Propagation Masterclass: Seeds, Cuttings and Clonex Step by Step

How to propagate plants indoors: sow seeds or root cuttings, and use Clonex rooting gel as the shortcut for cuttings. Propagation is producing new plants from seeds or vegetative cuttings rather than buying them in. To use Clonex correctly, decant a little into a clean pot, dip the bottom 10-20 mm (0.4-0.8 in) of a fresh cutting, then set it in moist media under a humidity dome. Never dip into the bottle — one contaminated cutting can spoil the whole tub.

Get it right and everything downstream is easier; get it wrong and you lose weeks to damped-off seedlings and rotted cuttings. This guide covers seed versus cutting, taking clones, using Clonex cleanly, propagator conditions, rooting times, troubleshooting and hardening off.

Who this guide is for: UK home and hobby growers starting plants from seed or clone in a tent, propagator or grow room. It covers indoor seed and cuttings only, not division, layering, grafting or bulbs. New to soilless growing? Start with our beginners' guide.

What is propagation, and should you grow from seed or take cuttings?

Growing from seed gives a fresh, vigorous plant with a taproot, but genetics vary and you wait for germination. Growing from cuttings (cloning) roots a growing tip from a healthy "mother" plant — an exact genetic copy that skips the seedling stage. Most growers use both: seed to find a keeper, then cuttings to reproduce it.

Factor	Growing from seed	Growing from cuttings (clones)
What you get	A new, genetically unique plant	An exact copy of the mother plant
Genetics	Variable — every seed differs	Identical to the parent
Time to a rooted plant	Germination (days) + establishment	Roots in roughly 1-3 weeks

How do you germinate seeds successfully?

Seeds need three things: moisture, warmth and air. Keep the medium damp (never waterlogged) and hold it in the warm band most seeds want — roughly 18-27°C (65-80°F), with 20-24°C (68-75°F) a safe middle. On a cold UK windowsill a heated propagator or heat mat often makes the difference between a 3-day pop and no-shows.

Three methods differ mainly in how much the young root is handled.

Method	How it works	Best for	Watch-out
Direct-sow in plug, coco or soil	Straight into moist media	Least root disturbance	Easy to over-water
Rockwool cube	Sits in a pre-soaked inert cube	Hydroponic setups	Must pH-soak the cube first
Pre-soak in water	12-24 h soak, then sown	Older or hard-shelled seed	Don't leave soaking too long

Whichever you pick, keep the medium moist and warm until the first true leaves show, then move into brighter light. Rockwool cubes need a pH-soak before use; the full method is in our rockwool and inert-media guide.

How do you take cuttings step by step?

A clean cutting is straightforward if everything's ready first — work fast, keep it sterile, don't let it dry out.

1. Pick a healthy shoot. Choose a strong, non-flowering tip 10-15 cm (4-6 in) long with a few nodes (where leaves join the stem).
2. Cut clean. With a sterilised blade (a scalpel works well), cut just below a node at a 45° angle — exposing more surface for roots to form.
3. Trim the lower leaves. Remove the bottom leaves so no foliage sits in the media, and reduce large upper leaves by half to cut water loss.
4. Apply rooting gel. Dip the bottom 10-20 mm (0.4-0.8 in) of the stem into decanted Clonex so the cut end is fully sealed (full method below).
5. Set it in media. Push the cutting into a pre-soaked rockwool cube, Root Riot cube, peat plug or coco so it stands up without wobbling.
6. Dome and warm. Put it under a humidity dome on gentle bottom heat and keep it out of harsh direct light for the first few days.

How do you use Clonex rooting gel correctly?

Clonex is a water-based rooting gel that seals the cut stem and feeds it the root-forming hormone IBA (indole-3-butyric acid) — about 3,000 ppm (0.3%) in the standard formula — plus an anti-fungal agent, nutrients and trace elements. It is made by Growth Technology, and it is the reference product this category is measured against.

Using it well is less about the gel and more about not ruining it:

1. Decant a small amount into a clean dish — only what you need for this batch.
2. Dip the cut end 10-20 mm (0.4-0.8 in) so it is coated, then plant the cutting straight away.
3. Bin the leftover rather than pouring it back, then reseal the bottle and store it in a cool, dark cupboard, out of direct sunlight. Don't refrigerate or freeze it.

The open-pot mistake. Dipping cuttings straight into the main bottle is the commonest error. Each cutting is an open wound carrying bacteria and fungal spores, so one dip contaminates the whole tub. That is why a bottle "stops working": not the hormone failing, but gel you inoculated yourself.

A foliar mist such as Clonex Mist works alongside the gel by keeping the leaves turgid while roots form. It is an optional extra, not a substitute for clean technique; powder works too if you tap a little into a clean dish and bin the rest.

What humidity and temperature do propagators and domes need?

A propagator is a humidity chamber — a tray, media and a clear vented lid — holding the still, warm, near-saturated air a leaf-only cutting needs until it grows roots.

Start high and wean down. For the first few days aim for around 90-95% relative humidity with air at 22-25°C (72-77°F) and the root zone a touch warmer if you have a heat mat — mats typically lift the media 5-11°C (10-20°F) above room temperature. From about day three, crack the vents daily so the young plants toughen up. A hygrometer with a probe inside the dome shows you what the air is really doing.

