Frequently Asked Questions

Propagation – Raising Seeds and Cuttings

In your objective to achieve the finest results attainable, producing strong and vigorous cuttings or seedlings is absolutely crucial. This is because the condition of your adolescent plants will be reflected during this period of their life cycle. The stronger they are during the vegetative stage, will maximise the plant's prospective through flowering.

Which hydroponic growing media is right for me?

Here at Rotherham Hydroponics, we offer a variety of high quality media for you to begin propagating effectively with. Regardless of the media you choose to commence with, you will always be free to relocate and plant into another form of media if this is what you wish.



Rockwell Cubes

Fast rooting times. Commonly used for rooting when transplanting to larger Rockwool blocks. Be careful not to over or under water.

Hydroton Clay Pebbles

The pellets drain freely and do not hold any excessive water, which is why they provide good oxygen levels around the root and why they are particularly suitable for flood and drain systems. They are also used extensively for rose growing.

Bio Nova Coco Bricks x 6

This block of compressed coconut results into 10litres of ready-to-use coconut substrate after adding 3 litres of water to it. Furthermore, its volume will increase approximately tenfold. As a result of its initial size, the substrate is fairly easy to transport.

Canna CoCo Pro-plus 50 Ltr

Made from the refined husks of coconuts, Canna Coco provides an airy and light rooting environment, perfect for encouraging vigorous and healthy root growth. A simple yet effective way of growing. Canna Coco has become very popular in recent years.

Jiffy coco 4" blocks x 6

The Jiffy Coco-Block offers hydroponic growers the first natural and organic alternative to stonewool blocks. The Coco-Block is designed to hold slightly less water than a stonewool block in order to improve early root development and establishment compared to stonewool.

Jiffy peat plugs 42mm x 50

No other growing media provides as many advantages as the Jiffy 7. Faster, superior root development. Using a match, create a hole for one seed. Insert seed and cover. Then propagate.

Vitalink Coco Coir Mix 50l

Featuring a unique blend of 70% fine coir and 30% coir chips, Vitalink Coco creates a light and airy environment with just the right density to support truly prosperous plants!

Vitalink Professional Coir Chips 20L

The chips are scientifically proven to deliver excellent root growth, prevent root disease and promote overall healthy plant development. Prevent the surface of the growing media from drying and guard against soil-dwelling pests, when used as mulch.

Pre-soaking Guidelines:

Rockwool Cubes and ROOT!T Rockwool Cubes

Soak in solution of 2ml/L of VitaLink BioPlus and 3ml/L of VitaLink PlantStart (pH approximately 5.5-6.0) for 4-5 hours. Gently brush off any excess water.

Jiffy Soil and ROOT!T Coir/Peat Pellets

Soak in solution of 2ml/L of VitaLink Bioplus (pH approximately 6.0) for 10 minutes. Gently brush off any excess water.

Jiffy Coco

Soak in solution of 2ml/L of VitaLink BioPlus and 3ml/L VitaLink PlantStart (pH approximately 5.5-6.0) for 10 minutes. Gently brush off any excess water.

Flexicubes and ROOT!T Cubes (optional)

If you choose to soak. Use a solution of 2ml/L of VitaLink BioPlus and 3ml/L of VitaLink PlantSTart (pH approximately 5.5-6.0) for 10 minutes. Gently brush off any excess water.

Feeding Guidelines

For all of the hydroponic growing media that you see above, soak in a solution of 2ml/L of VitaLink BioPlus and 3ml/L of VitaLink PlantStart at a pH of approximately 5.5-6.0 for 4-5 hours. Make sure that you gently brush off the excess water after this time.

For the aeroponics growing media, simply make sure that the tank is topped up with a solution of 2ml/l of VitaLink BioPlus and 3ml/L of VitaLink PlantStart. However make sure not to over water your cuttings as they respond only to being moist, not wet.

Which type of propagator should I use?

When you have determined the media you plan to root into, deciding on the best- suited propagator to match your requirements is next.

