# When does pre-fertilised soil run out of nutrients?

> A typical pre-fertilised bagged potting mix feeds cannabis for about 2-4 weeks, then runs short, usually in mid-veg. Heavily amended or super-soil-style mixes and big pots last longer. The sign is the oldest, lowest leaves turning pale yellow from the tip inward and climbing, which is nitrogen running out. Then start feeding at half the label rate, around EC 0.8-1.6 mS/cm, every second or third watering.

- Canonical: https://genetixbay.com/knowledge/answers/when-does-soil-run-out-of-nutrients.html
- Topic: Nutrients · Type: Troubleshooting
- Evidence: Grower practice · Status: Draft: awaiting expert review
- Full article: [Growing in soil (potting mix with bottled feed)](https://genetixbay.com/knowledge/systems/soil.md)
- Also asked as: When should I start feeding in soil? | How long does potting soil feed a plant? | How long do soil nutrients last? | My lower leaves are yellowing in new soil | Do I need nutrients with pre-fertilised soil?
- 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

A typical pre-fertilised bagged [potting mix](https://genetixbay.com/knowledge/glossary/potting-mix.md) feeds cannabis for about 2–4 weeks, so most plants run short in mid-veg. Richly amended or super-soil-style mixes and bigger pots last longer. When the lowest leaves start to pale and the fading climbs, begin feeding at half the label rate. *Grower practice.*

## Why

Bagged mixes carry a modest starter charge of fertiliser. A [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) barely touches it; a plant in fast veg strips it quickly, and each watering [leaches](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) a little more.

Nitrogen usually runs out first. It is mobile, so the plant moves it from old leaves to new growth, and the oldest, lowest leaves yellow first while the top stays green [4]. Cannabis trials show exactly that pattern: [nitrogen deficiency](https://genetixbay.com/knowledge/glossary/nitrogen.md) starts on lower leaves and climbs [1][2].

Organic mixes release nutrients through microbes, so their supply depends on warmth, moisture and how much was mixed in. Organic feeds need more nominal nitrogen to match mineral ones, around 389 mg/L N in one vegetative [coir](https://genetixbay.com/knowledge/glossary/coco-coir.md) trial [3], which is why lightly amended mixes [fade](https://genetixbay.com/knowledge/glossary/senescence.md) early.

## The numbers

| Mix | Typical feeding time before you add more |
|---|---|
| Light starter mix (seedling or general potting) | 1–3 weeks |
| Standard pre-fertilised potting mix | 2–4 weeks |
| Heavily amended organic / super-soil style | 4–8+ weeks, often longer |
| [Living soil](https://genetixbay.com/knowledge/glossary/living-soil.md) with [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) | Topped up by top-dress, not bottles |

When you start: half label rate, [EC](https://genetixbay.com/knowledge/glossary/ec.md) ~0.8–1.6 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md), every second or third watering.

## What to do

1. Water seedlings with plain, pH-adjusted water ([pH](https://genetixbay.com/knowledge/glossary/ph.md) 6.2–6.8).
2. Check the lowest leaves every few days from week 2.
3. When they pale evenly, check [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) pH to rule out [lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md).
4. Start feeding at half the label rate.
5. Check runoff EC monthly; back off if it climbs.

## Common mistakes

- Feeding from day one on top of a fertilised mix.
- Waiting until half the plant is yellow.
- Reading normal late-flower leaf fade as hunger.
- Treating a pH problem as a feed problem.

## Related

- Full article: [Growing in soil](https://genetixbay.com/knowledge/systems/soil.md)
- Answers: [feed every watering?](https://genetixbay.com/knowledge/answers/feed-every-watering.md) · [super soil](https://genetixbay.com/knowledge/answers/what-is-super-soil.md)
- Articles: [mobile vs immobile nutrients](https://genetixbay.com/knowledge/nutrients/mobile-vs-immobile-nutrients.md) · [yellowing lower leaves](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md)
- Terms: [top-dressing](https://genetixbay.com/knowledge/glossary/top-dressing.md) · [nutrient deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md)

## Follow-up questions

**How do I know when my soil is running out of nutrients?** Soil is running out of nutrients when the oldest, lowest leaves of a growing plant turn evenly pale, then yellow, and the fading climbs up the plant while new growth stays green. That is nitrogen, a mobile nutrient, being moved to new leaves. Check runoff pH first; if it is in range, begin feeding at half the label rate.

**Should I feed seedlings in fertilised soil?** No, do not feed seedlings planted in fertilised potting mix. The mix's starter charge usually covers the first 2-4 weeks, and seedlings need very little. Extra feed on top risks burnt tips and stalled roots. Water with plain, pH-adjusted water until the lower leaves start to pale, then start feeding gently.

**Do bigger pots hold nutrients longer?** Yes, bigger pots of the same mix hold more total fertiliser, so a plant in a larger pot of fertilised mix usually runs longer before needing feed. The concentration is the same, though, so a seedling isn't overfed by a big pot. Watering habits matter more there: big pots of wet mix stay soggy and slow a young plant.

## Sources

1. Cockson P, Landis H, Smith T, Hicks K, Whipker BE, 2019. Characterization of nutrient disorders of Cannabis sativa. Applied Sciences 9(20):4432. https://doi.org/10.3390/app9204432
2. Llewellyn D, Golem S, Jones AMP, Zheng Y, 2023. Foliar symptomology, nutrient content, yield, and secondary metabolite variability of cannabis grown hydroponically with different single-element nutrient deficiencies. Plants 12(3):422. https://doi.org/10.3390/plants12030422
3. Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307-1312. https://doi.org/10.21273/HORTSCI11903-17
4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9