Phase	Air temp	Humidity	Vents
Days 1-3	22-25°C (72-77°F)	~90-95%	Closed
Days 4-7	22-25°C (72-77°F)	~80-90%	Cracked open
Week 2	21-24°C (70-75°F)	~70-80%	Half open
Week 3 / removal	20-24°C (68-75°F)	Ambient	Off once rooted

Lift the lid briefly each day to swap stale air, and wipe heavy condensation so it doesn't drip and rot stems.

These figures are for the air under a closed dome. For the open room around it, see our grow room humidity guide; for the leaf-to-air balance, the target VPD for seedlings and clones. In summer, keeping clones at 22-25°C (72-77°F) takes more than a dome. In winter a cold room chills the media, so add bottom heat (winter grow room tips).

How long do cuttings and seeds take to root?

Cuttings usually root in 7-21 days and seeds germinate in 2-10 days. The commonest cause of failure is impatience: checking roots too early.

Task	Typical timeline	What success looks like
Seeds germinate	2-10 days	Taproot and first leaves emerge
Cuttings show roots	7-21 days (1-3 weeks)	White root tips at the plug base
Ready to pot up	When roots show at the base	Roots visible, plant standing firm
Hardened off	Over the next 5-10 days	Copes with grow-room light and RH

Soft tips root faster; woodier cuttings take longer. Don't unpot to "check" — you tear the new roots. Watch for white tips at the plug base, then open the dome fully and plan potting on without stress.

What goes wrong with seedlings and cuttings, and how do you fix it?

Problem	Likely cause	Fix
Damping off (seedling topples at the base)	Over-watering, stagnant air or dirty media	Use fresh media, water less, vent daily; bin affected seedlings
Wilting cuttings	Low humidity, strong light or no roots yet	Keep the dome closed early on; shade from harsh light
No roots after 21 days	Cold media, a woody cutting or dirty gel	Warm the base, take a fresh soft tip, decant clean gel

Keep new clones apart from your main plants (quarantine new clones). More in cutting and seedling problems.

How do you harden off young plants before the grow room?

Hardening off means gradually toughening a sheltered young plant to the harsher veg tent: brighter light, lower humidity. Skip it and healthy clones can collapse the day they leave the propagator.

Do it over roughly 5-10 days for a grow room (plants going outdoors need longer: the RHS puts it at two to three weeks). Once roots are established, open the vents fully for a day or two, then take the lid off for increasing spells until the plant copes with no dome. Move it into stronger light in stages, not straight under a full-power grow light, and ease off watering as the roots take over. Plan airflow once the dome is off. Feed lightly at first: see what NPK means for early feeding, when to start feeding seedlings and mycorrhizae for cuttings and seedlings.

FAQ

How long does Clonex take to root? Under a humidity dome with gentle bottom heat, most cuttings show white roots in about 1-3 weeks (7-21 days). Woody or slow species take longer. Don't unpot to check; watch for root tips at the base of the plug.

Can you mix Clonex rooting gel with water? No. The gel is used neat: dip the cut end straight into decanted gel. For a water-based product, use a ready-to-use rooting mist or clone solution; diluting the gel just wastes it.

Do you actually need rooting gel to take cuttings? Not always, but it helps. Gel seals the cut, delivers rooting hormone and an anti-fungal, and lifts strike rates, especially on woodier cuttings. Soft, easy cuttings often root in plain moist media, but gel makes the result more reliable.

Recommended kit and further reading

The propagation gear we'd point a UK grower to, from first cutting to potting on:

• Clonex Rooting Hormone — the water-based gel that seals the cut end and delivers rooting hormone plus an anti-fungal; the category workhorse.
• Clonex Mist — a ready-to-use foliar spray that keeps cuttings turgid and can bring roots on faster alongside the gel.
• Clonex Pro Start — a propagation nutrient for young roots; use it as a media soak, seed treatment or first feed for seedlings and cuttings.
• Shogun Start Propagation Booster — an alternative rooting stimulant for seedlings and cuttings.
• ROOT!T Propagator Tray & Lid — a dedicated warm, enclosed space for batches of clones and seedlings: tray and vented lid in one.
• ROOT!T Propagator 60 Hole Insert — tray insert to hold plugs neatly in the propagator.
• Root Riot cubes, Jiffy-7 peat plugs and the Plug Life Coco 104 Cell Tray — starter plugs and cubes.

Most relevant collection: if you click one link, start with Propagation — plugs, domes, trays and rooting products in one place. Or browse the full Clonex range. Building a full kit list? See our propagation kit shopping list.

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Why trust The Grow Superstore

We've been helping UK indoor growers since 2009, online and from our physical store in Peterborough. Cuttings and propagators come up on the shop floor every week, and the commonest fault we fix is a contaminated tub of rooting gel: growers dipping straight into the bottle, then wondering why nothing roots. It is exactly what we walk people through in store. Pop in for a free consultation and we'll help you build a propagation setup for your space.