You may think that nitrogen or phosphorus are the stars of plant nutrition – but have you thought about carbon? Plants are ~40% carbon, yet many growers ignore its targeted supply.
The science behind it
Carbon is the basic structure of all organic compounds in plants. While CO₂ is absorbed via the leaves, organic carbon (e.g. in the form of fulvic acids or molasses) can also be metabolized via the roots. Studies show:
- Up to 20% faster root growth with the addition of carbon sources.
- Improved nutrient absorption through chelation.
Critical question: But don’t plants absorb enough CO₂ from the air?
Not always! Indoors or under high light stress, the natural CO₂ concentration is often not sufficient. Root carbon can be a backup here.
Practical tips – How to use carbon correctly
1. choose the right sources
- Molasses: Inexpensive, but sticky and microbially active. Not suitable for sterile systems.
- Fulvic acids: Highly bioavailable, but more expensive. Ideal for hydrosystems.
- Humic acids: Slow-acting, but soil-improving.
2. dosage is everything
Too much carbon can trigger microbial blooms or bind nutrients. Start with 1 ml/liter and increase slowly.
Counter-perspective: Some growers argue that carbon only works in living soil – is that true?
Yes and no. In hydroponics without microbes, the effect is limited. But even there, carbon improves the cell structure of the roots.
Alternatives and risks
When you should do without carbon
- In sterile systems (e.g. NFT without biofilter).
- If the CO₂ content is already high (>1000 ppm).
- If fungal problems (e.g. Pythium) are present – carbon can promote pathogens.
Natural alternatives
- Compost tea: Contains natural carbon compounds + microbes.
- Biochar: Long-term carbon storage in the substrate.
FAQs
Does carbon make sense for autoflowering plants?
Yes, but only during the vegetation phase. It can disturb the nutrient balance during flowering.
Can I use household sugar as a carbon source?
No. Refined sugar promotes harmful bacteria. Use molasses or commercial products instead.