Growing media is used in net cups or plastic pots to provide support for plant roots. It protects roots from sunlight while giving them something to hold on to. Growing media helps to ensure that plants get the proper ratio of water and oxygen., both which are critical to healthy plant growth. You can use many different types of media, but all should provide the following: physical support for the plant, free passage of moisture (nutrient solution) to the root zone, proper drainage of moisture and adequate air circulation at the root zone.
Today there are a number of great environmentally friendly growing media on the market. Many of them can be re-used with microbe colonies alive and thriving within them. Others can be sterilized and reused, and others still can be disposed of by digging them into your yard to amend the soil.
Do I have to use a growing medium?
Using a growing medium is not entirely necessary in hydroponics, but utilizing a grow medium maintains a reserve of nutrient solution in the root zone along with a percentage of air pore space. This can act as a buffer and save crops from failure. THe growing systems which rely on grow media are Drip Sytems and Ebb & Flow Systems. These systems most frequently used by hobby and beginning growers as they are more forgiving and provide excellent results.
There are two types of systems which require very little growing media, NFT and Aeroponics. Both of these usually rely on a very small amount of media in which to root a very young plant, and the rest of the roots are allowed to grow in the enclosed growing chamber of the system. In these types of systems, watering and feeding of plants depend solely upon the flow of nutrient solution past the plants’ roots. If water flow is interrupted, even for a short druation, plants quickly die. At the other extreme, if the root zone is continually flooded, roots suffocate oxygen deprivation and plants quickly die. A good grow medium negotiates these extremes.
What is the best growing medium?
Different media work better for different growing systems and different plant types. There are many factors to consider such as water and nutrient retnetion capabilities, what kind of growing system you will be using, and whether or not you wish to reuse the media for subsequent harvests.
Rockwool is always a good choice. A fiber spun from rock, it holds a tremendous amount of water and offers a buffer against drying out in case of electrical outages or pump failures. Between 90-95% of the space between rockwool’s fiber is filled with air. Once saturated with water, Rockwool still has between 25-30% air within its medium. This air space makes oxygen, water and nutrient solution easily accessible to plant roots.
Coco (coir fibres, or husks) is another type of medium. As well as Rockwool, Coco also holds about 30% air within it. Coco is organic and is 100% biodegradable. Trichderma, a beneficial fungi is naturally present within its core, which protects and helps nourish the root zone of most plants. Coco also has naturally occuring enzymes which are soothing for a plants root zone as well.
Grow Rocks are another type of media which provides great aeration. Grow Rocks hold very little water and nutrient. Consequently, this medium will act only as a support system for plant roots, and provides very little water reserves. This is a great way to go if you’re using an automated container garden on a watering timer. Grow Rocks also work well in the net cups used in any type of tray system. They can be reused over and over agian for many, many crops. In well maintained garden, they would be sterilized between every crop. One downside to grow rocks is that they are heavy.
Soil is seeing a resurgence as of late. Not that it ever went anywhere, but with the recent popularization of beneficial micro-organisms and the introduction of coco coir fibre into the mix, many growers are returning to-or just starting up in soil rather than hydroponics. New Soil Mixes use custom blends of organic materials to add aeration, biology, and plant ready minerals into the mix. The everlasting debate between Hydro and Soil and which is the better medium is still on and kicking. These days many people are reporting larger and better yields from soil.
Rockwool is made of basalt rocks and chalk which are heated up to 1600C to creat lava. The lava is blown into a spinning chamber, which makes fibers similar to cotton candy. The fibers are packed into mats, from which cubes, blocks and slabs are cut. Rockwool is almost all based on recycled materials, often slag from primary preconsumer ferrous or nonferrous metals producers. One cubid yard of otherwise wasted rock becomes 37 cupic yards of rockwool. Seeds or clones may be started in small rockwool cubes which can then be transplanted to larger cubes which can then be used on top of slabs. The cubes may also be transplanted with other mediums such as grow rocks. Totally biodegradable, it may be plowed into your garden-it will break up into chunks and add aeration to the soil. Grodan Brand is our rockwool selection of choice. It is always clean, sterile, and consistent.
