Medium & roots
Pick the right root zone, run it properly, and most of the problems further down the line never happen.
Roots want air more than water, then the right pH, then food — in that order. Most beginners are best in soil or coco; hydro grows faster but forgives far less, so it asks for daily attention in return.
What good looks like
Choosing your root zone
- Soil
Soil
A quality cannabis soil from a grow shop, not multipurpose compost. Open structure with 20-30% perlite, pH 6.0-7.0, light mix for seedlings stepping up to a richer final pot. Forgiving and slow-release — the best place to learn the plant first.
- Coco
Coco coir
The middle ground — an inert medium you feed like hydro but touch like soil. Holds water and air in a ratio roots love, harder to overwater than soil. Buffer it, mix 70/30 with perlite, feed daily to runoff at pH 5.8-6.2 with CalMag every feed.
- Hydro
Hydro
Roots fed directly by nutrient solution, no soil buffer. Faster growth, bigger roots, but no safety net — pH, EC and water temperature become daily non-negotiables. Start with one DWC bucket alongside a soil grow, not a full switch.
- The pot
The pot
Fabric pots for a first grow — they air-prune roots into a dense fibrous mass, drain through the walls and forgive the overwatering instinct. Size up in steps: solo cup → 1-3L → final pot, roughly 11-15L for autos and 15-25L for photoperiods.
- pH & water
pH & water
Water to 10-20% runoff every time to carry salts out of the root zone, then let soil dry between waterings — heavy pot, leave it; light pot, water it. Know your tap-water baseline before you mix anything.
The numbers that matter
The numbers that matter
Do this
The medium & roots checklist
- Buy a cannabis-specific soil from a grow shop, not multipurpose compost
- Mix 20-30% perlite through the medium, never sprinkled on top
- Plant into fabric pots and size up in steps — solo cup, then 1-3L, then final
- Water to 10-20% runoff every time, then let soil dry between waterings
- Test your tap water’s EC baseline before you mix any nutrients
- In coco, feed daily to runoff at pH 5.8-6.2 and add CalMag to every feed
- In hydro, check reservoir pH, EC and temperature every morning; keep water below 22°C
- Do a full hydro reservoir change every week rather than just topping up
Watch for
Catch these early
The early sign, what it means, and the fix. The full stories are in the book.
Whole leaves going yellow, growth stalled, soil staying wet and sour
Roots are drowning — a dense waterlogged medium with no air pockets and nowhere to drain.
Fix: Switch to a structured soil with perlite in a pot that drains, and let it dry between waterings. Air in the pot comes before water.
📖 Dave’s first plant drowned in a six-euro bag of garden-centre mush and a pot with no drainage holes. The full story →
Growth slowing, the pot drinking dry in a day, roots poking out the bottom
She’s outgrown the pot and the roots are starting to circle and choke themselves.
Fix: Pot up before she’s fully bound — a week lost to root-binding is growth she can’t get back. Fabric pots air-prune instead of circling.
📖 The chapter walks the full pot progression and why a seedling in a 25L pot grows slower, not faster. The full story →
Lower leaves yellowing between the veins in coco within a week or two
Coco binds calcium and magnesium on its fibres, so the medium grabs them before the plant does.
Fix: Add CalMag to every feed, adjust to pH 5.8-6.2, and feed daily to runoff instead of treating coco like soil.
📖 Dave’s “Crossover” grower treated a coco brick like soil and starved the plant in front of a full table. The full story →
DWC water gone brown and cloudy, roots coated in slime that smells off
A warm, over-concentrated reservoir above 22°C has lost its oxygen and bred pathogens.
Fix: Keep the reservoir at 18-21°C, start nutrient strength low, change it fully each week and keep it opaque and clean.
📖 Dave’s first hydro bucket turned to warm acidic soup in four days. The full story →
Questions
Medium & roots FAQ
Soil, coco or hydro for a first grow?
Soil. It buffers your mistakes, needs less attention and lets you learn the plant before you learn the medium. Coco is the natural next step on your second or third grow, and hydro after that — different on top of everything else you’re already learning is one variable too many.
What pot should I use, and what size?
Fabric pots for a first grow — they air-prune the roots, drain through the walls and forgive overwatering. Size up in steps: solo cup, then 1-3L, then a final pot of about 11-15L for an autoflower or up to 25L for a longer-vegging photoperiod.
Is garden-centre multipurpose compost fine if it’s cheaper?
No. It’s built for bedding plants — mostly fine peat, poor drainage, pH usually too low, nutrient content all over the place. It compacts to sludge in a pot. The gap between four euro and twelve is the difference between a swamp and a soil engineered for the plant.
Why does pH differ between soil, coco and hydro?
Soil has an organic buffer holding things steady, so it runs 6.0-7.0. Coco and hydro have no buffer, so they run lower and tighter — coco ~5.8-6.2, hydro 5.5-6.5 — because that’s where the dissolved nutrients stay most available to the roots.
How much water should drain out the bottom?
Aim for 10-20% runoff every watering — a litre in, 100-200ml out. That runoff carries excess salts out of the root zone so the chemistry doesn’t drift. In soil, let the pot dry between waterings; in coco and hydro you feed daily, always to runoff.
The whole story is in the book
Grow Good Bud walks the whole root zone in plain terms — soil, coco and hydro side by side, the pot progression, and every mistake that taught Dave the numbers the hard way.
The web gives you the lesson; Grow Good Bud keeps the scars. The kit to grow it is at Dublin Indoor Gardening.