The table below shows the range of propagators that are available to purchase from us here at Rotherham Hydroponics. We offer a wide range of growing media that are specifically designed to suit your budget and at the same time ensuring that you get the best value for your money.



Fleximix Propagation Kit

The kit comes complete with a medium-sized Propagator, 40 cell FlexiMat that offers the latest and fastest rooting available today, a scalpel and a book on how to take cuttings or grow from seed.

Grodan Propagation Kit

A great cutting and germination kit. Comes complete with a medium size propagator, a 24 plug tray and resovouir excellent start kit for seeds and seedling.

Large Heated Stwerart Propagator

Large high quality propagator. Additional height ensures your seedlings wont run out of space too soon. 35 x 37 x 21 cms

Large Unheated Stwerart Propagator

This high quality propagator features high lid and ventilation slots. Perfect for the beginner small scale propagation.

Medium Heated Stwerart Propagator

Fixed temperature heated propagator featuring a sealed heating unit. Insulation beneath the carbon heating mat maintains selected compost temperature at 15-20 degrees under normal conditions. 35 x 21 x 21 cms.

Medium Unheated Stwerart Propagator

This high quality propagator features high lid and ventilation slots. Ideal for plant cuttings.

Which type of lighting is suitable for me?

In order to root your cuttings or raise seedlings successfully, you must supply them with the necessary lighting. This means using a particular propagation light that will provide a continual gentle light and heat, as opposed to the HID lighting used for vegetative and flowering stages; as these are commonly too strong for fragile juvenile plants. So regardless if you’re producing hundreds of plants, raising just a few cuttings – our range of lighting will meet all of your propagation needs on whatever budget you can afford.

Propagation Lighting


Maxibright Pl2 Propagation Light

Main body of reflector is finished white with an internal reflector made from hammered anodised aluminium, for high reflectivity. Strong hanging eyes are fitted allowing to be hung easily.

Maxibright Pl4 Propagation Light

4 x 55w flourescent tubes Maxibright Propagation Light units use 55watt lamps which are supplied with unit in a blue spectrum. Lamps also available in red spectrum so it can be used in both stages if desired.

Maxibright T5 2 Tube Propagation Light

Very little heat is emitted and so the unit can be placed very close to plant-top height without fear of scorching. These units also have low power consumption in relation to traditional HID lighting systems. 2 foot (600mm), 2 x 24w bulbs.

Maxibright T5 4 foot 4 Tube Light

Reduced heat output allows closer positioning to plants in addition to operation in enclosed spaces without the heat build-up associated with HID systems. 4 foot long, 4 x 6500 kelvin bulbs.

Maxibright T5 4 foot 8 Tube Light

The LightWave features a purpose designed wide dispersion reflector designed to cover a larger growing area than standard fluorescent fixtures. 4 foot long, 8 x 6500 kelvin bulbs.

Sun Mate Propagation Light

Built with the hobby grower in mind, the powerplant sun mate propagate 110watt is a low-energy lighting system. Ideal for your small scale propagation, it has been designed to help you produce healthy seeds and cuttings. Supplied with a 2m power lead.

Sylvania Lynx- 4-Pin 55W Bulb

15000 hours average rated life. 4-Pin Diameter: 38mm.

We also sell a wide range of grow lights for every stage in the plant life cycle, including; bulbs, reflectors, ballasts and much more here. (


Propagation is quite simply the creation of new plants. Many growers propagate using hydroponic techniques to benefit from premature rooting and rapid growth rates. This may be likely because hydroponic growing media provides the root zone with easy access to water, nutrients and oxygen.

Propagation: Seed vs. cuttings

To begin with, as with any type of propagation, you need to decide whether you want to grow from seed or from cuttings. In general, growers who begin propagating from seed do this because it gives them peace of mind that their plants will be disease and pest free.

However, the main disadvantage with seeds is that the characteristics of plants you produce can be inconsistent. Whereas when beginning with cuttings, you are producing plants that are identical to their healthy parent plant, this is why cuttings are also referred to as clones, as they are indistinguishable. Other benefits include:

  • Advanced flowering.
  • Enhanced plant collection.
  • Plant species which are much more adjusting to the inconsistent climatic variations.