LECA, Light Expanded Clay Aggregate or Grow Rocks
Grow Rocks are one of the only kinds of growing medium that can be used again and again with a minimum of breakdown. They are a good choice for the grower who plans on many harvests in the future. The brand we sell, Hydroton, is known worldwide for its superior quality. Expanded clay provides excellent aeration as the odd shapes of the rocks allow for the formation of air pockets throughout the root zone. The inside of the pebbles are filled with air pockets as well and they are fairly light weight. The pebbles do not hold much water, so plants must be watered frequently to prevent roots from drying out. They are often used in Ebb & Flow systems.
Benefits of Using Coco Fibre
Coco coir (coir fibre, Coir, Coco, Coco fibre) is a product derived from the husks of cocnuts. Visually it looks a lot like peat. Coco, when used properly, presents the best of soil and hydro in a single media. Coco can be extremely forgiving, and growth tends to be very consistant. Coco is pretty damn tolerant of over-and-under-watering. As you will see below Coco has many amazing properties making it an ideal medium to grow plants in.
Coco is almost a neutral medium, which means that aside from its limited qbility to adjust pH to optimum levels, it does not bind nutrients and feed them slowly to the plant over time like traditional “soils” do. (This means that Coco has a relatively low CEC compared to most soils. All the nutrients your plant needs to grow must be provided by you. Coco fiber does, however, create millions of tiny air spaces, which are great for the roots. This is due to the large surface area of the coir particles. Think of coco as a very porous, open cell spongs; it releases water very quickly and as it drains out of the bottom of the containers, it pulls in fresh nutrients and oxygen. The medium holds water, oxygen, and nutrients in a perfect ratio for the roots in these tiny spaces. As oxygen plays an all important role in respriration(roots pumping nutrient up to the plant), the structure of coco coir further promotes root and plant health. This factor should not be underestimated because healthy roots invariably lead to a healthy plant (and yield.)
Coco also has a remarkable capacity to insulate and protect the plant’s root system in hot weather. This meants that coco coir isn’t as prone to overheating, due to excessive ambient air temperatures, as many other mediums, making it ideal for warm climates. Because the root zone is cooler, there is more oxygen available for the roots to use.
On a less positive note, coir can also contain high levels of sodium (salt). If you’re growing in coir be aware that this can be a potential problem. We suggest you only use High-Grade Coco Meiums like Canna Coco. Canna is unique in their all natural “chemical” based Flush which brings the overall ppms/EC levels contained within the medium down to next to nothing. Canna Coco also has a great consistency of long to short fibres, and is pre-innoculated with their proprietary Trichoderma strain of beneficial Fungi to help ward off pathogens and help with the initial transplanting process.
Finally, Coir has two other very important benefits that make it excellent for plant growth. It has naturally occuriing enzymes which help ease the roots, and allow for some general stress relief and ease of new growth. It is also an amazing home for beneficial microbes of all kinds. It is organic, and as stated above, very prous, providing the needed aeration frm aerobic microbes to colonize and thrive. Anyone has grown in Coco, used microbes, and looked at their root zone when they were finished can attest to this. Roots are firm and fluffy. Usually with huge ropey swirls filling up the entire container (it’s hard to even see the coc by the end cause the entire container is filled with roots) with smaller tendrills coming off the larger coils and if done correctly, fuzzy micro-hairs throughout.
Tips on how to make Coco Fibre Work Best for You
Watering with coco is different than with soil. If you grow in soil, it can be much easier to “drown” the plant with too much water. Coco on the other hand is so light that there will always be more oxygen left and the plant will have a much harder time being oxygen straved. You can let the pot become dryer the first week only to stimulate root development. We suggest watering your medium until fully saturated(with at least 10% run off) and then letting your plants go from wet to “barely moist.” Coco can be used differently than this-allowing for multiple waterings a day. A grower must only let Coco go from wet and fully saturated to “moist” (usually a few hours when the lights are on) before watering again. We have had consistently great results off of the former method-going from wet to barely moist.
