What is the best medium for rooting clones?

Q: What is the best medium for rooting clones?

There's no single best medium for rooting cannabis clones; the best is the one that stays moist while holding plenty of air. Studies disagree: rockwool rooted best (up to 80%) in one hemp trial, but worst (0% at 9 days) when kept at full water capacity in another, where a 50:50 peat-perlite mix won. Rockwool, peat or coco plugs and aeroponic cloners all work if not waterlogged.

Short answer

The best medium for rooting cannabis clones is one that stays moist but airy. In trials, rockwool won in one study and lost badly in another, where a 50:50 peat-perlite mix rooted most. Rockwool, peat or coco plugs and aeroponic cloners all work when not waterlogged. Supported, with conflicting trials.

Why

Medium had the biggest effect on rooting in a hemp trial, with success ranging from 13% to 80% across four media; rockwool came out best ^[1].

A cannabis trial reversed it. After 9 days, peat-perlite rooted 41% of cuttings, coir 29%, peat 16% and rockwool 0%, with all media held at full water capacity; the authors credited peat-perlite's better air space and EC ^[2].

Read together, the lesson is water management. In the hemp trial, media were rewetted by hand only when cuttings began to wilt ^[1]; in the cannabis trial, everything stayed saturated ^[2], and rockwool, with less air space than the peat-perlite mix, failed.

Aeroponic cloners and water both supply oxygen differently, but warm, wet root zones invite Pythium and Fusarium ^[3].

The numbers

Medium	Trial result	Strength	Weakness
Rockwool cube	Best of 4 in ^[1]; 0% at 9 days when saturated ^[2]	Clean, uniform	Easy to drown; start at pH ~5.5
Peat-perlite 50:50	41% at 9 days, best in ^[2]	Airy, cheap	Messier; mix your own
Coir plug	29% at 9 days ^[2]	Airy, reusable stock	Can hold salts; rinse/buffer
Peat plug	16% at 9 days ^[2]	Cheap, easy	Can stay wet
Aeroponic cloner	Not tested in ^[1]^[2]	Lots of oxygen	Reservoir hygiene; bare roots
Plain water	Not tested	Free	Low oxygen, brittle roots

Verdict: pick the airy option you can keep moist without saturating; the setup and hygiene matter more than the brand of cube.

What to do

Pre-moisten the medium, then squeeze or drain the excess.
Lift trays and water only when they lighten.
Keep medium at 22–26 °C (72–79 °F).
Clean cloner reservoirs between batches.

Common mistakes

Sitting cubes in a puddle of water.
Rich potting soil for unrooted cuttings.
Unbuffered coir with high salts.
Never cleaning the cloner.

Full article: Clone-only cuts and how to preserve them
Rockwool · Can I root clones in water?
Do clones need nutrients?
Terms: rockwool · aeroponics

Rockwool is an inert growing medium spun from melted basalt rock into fibres, sold as plugs, cubes and slabs, that holds water and air in fixed proportions.Peat is partially decomposed sphagnum moss from bogs, the base of most potting mixes; it holds water and nutrients well but is acidic and needs lime.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Aeroponics grows plants with roots hanging in air inside a dark chamber, wetted by sprayed nutrient solution; low-pressure (LPA) systems use ordinary pumps and spray heads.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.Hemp is cannabis grown for fibre, seed or other uses and, in many laws, defined as Cannabis sativa with no more than 0.3% THC by dry weight.Air-filled porosity is the share of a container's volume that holds air rather than water after it has drained, a key factor in root oxygen and overwatering risk.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.A genus of oomycete water moulds, such as Pythium myriotylum and P. aphanidermatum, that cause brown, slimy root rot, especially in warm hydroponic systems.A soil-borne fungal disease, chiefly Fusarium oxysporum, that blocks water-conducting tissue, causing one-sided yellowing, wilting and brown streaks inside the stem.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.Potting mix is a manufactured container medium, usually peat or coco with perlite, lime and starter fertiliser, designed to drain and hold air better than garden soil.

Follow-up questions

Is rockwool good for clones?

Rockwool works well for cannabis clones if you manage its water. In one hemp trial it gave the highest rooting success of four media, but in another cannabis trial, rockwool kept at full water capacity rooted no cuttings within 9 days. Pre-soak it at pH about 5.5, squeeze out excess water, and let it lighten between waterings.

Can I root clones directly in soil?

Yes. Cannabis clones can root directly in a light, airy mix, such as seedling mix or peat with 30–50% perlite. In one trial a 50:50 peat-perlite mix rooted the most cuttings, ahead of coir, peat and rockwool. Heavy, rich potting soil holds too much water and salts for a rootless cutting. Keep it moist, not wet, and use a dome.

Is an aeroponic cloner better than plugs?

An aeroponic cloner roots cannabis cuttings in humid air sprayed with water, so oxygen at the stem is excellent and many growers find it fast and even. Its weak points are hygiene and transplanting: warm reservoirs breed Pythium, and bare roots need careful potting. Plugs are slower to set up wrong. Both work; pick the one you will keep clean.

Sources

Campbell SM, Anderson SL, Brym ZT, Pearson BJ, 2021. Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.). PLOS ONE 16(7): e0249160. doi.org/10.1371/journal.pone.0249160

Hwang SJ, Collado CE, Hwang HS, Yun JH, Hernandez R, 2026. Impacts of commercial and custom substrates on rooting and morphology of Cannabis sativa 'Suver Haze' stem. HortTechnology 36(3):429–434. doi.org/10.21273/HORTTECH05810-26

Punja ZK, Rodriguez G, 2018. Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants. Canadian Journal of Plant Pathology 40(4):498–513. doi.org/10.1080/07060661.2018.1535466