Budding from cuttings has a range of advantages, therefore here at Rotherham Hydroponics we usually recommend our customers to use this technique of propagation. On the other hand, for your first gardening mission you will most likely have to start growing from seed.

How do I take a cutting successfully?

We have put together step-by-step instructions on how to take a cutting successfully.

First of all you will need the following items:

  • Propagation cubes/plugs.
  • Rooting hormone.
  • Heated or unheated propagator
  • Fluorescent lighting.
  • Sterile scalpel.
  • Spray bottle.
  • Nutrient.
  • Rooting stimulator.

The following article explains how to successfully propagate. The procedure is on the whole the same for all types of propagation.

The Mother Plant

First of all you will have to grow you seedlings or cuttings under 18 hours of light until they are appropriate to take cuttings from. This is generally when they are on average sized between 12 and 18 inches or have 8 to 10 internodes on them.

The best thing to do is to label your seedlings with numbers or names so that you can label your cuttings you obtain to make it easier to correspond with the parent plant.

When your seedlings are ready and prepared, activate them to flower by giving them 12 hours of light and 12 hours of darkness. Obtain the seedlings to full matirity to determine which shows favourable characteristics, for example the quickest to root, best flower progress etc.

While the plants are flowering, cuttings will need to be stored in a vegetative condition in an individual growing area with 18 hours of light and 6 hours of darkness.

The cutting with the same name/number as the plant with the most favourable characteristics will be the plant that is to be kept as the mother plant.

Mother plants can be grown in a variety of propagation systems. We highly recommend choosing a media based growing system, as the plants will typically be kept for up to a year. Whereas systems using techniques such as deep water culture and aeroponics are more appropriate to short term crops.

The most common method of keeping mother plants is by using soil, or soil-less growing media in pots, which can be maintained by being watered by hand or by an automatic delivery system.

Quality of cuttings

If you want strong, vigorous cuttings it is absolutely crucial to consider the quality of the mother plant that they are coming from. Always make sure that the mother plant is regularly trimmed and pruned to encourage side branches to grow, as this will give you lots of available sites to take cuttings from. It is highly advisable not to feed your mother plant too much, as overfed plants will produce thicker-stemmed, woodier branches and cuttings that will take much longer to root compared to your everyday average-watered mother plant. The highest focus of growth is concentrated around the bottom third of the plant section around the inside shoots where you should be taking your cuttings from, also identified as the ‘zone of juvenility’.

Without stripping away more than 25% of the foliage, you must take away as my cuttings from the mother plant as possible. However it is most preferred to use cuttings that have few leaves. Cuttings that have large leaves are often unable to soak up sufficient water through their stem, as those with thinner stems will also root much faster than cuttings with fatter stems.

Fluorescent lighting

As previously stressed, seedlings/mothers need to be grown under 18 hours of fluorescent lighting and 6 hours in darkness however once they are well rooted, you will need to change to 12 hours of HID light and 12 hours of darkness to commence the flowering or fruiting.

In the first week previous to the roots being formed, cuttings will begin to execute best with a fluorescent lighting unit which is positioned approximately 25-50cm away from the lid of the propagator. When using HID lights for the propagation, you should only choose 250w metal halide lamps. These lamps must only be positioned 1m away from your propagator. Any higher wattage of HID lamps will give off too much light and heat that will most likely result in the unfortunate event of your cuttings failing to root.

Rockwool Propagation Cubes

The main advantage of Rockwell is that it holds much more air and water than any other growing medium on the market. Not only that, but it is also inert, sterile and does not hold onto nutrient in any way. The roots are also clearly visible, therefore it is easy to identify whether the cubes are moist or dry. These can be easily transplanted into larger Rockwell blocks or any other hydroponic media with the minimalist amount of fuss to the plant.

Cuttings should take approximately 7 to 14 days to root, at this stage you will need to transfer the cuttings into much larger Rockwool cubes or your chosen hydroponic growing medium.

