A Guide to Growing Cannabis in Coco and Perlite
We grow cannabis in a coco and perlite mix more often than any other growing style. It’s cheap to set up and combines the flexibility of a soil/pot grow with many of the advantages of a hydroponic grow.
What is Coco Coir?
Coco coir (pronounced coy-er) is made from the fibrous husks of coconut. Tough pieces are incorporated into most garden composts to act as a bulking agent, but it can also be bought separately. Some brands offer coco by the sack, such as this bag from Canna. Coco can also be bought in a dehydrated block form, which is light and easy to transport.
Growing in coco vs soil: the advantages of growing cannabis in coco-perlite:
Coco is especially suited for growing cannabis because:
- It is difficult to over-water when growing cannabis in a coco-perlite mix. The coco-perlite does not retain water in the same way that soil does, so excess water drains away. Over-watering is possibly the most common mistake new growers make. To understand why overwatering is such a big problem when growing cannabis please read about the wet-dry cycle. Because it is lighter than soil and holds more oxygen, root development is usually faster and stronger than a soil grow.
- Because coco doesn’t hold water, you have more control over the nutrients you give the plant. The plant’s roots receive only those nutrients it receives in each watering and excess drains away. This makes issues of over-fertilization less likely. If you do experience a nutrient overload, you can flush the material through with large amounts of plain pHd water to wash any residual nutes out. Plus if you see a nutrient deficiency its easy to increase the feed strength. In this way its very like a “lite” version of growing hydroponically without the expense of a hydro kit.
- If you are growing cannabis using LED grow lights, coco-perlite majes the perfect growing medium. When you grow cannabis under HPS grow lights, the high temperatures of these lights increases the surface evaporation of moisture from the soil, thus speeding up the wet-dry cycle. As this is not the case with LED grow lights, plants grown in soil often suffer from a lengthy wet/dry cycle, leading to sodden roots, lack of oxygen and possible EC buildups.
- You still grow in pots which makes it easy to rearrange your grow room depending on plant variance or finishing times.
- Coco is more environmentally friendly than peat soil.
- Coco is not a good environment for pests to thrive in.
- Its rot-resistent.
The disadvantages of using coco – perlite mix with marijuana.
- More watering days.
- Strict pH control is essential.
- The plant is more reliant on you to supply its needs.
- More attention needs to be given when choosing or brewing Nutrients.
For the purposes of this piece, I’m making some basic assumptions about anyone thinking about growing cannabis in coco:
- 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.
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.
- 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.
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:
- A root stimulant.
- Vegetative nutrients.
- Flowering nutrients.
- Epsom salts or Cal/Mag
- Bud Boosters (optional)
- 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.
Coco-coir watering schedule
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.
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.
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.