Short version? Most growers in coco or hydro should grab Canna Rhizotonic. It's from £12.49, it barely touches your EC and you can use it from seedling into flower. Growing organic in soil? Biobizz Root Juice, from £11.69. Want the strongest stuff on the shelf and happy to pay for it? House & Garden Roots Excelurator, at just 0.3ml per litre. And if you'd rather put living fungi on the roots, Great White Premium Mycorrhizae does a different job altogether.
The best root stimulators
Canna Rhizotonic
Seaweed extract from the North Atlantic, watered right down. Algae based, 100% natural, and Canna say it's fine at every watering from seedling into flower. It's the easy one.
- Ascophyllum nodosum seaweed
- Soil, coco and hydro
- 4ml/L first dose, then 2ml/L
- Adds next to nothing to your EC, so it won't knock your feed numbers out
- Works on cuttings and transplants as well as plants that are already rooted
- Comes in 250ml right up to 10L, so you can start small
House & Garden Roots Excelurator
House & Garden reckon this is the most powerful root stimulator on the market. Bold. What we can tell you for certain is the dose is tiny, 0.3ml per litre, so a 250ml bottle makes over 800 litres of feed.
- 0.3ml per litre
- Cuttings to flower week 3
- Soil, coco and hydro
- Forms a film round the roots that's meant to keep germs out while letting nutrients in
- Goes a very long way, which takes the sting out of the price tag
- Pairs with House & Garden Multi Zyme (from £13.00) to clear out dead root matter
Biobizz Root Juice
Humic acid and seaweed, all vegetable based. OMRI and SKAL certified organic. If the rest of your feed is Biobizz it just slots in.
- Humic acid and seaweed
- 4ml per litre
- OMRI and SKAL certified
- Made with soil in mind, though Biobizz say it works in hydro too
- Use it the first week after cuttings root, or keep it going all the way through
- Biobizz say it helps plants cope with stress, high EC included
Plagron Power Roots
Plagron's organic root stimulator. One ml per litre at every watering, from veg to week 4 of flower, then you stop. Nothing fancy, and that's fine.
- 1ml per litre
- Veg to flower week 4
- All substrates
- Plagron say the plant takes it up almost straight away
- Cheap to run at 1ml per litre
- Also helps the plant's resistance, according to Plagron
Atami Root Stimulator
Atami's take is all about the root zone in soil. It's pitched at quick branching, more root volume and giving the soil life a proper boost so the plant can pull food out of the substrate more easily.
- Soil focused
- Boosts soil life
- 250ml to 5L
- Roots branch out fast, according to Atami, which gives the plant more grip
- Atami say it has an inhibiting effect on Pythium, Fusarium and root lice
Great White Premium Mycorrhizae
A different animal. This isn't seaweed in a bottle, it's a powder of living fungi and bacteria: 9 endomycorrhizae species, 7 ectomycorrhizae and 14 beneficial bacteria. They colonise the roots and help them take up water and nutrients.
- 30 species in one
- Soil, coco and hydro
- Scoop dosed powder
- Helps cut down transplant shock
- In hydro it goes straight into the tank, one scoop per 10 gallons
- There's a 1oz pot if you just want to give it a go
Getting the most out of a root stimulator
A root stimulator can't fix a bad root zone. It helps good roots grow faster. That's it.
So the boring stuff still comes first. And most of the time the boring stuff is what's actually wrong when roots go brown.
- Use it when roots are under pressure. Cuttings, seedlings and transplants. That's where you'll see the difference.
- Stick to the dose on the bottle. More isn't better, and the doses vary loads, from 0.3ml to 4ml per litre.
- Know when to stop. Most of these finish somewhere around flower weeks 3 to 4. Check the card above for yours.
- Match it to your system. Recirculating hydro? Check the label first. Plagron Power Roots, for one, isn't made for it.
- Don't let roots sit in a pot that's too small. Our guide to root-bound plants covers that one.
At a glance
Dose and timing are where these really differ, so that's what the table's about.
| Product | Type | Dose | When | Price |
|---|---|---|---|---|
 Canna Rhizotonic |
Seaweed liquid | 4ml/L then 2ml/L | Seedling to flower (0.5ml/L) | From £12.49 |
 House & Garden Roots Excelurator |
Liquid | 0.3ml/L | Cuttings to flower week 3 | From £19.00 |
 Biobizz Root Juice |
Humic and seaweed, organic | 4ml/L | After rooting, all grow | From £11.69 |
 Plagron Power Roots |
Organic liquid | 1ml/L | Veg to flower week 4 | From £16.99 |
 Atami Root Stimulator |
Liquid | See label | Soil grows | From £16.00 |
 Great White Premium Mycorrhizae |
Mycorrhizae powder | 1 scoop per 10 gal (hydro) | Any stage | From £11.69 |
Prices as at October 2026. Check the product page for the live price.
How to choose
- Coco or hydro and want one bottle that just works? Canna Rhizotonic.
- Organic soil grower? Biobizz Root Juice, or Plagron Power Roots if you're watching the pennies.
- Running recirculating hydro on rockwool or clay pebbles? Plagron Hydro Roots, not Power Roots.
- Want maximum punch per millilitre? House & Garden Roots Excelurator.
- Want living biology on the roots? Great White Premium Mycorrhizae.
- Taking cuttings? Dip them in Clonex Rooting Gel first, then use a stimulator in the water once they've gone in.
Not sure whether to take cuttings or start from seed? Our seeds vs cuttings guide has you covered.
Quick answers
Do I actually need a root stimulator?
Not always. A healthy plant in a decent mix will root on its own. Where a root stimulator earns its keep is the stressful bits: cuttings, seedlings and fresh transplants, when the plant has to put out new roots quickly.
When should I stop using a root stimulator?
It depends on the bottle. Plagron Power Roots stops after week 4 of flower and House & Garden Roots Excelurator after flower week 3. Canna Rhizotonic carries on but drops to 0.5ml per litre in flower. Plagron Hydro Roots is the odd one out and goes right up to the final week.
Can I use a root stimulator in DWC or NFT?
Some of them, yes. Canna Rhizotonic is labelled for all systems. Plagron Power Roots is not suitable for recirculating systems like NFT, DWC or aeroponics, so Plagron make Hydro Roots for hydro setups instead.
What is the difference between a root stimulator and mycorrhizae?
A root stimulator is a liquid, usually seaweed or humic acid based, that prompts the plant to grow more roots. Mycorrhizae are living fungi that colonise the roots and help them take up water and nutrients. Great White is the mycorrhizae option in this guide.
Is rooting gel the same as a root stimulator?
No. Rooting gel such as Clonex goes on the cut end of a cutting before it goes into the cube or plug. A root stimulator goes into your water or feed and keeps working once the roots are there.
Still stuck? Give us a ring on 020 8686 9643 or email info@thehydrobros.com.
Or pop into the shop for a natter: Unit 12, Progress Business Park, Progress Way, Croydon CR0 4XD.
More grow guides
- Best pH and EC meters
- Best dehumidifiers for grow rooms
- Best grow tents by size
- Best hydroponic nutrients UK
- Organic vs mineral nutrients
- Root-bound plants: how to fix them
The Hydro Bros Team. We sell this kit and talk growers through it every day in our Croydon shop.