A simple step by step guide to taking cuttings

Finally, we are at that stage of the article that you have all been waiting for. The simple step by step guide to help you successfully take cuttings form your plants.

  • Clean down all work surfaces and wash equipment thoroughly with disinfectant.
  • Soak the Rockwell cubes in chosen nutrient solution for an hour, after which you must shake so as to get rid of any excess liquid that it may have collected.
  • Choose shoots which have at least 3 to 4 leaves, making sure that you take the cuttings from the base of the plant, around the outer shoots. Do this with a smooth motion, cutting at a 45 degree angle immediately below the joining of the branch and stem.
  • Immediately submerge the cut stems into a bowl of lukewarm water.
  • Remove the bottom leaves from the stem and if the cutting has more than one large fan leaf, remove the extra leaf.
  • Gently scrape the lower part of the stem with a scalpel to help initiate faster root growth.
  • Apply rooting hormone to the cut stem or cube exactly as directed on the packaging of the product.
  • Whilst lightly pinching the cube, gently hold in place and insert cutting into the cube.
  • Place back into plastic tray and position in propagator once all cuttings are inserted into the cubes.
  • Finely mist all cuttings with water and place propagator lid on tray.
  • Position fluorescent light over propagator.
  • Give cuttings 18 hours of light per day unless air temperature drops by more than 4ºC when the light goes out in which you must leave the lights on continuously.
  • Take off lid of propagator and finely mist propagator lid once a day.
  • Once there is evidence that roots are appearing within 7 to 14 days, the propagator vents can be opened.
  • If at this stage, you wish to transplant propagation cubes into larger Rockwool blocks, quite simply pre-soak block with suitable nutrient and rooting stimulator.
  • It’s important that Rockwell blocks are not too wet, therefore you must insert cubes into larger blocks and place them on a plastic tray or a surface where the plants can be ‘air pruned’. (see below)
  • Roots should become visible on the bottom of the blocks within 2 to 7 days and after 10 to 14 days there should be plentiful roots on the bottom of the blocks. At this point you can then plant into your chosen hydroponic system. However you must be careful not to place your plants into their system too early, only do so when there are an large quantity of roots on the bottom of the blocks should you consider planting on.

Air Pruning

Air pruning is a propagation technique that is used to help promote healthy root structure. Air pruning involves placing your plants in Rockwell blocks on a perforated tray or a wire mesh. This should be positioned carefully so that the air can naturally flow underneath the blocks. With using this technique as the root tip grows out of the blocks and detects the dry air and dies back which forces the root that is still inside the block, to branch out forming even more roots. This means that the roots will focus their growth within the block.

Eventually you will end up with a plant that has many small root tips extending beyond the block with a large mass of roots within the block. Soon after this has happened the plant is put onto its final system where the roots broaden away from the block very quickly, getting the plants existence off to a eminent start. This technique is on the whole very useful for NFT growing systems however is recommended to be employed for all types of systems.

Using Heated Propagators

If you have a propagation area that is too cold, your cuttings and seedlings will take a much longer time to begin growing. If the temperature of the propagation area is below 18ºC you will need to use a heating mat or warming pad for the bottom of the propagator or you could just buy a new heated propagator.

When using heat from a mat, pad or heated propagator we suggest that customers use a 2.5cm layer of perlite or vermiculite or also a combination of both can be used in your propagation tray. This will facilitate the spreading of the heat throughout the propagator and also avoiding the ‘hot spot’ areas at the same time.

Using ‘Aeroponic’ Propagators

Advances in propagation equipment has led to the UK’s primary systems manufacturer ‘Nutriculture’ to make a readily available and affordable compact range of media systems to be used for propagating cuttings using only aeroponics.

The use of aeroponic propagation means that there is no need for the use of any growing media at all. This is because the main stem of the cutting is clamped within a sponge collar, which is then inserted in to a net pot that is located inside the media system where the stem gets a continuous mist sprayed around it. This is done to promote the idyllic air to water ratio so that cuttings often root within an average of 5 days.

