of my regular plant food and can't get any more for a few days, what should I do?

Do not just give your plants plain water, as this would be a terrible shock to the plant- not to mention you would be starving your plant if even for only a few days. Buy an all-purpose water soluble plant food at your local garden center. If you can, measure the EC or ppm after mixing the solution, to make sure you are giving the same level of plant food as before. Your plants should continue to grow, until you can buy your regular plant food.

Do you have to germinate seeds before planting them in a hydroponic system?

In most hydroponics systems water either runs continuously or at least daily.
This is much too much water for seeds, so they would most likely rot before they germinate. Therefore you should first germinate the seed in a small pot or small GRODAN plug (around 1.5"). The little GRODAN plug holds enough water, that you do not need to water before the seed has germinated.

Most hydroponic systems have pots/containers that are much bigger than 1.5". For good germination & a healthy baby-plant the 'glove' should fit. Big pots just do not have the best conditions for a small seed. So even if you do not set the system to water, the pots are still too big for a good result.

Will airstones at the bottom of a flooded container work with Grow-Cubes?

Airstones will not provide enough oxygen in a stagnant system. You may still risk root rot with the plant's roots sitting in water. Also the plant's roots get lazy when they are being fed constantly. Grow-Cubes already have a high air capacity, but still hold plenty of moisture (much more than expanded clay). The best use of Grow-Cubesis on an ebb and flood tray (flooded 1-4 times per day) or by top feeding. You can place the airstones in your stock tank for added oxygen.

Can I recycle GRODAN?

Yes! Cut up the used stone wool, then pot up a different plant in it. Add it to clay or sandy soils to improve tilth. 

What about salt crust formation on the top of the block?

This is a typical problem in Ebb/Flood systems. Top watering the blocks weekly by hand can minimize this problem.

Where do I cut drain hole slits on the slab?

Optimum drainage splits diagram.

For drip irrigation make 3 cuts around the bottom edge of each side of the slab. The slits should be 2” long– running 1” on each side of the edge.

Should I be worried about stone wool dust?

No! The World Health Organization has confirmed it to be bio-soluble and safe.

Why do I get mushy or hard spots in the block?

Flushing the block with low pH water ( < 5.0) will dissolve the wool creating mushy spots, which then solidify into hard spots when correct pH water is used. Always use a pH range of 5.5–6.5 when watering.

Why does the pH of the nutrient solution in the block increase?

At initial wetting, pH increases due to residual lime left from the production of GRODAN . Later, pH increase is just a natural response to plant growth.

What causes mold on the GRODAN or root rot in my plants?

Overly wet conditions due to watering at night or when dark, or from too many flood cycles. (No light - no water)

What are the general feeding & watering guidelines for nft systems?

The rule of thumb is to replace the nutrient solution at minimum every two weeks. But do it more frequently if you have a large amount of plants relative to a small stock tank. pH can rise dramatically when using a small tank for a large amount of plants. So always keep an eye on the pH and adjust every 2-3 days to keep in the optimum range for whatever plant you are growing. A good guide for changing the solution is a high EC.

Also soft stems or less than perky green leaves would be an indication to change the nutrient solution. How often you should water depends on many factors. Best guide is to water when the GRODAN cube feels like it is 50% dry. Download the brochure "Watering and pH" for more information.

Is it a good idea to use emitters to help regulate flow to my plants?

We have found that emitters do not drip well if you use a small pump (under 10 psi). If you are using a small pump, then you might want to omit the emitters and have a flow direct from the tube attached to a drip stake.

How many gallons per hour flow do I need in a constant flow system using Grow-Cubes, if I have shelves feeding the plants on shelves below them?

Giving a watering recommendation is always difficult because it depends on variables such as the intensity of light you are using, how mature the plants are, etc. Please download the brochure “Watering and pH” from the brochure page for helpful hints. Also, I am concerned about using a constant flow system for two reasons: 

  1. Keeping the stone wool continuously saturated makes the plant’s roots “lazy”. So they will be weak because they don’t have to grow in order to get water.
  2. Watering into the night, when the lights are off, creates an environment conducive to the spread of diseases such as Pythium.

