# Which nutrients do I actually need for a first grow?

> For a first grow you need one complete base nutrient made for your medium (soil, or a two-part A and B for coco and hydro), Cal-Mag only if you use RO or soft water or coco, a pH down, and a pH and EC meter. Boosters, sugars and most additives are optional: cannabis trials found no yield gain above about 30-60 mg/L phosphorus or from doubling feed strength.

- Canonical: https://genetixbay.com/knowledge/answers/which-nutrients-to-buy.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: What is a basic nutrient line for beginners? | What nutrients should I buy? | Do I need all the additives? | Do I need bloom boosters? | Minimum nutrients for growing cannabis
- 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

One complete base nutrient made for your medium, [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) only if your water or medium calls for it, a [pH](https://genetixbay.com/knowledge/glossary/ph.md) down, and meters for pH and [EC](https://genetixbay.com/knowledge/glossary/ec.md). [Bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md), sugars and most additives are optional at best. Controlled cannabis trials found no gain above about 30–60 mg/L phosphorus or from doubling overall strength [1][2][3]. *Supported.*

## Why

A complete base feed supplies all the essential elements. That is all the plant can use.

Phosphorus has a plateau. Several independent trials agree that once the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) carries roughly 30–60 mg/L P, more does not raise yield or [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) [1][3]. Extra phosphorus raised leachate P instead [1].

Strength has a plateau too. Doubling feed from 2 to 4 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) in deep-flow hydro raised solution nutrients but not yield or cannabinoids [2].

Stacking products can backfire. Higher potassium supply lowered calcium and magnesium uptake in cannabis [4], which is what a PK booster on top of a complete base does.

House positions apply here: Cal-Mag need is driven by cultivar, [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) and [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md), not by [LEDs](https://genetixbay.com/knowledge/glossary/led.md), and [molasses](https://genetixbay.com/knowledge/glossary/molasses.md) feeds microbes, not the plant.

## The numbers

| Item | Need it? | Notes |
|---|---|---|
| Complete base (soil one-part, or [A and B](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) for coco and hydro) | Yes | Matched to medium |
| pH down | Yes, for coco and hydro | Mineral acid |
| [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) + buffers | Yes, for coco and hydro | Calibrate weekly |
| [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) | Yes | Read in mS/cm |
| Cal-Mag | Only with RO, soft water or coco | Fill the gap to Ca 150–200, Mg 40–70 mg/L |
| Silica | Optional | Thin cannabis evidence |
| [Bloom](https://genetixbay.com/knowledge/glossary/flowering-stage.md) / PK booster | No | P plateau at ~30–60 mg/L |
| Molasses, sugars | No | Feeds microbes, not the plant |

## What to do

1. Pick your medium first.
2. Buy one complete base made for it.
3. Get a water report or measure your water's EC.
4. Add Cal-Mag only if the numbers say so.
5. Spend the rest on a good pH meter and fresh buffers.

## Common mistakes

- Buying the whole ten-bottle line.
- Stacking boosters on a complete base.
- Running Cal-Mag with [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md).
- Skipping the meters to buy additives.

## Related

- Full article: [Building a cannabis feed by stage](https://genetixbay.com/knowledge/nutrients/feed-by-stage.md)
- Articles: [bloom boosters](https://genetixbay.com/knowledge/nutrients/bloom-boosters.md) · [Cal-Mag](https://genetixbay.com/knowledge/nutrients/cal-mag.md)
- Answers: [meters you need](https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.md) · [full-strength chart?](https://genetixbay.com/knowledge/answers/full-strength-feeding-chart.md)
- Terms: [A-B nutrient](https://genetixbay.com/knowledge/glossary/a-b-nutrient.md) · [cal-mag](https://genetixbay.com/knowledge/glossary/cal-mag.md)

## Follow-up questions

**Do I need bloom boosters?** No, you do not need bloom boosters. Controlled cannabis trials found no yield or cannabinoid gain once the feed supplies about 30-60 mg/L phosphorus; extra phosphorus mostly ended up in the runoff. A complete base feed already covers flower. Stacking a PK booster on top can push potassium high enough to suppress calcium and magnesium.

**Do I need Cal-Mag?** You need Cal-Mag only when your water and base nutrient together supply too little calcium and magnesium: RO or very soft water, new or unbuffered coco, or a base made for hard water. Need also varies by cultivar. LED lighting does not create a Cal-Mag need; that claim is a myth. Check your water report before buying.

**Do I need molasses or sugar additives?** No. Molasses and sugars feed soil microbes, not the plant, which makes its own sugars by photosynthesis and does not take up meaningful sucrose through its roots. In soil they are harmless at small doses; in hydro they feed biofilm, strip oxygen and raise root rot risk. Taste comes from plant health, drying and curing.

## Sources

1. 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
2. Hershkowitz JA, Westmoreland FM, Bugbee B, 2025. Elevated root-zone P and nutrient concentration do not increase yield or cannabinoids in medical cannabis. Frontiers in Plant Science 16:1433985. https://doi.org/10.3389/fpls.2025.1433985
3. Shiponi S, Bernstein N, 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323
4. Saloner A, Sacks MM, Bernstein N, 2019. Response of medical cannabis (Cannabis sativa L.) genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369