FAQ About Activated Carbon: Everything You Need to Know for Happier Plants

Activated Carbon (also called activated charcoal) might not be the flashiest part of your plant care setup, but it plays a powerful role in keeping roots healthy and pots smelling fresh. Used correctly, it helps prevent root rot, absorbs toxins, and improves drainage — especially in semi-hydro setups, terrariums, and closed pots.

But how exactly do you use it? Does it work in regular soil? And how often should you replace it? That’s why we created this FAQ — to answer everything you might wonder about regarding activated carbon for houseplants.

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General Use

What is activated carbon and how is it made?

Activated carbon is a form of carbon that’s been processed to have a very high surface area and porous structure. It’s usually made from coconut shells or wood, then heated at high temperatures in the absence of oxygen to activate it.

What does activated carbon do in plant care?

It binds to impurities like toxins, odors, and some bacteria in the soil or water. It also helps prevent root rot and keeps closed environments like terrariums clean of mold.

Is activated carbon the same as charcoal?

Not exactly. Regular charcoal (like BBQ charcoal) is not the same — it often contains chemicals or fillers. Activated carbon is purified and processed for high absorption and plant-safe use.

Do houseplants need activated carbon?

Not all houseplants require it, but it’s highly recommended in certain setups, especially closed pots, semi-hydro, terrariums, or when dealing with root rot or overwatering concerns.

Is activated carbon safe for all plants?

Yes, it’s safe for nearly all indoor plants when used correctly. It doesn’t release chemicals or alter pH significantly.

Can I use aquarium charcoal for plants?

Yes, as long as it's labeled as activated carbon and contains no chemical additives. Avoid carbon pads or mixed filters. If you want to be sure, always check with the brand!

What is the difference between activated carbon and biochar?

Biochar is similar in appearance but made for long-term soil enrichment and carbon sequestration. Activated carbon is processed at higher temperatures to increase porosity, making it better at absorbing toxins.

Biochar is often more alkaline and can hold nutrients for longer, while activated carbon is better for filtration and odor control.

What does the iodine number of activated carbon mean?

The iodine number is a measure of how porous and absorbent the activated carbon is. Higher iodine numbers (e.g. 900–1200 mg/g) indicate better adsorption capacity.

For plant use, a number above 600 is generally effective. Our activated carbon has a high iodine number (600 - 750 mg/g), ensuring strong absorption performance.

Applications and Setup

How much activated carbon should I use?

This depends on your setup:

  • In soil: 1–5% of your mix
  • In semi-hydro: 1–2 cm layer at the bottom
  • In terrariums: thin layer below the substrate to absorb excess moisture and smell

Where do I place it in the pot?

For soil setups, mix it evenly. For closed pots or semi-hydro, you can place a layer under the main medium to absorb stagnant water or odor.

Can I mix activated carbon into soil?

Yes, it’s safe and even beneficial when blended into your mix. It helps reduce toxins and excess moisture around the roots.

Can activated carbon replace drainage materials like perlite or pumice?

No. It supports drainage but doesn’t offer the structure or aeration that Perlite or Pumice provides. Use it alongside, not instead of, those materials.

Should I rinse activated carbon before use?

Yes, always rinse it thoroughly. It often arrives dusty, and unwashed carbon can cloud water or stain your mix.

Does activated carbon affect soil pH?

It’s generally neutral, but some sources may be slightly alkaline depending on origin. In our mixes, its pH is 6,8 which is safe for plant use. 

Terrariums, Semi-Hydro and Special Setups

Why is activated carbon used in terrariums?

It absorbs odors, keeps the substrate fresher, and reduces the risk of fungal growth or anaerobic conditions in closed systems.

How do I layer activated carbon in a terrarium?

Usually, it goes just above the drainage layer (like LECA or stones) and below your soil substrate. A thin, even layer works best.

Is activated carbon useful in semi-hydroponics?

