If your lettuce or other leafy green plants are developing brown or black edges, they are likely suffering the effects of tip-burn.
Why are my lettuce leaves turning brown?
Update: This article has some good information about identifying, and treating tip burn. The issue I describe below was actually a result of a calcium deficiency, that I was able to correct by using a liquid calcium/magnesium supplement called CALiMAGic. It works so well that I use it full-time as a supplement in all my hydroponic systems. If you’re experiencing issues with “tip-burn” or blossom end rot on fruiting plants like tomatoes, give it a try. It works fast and just might save your tomato crop!
To be completely up-front, your lettuce leaves are turning brown or black at the tips because they are dying. Don’t freak out! The tips are dying.
Tip-burn, as the name denotes, is easy to identify. The tips of otherwise healthy leaves begin to look a burnt brownish or even black color. In the early stages of plant development tip burn may prevent a loose leaf lettuce plant from “opening up” as it normally would. Instead, the center of the plant will develop in a way similar to a head lettuce.
While the term tip burn sounds like something dry and burnt, the leaves will actually be wet and may develop mold spores due to necrosis. While this may look really bad, it doesn’t always mean complete disaster for your plant. Keep reading to find out what I did to save my badly tip burned plants!
What is Tip-Burn?
Hydroponic lettuce, and other similar leafy greens, are successiptable to a physiological disorder commonly called “tip-burn”. The disorder is related to a calcium deficiency at the tip of the leaves, but it is rarely actually caused by a lack of calcium in the nutrient solution.
You can read a bunch of scientific articles related to the topic, but they won’t give you much actionable advice. The aim of this article is to help you identify, and correct the conditions that are causing tip-burn.
Common Causes of Tip-Burn
Common causes of tip burn are nutrient deficiency, over fertilization, limited air movement, humid conditions, and too much light.
To minimize the risk of nutrient related tip-burn, make sure the electrical conductivity of your nutrient solution is at a healthy level for your plant type. Also, use appropriate nutrients for the plant you’re growing.
Too much light is the most common cause of tip-burn. If you think your plants are getting too much light, there are 2 or 3 changes you can make depending on your light source.
Raise the Light
If your plants are tip burned, increase the height of your light by 2-3”.
Reduce the Light Interval
Reduce the time the light stays on by 1 hour.
Lower the Light Intensity
If your light has adjustable intensity, reduce the intensity by 10-20%.
Increase Air Movement
Adding fans can help improve the transpiration process by providing airflow over the inner leaves of plants.
Normally raising the light higher above the plants will eliminate tip burn, but this will give you multiple options if you’re unable to increase the height of your light.
Make adjustments, and keep an eye on your plants over the next several days. If their health is improving further adjustments are probably not needed.
Is Tip Burn Permanent?
Unfortunately, tip-burn is permanent.
Don’t lose hope though! While tip burn is permanent on affected leaves, it doesn’t mean your plant is totally trashed. Read below to learn what I did to salvage my tip-burned lettuce plants recently.
How to Save a Tip-Burned Lettuce Plant
Recently I was experimenting with a new setup for my main ebb & flow system. Mildew is a constant battle with an open top flood tray design. To reduce mildew, I covered my flood trays with aluminum foil. Something I didn’t account for was the additional light that would be reflected onto my plants.
About 20 days into their growth cycle, all but one lettuce plant had developed severe tip burn, to the point where the loose leaf lettuce wouldn’t open up and looked like a malformed head lettuce. I thought my crop of 12 butter lettuce plants was wrecked.
Thinking I didn’t have anything to lose, I began pulling off the outer leaves of the plants. To my surprise, the inner leaves were in pristine shape. I removed enough of the malformed outer leaves to allow the plant to open up. Additionally, I reduced the intensity of my grow light from 90% to 50% as well as reducing my light timer from 12 hours to 11 hours.
After a few days the inner leaves began growing wonderfully. While the initial damage was done, it didn’t permanently destroy the entire plant. This is something to keep in mind when you run into problems in your hydroponic garden. Experimentation is a big part of the fun!
Update 10 days later:
There is no new evidence of tip-burn.
The reduction from 90% to 50% intensity was a little extreme, which is evidenced by reduced production and the tilting of the lettuce plants toward the light source. I have since adjusted the intensity of my grow light up to 70%.
During this time I have also introduced two seedling lettuce plants into the grow box. This will help determine if the new light intensity and timing is more appropriate for preventing tip burn. This section will be updated again once I have time to observe the plant behavior at the new setting.
Update Several Months Later:
I discovered the actual cause of the issue was a calcium deficiency. I ordered CALiMAGic from General Hydroponics, and while it didn’t correct affected leaves it did prevent any further issues. CALiMAGic is a calcium and magnesium supplement that can be added to nutrient solution. I now use the supplement in all my nutrient reservoirs, and am completely free of “tip burn” even at higher light intensities.