Although Coco has a very good water-to-air ratio (even trumps Rockwool which also claims to have a 70% water-30% air holding capacity); however coco offers the unique ability of being cut with a further aerating substance like perlite. Adding perlite can increase your overall oxygen levels within the root zone immensely. We suggest one 1cu.ft. bag of perlite to one 50L Canna Coco. This will give you roughly 60% Coco/40% Perlite mix, which has ideal aeration levels as well as maintaining an adequate water-holding capacity.
Coir holds a considerable amount of water within. It also evenly distributes the water throughout the medium. This is great for growers using drip systems because you only need one to two drippers to create full saturation throughout the entire container. However, since Coco holds onto water and nutrient within its structure it creates a pH Buffer within the medium itself. Coco also has a natural tendency (because of its high levels of Potassium contained within) to hold onto certain salts. This tendency (which contributes to its mid to low CEC value) tends to make Coco’s buffer rather difficult to bust, thus making it harder to change the pH of the medium . Do not fret though because the Buffer CAN be broken. It just takes flushing copious amount of pH corrected 300 ppm nutrient solution (50% of which should be Cal/Mag) with Final Phase (Flushing agent mixed in) Through the medium before you even start to grow in it. In this way you can ensure that the pH of the solution going into the medium and the pH of the solution coming out of the solution match. (An example of this would be 6.0 pH going into the medium and 6.0 pH coming out as run-off. This is a very important concept to grasp when using Coco based mediums.
Another issue a grower should be aware of when using Coco based mediums is that Coco naturally holds onto some nutrients (Ca, Mg, Mn, S) therefore we will want to Flush the medium on a regular (weekly or bi-weekly) basis or water with very low ppms/EC values. When flushing, we also suggest collecting and testing the run off to make sure that the ppms have gone down to almost nothing, and the your pH coming out of the bottom of the containers matches the pH being fed to the plants.
Coco is most suited to a run-to-waste system. A runoff of 10-20% of the volume watered each watering is the most common recommendation to avoid the possibility of salt buildup in the coco media. Drainage helps control ppms/EC values and pH levels, and flushes unnecessary salts out of the media. Since not all plants use similar amounts of nutrient, and they also secrete salts, any surplus of nutrient makes the coco brackish and changes the pH. By means of drainage you flush the media every time you give nutrient, which prevents it from becoming brackish. This does not mean that you should not flush as indicated, but by regularly testing the run-off you can do less flushes. Many seasoned Coco growers will only flush once every 3 weeks.
Perlite & Vermiculite
A combination of perlite and vermiculite is a popular hydroponic medium. Perlite is hard and brittle, providing excellent drainage and root aeration. Vermiculite is soft and spongy, providing good water and nutrient retention. Perlite and vermiculite when mixed together in a ratio of 3:1 are an ideal medium for hand watering as together they hold plenty of moisture but still retains good drainage.
Vermiculite is shiny, gold color flecks that can soak up to 3-4 times its volume in water. It’s sterile and attracts nutrients such as calcium, magnesium, potassium, and phosphorous. Vermiculite is the mineralogical name given to hydrated laminar magnesium-aluminum-iron silicate, which you probably don’t need to know. It resembles mica in appearance and is another volcanic silicate mineral. Its surface mined in places like Australia, China, Kenya, South Africa, and the US. Unlike perlite, vermiculite is spongy, super light weight, and tailor-made for water absorption.
Perlite looks like tiny, white, crystallized popcorn kernels. Perlite is not a trade name but a generic term for naturally occurring siliceous rock. When quickly heated to about 1600°F, the crude rock pops in a manner similar to popcorn as the water inside vaporizes and creates countless tiny bubbles which account for its amazing light weight and other exceptional physical properties. Perlite combines well with almost any base soil mix. It will help aerate the soil and improves drainage and oxygen content.; mix at a 50-50 perlite to soil ratio.