My recommendation is to water 2-3 times per day, but again depending on the light intensity and maturity of the plants. Bigger plants will of course need more water. You don’t want to keep the Grow-Cubes™ fully wet all the time- it’s good for them to just be slightly wet for most of the day. The best thing to do is to start with a low flow, such as 0.5 gph. For the first watering, let it drip through the entire 6 shelves, and measure the time it took to saturate all 6 shelves and get some drainage from the last shelf. If later in the day the Grow-Cubes feel like they are drying out, repeat the watering; but not as long as the first time (remember you don’t want to fully saturate the Grow-Cubes again). You can repeat this watering as many times during the day as needed for your plants. Once you get an idea of what your plants need, you can set the system up on a timer. Also, always remember not to water at least two hours before shutting off the lights and whenever it is dark. You can find much of this information in the brochure “Watering and pH”.

Can I use a 6” block (Hugo) in an ebb & flood system?

Stone wool will have good capillary movement (ability to pull up a nutrient solution against gravity) in up to 4” tall blocks. Any block higher than this such as the Hugo will remain drier on the top, depending on how high the tray is flooded. So if your flooding is less than 2” high, then go with the 4” blocks. But you never want the GRODAN to just be sitting completely in water. 

The best bet is to water like Mother Nature does- from top to bottom. That’s why we recommend top watering over ebb & flood for GRODAN products. Download the brochure “Watering and pH” from the brochure page to learn more on watering tips for drip irrigation.

It’s easy to convert your ebb & flood system into a top feed system. Disconnect the ½” tubing from the valve. Bend the end of the tube and tie it. Insert a piece of ¼” tubing into the ½” tubing. The ¼” tubing should then run up the outside of the pot and with a drip stake be secured to the blocks at the top of the pot.

Is stone wool safe? It feels like fiberglass?

Stone wool is spun mineral fibers made from natural rocks (see question #2). IT IS NOT FIBERGLASS. The World Health Organization (WHO) has classified stone wool as a bio-soluble product, meaning if you inhale or ingest the fibers they will dissolve into minerals in your body. The Material Safety Data Sheet (MSDS) contains this information. It also states that in the dry form, stone wool, like most minerals, can cause a slight mechanical irritation to the skin. This can be avoided by wetting the wool before you handle it or spraying hairspray on your hands and arms before handling. After handling the stone wool, rinse with tap water, but don’t scrub. To read more about the safety of GRODAN stone wool, download the MSDS. 

What is the purpose of the plastic covering on GRODAN?

The white plastic that surrounds the blocks helps keep the plants separate, prevents algae growth on the side of the block, keeps diseases from spreading, and prevents light damage to roots that may extend out of the block. So keep the wrapping around the blocks unless you plan to pot up the plant into a loose medium such as clay pellets or GRO-WOOL™.

However, there is also a clear shrink-wrapping on the strips of blocks and the sheets of propagation plugs. The wrapping is there for ease of handling in the retail store. This shrink-wrapping should be removed prior to use.

How do I condition GRODAN Grow-Cubes in large bags for pH?

Make up a nutrient solution that doesn't go below pH 5.5 to soak the cubes. You can soak them right in the big bag if you plan to use all of it at once (but it will get heavy). If not, partition in smaller bags. After they have soaked a few hours, make a slit at the bottom of the bag and let it drain out in the sink.

I have read that it's important to soak these cubes in water adjusted to a PH of 5.0. Thus conditioning them prior to planting. Is this information correct and if so just how do the commercial growers soak a 1,000 or so at a time?

First, the reason we recommend "conditioning" the GRODAN products is to remove a lime stone residue in the block. The lime stone, which is pH 8, dissolves easily with pH adjusted water. Once the lime stone is flushed out, the GRODAN product is pH neutral. 