As soon as you can see that roots are beginning to develop on the cutting, you can then transplant them into a pot containing growing media. You can transplant your cuttings into Rockwell cubes and fill the space left over with perlite, vermiculite, coco coir or small clay pebbles. Or it is also viable to use small clay pebbles in the net pot, to position your unrooted cutting and place in the aeroponic propagator. This will mean that the roots will still grow out quickly and the net pot placed straight into a transplant block.


Why wont my cuttings root?

This is a regular question that is asked, and the answer is just this:

It can be caused by many different factors; the most common being that the growing media that is being used is being kept too wet. If you are using Rockwool, after pre-soaking make sure that you shake the cube well to rid all of the excess water within the cube. When you spray your cuttings, be sure that you spray the foliage very lightly and not to spray the cubes and ensure that you never leave water standing in the bottom of the propagator.

Cuttings will take a much longer time to root if they are too big, therefore try and take much smaller cuttings around 3” (7-8cm) and remove the big leaves from them to reduce the leaf surface area.

Always check that your rooting hormone is still in date before using it.

Refrain from using strong nutrients to pre-soak cubes with as this will prevent root formation.

Make sure that the temperature is between 18-24ºC at all times and is kept constant. If temperatures fall more than 4ºC between day and night make sure to change to continuously keeping lights on to maintain a steady temperature.

Make sure that you use a propagator, and that the vents of it are fully closed up until roots appear.

Be patient. The average time for cuttings to root is between 7 and 14 days.

Why are my cuttings wilting?

Wilting cuttings can soon happen after taking the original cutting, however they should come back around. If they continue wilted, then this is usually an indication that the temperatures are much too high. This can be a common problem in the summer months but can soon be cured by reducing the temperature in the propagation area.

Why is the base of the stem on my seedling/cutting turning brown/black and rotting?

Brown/black and rotting stems often happens when the growing media is kept too wet. This means that it has invited fungal diseases that attack the plant, also identified as ‘damping off’ diseases. This can often be problematic in warm and wet propagation conditions.

Indoor Grow Lights

Light is one of the most vital factors to consider when growing plants. It is very straightforward, no light means no development. The general rule is that the more light that your plants have contact with, the quicker they will grow and more they will produce. The benefit of an indoor grow light is that it allows you to grow any plant, anywhere, anytime. However, to get the very finest out of your indoor grow light and growing, it is helpful to be aware of the basic principles of light.


Anyone who has seen a rainbow will recognise that sunlight is made up of different colours. They can be differentiated by their wavelength, which is measured using nanometres or nm.

The human eye is at it’s most sensitive to light around the centre of the spectrum, between 500 and 600nm. Plants use wavelengths between 400 and 700nm useful for turning light into energy, formally known as photosynthesis. This area is referred to as Photosynthetically Active Radiation, commonly known as the abbreviation PAR.

While the human eye discovers light at 555nm – as a result more useful, plants find two separate areas of the spectrum most useful. Those areas being the blue area between 400-460nm and the also the red area between 580-700nm.

(Diagram reprinted with permission from Gavita Holland

Measuring Light

The term ‘lumens’ is the measurement of light intensity and is frequently used to define the output from artificial lights. This is handy for lights to help us see in the dark however becomes particularly poor when measuring horticultural grow lights because lumens are measured according to what the eye is sensitive to. Therefore using lumens is not an accurate representation of the properties of a lamp that are useful to plants.

Light-measuring devices commonly use ‘lux’, which is quite simply the measurement of how many lumens fall on each square metre of surface. So the illumination of 50,000 lux is 50,000 lumens falling on each square metre. Lux measurements are handy for measuring intensity from grow lamps, be used to help determine the accurate height to position the light above the plants or to check for lamp deprivation. However lux is still not a good measurement for determining the quality of light, nor how good it is for growing plants.