Soilless Potting Mixes
Soilless potting mixes are traditionally made from peat moss and then supplemented with perlite, vermiculite, micronutrients and macronutrients. Today more options exist than just peat moss, and potting mixes are made from a variety of substances.
The soilless potting mix we carry, Ready-Gro is a mixture of perlite and coir fibre, among a variety of other great organic additions. Coir fiber is a by-product of the coconut harvest and is a renewable resource. It holds 10 times its weight in water and does not shed water like peat moss. It holds and releases nutrients over extended periods. It is also said to provide excellent aeration.
Organic Soil Mixes
There are a sleu of good soils out there. A couple of our favorites are Roots Organic and Ocean Forest. These soils are made of the highest quality organic base ingredients. They all contain Organic Peat as their base and have other amendments (such as Coco Coir Fibre, Perlite, Pumice, Guanos, Fish and Crab meal, Earthworm castings, organic compost, etc.) added for extra nutrition or for better aeration or drainage.
What should I use for seed starting or cuttings?
You are looking for a medium which will keep the right level of moisture and which will promote strong root growth. The most commonly used for cuttings are Grodan Rockwool cubes which transplant easily into larger Grodan Rockwool Blocks. Great for propagation, they stack neatly together in nursery trays and hold young plants upright and steady. Our favorite method for starting seeds is an all natural soiless organic grow plug made of composted tree bark and organic materials. Transplant into any kind of growing medium, including soil.
How and Why to do a Proper Flush?
Why Bother Flushing?
Flushing is an integral part of growing healthy happy plants. Flushing a system and plants will remove any excess salts that have built up over time. Flushing will also help restore an even CEC balance to a medium. Most mediums hold on to salts and release them back into the root zone over time, or attract more salts to the salts that have already begun to form, promoting an ever downward spiral towards “nutrient lockout.” Put another way, the more salts in a medium to begin with, the greater the potentiality of attracting ever more salts until eventually the plants can no longer pull any water (or nutrients) up at ll. Lock out can easily be avoided by flushing from time to time. Some mediums need flushing more than others. A list of mediums and their unique flushing needs is presented below.
How do I Flush?
Flushing is fairly easy to do. First drain your reservoir and then refill with fresh RO water. Add a flushing agent like Final Phase and/or pH the solution (Never forget to pH your plants right before watering.) Run at least 3 times your normal watering amount through the plants. If running a recirculating system, make sure to run for at least 2 waterings) then drain the reservoir and re-up the nutrient solution as normal. You can either wait to feed until the next scheduled time or feed them right away. (Watching the water running off to ensure that it comes out “dirty” on the bottom; the nutrient run off should be coloring the water.
Checking the Runoff can be a Very Useful Tool
By testing the runoff that is coming out of your drain before it hits the reservoir (after a flush has been running) one can tell what the pH and TDS of the medium is resting at. Ideally, whatever the water is going in should measure the same as the water coming out. An example would be as follows: Fresh Water Flush solution “going in” has a pH of 6.0 and a TDS of 0-50 ppms (RO/purified water). The pH of the drain water coming out should be 5.8-6.2 (.2 pH slide in either direction). The TDS of the drain water coming out should be within 50-100 ppms.(50 ppms off from teh Fresh Flush water coming in)
Different Mediums & Their Flushing Requirements
Rockwool-Flush every other week. Holds salts with a low CEC. Fairly easy to adjust the pH of medium.
Coco-or Soiless Mixes with Coco-Ideally flush every week (can Flush every other week). Low-Medium CEC. Somtimes has a buffer (think in terms of armor or shielding) that needs to be broken through before pH will adjust. Flushing can be long and arduous at first, until buffer is “broken” than pH adjusts.
Hydroton-Flushing medium once a month is enough. Virtually no CEC. Super easy to adjust pH of medium.
Soil-Varies on the soil. Usually, the method of feed, feed, and then flush is applied to soil growers. This breaks down to once a week flushing. (Most soils as the plants start growing faster and faster need water every other day) Soil has a medium-high CEC. Sometimes has buffer which needs to be broken before pH can be adjusted.