Due to the difference in equipment and especially in stock tank size, the recommendation for commercial grower and for hobby use varies.

Hobby: We recommend soaking and flushing the products, as you typically use a recirculation system. Having the dissolved lime circulating around in a small tank would make it harder to maintain the proper pH in the system. Also an important aspect of using stone wool is that the product most be fully wetted before use. By recommending the conditioning we are sure the product is fully wetted before use.

Commercial growers will wet up the GRODAN slabs typically 24 hours before use. When they wet up the blocks varies a little from grower to grower. However, most growers in North America 'water to waste' (as in non-recirculating).This means the lime stone is flushed out as soon as the irrigation system starts. Those growers with a recirculation system have computer controlled automated fertilizer injection. This means the computer will automatically compensate for any undesirable E.C. or pH fluctuation.

Important Note: GRODAN does not tolerate lower that pH 5.0 - it starts to dissolve. So to be on the safe side, I would suggest you soak in pH 5.5. This will dissolve the lime fast. After an hour or so, you simply water from the top with your balanced nutrient. For each "HUGO" block you need to top water at least one gallon of water, as the block holds near that amount of water. Now your block is perfect for planting and you can transfer it to your system.

You can use a garden hose to soak your blocks with. However the tap water is often very close to pH 8, so it is best to soak the block overnight.

Thank you for using GRODAN!

Soaking GRODAN to proper Ph for growing

Question 11: Soaking GRODAN to proper Ph for growing

Hello. I use propagation cubes and 3x3" blocks. I soak them overnight in pH 5.0 water to achieve a pH 6.0 for growing. My friend soaks in pH 3.5 water because she says the natural pH of GRODAN is around 8. What is the correct method? My water reads at 6.0 after the 24 soak. Why couldn't we just put the dry cubes on the table and set it to cycle every 30 minutes overnight. If we did this with a pH solution of about 4.5, it should give us a proper pH of 6.0, correct? Please advise. Thank you.

GRODAN stone wool is pH Neutral! It is a common misunderstanding that GRODAN is alkaline and that one has to continuously adjust the pH, when in fact stone wool is pH neutral.

The confusion stems from the fact that GRODAN has some residual lime from production. Follow this simple procedure to remove this un-buffered lime. Begin by saturating the stone wool in pH 5.5 water ½ hour before use. There will be a rise in pH of about 1.0 from the residual lime dissolving. The final step involves flushing the "dissolved Lime" from the stone wool with your nutrient solution just prior to planting or sowing. From this point onwards, the pH neutral GRODAN stone wool will not contribute to any changes in the pH of the solution.

Note: Ensuring pH values remain between values 5.5 – 6.5 is essential for optimum plant development and optimum substrate integrity. If you condition GRODAN products with a solution pH lower than 5.0, you risk damaging the stone wool, so take steps to ensure values do not go below pH 5.0

Why does pH change ?
When the plant grows the pH goes up because of the root activity involved in nutrient uptake of the plant. If the pH is not going up, your plant is not actively growing!
When the plant gets ready to set flowers or fruit, the pH will briefly drop. So when you notice this drop, the plant is signaling that it is time to change to your bloom-solution.

So in answer to your questions; You should always stay above pH 5.0 (better to use pH 5.5), because GRODAN begins to dissolve below pH 5. You can soak the cubes on your table. You don't need to cycle, as long as the cubes are soaked initially. However, you do need to add the final step of watering from the top in order to flush out the lime residue. You should also get rid of the drained water, as it contains the lime residue.

Please download the leaflet “Watering and pH” or pick it up at your local hydroponic store for more information.

How dry should GRODAN blocks be before they are flooded again in an ebb & flow system?

The rule of thumb is the blocks should be flooded again when they are 40-50% dry.

In an ebb & flow system, why should GRODAN blocks be top irrigated (flushed) once a week?

