Preventing Tip Burn: Hydroponic Lettuce (Indoor LED Grow Light) PPFD Experiment

Growing lettuce indoors under artificial lights may results in deformity of the leaves. Brown necrotic tissue at the leaf edge is known as tip burn. What causes tip burn? Whether you're a home gardener of a commercial greenhouse grower, this is an important issue to address.

Watch PART 2 of this series covering Light Duration:

OUTER TIP BURN:
Causes of outer tip burn are not as clear as inner tip burn. Outer tip burn seems to relate to insufficient water or high salt levels. Low humidity and excessive air flow can contribute to this problem.

INNER TIP BURN:
Causes are easier to explain and relate to poor calcium supply in young, developing leaves. But often, it's not because the nutrient solution lacks calcium. Instead, the cause is linked to insufficient evapotranspiration.

As plants transpire, they pull nutrients up through their tissues. Under high light levels, growth rate is boosted. But if the plants can't transpire fast enough, they can't adequately supply their increasing demand for calcium.

TEST BED - PRODUCT LINKS (# CommissionsEarned):

My PPFD Meter (Apogee Instruments):

Test 1: In my initial test, I used a 15w Red/Blue LED from SANSI. The spectral composition of the lights caused a shade avoidance response. This test was ultimately ruined due to unexpected elongation of the lettuce plants.

Test 2: In this 2nd test, I switched to full spectrum white LEDs (SANSI, 15w). The plant growth was dramatically different, resulting in a successful experiment.

Light 1: 9.5" Distance - 575 PPFD @ 16hr = 33 DLI
Light 2: 13.5" Distance - 278 PPFD @ 16hr = 16 DLI
Light 3: 22" Distance - 175 PPFD @ 16hr = 10 DLI

Solution: 6.2pH 1720 EC
Experiment Day 1: 09/18/17
Harvest: 10/16/17

Fresh Weight (tops only):
575 PPFD = 80g
278 PPFD = 55g
175 PPFD = 9g

The lettuce grown under 278 PPFD white light grew very well. It exhibited fast, healthy growth without any deformities from inner tip burn.

SOLUTIONS TO INNER TIP BURN:
1) Increase Air Flow - A fan can be used to increase air flow, resulting in higher plant transpiration rates. This, in turn, results in more calcium being pulled through the plants roots and into the leaves.

2) Decrease Light Intensity - Reducing light intensity reduces the rate of growth. This, in turn, reduces calcium requirements, allowing leaves to develop without defect.

Lettuce is considered a low light plant. Typical maximum DLI values can be from 15 to 17 DLI. Ideal PPFD is from 250 to 300, with a maximum of 400 PPFD. This is just a general guide and can vary with cultivar and environmental factors.

HORTICULTURE REFERENCES:

Hydroponic Lettuce Handbook:
© Cornell University CEA Program

e-GRO Alert:
Volume 4, Number 31 April 2015

#Hydroponics #GrowLights #GrowingTips #IndoorGrow #Lettuce #UrbanGardening #knowledge

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[Albopepper]

*Watch PART 2* of this series covering Light Duration:

_Check out my other reviews:_

This UPS power station can backup a grow light!


_Learn more about artificial lighting and plant growth:_

[mrs]

Finally! One of the first gardening youtubers I've ever seen to reference an academic research paper.

[KENNETHFRANCISRODRIGUES]

This is one of the best channels for indoor gardening. I was impressed by the technical data on lighting. Saved me a lot of money as I do not have to redo the tests. This practical research of high academic value!

[oAvalono]

I never knew this was so complicated, but I love learning about it anyway

[elmerkilred]

I just started using indoor lights (this year) for my starts because the price-point came down for LED lamps, and Sansi has the E-26 socket bulb, so I don't have to invest money into some sort of pricey fixture. The Sansi 15w Full spectrum lights are pretty nice to use... Thank you for reviewing this brand, it's one of the reasons I purchased them.

One of the things that I have found that using these lights are that a lot of my cactus and succulent plants that are in the proximity of the lights are all growing/turning/bending toward that light source. Since I grow on old recycled plate glass shelves, the light that penetrates the shelf onto the cactus and succulents below are actually stimulating growth in the plants. (about a distance of 42" to 48"). This is pretty impressive because the shelves are 1/2" plate glass. There is a refraction element going on that probably dims down a UV spectrum/or IR spectrum.

Anyway, thank you again for your review.

[randomjohn]

This is the video that keeps on giving. Just had my first case of inner tip burn with some Baby Butterhead lettuce. I think I've had my light source too close on all of my lettuce, I'm going to bump up the height a few inches. I just got a 30W full spectrum Sansi for my dwarf determinate tomato plant, they certainly pump out some serious light.

[Familytripyoutube]

Great video!! The art of a good teacher: speaking simple about something not so simple. ;-)

[hye]

Your speaking sound is easy to understand. English is not my first language.. but your channel is so helpful to me. thank you so much.

[avguru]

I'm a NEWBIE an I have setup a small grow table 5' x 3'. My lettuce has tip burn and a different kind grew super tall. now I can start figuring out which cause and effect i'm having. THANK

[waynecribbs]

Great video! I enjoy your plant experiments and dedication to finding the best combination of environmental factors. Keep up the good work!

[inkpen]

How thoughtful to share your expirement. Saving us all the time and wonder. I truly appreciate this work 👍

[Mrosh]

I use 12 on and 12 off. I use two twenty watt colored LEDs AND one 50 watt white CFL at 10 inches with a computer fan for circulation and I am getting leaf burn! Great info! Thank you,

[jeffsullivan]

I have a lettuce experiment of my own going on right now. I have 5 week old lettuce from seed growing in 2 different systems, 1 aquaponic, the other hydroponic w/ air stones. I've attempted to keep everything the same (except nutrients of course) using regular HO T-5 fixtures at the same height. The hydroponic lettuce shows inner and outer tip burn while the aquaponic lettuce seems fine and actually a little better growth. Only other difference is water temperature and occasional ph fluctuation in the aquaponics. Just wanted to add this info to your findings. I raised the lights.

[robertovelazquez]

Thanks for this video, very useful. I love that you always try to explain the concepts with experiments.

[Pamlg]

thank you for this. I have not been able to grow lettuce without inner tip burn. I thought I needed to keep them closer to the lights. Most videos say it'd due to calcium deficiency but don't explain it the way you have in this video as it relates to the lights. I'll come back and update in a couple month once the next batch is ready...with no tip burn I hope 🤞

[Topsrite]

An oldie, but truly good information, thanks

[CVoyage]

Very good video AP. Enjoyed the testing and results!

[NiMareQ]

Incredible this is already 5 years old. How did I stumble upon this only now?

[JebGardener]

Really good info. I think temp is the bigger cause compared to light. I'm trying to think how to properly isolate heat though. Maybe a glass separator or something?

[NiMareQ]

At 6:50 you say you switched to full spectrum white. What color temperature would be optimal?
Would e.g. 3800K have more "red" light in it than 5600K?