Adjusting the pH and/or PPMS to Equal the Water Coming In
If the ppms of the water coming out of the drain are higher by more than 50 ppms of the water coming in from the reservoir, continue to flush until the ppms are down to their appropriate level. This is the easy one. The pH is a little trickier. If the pH of the flush solution going in and pH coming out match then we are sitting pretty. If the pH does not match the pH of the solution going out(through) the drain then we need to play with the solution going in until the pH coming out matches.
The concept is what is important to understand here. Now, once the pH of the water coming out (down the drain) matches the water solution coming in, one final test is necessary. Flush again with the water going in and make sure it lines up and is equal to the pH of the water coming out. This last step is necessary because the water coming out is not necessarily where the actual medium is at. Once the pH of the water coming in matches the pH of the water coming out, you are done and the medium is “set.”
Why Drain to Waste?
Drain to Waste provides more control over your plants and helps to prevent diseases. A vey common concern is that the system will waste too much nutrient due to the excessive amount of “waste runoff.” This is simply not the case. A dialed in drain to waste system will only waste 10-15% of the fed nutrient solution as runoff. An example of this is as follows: A given garden uses 5G of water to feed all the plants within, the waste runoff will only be 1/2-3/4 of 1G of solution. If using Drain to Waste with Coco, Soil, or Rockwool, the frequency of watering is down to a minimum. (Usually once a day or once every other day).
The 3 Principal Reasons to Run a “Drain to Waste” Hydroponic System
- Less chance of getting root rot. Most common root rot issues spawn from pathogens that produce spores as a way of spreading their colonies and infecting further plants. The disease starts in one(usually the weakest) plant in the garden and uses this plant as a factory to produce more spores (in an attempt to infect more plants with larger, stronger colonies). In a recirculating system, the spores generated from this one plant than drain out of the plant and collect into a main reservoir where they mass produce with the water supply and then infect all the plants in the garden on the next waterings. With “Drain to Waste” this cannot happen because any water leaving a given plant goes to a drain and not back to the main reservoir. Therefore no spores can infect a reservoir.
- Always feeding fresh nutrient rich solution to your plants in a “drain to waste” reservoir the nutrient rich solution feeds the plants and the runoff gets drained out of the bottom of the plants and runs to waste. This ensures that plants get fed only fresh non-recirculated nutrient every time. The difference between “Drain to Waste” and “Recirculating” reservoirs is as follows: In a recirculating reservoir the nutrient solution starts out complete as per the original recipe contained in the bottles. As the waterings/feedings continue and the plants feed off of the nutrient solution for the course of the week the solution loses key minerals to the plants unique feeding needs. This also causes precipitates to form as certain minerals (now in new molecular arrangements) “lock up” and fall out of solution. Now the original recipe is no longer intact. With “Drain to Waste” this is not the case. The recipe stays intact and the plants always get the complete line of food required every time. This provides for healthier, stronger, and faster growth.
- The ability to do flushes and drenches. Flushes are very important in a coco-based or rockwool-bases medium. Flushes allow for the resetting of the medium as well as drawing out of un-wanted nutrients from within the plants themselves. Flushes can be very instrumental for good healthy plant growth. Under normal conditions (recirculating system) a Flush will pull the salts out of the medium as well as the plant, draw them into the reservoir, and then keep pumping them back into the plants again and again, until the reservoir is drained and the cycle is repeated a few times. With “Drain to Waste” this is not neccessary. We can run a “Flush to Waste.” All salts and excess minerals are drained from the plants and truely flushed away.
The Ability to run Drenches
Drenches are also another nice feature of “Drain to Waste” systems. For example, products like Gnatrol were made to be used in a soil based system and not designed for a recirculating hydroponics system. With a Drench, one can load the reservoir up with any given product and run it once or twice through the system and then either flush or change out the reservoir and re-up the regular nutrient regimen and feed as normal. There are many producs that are made for a Drench application.
What is Growing Media?