The capillary movement of the blocks draws nutrients (salts) to the top in an ebb & flow system. If left unchecked, the salt levels in the top of the block can reach high levels, possibly damaging the roots.

This is why we recommend flushing the blocks once a week by top irrigating with standard nutrient solution. In fact, we recommend top feeding over ebb & flow systems for GRODAN stone wool. Refer to the brochure Watering and pH, Tips on watering and pH when using GRODAN stone wool for more information.

I have a really bad algae (slimy green stuff on the surface) problem using stone wool. Is there anything that you can suggest to stop this problem from occurring?

With the wool being wet, and light shining on it, it is natural to get algae. In itself, Algae is not harmful to the plant, however it might be an invitation to fungus gnats, which can be a nuisance.

There are two things you can do to prevent or minimize the algae growth:

  • Cover the exposed area of the wool with black plastic. If you already have a lot of algae growth, scrape it off before covering with plastic.
  • If you are getting clay pellets (hydroton/hydrokorrels) you will see some brown clay dust in the bottom of the bag. Put that dust in a salt shaker and sprinkle it on top of the wool. The brown dust does not dissolve.

I just started using mini GRODAN Grow-Cubes and the pH is dropping rapidly. What am I doing wrong? (The plant is flowering.)

You will see a drop in pH for many plants as they begin flowering. It simply shows that the plant is eating different food than during leaf-setting. If you measure pH in the drain water on a regular basis, you can see the pH drop starts before you see flowers on the plant. It is a signal to you that you should change to your bloom-nutrient. The pH might drop so much that you will need to use some ‘pH-up solution’.

The leaves on my plants curl downwards…. why and how do I fix it?

First the quick rules: 

  1. Young leaves curling; the humidity in your grow room is probably too high; open the door!
  2. Old Leaves curling: something is probably wrong in the root zone. Often it could be a bit of root rot. You can minimize the risk of root rot by stopping the watering 2-4 hours before switching the light off. The stone wool should only be 50-60% wet over-night.
  3. Sometimes your general humidity is just fine, but your plants are so bushy that there is not a good air movement between the branches. Use fans. As an example, I can see that my cherry tomatoes are most happy in 15 mph "fan-winds".

More technical detailed explanation to curling leaves
If the youngest leaves are curled downwards, it more than likely indicates a calcium deficiency. If old leaves are curled; something is probably wrong in the root zone (which also reduces the calcium uptake). 

Calcium deficiency is the result of insufficient water movement through the plant. Remember, calcium only travels in the water stream of the plant, not in the nutrient stream. Therefore, calcium deficiency is usually (90% of the time) related to the climate in the growing area. High humidity will prevent calcium uptake even if there is sufficient Ca in the feed solution. Also, large day/night fluctuations in humidity will disrupt the Ca flow within the plant and lead to blossom-end rot (BER).

Another cause of BER or obvious Ca deficiency in the leaves is poor root development. This is a result of low substrate temperatures or the presence of a root pathogen such as Pythium or Phytophthora. Calcium is taken up by the area of the root immediately behind the root-tip. If the roots are not actively growing, new root tips will not be formed and consequently, Ca uptake will be reduced.

How do I prepare the Hydrokorrels for use with my hydroponic plants? I need to know if I should remove the seedling from the starter cube before placing it in the cup with the Hydrokorrels around it. Lastly, how low should I keep the light unit from the s

If you started the seedling in a GRODAN starter cube - do not pull the seedling out of the product, this will kill the plant. The GRODAN product has great moisture retention, whereas hydrokorrels (hydroton) have very limited moisture retention.

If you use a GRODAN cube wrapped in plastic (e.g. the mini cube), then remove the plastic before inserting the plant in the hydrokorrels. The top of the cube should be visible, but cover the sides with hydrokorrels.