Absolutely! It helps purify water in the reservoir, reduces bacterial buildup, and keeps the root zone healthier in closed systems.

How often should I replace activated carbon in semi-hydro?

Every 3–6 months is ideal. It becomes saturated over time and loses its absorption power. If the water in the water reservoir turns cloudy or smells it is best to replace it!

Can I use activated carbon with LECA or pon?

Yes! It blends well with both and adds protection against stagnant water or root rot.

Maintenance and Reuse

How long does activated carbon last?

Roughly 3–6 months in active use (e.g., semi-hydro, terrariums). In passive use (e.g., in soil), it can last up to a year.

How do I know when to replace it?

When you notice unpleasant smells, stagnant water, or reduced effectiveness in water clarity or root health, it's time to replace.

Can I recharge or reuse activated carbon?

Technically yes, but not practically. Heating it to reactivate requires high temperatures that are hard to achieve safely at home.

Can I compost used activated carbon?

No, it’s not biodegradable. Dispose of it in regular waste or recycle it through a waste facility if possible.

Advanced

Does activated carbon kill beneficial microbes?

No, it doesn’t actively kill microbes. It filters out harmful substances and excess nutrients, but doesn’t sterilize the soil.

Can I use too much activated carbon?

Yes. Using more than 10–15% of your soil mix may dry out the soil too quickly or interfere with nutrient absorption.

Does activated carbon absorb nutrients from fertilizer?

It may absorb some excess nutrients, but not enough to harm your plant if you're feeding correctly.

Can I use activated carbon in organic plant care?

Yes, it's a natural product and aligns well with organic practices — especially if sustainably sourced.

Is activated carbon environmentally friendly?

It depends on the source. Coconut shell-based carbon is one of the most sustainable options, which is what we use at Sybotanica.

Do your soil mixes already contain activated carbon?

Most of them do! We include it in blends where it offers clear benefits. Check individual product pages for full ingredient info per SYBASoil mix!

Special Cases and Tips

Can I use activated carbon in worm composting setups?

Yes, in small amounts. Activated carbon can help absorb odors and excess moisture in worm bins. However, avoid overuse, as it may interfere with the microbial balance in vermicomposting.

Does activated carbon help eliminate fungus gnats?

Indirectly, yes. It keeps the soil drier and more aerated, reducing the ideal conditions for fungus gnat larvae to thrive. It's best used alongside other preventative methods.

Can I add activated carbon to water propagation jars?

Yes. A small amount can help reduce algae buildup, absorb impurities, and keep the water fresher for longer.

Is activated carbon useful in bonsai care?

Yes, particularly for bonsai in enclosed pots. It helps prevent root rot and keeps the soil fresh in compact spaces.

What’s the difference between granular and powdered activated carbon?

Granular carbon is chunkier and better for soil use, as it allows airflow. Powdered carbon is finer and more absorbent but can compact and block drainage. We recommend granular for most plant care applications.

Can activated carbon help with salt buildup from fertilizers?

It can help to some extent by absorbing excess nutrients and impurities, but regular flushing is still recommended to manage salt buildup.

Does activated carbon remove chlorine or chloramine from tap water?

It can reduce chlorine effectively, but chloramine (a chlorine-ammonia compound) is more resistant. For full removal, a water filter designed for chloramine may be necessary.

Can activated carbon stain surfaces or pots?

Yes, especially if not rinsed well before use. The fine dust can leave black stains. Always rinse thoroughly before adding to soil or hydro setups.

How should I store unused activated carbon?

Keep it in a sealed, dry container away from moisture, light, and strong odors. It can absorb smells and moisture from the air, which lowers its effectiveness.

Is there a difference between coconut-based and wood-based activated carbon?

Yes. Coconut-based carbon usually has higher microporosity, making it ideal for water purification and plant use. Wood-based carbon tends to have a broader pore size range but may be less efficient in water-heavy applications.