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How To Grow Weed With LED Grow Lights - 3 Key Differences From HID Are Hampering Your Grow

How To Grow Weed With LED Grow Lights - 3 Key Differences From HID Are Hampering Your Grow

How to grow weed with LED grow lights

"LED lights suck!"

"LEDs are the greatest thing ever! Your (sic) an idiot!"

And on and on and on.... I'll spare you the rest of the conversation.

If you've spent any time on a growing forum, you'll know how it goes anyway.

There's a reason for the vastly different opinions on LED grow lights.

Manufacturers have made a lot of claims and those growing with LED lights for the first time have seen those lights fall short of the claims.

Yes, many of the claims made, especially those from low-end manufacturers, are highly exaggerated.

But claims from reputable manufacturers are generally backed by data from actual grows.

Why then are home growers not seeing the same results?

It's simple.

Growing marijuana with LED grow lights is different.

The techniques that worked well with HID lights will NOT work as well with LEDs.

New growers see lower yields as a result and quickly denounce LEDs as worthless. But if you make adjustments and try again, you'll see huge improvements.

Quality LED plant lights DO deliver on the promises made. IF you make the necessary adjustments.

Here are the main adjustments you'll need to make when growing with LED grow lights:


Growing Cannabis With LEDs: What's Different

1. Keep Your Canopy Flat And Even

You want your LED lights to hang 2 to 3 feet from your plants during the vegetative cycle. Lower it to 15 inches to 2 feet for flowering.

It is vital that all your plants get an even dose of light.

Since LED lighting is more directional and also more prone to shading, you need to have an even canopy.

Your plants need to be the same height.

Sea of Green (SOG - tutorial here) or Screen of Green (SCROG - tutorial here) techniques are especially effective with LED grow lights, since they result in an even canopy height.

If not using SOG or SCROG techniques, you'll need to top and prune your plants to minimize shading and to achieve the proper light exposure across your entire garden.

If done correctly, you can get a flowering depth of 12 to 16 inches below the canopy.

Any flowers below this level should be pruned by the end of week two of the flowering cycle.

You don't want your plants to waste energy on these flowers. That energy is better spent on flowers higher up the plant that can get the proper amount of light.

Remove large fan leaves above your 12 to 16 inch flowering zone, especially those leaves shading your lower flower sites.

Don't remove them all at once, though. Do it gradually.

By the time you get to the fourth week of the flowering cycle, all the large fan leaves should be gone.

The canopy should be as even as possible. The top should be 15 to 24 inches from the light.

And all your flowering sites should be directly exposed to the light.


2. Increase Grow Room Temperature

The optimal temperature for most plants is 78° Fahrenheit, when growing in sunlight and at atmospheric CO2 levels.

Sunlight and HPS bulbs both give off a lot of infrared light, which increases the temperature of the leaves.

Since LED light does not contain this infrared light, you need to make up for the difference by increasing the room temperature.

The correct temperature is unique to every grow environment. It will take a few grows to figure out the correct balance.

For your first grow, start with a temperature of 83°F to 85° F. You can increase it gradually on successive grows.

If you use supplemental CO2, you can run higher temperatures, but remember that root zone temperatures can not go above 75° F.

Higher daytime temps will have to be balanced by lower nighttime temps. If the roots get too hot, they will not be able to absorb enough oxygen.

You could also use cooler nutrient tank temperatures to help maintain the root zone temperatures, but make sure the nutrient temperatures are never below 60° F at the time of watering.


3. Use Fewer Nutrients

With higher room temperatures, water evaporation from pots or growing media increases.

This results in higher nutrient concentrations in the media and can lead to toxic levels in the root zone. This is especially true with highly aerated pots (i.e. fabric) with soilless media.

To compensate, you'll want to reduce nutrient concentrations by around 25-30%.

You could also balance the root zone nutrient levels by watering with plain water 1 out of every 2-3 watering cycles.

A higher relative humidity (RH) level will also reduce the evaporation problem.

Optimum RH levels are around 50% (60% max), but this depends on your strain and its mildew tolerance.

During the last 2-3 weeks of the flower cycle, you'll want to keep RH below 40% to prevent molds that develop in the flowering structures.


I realize that was lot of info, so I'll summarize the most important points:

  1. Keep an even canopy height and make sure all flowering sites are directly exposed to the light
  2. Keep daytime room temperatures at 83° to 85° F
  3. Reduce nutrient concentration by 25 to 30%


Take care of these 3 things when growing cannabis with LED grow lights and you'll see drastically better results than most do after switching from HID.

Take detailed notes of everything you do, so you can figure out what works and what needs improving for subsequent grows.

Continue fine-tuning your methods and after a few grow cycles, you'll be getting the same results as the test growers.

Good luck!

P.S. If you're not sure which LED grow light is best for you, check out our groundbreaking PoCoCo Method for ensuring you get the exact light you need at the right price.

P.S.S. If this article has helped you at all, please share it on Facebook or Twitter to help spread the word. We definitely appreciate it!


For new growers who don't have previous experience with HID:

If you're sick of wasting time searching online for quality info on how to grow weed (LED or HID), I highly recommend Growing Elite Marijuana by Ryan Riley.

The sales page is annoying and some of the bonuses aren't all that useful, but the book itself is the best guide I've seen on growing.

It's huge (839 pages), but includes absolutely everything you'll ever need to know. And luckily, it's laid out so you can easily find the parts you need. Trust me, you don't want to read the whole thing at once—way too much info!

The quick-start guide is especially useful.

And yes, I know you can find most of the info online for free. If you have the time to do that, this isn't for you. A guide like this is for busy people who can't afford to waste time searching.

Check it out here (again, sorry about the crappy sales page).

It comes with a 30-day money-back guarantee, too.

If you don't like it, just send Ryan an email and get your money back (I'll be honest, I bought it because I was looking for a good guide to recommend and was fully planning on returning it for a refund, but I was so impressed, I ended up keeping it; and now I recommend it to everyone).

Previous article Beginning Pot Grower? Don't Make These 11 Common Mistakes!
Next article The Ideal Marijuana Grow Light Setup


Ron Beaulieu - February 13, 2023

So now fluorescent lights? Wait no leds now deliver the perfect spectrum and another tip to max out your grows is mix clay pebbles in your medium for better drainage and keep your fabric pots off the tent floor. U will use less nutrients and use an enzyme if it looks like plant leaves are drying or burning it most likely due to lower temperatures that the root ball is is being attacked by mildew molds or or pests. But ive gotten good plants using leds more and more potent at the end but use less til mid flower then pour on the bud fatteners to ensure a lush harvest oh and flush more to. Ive been using leds for almost 10 years they DO work better on potentcy. That i know they have paid for themselves over and over again.

Henry - August 3, 2016

@Muddy Little Farm
Thank you for leaving a comment! And I agree: LEDs are now a perfectly viable alternative to HID and it won’t be long before they are clearly superior.

Muddy Little Farm - August 3, 2016

Nice job, thank you for publishing this. Simple & to the point. LED’s aren’t the future of growing anymore.

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