# Can I use regular garden fertiliser on cannabis?

> Yes, regular garden fertiliser works on cannabis in soil, because roots take up the same ions whatever the label says. Pick a complete feed with calcium, magnesium and micronutrients, and dose by element: aim for roughly 150-200 mg/L nitrogen in veg and 30-60 mg/L phosphorus. All-purpose feeds suit veg, tomato feeds suit flower. Avoid lawn feeds with herbicides, and use fully soluble salts in hydro.

- Canonical: https://genetixbay.com/knowledge/answers/use-regular-plant-fertiliser.html
- Topic: Nutrients · Type: How-to
- Evidence: Supported · Status: Draft: awaiting expert review
- Full article: [Building a cannabis feed by stage: ppm targets per element and how to hit them](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)
- Also asked as: Can I use tomato fertiliser for weed? | Is all-purpose plant food OK for cannabis? | Can I use slow-release fertiliser on cannabis? | Do I need special cannabis nutrients? | Can I use lawn fertiliser?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

Yes, in soil. Cannabis roots take up [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), potassium and the rest exactly as any crop does, so a complete garden fertiliser works if you dose it by element. All-purpose feeds suit veg, potassium-rich tomato feeds suit flower. Avoid weed-and-feed lawn products, and use fully soluble, complete salts in hydro. *Supported.*

## Why

Plants absorb ions, not brands [1]. A "cannabis" bottle is a blend of the same salts sold for tomatoes and houseplants.

What matters is the analysis. [NPK](https://genetixbay.com/knowledge/glossary/npk-ratio.md) percentages convert to dose: 1 g/L gives the element percentage × 10 in mg/L, after converting P2O5 × 0.44 and K2O × 0.83 [2].

Nitrogen is the main lever in veg. In a controlled cannabis trial, vegetative growth peaked at about 160 mg/L nitrogen [3]. Phosphorus has a ceiling: elevated root-zone phosphorus did not improve yield or quality [4], so a high-P "[bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md)" garden feed adds nothing.

Garden feeds often skip calcium, magnesium or [micros](https://genetixbay.com/knowledge/glossary/micronutrient.md). Soft water or [RO](https://genetixbay.com/knowledge/glossary/ro-water.md) then leaves a gap.

## The numbers

| Product type | Typical use | Watch for |
|---|---|---|
| Complete soluble all-purpose (e.g. 20-20-20 + micros) | Veg in soil | High P relative to need |
| Tomato feed (K-rich) | Flower in soil | Low N for veg; check Mg |
| Controlled-release pellets | Soil, outdoor pots | Can't taper or adjust |
| Lawn feed | Avoid | Herbicides, very high N |
| Agricultural-grade granular salts | Soil only | Insoluble fillers in hydro |

Targets: N ~150–200 mg/L in veg, P 30–60 mg/L, soil [feed EC](https://genetixbay.com/knowledge/glossary/input-ec.md) 0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md).

## What to do

1. Read the label for Ca, Mg and micronutrients, not just NPK.
2. Convert to mg/L and compare with stage targets.
3. Start at half the label rate in soil and check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) [EC](https://genetixbay.com/knowledge/glossary/ec.md).
4. Switch from an all-purpose to a K-rich feed in flower.
5. In hydro and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), use complete fully soluble feeds only.

## Common mistakes

- Using weed-and-feed lawn fertiliser.
- Assuming a cannabis label means better chemistry.
- Doubling up a garden feed on fertilised [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md).
- Granular field fertiliser in a hydro reservoir.

## Related

- Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)
- Answers: [what NPK means](https://genetixbay.com/knowledge/answers/what-does-npk-mean.md) · [which nutrients to buy](https://genetixbay.com/knowledge/answers/which-nutrients-to-buy.md) · [kitchen scraps](https://genetixbay.com/knowledge/answers/kitchen-scraps-as-fertiliser.md)
- Articles: [organic vs mineral](https://genetixbay.com/knowledge/nutrients/organic-vs-mineral.md)
- Terms: [mineral fertiliser](https://genetixbay.com/knowledge/glossary/mineral-fertiliser.md) · [NPK ratio](https://genetixbay.com/knowledge/glossary/npk-ratio.md)

## Follow-up questions

**Is tomato feed good for cannabis in flower?** Tomato feed is a reasonable flowering feed for cannabis in soil. It is usually potassium-rich with moderate nitrogen, which suits flower. Check the label for magnesium and micronutrients, dose to about EC 0.8-1.6 mS/cm in soil, and add a calcium source if your water is soft. It is too low in nitrogen for veg.

**Can I use slow-release fertiliser pellets on cannabis?** Controlled-release fertiliser pellets work for cannabis in soil and outdoor containers, mixed into the potting mix at planting at the label rate for container plants. They release nutrients with temperature and moisture, so you can't taper or adjust them quickly. Avoid them in coco, rockwool and hydro, where you need precise, adjustable feeding at every irrigation.

**Why shouldn't I use lawn fertiliser on cannabis?** Avoid lawn fertiliser on cannabis because many products are weed-and-feed mixes containing broadleaf herbicides, which cannabis is very sensitive to. Plain lawn feeds are also very high in nitrogen, often with little phosphorus, magnesium or micronutrients, and some use urea or ammonium heavily. A complete general-purpose or tomato feed is safer.

## Sources

1. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9
2. Waltz C, 2003. Know the numbers on a fertilizer bag. University of Georgia CAES Field Report. https://fieldreport.caes.uga.edu/?p=19743
3. Saloner A, Bernstein N, 2020. Response of medical cannabis (Cannabis sativa L.) to nitrogen supply under long photoperiod. Frontiers in Plant Science 11:572293. https://doi.org/10.3389/fpls.2020.572293
4. Westmoreland FM, Bugbee B, 2022. Sustainable cannabis nutrition: elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality. Frontiers in Plant Science 13:1015652. https://doi.org/10.3389/fpls.2022.1015652