Plant growth regulators

The Hydroponics Industry’s Most Closely Guarded Secrets Exposed

I made an error in Integral Hydroponics Edition 4 when writing up the second Plant Growth Regulator formula (page 132, 2 part PGR formula) that is included in Edition 4, due to a rush to get files uploaded to the printers. It’s a long story (being on the road in India just part of it) but I pasted in the wrong material without scrutinising the data first.

Upon receiving a draft of Integral Hydroponics (and proof reading it) I picked up on the error and therefore thought it best to amend it here. I apologise for any inconvenience this may cause readers of Edition 4. I will be uploading new files to Amazon shortly to correct the 2 part PGR formulation that is briefly covered in the book. For now Editon 4 remains available through Amazon and their affiliates. Grab the new copy of the correct formulation here and feel free to share it with your friends. I’ve added some material here that is not in the book. E.g. Use of these products.

I’ll also post in the single part PGR formula that features in Integral Hydroponics Edition 4. Enjoy – the hydro industries most closely guarded secrets exposed.

Now let’s look at some of the “hydro” industries most closely guarded secrets. PGR (Plant Growth Regulator) flowering additives. What’s in them? How do we make them?

Our first PGR formula – a similar product to this (same actives) was banned in several countries in 2003. I’ve modified it somewhat (g/L of actives) to the original after running a few trials with the original formulation.

Single Part PGR Formula (1L) SX

FOR DEMONSTRATION PURPOSES ONLY. Agricultural codes should be adhered to.

For use in ornamental crops only

I would stress that this product comes with a strong warning – it has long withholding periods and the actives are systemic, meaning they, in all probability, remain residual in the plant after it is harvested; one of the actives was banned for use in ANY consumable crop some years ago after a massive controversy in the US (“the Alar scare”) and both actives are poisons with possible toxicity issues when used in a short term deciduous crop.

Chemistry to Potential Hazard and History

Daminozide/Alar: The Daminozide atom converts to hydrazide when heated. Hydrazide is highly carcinogenic and “the Alar scare” (1989) exposed that Daminozide was being used by US apple growers. The apples were then being stewed (i.e. heated) for baby food etc and the allegation was that a “potent human carcinogen” was finding its way to consumers.

On the flipside: The “Alar Scare” today is regarded by many as an example of sensationalist media coverage, where vested interest groups were able to influence the mainstream media with questionable facts to support the claims made against Alar. While Alar may prove hazardous when heated, research found the quantities required to be carcinogenic were substantial and that its use in the US apple industry, in all probability, posed no health problems to the end consumer.  The manufacturers of Alar voluntarily withdrew the product from the market for some time after the controversy and now list it as not suitable for use in any consumable crop.

Mixing Instructions 

Safety Precautions: Wear gloves, eyewear and a mask when mixing.

What you will need for the mixing process:

A 1000ml mixing vessel (larger is fine as long as increments are marked for accurate measurement)
Accurate scales (1 gram increments minimum – ideally 0.1 increments)
Pipette for small fluid increment measurement/1ml increment measuring vessel
A mixing implement/stirrer
A 1L Bottle


880 micrograms per litre Paclobutrazol
200 Grams Alar WP (850 g/kg)
5 grams Urea
30ml 8% fulvic acid
Demineralised (e.g. Reverse Osmosis) Water


1)         Heat at least 1L of demineralised water. All mixing should be done with
hot water
2)         Add 500ml of hot water into mixing vessel
3)         Add 200 grams Alar WP (850 g/kg). Stir thoroughly until dissolved. Let foam settle before going to step 4.
4)         Add 5 grams of Urea. Stir thoroughly until dissolved. If any foaming occurs let settle before going to step 5
5)         Add 30ml 8% fulvic acid to the SX mix and stir
6)         Add Paclobutrazol at rates pertinent to the brand you have purchased to achieve 880 micrograms/L in the mix. For instance, if the original product is Active Constituent: 250 g/L Paclobutrazol you would add approx 3.52ml to your 1L of SX mix. (We will be going into much more detail about chemical weights (g/L) and formulation straight after this)
7)         Top up to 1L with hot water and stir thoroughly
8)         Let cool…. Pour contents of mixing vessel into 1ltr bottle using a funnel


Ready to use. Always shake before use.

