Coco for beginners — pH 5.5–6.5, how much Cal-Mag, how often to water under LED

Why coco?

Coco coir (fiber from coconut husk) drains fast and brings lots of air to the roots. It doesn’t feed the plant by itself — you feed every watering with nutrient solution and the excess drips into the tray. That gives fast growth and full control over what the plant drinks.

What to buy to start (roughly, in EUR)

• Pre-buffered coco 50 L (washed and prepared): 15–25 €
• Perlite 10 L (mix it in for more air): 6–10 €
• Base nutrients A/B 1 L + 1 L (for coco): 18–30 €
• Cal-Mag 1 L (calcium + magnesium): 10–18 €
• pH- (and optionally pH+) 0.5–1 L:8–15 €
• pH and EC meters (basic models): 30–80 € each
• Fabric pots 3–12 L:3–10 €/pc
• Drain tray 60×60 / 120×120: 10–20 € / 20–35 €

Starter pot mix:70% coco + 30% perlite.

pH — set it and almost forget it

Goal: keep the pH of your nutrient water between 5.5 and 6.5. Safest is 5.8–6.2.

How to do it, step by step:

1. Fill with water.
2. Add Cal-Mag (doses below).
3. Add base A/B and any manufacturer’s additives.
4. Measure pH and use pH- / pH+ drops to set 5.8–6.2.

Check: every few waterings, test the pH of the water that drains into the tray. If for several days it’s clearly outside 5.5–6.5, water 2–3 times a bit more generously (so a bit more drains to the tray) and set your input closer to the middle (e.g., 5.9–6.0).

Calcium and magnesium (Cal-Mag) — why and how much under LED

LED fixtures often make plants want a bit more calcium and magnesium.

• Soft water (low minerals, e.g., filtered): add Cal-Mag so the solution “strength” rises to about 0.3–0.4 mS/cm before you pour in base A/B.
• Medium/hard tap water (you can “taste” the minerals): usually half the label dose is enough.

Most common deficiency signs:

• Magnesium: lighter areas between veins, first on older leaves.
• Calcium: dry, brittle edges, small specks/necrosis.

If you see this: gently raise the Cal-Mag dose and watch for a week.

Solution “strength,” a.k.a. EC — the simplest way

EC (mS/cm) is a number that shows how much nutrient is in the water. It helps you avoid overfeeding and underfeeding.

Easy EC ranges:

• Seedling (days 1–10): 0.6–0.8
• Early veg: 1.0–1.3
• Late veg: 1.4–1.6
• Early flower (weeks 1–3): 1.6–1.8
• Mid flower (weeks 4–6): 1.8–2.0
• Late flower: 1.6–1.8
• Optional “lighter” last 3–7 days: 0.6–0.8

If leaf tips brown slightly: you’re at the edge — drop EC by 0.1–0.2.

How often to water in coco

In coco it’s better to water more often with smaller portions than rarely with huge ones.

• Small plant / small pot (0.5–1 L): every 1–2 days.
• Veg in 3–5 L: usually daily; in heat even 2× per day.
• Flower in 7–12 L:daily; when roots fill the pot — sometimes 2× per day (morning/evening).

How much to pour? enough that a little water appears in the tray (about 10–20% of what you poured). That prevents leftover salts from building up in the medium.

Simple “day-by-day” recipe

Assumptions: LED, 70/30 mix, one plant in 5–8 L.

1. Add Cal-Mag to the water (soft water: up to 0.35 mS/cm).
2. Add base A/B until you reach the target EC from the table.
3. Set pH to 5.8–6.2.
4. Water daily until a bit shows up in the tray.
5. Once a week check the “strength” of the tray water. If it’s clearly higher than what you pour in, for 1–2 days water with a slightly weaker solution and let a bit more drain to the tray.

Pots and plant size

• Fast turnover / small bushes:3–5 L pots, frequent watering.
• Big bushes / long veg:8–12 L pots, sometimes 2 waterings per day near the end.
• Start in a smaller pot and transplant once roots have “grabbed” it. That avoids overwatering and dead zones.

Mini-plans for popular tents

60×60 cm

• 1–2 plants in 8–12 L or 9–12 plants in 3–5 L.
• LED 150–220 W.
• Daily watering; in heat 2× per day.
• pH 5.8–6.2, EC per stage.

120×120 cm

• 2–4 plants in 8–12 L (bigger bushes) or 16–25 plants in 5–7 L (smaller).
• LED 480–650 W.
• Consider a simple drip system for consistent watering.

Most common mistakes and quick fixes

• Pouring plain water “to rinse.” In coco always feed (even mildly).
• No pH control. Set 5.8–6.2 — outside that, the plant “eats” worse.
• Pot too big at the start. Start smaller, then transplant.
• No water ever appears in the tray. Increase the portion — salts may be building up.
• No calcium/magnesium under LED. Add Cal-Mag and watch leaves for a week.
• Standing water left in the tray. Dump the excess after a few minutes and keep airflow up.

FAQ (short)

Can you overwater coco? It’s harder than in soil, but possible. The key is small, frequent waterings with some drain to the tray.
Do I need to “flush” before harvest? You can switch to a weaker solution for the last 3–7 days. It depends on taste and on your nutrient line.
What water temperature?18–22 °C works best.
No EC meter — now what? Follow label directions and watch the leaves. A meter makes life much easier, worth buying.

TL;DR — coco in five steps

1. pH 5.5–6.5 (aim 5.8–6.2).
2. Cal-Mag first, then base A/B.
3. Water daily with a small portion until a bit drains to the tray.
4. Set EC to the growth stage (see table).
5. Mix 70% coco + 30% perlite, use fabric pots, keep the tray clean and air moving.