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A Guide to Growing Cannabis in Coco and Perlite

A “soil -free” growing medium.

For the purposes of this piece, I’m making some basic assumptions about anyone contemplating using this grow medium. They are:

  • That you have a few successful marijuana grows under your belt, but feel you could do better – or that you have grown in soil and encountered problems.
  • That you understand the wet/dry cycle.
  • That you possess a pH pen, properly calibrated and use it every watering. Strips are not good enough – buy a pen. Don’t continue reading this til you have.
  • That you are prepared to spend money on nutrients.
  • That you are growing in pots, either under lights or outdoors.

The advantages of using coco – perlite mix with marijuana:

Why use coco – perlite to grow cannabis?
  1. Drainage. With this mix it is difficult to over-water once the plant’s roots are established. This is a big plus for new growers as over-watering is the most common mistake made by “newbies” – especially those who have planted in peat. Those growing in colder climates will benefit from the faster watering cycle as it facilitates more opportunities to adjust the Nutrient supply-
  2. The lightness of the growing medium allows the roots more access to Oxygen.
  3. I’m a strong advocate of regular root flushing – taking the medium back to neutral and removing salts produced by used nutrients. This mix allow a rapid and more efficient flush. Sick cannabis plants can be treated more quickly.
  4. Tight control over your plant’s diet.

The disadvantages of using coco – perlite mix with marijuana.

  1. More watering days.
  2. Strict pH control is essential.
  3. The plant is more reliant on you to supply its needs.
  4. More attention needs to be given when choosing or brewing Nutrients.

What’s the best coco to buy for a cannabis grow?

I use the blocks which need soaking. I find this makes for a much lighter mix than the bagged, finely chopped stuff which seems to retain water longer. This latter however may be an advantage in a hot summer.

GENERAL HYDROPONICS COCOTEK 5KG BAIL: $23.81

  • organic
  • high quality
  • few contaminants
  • low sodium content
  • makes approx 3 cubic feet of growing medium
  • provides plenty of aeration and drainage

 Mixing the coco and perlite to make a growing medium.

Before mixing you must first ensure that your coco is clean. It depends on your source of coco but some is produced using seawater as a flush. To be safe, flush the coco three times with fresh water (to rinse out any residual salt etc).

Mix 50:50 by volume with perlite. Do not be tempted to add a bit of this or that – no Bat, Goat or Horse poo nor your Uncle Arthur’s special additive. How would you know how much to feed after that?

You are not finished yet though.

Fill a pot with the mix and bleed some pH 6 water through until you are getting run-off. Collect some of the run-off and test its pH. If necessary, continue flushing until the run-off is consistently similar in PH as the water going in.


Hydrofarm GMPER100L 100-Liter Super Coarse Perlite: $34.93

Perlite is a volcanic material which expands up to 20 times its orginal volume. Because it is sterile ( it is free of diseases, plant or animal material) and hugely expansive, it makes an excellent neutral means of holding nutrients and water and making them available to plants roots.

 

A sideline note on PH.

 
As a cannabis seed breeder, I can’t stress the importance of pH enough. We put our breeding stock through a number of tests prior to selection – and this includes pH stressing. Why? Because a way out pH can cause sex reversal (hermie, if you like). This is a trait not wanted in commercial female seeds.
I met a guy last year who was complaining that his plants were not budding. “I’m doing everything right mate! I can’t understand it”.
I could. Because I’ve also heard the same guy tell people: “I don’t bother with pH, its a Weed for F’s sake – it will grow anywhere”. 
I left him in blissful ignorance – some people are happier that way.
 
My final point on pH is this. If you have got this far down my writing, I assume you are serious about growing cannabis – buy a pen. ‘Nuff said.

 

 

 

Hanna Instruments HI 98129 Waterproof pH/Conductivity/TDS Tester

 

 

Nutrients for growing cannabis in coco – perlite medium.

I’m not going to recommend any brands. Everyone has their favourites. I will say this though. If you are using only one brand, you are basically saying: “This is the best”, right? I can’t think of any other reason. No nutrient brand is the best and no nutrient formula performs perfectly in all growing conditions and importantly, with all strains and / or growing mediums.

Your basic needs will be:

  1. A root stimulant.
  2. Vegetative nutrients.
  3. Flowering nutrients.
  4. Epsom salts or Cal/Mag
  5. Bud Boosters (optional)
  6. Molasses (optional, but recommended).

I only use organic products produced for a hydroponic grow – we are using basically a hydroponic medium. Also, as I have hinted, I buy 2 different brands of each and alternate.

The fun bit: How to grow cannabis using coco – perlite!!

Your marijuana seedlings are well-rooted and sitting in 1 pint pots of our mix. Your run-off is hovering around pH 5.9-6. They are at first node and as yet, have not been nuted. Good. Resist your urge to try to turbo charge them. A quarter to half strength dose of Root Stimulant every other watering will be enough for now.

Node 2. This now becomes a flying by the seat of your pants thing. A gradual introduction to the vegetative nutes, quarter strength, is good – every other water as a general guide – they are still babies. Depending on your growing temps, you will be watering every 36 hours to 4 days.