 Keep out of reach of children.  If poisoning should occur contact the poisons information help line in your locale…. inform them that Daminozide and Paclobutrazol are the cause of the poisoning

Other Info

Purchasing Alar/Daminozide
If in Australia purchase Alar WP 850g/kg active constituent. The supplier/importer is Crompton Agribusiness Pty Ltd. – It can be accessed through large Agricultural suppliers such as Wesfarmers etc.

For other countries contact Crompton Corp or phone agricultural suppliers and ask for Alar WP at 850g/kg – Alar is a global brand name licensed by Uniroyal Chemical Company (US) which is now part of Crompton. Visit their website: if you require more information.

Purchasing Paclobutrazol
There are many Paclobutrazol products available on the market. Just some brandnames include Cultar, Clipper, Bonzi, and Payback.

Payback and Cultar both contain 250g/L active. Cultar should be available in most countries and is manufactured by Syngenta (visit their website to locate suppliers in your country). In just about all instances, regardless of where you live, you should be able to find a Paclobutrazol product at 250g/L active (if not we’ll talk about this shortly).

Available through all agricultural suppliers

Fulvic acid
Locate suppliers near you through searching the internet.


It is important to note that Plant Growth Regulators (PGRs) are exactly this (they regulate plant growth) and that by using them at the right times and at the right rates it is possible to achieve a high degree of control over plant height and formation.

The period that our single part formula should be used for is recommended to be a maximum of 14 days for recirculating systems and 9 days for RTW systems (e.g RTW coco substrate growing).

It is recommended that you add the product at the onset of flowering, or within the first two weeks of switching to the 12/12 light cycle.

If the plant is allowed to flower normally for 2 weeks (without the use of SX) the plant will have increased internodal length. When adding SX at this stage the buds will be dense and small to medium sized but because of increased internodal gaps there will be greater area for potential bud sites to join, possibly increasing yield (comparatively to adding SX when first switching to the 12/12 light cycle).

After the desired period of use, dump the nutrient tank/reservoir and go back to a standard fertiliser regime. In addition, flush the medium to ensure that any remaining SX (PGR product) is flushed from the system/medium.


Possible/probable toxicity issues when used in a short term deciduous crop

Lessens essential oil production


Let’s go over the math for the SX formulation and let’s say we can’t get a Paclobutrazol product with 250g/L active. Grab a calculator and pen and paper at this point and take a few notes as we go. We’ll be covering the same equations again in a moment and by the end of this section you should have this very easy chem worked out. (At the back of the book you’ll find some blank pages where you can add some notes and referrals to page numbers to refresh later when and if you need to use these sums)

We’ll now look at how simple all of this is where basic chemistry equations are concerned. That is, looking at the example in the ‘Sample X’ (SX) mix of, “add Paclobutrazol at rates pertinent to the brand you have purchased to achieve 880 micrograms/L in the SX mix. For instance if your original product is Active Constituent: 250 g/L Paclobutrazol you would add approx 3.52ml to 1L of the stock SX concentrate.

From this we know if we have a 250g/L stock ‘Paclobutrazol’ (Paclo) product we add 3.52ml of this stock to the 1L SX mix.

For example, let’s say that the product you are working with is 350g/L active Paclo. How do we turn this into 250g/L of stock Paclo mix and add 3.52ml of this to our 1L SX concentrate?


So the Paclo product you have purchased is 350g/L. We can easily convert this to the desired 250g/L stock Paclo solution by using a simple equation of the concentration you want times the volume you want divided by the concentration that your product contains.

The sum then becomes (the concentration you want) = 250g/L x (lets say a stock 2L mix of 250g/L) 2 ÷ (by the concentration we have) = 350g/L.

Put simply 250 x 2 ÷ 350 = 1.4255 meaning we take 1.4255 (1.425L or 1425ml) of our 350g/L Paclo solution and add it to 575ml of demineralised water to achieve a 2L stock solution of Paclo at 250g/L. Add 3.52ml of this to the 1L SX mix.

Let’s take another example and imagine we have a product that is 582g/L and we wish to make a 5L stock Paclo solution @ 250g/L.

Our sum then becomes: 250 x 5 ÷ 582 = 2.14L or 2140ml 582g/L Paclo solution added to 2860ml demineralised water to achieve 5L of 250g/L stock solution.

Take 3.52ml of your 5L 250g/L stock Paclo solution and add this to your 1L SX mix and there you have it.

As the book progresses we’ll be covering many more equations that refine chemical calculations even further, but by using this very simple method you are now adept enough as a chemist to formulate the SX mix with Paclobutrazol products available in your locale.

