What is fertilizer, and why do cannabis plants need it?

Fertilizer provides essential nutrients like nitrogen, phosphorus, and potassium to help cannabis plants grow strong, healthy, and produce high yields. In most grow setups, regular feeding is required to avoid deficiencies and promote optimal growth.

What nutrients are essential for healthy cannabis growth?

Cannabis needs macronutrients like nitrogen, phosphorus, and potassium, plus secondary nutrients like calcium, magnesium, and sulfur. Micronutrients such as iron, zinc, and boron are also vital for plant health and development.

When should I start feeding cannabis plants nutrients?

Start feeding once your cannabis seedlings develop their first true leaves. In coco or hydro, feeding may begin as early as day 7–10. In soil, wait until the plant shows signs of slowed growth or pale lower leaves.

What do NPK values mean on cannabis fertilizer?

NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K), the three primary macronutrients. Ratios like 3-1-2 or 1-4-5 guide what stage of growth the fertilizer supports—veg or bloom.

How do I know if my cannabis plant is overfed or underfed?

Check the EC/PPM of your runoff water. If it's much higher than your input, nutrients are building up—overfeeding. If it's much lower, your plant may be hungry—underfeeding.

PPFD stands for Photosynthetic Photon Flux Density. It measures how much usable light (in μmol/m²/s) actually reaches your plants' leaves.

What does μmol/s mean?

μmol/s is a measure of total light output, also known as PPF (Photosynthetic Photon Flux). It's usually listed on grow light specs or packaging.

What’s a good PPFD number for cannabis?

Seedlings: 100–300 μmol/m²/s, Veg: 300–600 μmol/m²/s, Flower: 600–1000+ μmol/m²/s.

How can I raise my PPFD?

Lower your light (if heat allows), use a higher-output fixture, or add reflective material like Mylar to your grow space.

What if my PPFD is too high?

Raise or dim your lights and monitor for signs of stress like leaf curling or bleaching. Too much light can harm your plants.

PPFD Calculator

Light. Data. Growth. Smarter cultivation starts here.

PPFD Calculator for Grow Light Coverage

Estimate how much light hits your plant canopy by entering your light’s total output and grow area size.

Total Light Output (µmol/s) [?] Grow Area Length (ft) [?] Grow Area Width (ft) [?]

Grow Journal

Plan, track, and reflect on your grow. The Grow Journal helps you organize tools, notes, schedules, and specs — all in one place.

Learn About the Grow Journal Open Dashboard

About PPFD

PPFD (Photosynthetic Photon Flux Density) tells you how much usable light is reaching your plant canopy. It’s measured in µmol/m²/s.

Ideal Ranges

Seedlings: 100–300 µmol/m²/s
Veg: 300–600 µmol/m²/s
Flower: 600–1000+ µmol/m²/s

Helpful Tools

DLI Calculator – Convert PPFD to Daily Light Integral
Wattage Calculator – Estimate wattage needed per stage
Light Distance Calculator – Find PPFD based on hanging height

Tool by GrōHaus — helping growers dial in their light, space, and yield.