When using hydrokorrels and watering on a timer, the fine active root tips of the plant will dry out a bit between the watering. Consider adding a few of the GRODAN Grow-Cubes™ (also known as the 'croutons'). They will provide moisture to the roots. Even if you are using continuous watering, these 'croutons' will help distribute the water more evenly into your pot.

Distance from plant to light; it depends on several things; how many watts, plant type, nutrient level, etc. Some people go all the way down to 18 inches. I use 3 feet with a 750-watt light and 2 feet with 400 watt. My best suggestion is that you start a little higher than you think you want. Watch the plants! If they grow well and don't get stretchy, then you are fine. If you get dark or wilted spots, you are too close. Stretching plants means that the light is too far away. The heat from the lamps can also burn the plant. A fan can help offset the problem.

For further questions, please contact the store you purchased the products from. They always have good tips.

I ordered two hydroponics kits; both of them came with gro rocks. I was curious to know if I could use the Mini GRODAN Grow-Cubes instead of the gro rocks? I'm afraid since they would be constantly wet without drain that the roots would not survive.

In most cases you can quite easily use the Mini GRODAN Grow-Cubes instead of gro rocks. The only time I would not recommend it is if the Grow-Cubes were completely submerged in water 100% of the time. That situation is not really suitable for any other plants that swamp-plants (even with gro rocks).

I am guessing that your kit must be some sort of ebb and flod system… Normally the pots in these types of systems have holes in the bottom. Primarily so water can get in and out.

With regards to gro rocks, you would be required to water continuously. Using GRODAN Grow-Cubes you can do the same as if you are growing a water hungry plant. However, you must stop watering about 2 hours before the sun goes down. This allows the cubes to be drier at night. Remember the plant does not grow in the dark; no light, no water.

I would highly recommend that a timer is attached to the system when using GRODAN and that you only run 1-3 water cycles per day.

What are the benefits of hydroponic growing?

Cultivating plants hydroponically is an easy and environmentally sound way to grow a wide variety of healthy plants. It offers numerous benefits over growing in soil, including:

  • Plants grow up 50% faster because they have easy access to food and water.
  • Plants become "vacation-proof" and "neglect-resistant" as stone wool retains water so well.
  • Plants can "tell" you when to water, because they droop before wilting and damage occurs.
  • The absence of a buffer in the growing medium means plants get all the nutrients available (they don't remain "bound up" as occurs in buffered mediums like peat moss and coco fiber).
  • Little or no pesticides are necessary. Plants start out in a disease-free medium.
  • If disease occurs, it may only affect one plant, not a whole row.
  • You use smaller containers, because the roots can grow throughout the media without being rootbound.

What is GRODAN stone wool?

Stone wool products are made from basalt rocks, which come from the Earth. Stone wool is composed roughly of the following elements:

46% Silica, 16% Calcium, 14% Aluminum, 1% Magnesium, 8% Iron, 2% Sodium, 1% Titanium, 1% Potassium, and 1% Manganese (Source: Cultivos vegetales en substratos C.T.I.F.L.)

In the production process, a biologically derived binder is used and some lime stone which can leave some lime residue on the surface of the fibers.

Mimicking Mother Nature's production of "angel hair" during volcanic activity, the GRODAN stone wool manufacturer heats rocks to 1600°C, to create lava. The lava is blown into a spinning chamber, which makes fibers similar to cotton candy. These fibers are bagged loosely as "stone wool granulate". They are also packed into mats, from which GRODAN cubes, blocks and slabs are cut. The products make excellent use of natural resources: one cubic yard of rock becomes 37 cubic yards of wool!

What is Hydroponics?

HydroponicsWhen you grow a plant hydroponically, all the nutrients and all the water is readily available to the plant (traditional potting mixes only release about 70%). Thus in hydroponics the plant does not have to work hard to get its food and water. It can therefore spend all it's energy on growing vegetation and setting flowers and fruit, instead of growing roots. In soil a big network of roots is necessary in order for the plant to be able to find enough food and water.

Subscribe to FAQ