Now your plants are 8″ high and have filled the 1 pint pots with root. You are watering until there is good run-off and you are regularly checking your run-off pH right? Time to pot up into their flowering pots, give root stimulant and spray once with Epsom Salts (Magnesium Sulphate) at 1/4 teaspoon to a pint of water.

The rest is by feel. Get to know your plants – each strain has different needs.

 

I can liken the uptake of nutrients using this growing medium to sending an email as opposed to snail mail (= peat medium): err on the light side until you get the hang of it. Over nute and you’ll kill or seriously damage the marijuana, under nute and you can fix that with one dose.

  • If your cannabis plants look poorly, don’t try to fix with a nutrient hit; firstly, flush them – 5 times the pot volume of water pH 6, then let them rest. Next water, slowly introduce the nutes again.
  • A bi-weekly Espom Salts foliar feed is sufficient – no more, it can burn.
  • Molasses. “Molasses mate, they don’t need f**ing molasses – they’re weeds, they grow anywhere”. Well coco – perlite mix needs help to provide for the plants. The sugars break down into aminos and other micro whatsists which feed the organisms that make our mix fertile. Some mj growers use it to smooth and sweeten the bud and apply it only in the last stages of flowering. I use it all the way from node 3. Again the application frequency is ramped by age at one tablespoon per gallon.

 

Summary

I will emphasize that this is the way I grow. I do not present this as a “This is how you MUST do it” guide to growing cannabis. It works for me. Its more fun than watching claggy peat take days to dry out while the roots rot and the leaves yellow and dry.

By its nature, its a labour and brain intensive grow. You can’t sit back and hope that the soil will deal with all your problems, cos you’re not using soil. You need to develop forethought and feel your cannabis plants needs before they do. This is experience and I can’t help you with that bit.

I know others growing this way and some of them do add to the mix when potting up for flowering. A typical addition would be 10-20% of a professional soil with added perlite. The idea being that a Pro soil will help with providing all elements required for great buds. This is strictly speaking no longer a soil-less grow, but I’m no snob. If it works – and it may well do, great. An adjustment to the watering pH would be needed due to the buffering nature of the soil.

General Hydroponics Flora Series QT – FloraGro, FloraBloom, and FloraMicrostyle

So which nutrient solution is best for growing cannabis? Like Clone Ranger writes above, its always an idea to mix and match a little to make sure you are covering all bases …

That said, the one nutrient regime which we find works wonders and is great value for money has to be GH Flora, which despite its name, is suitable for VEGETATIVE growth as well as FLOWER.

 

 

 

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Comments
  • we’ve had a few people come to this post asking if they can skip the Cal-mag when using coco-perlite mix. Quick answer is yes you can .. but keep an ever-beady eye open for signs of deficiency. Better answer would be to avoid pricey specialist nutrients and replace with say Magnesium Sulphate powder available cheap from the pharmacy

  • My answer is slightly different to Weed Widow’s unfortunately.
    It really depends on a lot of variables particular to your own growing circumstances. Water quality and the nutrient brands that you are using being 2. Calcium/Magnesium deficiency will affect bud or seed growth.
    There should be no adverse effects in giving a bi-weekly, half steength dose of Calmag – wether you think they need it or not. This is better than dealing with a deficiency retroactively – you will have already suffered a blow to your product.
    My water contains Calcium and therefor, I only give Magnesium Sulphate (MG.S04) – better known as Epsom Salts every other watering. Cheapest source is a horse feed supplier where a 2 kilo tub should be around 6 Euros.
    I think/hope I made it clear in the article that this medium requires a far more hands on attitude to growing as opposed to peat based mediums.
    So, my answer is in short is yes – bi-weekly half strength – either Calmag or Epsom Salts – depending on your water, Nutrients or pocket.
    The Author.

    • thanks to The Author for his expert advice on this. I guess I didn’t make it clear in my response that yes you can skip it .. but at your own peril :) (if you do choose to omit it you will need to know what the signs of deficiency are and be ready to treat accordingly) and that if price is the problem, you need not stick to expensive brand additives but can buy alternative sources of magnesium and calcium from other sources

  • Thing is, if your plants are showing a deficiency, it didn’t happen today because today you see it – it happened a while back and it’s just begining to show – that’s a while where the plant has been suffering – then you try to remedy it – thats another long time for the plant to recover.
    Could easily be a month with a plant not performing well.
    Lot of lost time for the small expense to avoid it.
    Yep, and I forgot to mention that my plants receive a weekly spray of 10% milk to water ratio – this is a preventative for Powder Mold and also (I’m guessing – but not stupidly)a further source of Calcium.

  • [...] 3 gal pots as the cheapest and easiest step into hydroponics there loads of information on the site here’s  a link to get you started . There’s ideas in there on how much coco & perlite costs too. You can use standard pots [...]

  • [...] I try out these LEDs with a hydroponic system, I’m definitely convinced that growing in a coco – perlite mix (50:50) in 10 litre pots, and using a feed/water to waste watering system is the way [...]

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