Professional growers and light manufacturers have moved ahead of measuring light in lumens and lux to photon counting in the PAR area. Without going into too much detail; A photon is a particle of light. There are two types of photons; A blue photon and a red photon. A blue photon has a short wavelength and does not have as much energy as a red photon, which has a long wavelength. The plant however is only interested in the number of photons, as it does not use the energy in the photon for photosynthesis. A plant needs 8 to 10 photons to bind one molecule of CO2. Therefore a blue 600w light produces less photons than a red 600w light and is also less capable for use in photosynthesis, however more than just red colours in the spectrum is needed to grow a plant healthily.

A quantum meter is a device made to measure photons. The entire amount of photons is known as the photosynthetic photon flux (also identified as PPF) from a lamp can be measured with a quantum meter to give you precise data on the amount of photons coming from your lamp.

If you are interested in the scientific facts; photons are counted in micromoles (µmol). One µmol is 602214150000000000 photons. The unit used for PPF is micromole/second (µmol/s), and a good 600W HPS lamp will emit 1100 µmol/s.

In conclusion, if you have two lights with one of the lights having a higher lumen output, it is not an indication that it is better for growing plants. The most constructive light output data is plant useable light measured in micromoles.

Day Length

The length of time that your plant collects light in a 24-hour instalment is called the ‘photoperiod’ or ‘day length’. Some plants use it as a signal to know when to produce leaves, flowers or fruit. Using this tool, indoor flowers can adjust the photoperiod using timers to control their lights and their plants at the same time. Long day lengths of 16 to 24 hours are generally used for vegetative growth and short cycles of light of 12 hours and are used for flowering or fruiting.

Light and Environment

All lights on the market produce heat as well as they give off light. Therefore when growing indoors, the heat generated by the grow lights needs to be removed using an extractor fan to keep the growing environment for the plants comfortable. If you position the light too close to your plants, the heat from the lamp may possibly burn them. Therefore it is essential to suitably hang your growing lights.

Types of Grow Lights

There are two categories of lights regularly used for growing plants. These are fluorescent and high intensity discharge (HID).

Fluorescent Grow Lights

Fluorescent grow lights are much more suitable for propagation and vegetative growth. They have good colour rendering properties and produce less heat than HID grow lights, which allows them to be positioned closer to your plants to get the most out of their output.

There are two types of fluorescent light used for growing. The first being Compact Fluorescent Lamps (CFL) and T5 lamps. CFL’s are large ‘energy saving’ lamps and have the electronics to alight the lamp at their base. These can be screwed into a reflector or easily hung vertically above the crop. T5’s are the most efficient fluorescent tube light and need separate electronics to ignite the lamps. These electronics are built inside T5 reflectors. Due to the size of the T5 tubes, they generate a very uniform level of light over a larger area in contrast to CFL’s.

Compact Fluorescents are available in 150W and 250W, as well as a propagation lighting system utilising 2 x 55W PL lamps. T5’s are available as 2ft 24W lamps and 4ft 54W lamps. These are available individually (without a reflector) or as an inclusive lighting system with two, four or eight lamps.

Fluorescent lights are great for seedlings and cuttings, as plants at this stage do not need intense light. Both CFL and T5 are low intensity, so they need to be placed close to plants to be successful at promoting growth. If you are using fluorescent lights above propagators, make sure not to place them too close, as this will cause the internal propagator temperature to get too high.

The amount of light emitted from a fluorescent lamp can vary, depending on the lamp colour. Fluorescent lamps are available in a range of colour variations differentiated by the Kelvin colour temperature scale.

The Kelvin scale has become industry standard for differentiating commercial and domestic lighting, however is rarely referred to in horticultural lighting other than for fluorescent lamps.

Fluorescent lamps that have a high Kelvin, are most commonly used for propagation or vegetative growth; these usually come in around 6400K. Lamps with a low Kelvin are used for flowering and usually emit light around 2700K.

A combination of both (1 x 27K for every 3 x 64K) is a good method for vegetative growth, and the reverse (3 x 27K for every 1 x 64K) fruiting or flowering.

Top Tips:

  • Due to their lower light output, fluorescent grow lights should not be used instead of HID lights during the flowering stage. However, they are effective as supplementary lighting when hung between your plants with CFL lamp hangers, or as side lighting with T5’s.
  • All of our fluorescent lights can be plugged into a timer to control the photoperiod. A relay or contactor is unnecessary.

