Hydroponics Growing Mediums

The Cannabis Grow Bible

by Greg Green

hydroponic grow medium

There are many hydroponics mediums to use that your plant will take root in. Rockwool appears to be the most popular and comes in either slabs or cubes. These cubes vary in sizes from 1? to 6? cubes. The slabs can be cut to suite the shape of your pot or container.


Many growers like to use the cubes for seed germination and for rooting cuttings. This seems to be the easiest to use. Many growers claim that rockwool should be pre soaked for 24 hrs in water with a pH level of 5.6. This is to stabilize the pH level of the rockwool.

How to make up nutrient solutions:
Always follow the very simple instructions on the products. All you need is a container to make up the nutrients in and the nutrients themselves. Each of the packs should have A, B, and C written on them. The mixture is usually 3.5mls of A and B and C per litre of water. This is called a 100% strength mixture if you follow the guidelines as stated exactly on the label.

Hydroponics pH

After you have mixed up your nutrient solution you will want to take a pH reading of it. If you have any problems, just like in soil growing, you will need to adjust your pH level. Now, you do not use the same method to adjust pH levels as described in the soil chapter. For hydroponics you need to buy a pH Up and pH Down adjusting solutions. These are cheap and can be added to your solution to balance the pH level.

Cannabis plants in a soil systems like a pH of 7, but in hydroponics systems they like a pH of 5.2 to 6.3. You will discover it is easier to maintain a pH range and not a set level. Always check your hydroponics pH level as often as you can. pH can slip up and down very quickly in hydroponics systems.


Algae is part of a large group of non- vascular mainly aquatic cryptogams capable of photosynthesis.

Always keep your container away from exposure to direct light, as algae will grow in the container if you do not. This seems to be something of a problem because we grow plants under lights and we may have a system that has to be sitting near the light so the plants can grow properly. Most hydroponics systems have been manufactured ‘light tight’ to eliminate this problem. If you built your own system then you may want to keep your solution sealed from the light by using thick black PVC tape to cover the lid and the entire reservoir. This will help prevent alga from growing in your system.

hydro grow medium

If you do have algae growth then you need to clean your system out. Wash the unit and replace the nutrient solution with a fresh mix. Also try to find the source of the light leak and patch it up. Using a thick black garbage bag works well to keep the light out.

Grow and Bloom

Some of the double packs come in two different sets – Grow and Bloom. Basically the Grow solution is used during the plants vegetative stage and the Bloom is used during the flowering stage. The Bloom formulas contain more Phosphorus and Potassium and less Nitrogen.

Other packs have a complete all in one function, but they are lacking some additional extras.

Cannabis may find a lot of the nutrients that are mixed full strength to be too strong and it will burn them. It is recommended that when using hydroponics formulations with cannabis that you do so in MODERATION for your first grow. Many cannabis growers have bought these products with anticipation of producing great buds only to get great plant burns instead. It is best to start off with 30% strength at first and then increase if needed.


Marijuana cultivators have found that full strength nutrient solutions are not a good thing. In fact even medium strength formulas have the power to burn your plants. Consult the information on the packs, but in general 3.5 mls of A and B and C per litre is usually called 100% strength. The same amount mixed with 2 litres of water is 50% strength. Marijuana can grow very well between 30% and 50%. Never go full strength with your nutrients if this is your first time. Try 30% for the first attempt and see how your plants do. You will be surprised at how rich a bud content you will produce with this amount of nutrients. The most common problem associated with hydroponics is plant burns. I have rarely heard of someone under-feeding his or her plants in a hydro system. I have heard plenty of reports about overfeeding plants in hydro systems. Over time you will get to know your strain and what it likes. The better you know your strain the better you will be able to control your feeding amounts.


If you have scales in your bucket or what looks like kettle rust then you have not been maintaining your pH level. Scale is caused by very acidic pH levels. Your local water company will provide you with a read out of your water. You can buy nutrient products to use with hard water. If this problem persists just drain and clean your reservoir and mix a new batch of nutrients to the correct pH level. Some use a Reverse Osmosis water filtering system to clean their tap water. Distilled water has a stable pH level of 7.0.


This is easy and not so easy. Beginners rely on a ppm meter, but a veteran grower learns to read the plant. The plant will tell you if is getting enough or too much or too little. It takes a few grows to learn to read the plant but you can do it with experience. The plant may have drunk all the nutrients up or just some of them. Some nutrients are taken up by the plant and stored within the plant until it needs more. A top up can be done if you do not want to change the reservoir totally. If you do not have a PPM meter to calculate this accurately, simply write down your nutrients mix ratio from day 1. Let’s say we used 3.5 ml of A and B and C in a 1 litre drum. Now the plant has drunk 1/2 a litre, now all you need to do is make another litre of 3.5ml mix in another container and add 1/2 of it to the reservoir. This is one simple way of doing it, but you are left with a half litre of solution, so do your math and make a mixing chart so you can mix up different amounts as needed. Local grow shops will help you most of the time with any questions that you might have about their products.

Cannabis Grow Bible

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>




Instagram Feed

Something is wrong. Response takes too long or there is JS error. Press Ctrl+Shift+J or Cmd+Shift+J on a Mac.