Growing media helps to ensure that plants get the proper ratio of, water and oxygen – both which are critical to healthy plant growth. Growing media also provides support for plant roots and it protects roots from sunlight. You can use many different types of media, but all should provide the following:
- Physical support for the plant
- Free the passage of moisture (nutrient solution) to the root zone
- Proper drainage of surplus moisture
- Adequate air circulation to root
Do I have to use growing media?
Growing media is not entirely necessary in hydroponics, but utilizing a grow medium maintains a reserve of nutrient solution in the root zone along with a percentage of air pore space. This can act as a buffer and save crops from failure. The two kinds of growing systems which rely on grow media are Drip Systems and Ebb & Flow Systems. These systems are most frequently used by hobby and beginning growers as they are more forgiving and they provide excellent results.
There ARE two types of systems which require very little growing media, NFT and Aeroponics. Both of these usually rely on a very small amout of media in which to root a very young plant, and the rest of the roots are allowed to grow in the enclosed growing chamber of the system. In these types of systems, watering and feeding of plants depend solely upon the flow of nutrient solution past the plants’ roots. If water flow is interrupted, even for a short duration, plants quickly die. At the other extreme, if the root zone is continually flooded, roots suffocate of oxygen deprivation and plants quickly die. A good grow medium negotiates these extremes.
Rockwool is great for example of how growing media works, because it provides an optimum buffering reservoir of nutrient while maintaining the volume of air in the root zone. The reserve of nutrient solution will be available even when the irrigation system is off for periods of time, or optimally, irrigation systems can be “pulsed” on/off to provide plants with that happy medium of air and water.
There is a new rockwool product that we love, called Grodan® Growcubes. These cubes can be used in a container just like grow rocks, but they weigh almost nothing! They are reusable, and when the time comes, they are easy to dispose of. These just might be or new most favorite grow medium.
What kind of media is best for seed starting and/or cloning?
You have several choices when it comes to seed starting. Basically what you are looking for is a medium which will keep seeds or clones at the right level of moisture and which will promotes strong root growth.
Our Grodan Pargro line has been modified to be the driest value-priced Rockwool on the market. Pargro is the leader among affordable horticultural Rockwool. There are other brands that offer the same low price, but you end up sacrificing quality. Not with Pargro! Since it is made right in the Grodan factory, you can be assured of a high quality product at a great price.
Another choice is Grodan® Two-Inch Rockwool Blocks which fit easily into larger Grodan® Rockwool Blocks. Great for propagation, they stack neatly together in nursery trays and hold young plants upright and steady.
Is Rockwool organic?
Rockwool is not considered organic, although it does make excellent use of natural resources: one cubic yard of rock becomes 37 cubic feet of wool! Rockwool can be reused for many crops. When you are finished with it, you can break it up and add it to your outdoor garden soil and the added aeration will be beneficial to your outside plants. Rockwool is inert, so it does not add or take anything away from plants. It can be used with organic nutrients.
Are there any organic growing mediums?
We sell a few organic growing mediums that are proven to work. You may also experiment on your own and try things such as coco fibers, wood chips or gravel and sand. The most successful organic substrates are those that did not break down readily. A coarse open structure is better for maximum rooting.
Ready Grow is a specialized blend of good things to help your plants grow, along with a nice helping of organic compost. For organic seed starting and cloning you can try Rapid Rooter, an organic plant starter from General Hydroponics.
I heard that you need to prepare rockwool before using it, What is involved?
When Grodan is new it contains some residual lime from production. Rockwool should be soaked in pH 5.0 water for about 24 hours before use. This is done to dissolve the lime. The lime will make the pH value raise to 6.0. Immediately before use, flush the rockwool with your nutrient solution. When you flush, you also flush out the dissolved lime. From this point onwards rockwool does not change the pH in anyway.
It is important that you don’t condition your rockwool with water at a pH lower than 5.0. If you do this, you can damage the actual fibers of the rockwool. If you use pH 4.0 water, you will find that your pH jumps all the way to 7.0 . The lower the pH you use, the higher it jumps. If the fibers are damaged it can be difficult to re-establish a stable pH level, so never go below pH 5 with rockwool.