OK, now let’s look at a 2 part PGR formulation.

2 Part PGR Formula (3L stock concentrate) to be used at 3ml/L

Actives: Paclobutrazol and Chlormequat Chloride (as Cycocel 750a @ 580g/L active).

Both products are available through agricultural suppliers

Other ingredients: 8% Fulvic Acid

Our Formula for a 2 part PGR product (amended and corrected)


Part A, Paclobutrazol Product @ 250 g/L to be used at 4gram/L in the working solution

  1. Stock Paclo concentrate product @ 250g/L. Use at 16ml to 1ltr stock concentrate. I.e. if you wish to make 3L stock concentrate use 48ml to 3L

Use at 3ml/L

Part B ‘Cycocel 750a (Chlormequat Chloride) @ 582g/L’ to make 3L Concentrate

Add 396ml Cycocel to 2.5L demineralised water
Add 30ml 8% fulvic acid

Top up to 3L final working solution

Use at 3ml/L

Purchasing Chlormequat Chloride

Chlormequat Chloride is available through agricultural suppliers.

There are several commonly available brands of Chlormequat Chloride (CC) as active products. Other than Cycocel 750A @ 582g/L CC, which is widely available through agricultural suppliers in Australia, BASF makes a product called BASF 3C Chlormequat 720 which is 720g/L active CC and another product called CeCeCe 750 which is 750g/L active CC.

Search the internet and/or contact Agricultural suppliers in your locale and ask whether they stock Chlormequat Chloride products.


Grow the plants to the approximate height that you want them to finish at and switch them to the 12/12 light cycle.

At this point add the part A, Paclobutrazol (Paclo) concentrate to the nutrient tank for 1-2 days. The Paclo inhibits vertical growth and helps to induce early flowerset. You can control this somewhat (alter the time of use) and not add the Paclobutrazol for a week or so into the 12/12 light cycle (for instance, many growers introduce the Paclobutrazol at about 7 days into the 12/12 cycle when they are happy with the height of the plant/s) – just keep in mind that once the paclobutrazol is added you will see very little –if any – additional vertical growth

Next, dump the nutrient containing the Paclobutrazol and refill it (add nutes to desired EC without adding any PGRs) and wait approximately 5 days until flowers begin to appear/form. At this point introduce the CC (Part B at 3ml/L) and run this for 3-5 days.

After this period dump the tank/reservoir and go back to a standard nutrient regime.

The CC further inhibits vertical growth, reduces apical dominance (nodes form closer to each other than they otherwise would) and helps in creating densely formed flowers.

It is important to note that many growers alter the ways in which they use these products (time of use, application period/times and application rates) and some experimentation is recommended. For instance, genetics (to some extent) may play a role in determining the best method of use.

Other options:

Anecdotal evidence from South Australia, suggests that removing the Paclobutrazol (part A) from the mix and using just CC (part B) at double the recommended rate may provide better outcomes than using both part A and B.. This one is pretty simple using our 2 part formulation. Add 6ml/L part B and give the Part A (Paclo) a miss altogether. You’ll probably find this product performs very much like another highly touted (bells and whistles) single part PGR formula that was released into the Australian and other markets in or around 2004.


Both Cycocel and Paclobutrazol have long withholding periods and at least some traces (residual) will/may remain present in a short term deciduous crop.

Technically, these actives (CC and Paclo) and other chemical PGRs are rated as schedule poisons (e.g. CC is an S6 poison) and classified as hazardous. It’s MSDS (Material Safety Data Sheet) can be found here.

Keep these products safely stored and out of reach of children. Be sure to read the MSDS on the various products before use or disposal.

Use of Silica and Antifungal foliar sprays with PGR products 

Produce grown with PGR products is prone to botrytis (grey mould/bud rot).

In order to prevent botrytis from occurring:

  • Ensure there is adequate airflow through the growing environment to ensure RH levels are within the correct parameters (approx 60 – 65% – this applies both to the day and night cycle)
  • Use a silica product (Potassium Silicate) throughout the grow and bloom cycle. Potassium silicate helps in creating cell integrity, increases disease resistance and, as an added advantage, increases final flower weight. As a tip, use only half the recommended rate of silica in the last 3 weeks of flower
  • Apply an anti fungal spray once weekly to prevent botrytis (I’ll provide you with a formula next)