HID Grow Lights

HID (High Intensity Discharge) lighting is the most effective way to transfer electricity into light and is the most common form of horticultural grow light.

HID grow lights are offered in a large choice of wattages; the most common are 250W, 400W, 600W and 10000W – with the 600W being the most popular option. A HID grow light is made up of three parts:

  • The first part is the ballast that contains the necessary electronics to ignite and run the lamp.
  • The next part is the reflector, which holds the lamp firmly in position and reflects light down to the plants.
  • The final part is the lamp itself that can be either a High Pressure Sodium (HPS) or Metal Halide (MH).


A ballast or power pack as it can also be identified as, is at the very heart of a HID lighting system. There are 2 types of ballast available; your average everyday electromagnetic ballast and also the more recent electronic or ‘digital’ ballast. Both which deliver a surge of electricity at a high voltage to ignite the HID lamp. After ignition, the ballast then regulates the electricity being transported to the lamp for safe operation. Electronic ballasts are around 3-4% more efficient than electromagnetic ballasts, as they run much gentler and can have dimming functions to influence the lamp power.


HID reflectors come in a range of different shapes and sizes, however they are all designed to do one job. That job is to reflect as much light as possible down onto your plants. The most effective reflectors are about 95% efficient, meaning that of the 100% light being reflected from the lamp itself, only 95% of it is emitted by direct light from the lamp or reflected light being caught from the reflector. However, even the best reflectors on the market will only have roughly a 5% loss. A reflector should help to create a standardised spread of light whilst also avoiding, commonly known as ‘hot spots’ of intense light. Some reflectors are sealed using a glass plate or tube and are air-cooled using an extractor fan to reduce any further heat from being released from the lamp and keeping grow room temperatures down.


Metal Halide lights produce a lot of light in the blue spectrum. This is because the blue colour of the light promotes leafy green plant growth and keeps your plants short and compact. Metal Halide lamps produce a broad spectrum of light and also a small amount of UV that can help to improve the quality of your produce. However, Metal Halide lights are not as capable as High Pressure Sodium lights, producing roughly 30-40% less micromoles.

High Pressure Sodium lamps give off mainly orange-red light. This type of light is best for fruiting and flowering plants, however it can also be used for vegetative plants with good results. High Pressure Sodium lamps are the most effective grow light currently on offer and produce the very best yields. Standard High Pressure Sodium lamps are slightly ineffective in the blue spectrum. In addition this, you can use fluorescent lights or use a ratio of three High Pressure Sodium lamps to one Metal Halide lamp in the flowering stage. Some High Pressure Sodium lamps are also known as ‘Dual Spectrum’ or also meaning that they have an improved output in the blue spectrum. Dual Spectrum lamps are also touted as being an all-in-one vegetable and flower lamp, however their spectrum is still much more suited to flowering plants. Best results will be accomplished using a Metal Halide lamp for vegetative growth and High Pressure Sodium lamp for flowering.

Top Tips:

  • If you want to supplement your High Pressure Sodium lamp with extra CFL’s, use the 6400K ‘Cool White’ lamp as these will provide the blue light that your High Pressure Sodium lamp is missing.
  • Switching from a High Pressure Sodium lamp to a Metal Halide lamp in the last 1-2 weeks of the plants life cycle can significantly develop the quality of your produce by enhancing essential oil production.

Relays and Contactors

When a ballast starts up, it draws a great amount of electricity for a split second so that it ignites the lamp. This spike of high voltage is enough to burn out a standard plug-in timer, so to automatically turn on and off a HID light, therefore you need to use a relay or a contactor. These devices use the timer as a signal, and can draw the power through a 13-amp plug, rather than through the timer. One 13-amp relay can switch 1 x 1000W, 3 x 600W, or 4 x 400W HID lighting systems. Contactors are more heavy duty than relays and are largely used for indoor gardens with 4 or more 600W lights.