To soak cubes, put them in a bucket filled with water. To soak slabs, cut a hole in the plastic bag they come in and fill it with water until totally saturated. After 24 hours, cut drainage slits in the bottom
I’m using a NFT / Aeroponic growing system. What kind of medium should I use?
One of the brilliant aspects to these growing systems is their lack of reliance on a large amount growing medium. The only media you may need is a small root starter cube which can be then transplanted into a second, larger cube or into a plastic net cup. the roots will grow freely down into the nutrient and oxygen rich environment.
How do I sterilize my media between crops?
After you harvest your crop you can wash the media to remove all the old roots and then sterilize with a 5% bleach and water mix (apply one cup of bleach for each five gallons of water. ) Some people dislike using bleach because it can leave a slight residue. Plants can handle a certain amount of chlorine, and so long as it is very diluted, they should be fine. Flush or soak the media with the bleach solution for at least half and hour (an hour is best.) Then rinse the media in clean water and keep rinsing until the telltale ‘bleach’ smell is gone.
You may also choose sterilized by using a mixture of Hydrogen Peroxide and water (use a glug of 35% food grade hydrogen peroxide per gallon of water). H202 breaks down quickly to leave only water and oxygen. For this reason, it does not require as much flushing. You should soak the medium for at least an hour and you should then r flush the solution out of the medium with clean water. H202 is good for plants (it adds extra oxygen to water) so if there is a small amount left in the media, your plants should be fine.
No matter which method you use, be careful! Both bleach and H202 will stain clothes and they should both be handled with care. H202 is especially corrosive and you should never let it get on your hands. Wear gloves!
I have green, slimy growth growing on my rockwool, Should I be concerned?
Algae flourishes in wet, well-lit locations, and since rockwool stays moist, it can become an excellent algae breeding ground. Although algae is really ugly, it doesn’t directly harm your plants because it does not compete with the plants for nutrients. Algae CAN become detrimental to plants if it starts to die and decay. (it will be black and slimy) In this case it can attract fungus gnats, it can invite bacteria and viruses and it can compete with your plants of oxygen necessary for nutrient uptake.
The best way to handle algae is to prevent it from occurring. Algae needs light to grow, so cover the rockwool with a dark plastic to prevent light from reaching it. The authors of the book, Gardening Indoors with Rockwool suggest that a thin layer of gravel or expanded clay over the top of rockwool will help prevent algae growth and gnat breeding. You should also take care to prevent algae growth in the nutrient tank. Shading the tanks, input and output pipes, and other “wet” equipment will inhibit algae growth.
Another option is to cover the rockwool with black/white 6 ml plastic or any other type of plastic covering. We offer Root Guards in our pots section.
Algaecides are not recommended for use on food crops. If you choose to use a chemical product, use very little and take great care to not expose yourself, your pets or other people to toxic products.
I have gnats breeding in my growing media, Should I be concerned?
Those little black critters are known as fungus gnats. The term refers to a large group of insects, most of which have not been extensively studied. They reproduce in moist, shaded areas in decaying organic matter like leaves and algae. The life cycle is about four weeks, with continuous reproduction when warm temperatures are maintained. Larvae not only feed on fungi and decaying organic matter, but on living plant tissue, particularly root hairs and small feeder roots. Usually, there are very few ill effects from these flies, but control is advised. After the roots have been injured, root rots may attack the plant. Entire crops have been lost in this manner. The plant symptoms may appear as sudden wilting, loss of vigor, poor growth, yellowing and foliage loss.
Fungus gnats can be easily controlled with a pyrethrin spray. They can also be physically captured with yellow sticky cards.
Perhaps the most important weapon you have against fungus gnats (and all pests) is good grow room sanitation. Don’t allow decaying plant material to buildup. Always remove fallen leaves, algae, or any sort of organic material that collects around the base of plants. This material is a breeding ground for pests and diseases.