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Cannabis Soil and Nutrients Guide (Simple and Canadian)

Cannabis wants light, well-draining soil around pH 6.5, modest nitrogen-forward feeding in veg and phosphorus-forward feeding in flower, always started at quarter strength: most problems are overfeeding or pH, not deficiency.

Last updated: August 2026

More grows are lost to enthusiasm with the nutrient bottle than to neglect. This guide keeps it simple: what to plant in, what to feed, and how to read the leaves before a problem costs you yield.

The right base soil

Buy a quality light potting mix and cut it with 20 to 30 percent perlite for drainage. Skip soils with synthetic slow-release pellets; they feed on their own schedule, not yours. For outdoor beds, work in compost the fall before, or simply sink a large fabric pot of good mix into the ground.

Feeding by stage

Stage What it wants How much
Seedling, weeks 1-2 Nothing. The seed and a good mix carry it Plain water only
Vegetative Nitrogen-forward veg formula Start at 1/4 dose, work up to 1/2
Early flower Switch to bloom formula, more P and K 1/2 dose, watch the leaves
Late flower Taper off, then plain water Flush the last 1 to 2 weeks

pH: the silent yield killer

In soil, roots absorb nutrients between pH 6.0 and 7.0. Outside that range, feeding harder makes things worse. A $20 pH pen and a bottle of pH down pay for themselves in the first grow. If leaves show odd spotting or yellowing while you are feeding properly, check pH before changing anything else.

Reading the leaves

Pale bottom-up yellowing means hungry, feed slightly more. Dark green clawed tips mean nitrogen excess, back off. Crispy edges mean nutrient burn, flush and halve the dose. Yellowing between veins on new growth points to pH or micronutrients, fix pH first.

Autoflowers eat less

Autoflowers run smaller and faster than photoperiod plants and want roughly half the feed. Details in the autoflower growing guide. Whatever you grow, strong genetics tolerate mistakes better; browse feminized seeds bred from stable stock, covered by our germination guarantee.

Frequently asked questions

What soil should I buy for cannabis?

A light, well-draining potting mix with added perlite. Avoid heavy garden soil and anything with slow-release synthetic fertilizer built in, which overfeeds seedlings.

What NPK does cannabis need?

Higher nitrogen in veg, higher phosphorus and potassium in flower. A two-part veg and bloom nutrient line, started at quarter strength, covers the whole cycle.

What pH should my water be?

6.0 to 7.0 in soil, ideally around 6.5. Most mystery deficiencies are actually pH problems locking nutrients out at the root.

Can I grow in Canadian garden soil outdoors?

Yes, after improving it. Dig in compost and perlite in a sunny spot, or sink a 40 to 60 litre fabric pot of quality mix into the ground and plant into that instead.