Other Types of Grow Lights

New technologies currently trying to improve horticultural lighting are Light Emitting Diodes (LED’s) and Light Emitting Plasma (LEP).

Unfortunately, there has been a flood of cheap LED’s that have been launched in the hydroponics market over the years that have all over-promised and under-delivered. Many companies claim that their LED’s are more efficient than High Pressure Sodium lights, however currently there are still no LED units that can produce yields that are as good as.

On the other hand, LED’s are a very promising area for supplementing light to change or ‘steer’ the plants growth. The benefit of LED’s is that they can be tuned to a specific wavelength to activate a certain response or improve a particular growing stage.

The regular LED grow lights on the market that have a combination of blue and red LED’s state that they are tuned to match the two PAR peaks and drive targeted photosynthesis, yet they are missing all of the other wavelengths (colours) that plants also need. Interestingly, the most capable LED’s to come to market during 2012 are the ‘full spectrum’ LED’s that are designed to produce light across the whole PAR spectrum. However, the diode wattage and unit cost still means that LED’s are not able to replace High Pressure Sodium lamps.


Light that is emitting plasma has come to market for the purpose of ‘solar simulation’. They produce a very broad spectrum of light, including UV’s, which are close to natural sunlight.

LEP units can be used on their own for vegetative growth, but are lacking in the red spectrum to produce good yield of fruits or flowers. They are highly recommended for supplementary light, particularly for adding UV light to improve quality that is missing from most High Pressure Sodium lamp. The market leaders in LEP technology is Gavita Holland and we are sure that there will be some great further developments in LEP lighting systems over the coming years.

HID Lighting - Helpful Tips

What lighting should I use in my grow room?

Your choice of grow light should be decided upon by the size of your growing area. Each type of HID grow light is suitable for a specified area. For guidelines on the type and number of lights you can put in your growing are see below.

Lamp Area Coverage:

  • 250 Watt = 0.25m2 - 0.5m2
  • 400 Watt = 0.5m2 - 1m2
  • 600 Watt = 1m2 - 1.5m2
  • 1000 Watt = 1.5m2 - 2m2

Hanging Height

Due to the heat that is produced from HID lights, you should hang your lighting system in accordance to size. The following is the suggested distance between the lamp and the plant canopy.

  • 250W = 30 - 40cm
  • 400W = 40 - 60cm
  • 600W = 50 - 70cm
  • 1000W = 75 - 100cm

Top Tips:

  • Metal Halide lamps release more heat than High Pressure Sodium lamps, therefore mounting heights will need to be adjusted depending on your chosen lamp.
  • Use the back of your hand as a guide; if it is too hot for your hand to cope with, then it is definitely too hot for your plants.

How Much Will it Cost?

To get the correct operating cost per hour for light, take the lights combined wattage and divide it by 1000 to get the kilowatts used. Then multiply that number by the amount that your electric company charges per kilowatts an hour (usually found at the top of your electricity bill).

HID lights will use a little more than the stated wattage; a typical 600W system will use 640-660W. But to find out the precise usage you can purchase a plug in power meter for less than £10 and these will give you a digital reading of the actual power consumption.

Example: A grower with 1 x 600W HPS lighting systems finds his power consumption is 655W per light.

  • (power consumption wattage  / 1000) x electricity cost per kilowatt an hour = Operating cost per hour.
  • 655 / 1000 = 0.655
  • Electricity cost = 12.5p per kWh
  • 0.655 x 12.5 = 8.2p

This grower example shown above is paying 8.2p for every hour his 600W light is on. That equates to £1.48 per day for vegetative growth (18 hours) and £0.98p per day for flowering growth (12 hours).

How do you provide a more uniform level of lighting?

If you find that your reflector is not throwing enough light out to the edges of your room, or is creating hot spots then we recommend that you look at investing in a better reflector to improve uniformity. If you are using a high wattage HID light such as a 1000W then you can use an overhead moveable track, also recognised as a light mover, to move your light back and forth to create more uniform growth. These systems are highly worth investing in for high value hydroponic crops because a more uniform lighting pattern can help optimise yield.


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