What is the best grow light setup for seedlings and clones?
Seedlings and clones are young plants which have yet to form a good root system. You should not use too much light as you may over stress them. They may struggle to take up enough water and nutrients in those early stages. For this reason you should choose a seedling grow light designed for this situation.
After about two weeks when the roots have fully developed you can increase the light intensity rapidly. This will maximise the growth rate of your young plants and shorten the vegetative stage.
There are no particular light color or spectrum requirements, any general purpose white grow light spectrum will do.
What type of grow light is best for seedlings?
LED seedling grow lights are now the most efficient and cheap solution for seedling lights. They are available in strip or LED bar form which is perfect seedling trays and shelves.
White LED grow lights provide a high quality light that allows good visual inspection of the plants. LED grow lights do not radiate heat which can stress very young plants.
Most LED grow lights are dimmable. It is ideal to be able to dim a seedling grow light in order to be able to control the light intensity from a low level for very young seedlings to more mature plants.
Fluorescent seedling lights are not a good solution
Indoor growers used fluorescent grow lights in the past because of their low wattage. However LED seedling grow lights are now 3 x times more efficient and cheaper to buy & to run. Fluorescents also contained mercury and required regular replacement. Fluorescent lights are very bad for the environment and are being phased out in most countries.
HID seedling lights will heat stress your plants
HID lights such as high pressure sodium and metal halide bulbs are reasonably efficient. However HID bulbs emit a lot of radiated heat which will heat the delicate upper leaves of young seedlings and stress them.
How much light do I need for my seedlings?
For the first 2 weeks we recommend a low PAR intensity for Seedlings and clones until the roots develop. Once a root system has developed you can increase the PAR intensity rapidly over the next few weeks.
High light intensity will result in hight growth rates. If the plants grow quicker in the vegetative cycle you will shorten the time they get big enough to switch to the flower cycle.
|
Seedling/Clone Growth stage |
PAR intensity (µmols/m²/sec) |
Watts per ft² | Watts per m² |
| 1 - 2 weeks | 150 - 250 | 7 - 11 | 65 - 100 |
| 2 to 4 weeks | 250 - 400 | 11 - 20 | 100 - 170 |
| 4 weeks and older | 400 - 1,000 | 20 - 45 | 200 - 420 |
Reduce your grow cycle time using a seedling light
A lot of growers have one grow tent. The same tent is used to grow plants from young seedlings through the vegetative and flowering cycle to harvest.
The chart below shows you can reduce the time to harvest in your grow room by the use of a main tent (green bar) and a seedling or clone tent (blue bar).
Grow seedlings close together and pot them up
Growing seedlings in small pots, plugs or trays will maximise the use of light from your LED seedling grow lights. This is a concept called 'photon capture'. Seedlings has a small leaf surface area. The more densely packed the seedlings are the less light photons are wasted.
Once the roots of the seedlings or clones reach the edges of the plug, pot or tray they should be transferred to a larger pot that you will use up to flowering. You will see the white tips of roots poking out of the holes at the bottom of the pot or plug. This will usually take 3 or 4 weeks in a small pot.
Summary of benefits of a seedling grow light
- Increase your harvests per year by 1/3
- Precise control of light intensity for new and delicate seedlings
Top tips for choosing a seedling grow light
- LED grow lights are the most efficient options
- Target PAR intensity of 150 to 250 µmols/m²/sec
- Any white LED spectrum will work
