LED Propagation

• By Hydro Harvest
• 17 February 2025

Propagation LEDs are just the ticket for bringing on seeds, seedlings, cuttings, and young plants. They are inexpensive to buy and run, take up minimal space, and can be adjusted to dose out just the right amount of light to your valuable infant crop.

Here we look at your aims and needs when propagating with LEDs, how to set up and use your kit, and consider exactly what it can do for you.

Aim Of the Game

When propagating, your lighting should be precisely balanced, uniform, and with a focus on blues and cool whites. Set up correctly, propagation LEDs can provide you with all these things.

A side note – you will of course be needing a propagator, your choice of rooting media, and a heat source. Warmth and an enclosed environment will combine with the light supplied by your LEDs to create humidity. And atmospheric moisture is a huge deal for young plants. Think 90% humidity as a minimum for early stages. Efficient, space-saving options for introducing warmth include heat mats or tube heaters.

Setting Up – Maximising Your Space

Because of the task-specific size of propagation LEDs you can easily use them to set up a compact, tidy, productive propagation area. Doing so also saves you having to needlessly fire up your principal growing space to propagate in.

By not propagating in your principal growing space, you can maximise productivity there with other projects. Or simply keep your main space on standby, with your big appliances switched off and your overheads minimised as a result. With your focus fully on your propagation area let’s look at exactly how you use those lovely little LEDs.

Setting Up – Striking A Balance

Low-intensity output is key during propagation. Too much light and you’ll upset your humidity levels, stress vulnerable plants, and risk drying them out. However, you do need to ensure that there is enough light to stimulate sufficient rooting to sustain onward growth. This is the ‘precise balance’ described above.

Because propagation LEDs require almost no headroom at all they immediately help you achieve the precise balance required. You can hang them at exactly the height you need to cast the right amount of light at any given time in development.

Setting Up – How High?

Most grow lights come with information as to what appropriate hanging heights are. But failing that you can use a PAR meter in conjunction with the following guidelines:

Early propagation: 150-200 µmol/m²/s-1

Roots visible: 200-400 µmol/m²/s-1

Roots filling out: 500-800 µmol/m²/s-1

Setting Up – Uniformity

With LEDs inherent level of height adjustability, it’s also easy to achieve uniformity. Getting uniform coverage minimises the chance of hot or cold spots and helps you maximise strike rates. The dimmers on LEDs make your output even easier to manage.

Setting Up – Spectral Output

The joy of setting up LED propagation lights is that all the spectral output you require comes built in. As LED fixtures are made up of many small individual diodes manufacturers can create detailed, sophisticated lighting profiles that help you propagate brilliantly.

You’ll find that your propagation LEDs are oriented towards blues and cool whites. These colours stimulate the right root and plant structure for robust onward growth. Such tones also play a part in developing plant processes such as chlorophyll production. Some reds may be included in order to help early stem growth, but they’ll almost certainly be in the minority.

Switching On

If you maintain low light intensity you can switch on your LEDs right from the beginning of your plant’s life. That includes seed germination which is actively stimulated by the presence of light.

Operation

Although very young plants can’t deal with intense lighting, they do thrive on longer photoperiods than mature plants. This means you can (and should) leave propagation LEDs running for 18-20 hours a day during early stages.

Once your plants have rooted dial that down to 12 hours a day or thereabouts to prevent early flowering. Because LEDs are highly efficient and emit little heat, you’re free to run lighting patterns like this affordably and safely.

Monitoring

It’s essential that you closely observe plant development during propagation. You need to ensure that your latest prospective crop is getting exactly the right conditions to thrive. Knowing where they are with rooting, leaf, and stem development in relation to necessary PAR levels is also an easy way to avoid deficiencies or excesses.

If roots aren’t developing as hoped, then it is possible that your plants are not getting enough light. Curling, yellowing, or otherwise discoloured leaves are a possible sign of excessively intense lighting. It should be stressed that you should check other inputs and conditions such as temperature, humidity, irrigation, and nutrients (if using) as well as lighting.

The Alternatives

It’s worth discussing the alternatives to LED propagation lighting if only to ‘eliminate them from our enquiries.’

The Alternatives – Metal Halide

Metal Halide (MH) lighting is appallingly inefficient when it comes to propagation. Not only that, but the heat that it gives off requires careful management – both in terms of your young plants and in terms of balancing the climate in your growing space.

The units commonly used to run MH lights are quite bulky and often need an experienced hand to calibrate – costing you growing space and time respectively. All in all, Metal Halide propagation currently is rather like using a sledgehammer to crack a nut.

There may be die-hard MH users out there who insist the blues from such lights are just that bit better. But the work and cost required to even test such claims really isn’t worth it.

The Alternatives – Fluorescents

Fluorescent or CF (Compact Fluorescent) Lighting in the shape of bulbs or tubes is a more efficient alternative to MH. It’s user-friendly, inexpensive, space saving, and has roughly the right lighting profile. However, when you put Fluorescents up against LED they pale in comparison on every count.

Fluorescents are also becoming vanishingly rare. The metals they require are being banned on environmental grounds, so the bulbs are difficult to get hold of. Happily, for owners of fluorescent fixtures you can now get LEDs that directly replace the old bulbs. Yet more proof that LED is taking over propagation.

Get Started

It’s exciting to think just how easily you can get going with LED propagation. The performance, price, efficiency, space-maximising compactness, and adjustability make such lighting a truly brilliant choice for you and your plants. Enough thinking, time to get started.