Edges of lettuce leaves brownish

[Xandi]

Dear all,
it is now day 37 since I seeded my grow cube with tom thumb lettuce seeds - the plant have been growing well, but the leaves nearer to the ground (the first ones that were born, the larger ones) seem to suffer from something.

Basically, the edge is turning brown. At the start I thought it was lack of air change, since it started when I went away for a week and I did not open the growhouse for a while. I read that this can be a problem since transpiration cannot occur at the necessary rate, and the plant develop a brownish/yellowish edge.

So I installed a couple of small fans to aerate. Now it seems that is diminishing, but still there.
Can it be something else?

[applestar]

What kind of nutrients are you using? At a guess, you would need to change up the mix.

I’m not familiar with hydro culture, but I would suspect micro nutrient/mineral deficiency. Also maybe pH? (I only say that because my soil tends on the acid side and I have to always add more lime than I think I need) ... I always use Dolomitic lime — in the soil culture — for added minerals/micro nutrients like magnesium, boron, silica, etc.

...it is also normal for the youngest, smallest leaves to become old and die, so at the very simplest, be sure to clip off any damaged leaves so they don’t invite disease and pests.

[Xandi]

Thanks applestar.

I'm using nutrients specifically for lettuce, diluted in 60l of water.
I'm monitoring pH as well, has always been between 5.5 and 6.5 as suggested by some books.

So it is normal for the very first leaves to die? Should I clip them before they reach that stage?

Another question: I'm growing to thumb lettuce - I can understand when it is time to pick it up?

Thanks again

[applestar]

Is there any instructions about changing as the lettuce becomes ready to head up. I would think the plants requirements would change — Tom Thumb if I remember correctly is a miniature heading lettuce that makes tennis ball sized head, right?

As with all/ANY lettuce, it’s also perfectly OK to harvest outer leaves when they seem big enough to eat, though doing this will affect the appearance of it and it may not form perfect heads.

[applestar]

Also, it could be an early indication of fungal issues so The fan you set up should definitely help — it will also help the plants grow sturdier. Clipping the small youngest leaves would “pick up their skirts” as it were so probably a good idea, too?

Start thinking about what kind of fungal preventive you are willing to use. I don’t know what is the best for hydro set up, and I only use organic remedies like chamomile tea, willow tea, milk, whey, or actively aerated compost tea ... most recently cultured bokashi leacheate and green juice ..... If pressed, I might go with chemical remedies like — hydrogen peroxide and potassium/sodium bicarbonate, borax, Epsom salts.....

[imafan26]

We have gotten that.
In the summer heat, there is more tipburn as the lettuce actually dries out too fast in the heat.
Thrips or aphids are the biggest issues for browning leaves. It starts on the older leaves first. Thrips can cause stippling or white spots on the lettuce leaves and both aphids and thrips can cause the edges of the leaves to curl and look withered from their sucking of the plant juices. If you cut the lettuce and look between the leaves you can see them.
Fungal rots and TSWV are also problems usually transmitted by thrips.
Remove the older leaves. Check your water levels especially if this is not a raft system. The roots should be white. If they are browning, they are not doing well and you may have a fungal or bacterial issue. It would be better to clean out and resterilize your system.

[Xandi]

Thanks Imafan26.

I checked between the leaves (as suggested by applestar, I harvested the outer leaves), and I do not seem to see any aphids/triphs. Looking in internet, they should be visible with a naked eye, right?
Also the roots seem to be quite white - no brown/yellowish.

Following the link https://landresources.montana.edu/soilfe ... Mobile.png, it looks like potassium deficiency, even if visually is quite similar to Calcium deficiency. Before I was thinking Potassium, since is a mobile nutrient, therefore should start from the lower/older leaves, but then I started to see some little tip burn also in the youngest one, and I think it is a calcium deficiency, but not due to the lack of calcium itself, but to the closed and little volume, and the lack of ventilation.

Now I have a little fan, and let's see if the plants "transpire" better.

Kind Regards

Xandi

[imafan26]

https://www.e-gro.org/pdf/2015_431.pdf

I thought this might be helpful to find out if there are any environmental factors that may be contributing to the problem.
We would see tip burn in extreme heat conditions when the temperature was 90 degrees and humidity was relatively low for us 69%. During the summer months June, July, and August. The lettuce looks like small cabbages. We did try a misting system on one section of beds and it seemed to help. However, it also helps to have a new bed that is not full of roots, soil, and fills and drains well. The tanks also had to be drained about every 2 weeks to keep the water quality for the fish and the lettuce from deteriorating. Higher evaporation in summer from the beds and the tanks meant the tanks had to be topped off more and that made it hard to maintain an EC that did not fluctuate as much.