Purple undersides of tomato leaves

Greatgardens
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Purple undersides of tomato leaves

#1

Post: # 570Unread post Greatgardens
Fri Dec 13, 2019 7:14 am

I've started several test seedlings, and they now have 2 good-sized sets of true leaves. The largest leaves are taking on a light purple hue visible only from the bottom of the leaves (looking up toward my "daylight" 6K grow lights). I've seen this before -- if I don't do anything the purple areas will start to get dry and leathery and die. Had this bad with some cherry tomatoes a couple of seasons ago. These happen to be Mat-Su Express, but I've seen this fairly randomly with quite a few different varieties. They were started in Burpee's Organic Seed Starting Mix which is Coir. They haven't had any stresses that I'm aware of. I lightly fertilized at the last watering with 10-10-10 liquid at half-strength. So what do you think? Temps have been kept around 65-75 deg. F. (cooler at night, warmer in the day).
Nutrients?
Moisture?
Light (too much or too little)?
Disease? (I don't think so, but still possible)?

My guess is nutrients. But what specific product to use? Preferably a liquid. Something high in P, I'd think, without being high in N or K. Or your thoughts on something different?
-GG

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Re: Purple undersides of tomato leaves

#2

Post: # 598Unread post bower
Fri Dec 13, 2019 9:07 am

Are they too close to the lights?
Why I ask, it seems to me the phosphorus deficiency usually shows up strongest on the lower leaves. Could the leaves be drying out because they're getting heat from the lights?
Your temperature is not too cold, so that's not likely a reason.
pH can be another cause of P deficiency, but sounds like a neutral medium. So it sounds like either the lights are too close, or they need ferts.
What size of container are they in? Perhaps they need potting up at this stage too.
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Re: Purple undersides of tomato leaves

#3

Post: # 603Unread post Greatgardens
Fri Dec 13, 2019 9:42 am

Hi-
They are about 6" below the Fluorescent lights 2ea. 40" T-8. Yes, they are getting somewhat close to needing potting up to a larger container. Right now they are in a 4-pack that fits 12 to a flat, so they aren't terribly cramped yet, IMO.
Any specific thoughts about the fert.?

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Re: Purple undersides of tomato leaves

#4

Post: # 698Unread post bower
Fri Dec 13, 2019 3:04 pm

Well, if I was in a similar situation I would probably use fish fert because it's liquid and I have some.
When I start tomatoes I always use a bit of bone meal to ensure that P is adequate - works well for starting in the cold where access to P might be limited. Mixed in the bottom half of the cell, using a bit more each time potted up a size. It is very reliable for getting good root systems. I usually see some purple leaves but they don't dry up or suffer any permanent harm as you were describing.
Six inches certainly sounds far enough from fluorescent lights, so that shouldn't be the cause. :? :?:

I discovered that my LED shoplights (warm white, not designed for plants) actually don't support anthocyanin production in cabbage leaves. I can put red russian under it and all the red will fade away to a pale pink in a week, although looking otherwise normal. Strange color effects in lettuce last year too.
So pigment in plants can be affected by the spectrum available from lights. Fluorescents don't have such a narrow band, but if the lights are old is it possible some frequencies are getting weaker? I'm speculating, don't know.
Do your plants get any natural light as well?

The other thing about drying leaves, maybe it's just too dry for them. :idea: This is a problem for anything indoors, which increases as your temperature goes up, and your relative humidity goes down. Lettuce for example likes RH of 50%, which is doable in winter indoors if you keep the temperature 12-15 C that is below 60 F...
RH meter might answer some questions.
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Re: Purple undersides of tomato leaves

#5

Post: # 830Unread post Greatgardens
Fri Dec 13, 2019 11:38 pm

Thanks for the ideas! Adding bone meal to mix sounds like a good idea. Certainly can't hurt anything, so I'll add some to the seed starting mix. I also will change out one of my T-8 lamps to a Gro-Lux. There is little natural light in that room, so whatever I do will have to be with bulbs.

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Re: Purple undersides of tomato leaves

#6

Post: # 841Unread post Shule
Sat Dec 14, 2019 12:32 am

Purple leaves can often mean that the plants are cold and phosphorus-deficient as a result. Sometimes it can mean sulfur deficiency (if its the veins that are purple and the leaves look translucent). Cold seedlings being started in seed-starting mix are quite prone to this, as I've discovered in my unheated greenhouse. I usually just give them some phosphorus (either monopotassium phosphate or monoammonium phosphate) and a sulfate mineral (such as potassium sulfate). Monoammonium phosphate does have some nitrogen (but not very much, and I've never burned seedlings with it).

Bower's right about the lower leaves being affected first by phosphorus deficiency. But, Sulfur is an immobile nutrient (which affects new growth).

If you want to do things the organic way, try sprinkling a little wood ash on the top of your seed-starting containers, and watering it in. It's great for keeping young plants green and strong, and believe it or not, plants react fast to it. It's what I use when I'm tired of trying to figure out what deficiency the young plant in seed-starting mix has (and so far, it's worked every time, for me; it won't cure a nitrogen deficiency, however!) But, as with many organic soil amendments, it doesn't have a guaranteed analysis. One tree may have a different composition than another, and so may the ash from it. However, wood ash tends to be high in calcium and carbon with appreciable amounts of potassium and phosphorus, and maybe one or two other things, and trace amounts of pretty much every other mineral. Because of the calcium content of wood ash, it can raise the soil pH (but I've never had issues when using it with seedlings, and tomatoes like a certain amount of calcium anyway). For comparison, eggshells are roughly 40% calcium. Wood ash is roughly 25 to 50% calcium. (Both according to Google; I'm paraphrasing.)

Although it's not organic, I find that adding some monoammonium phosphate along with the sprinkling of wood ash can be even more helpful. I only sprinkle wood ash once or twice before the transplant, and I usually only add monoammonium phosphate once, too. Don't do it every week or anything! Monoammonium phosphate does contain some nitrogen (but it's a low amount, and I've never had it burn plants). IMO, that nitrogen helps to offset the calcium and potassium from the wood ash. Normally, giving nitrogen to pre-transplant plants is a bad idea unless they're fairly mature, but there's not very much here.

Seedlings with plenty of phosphorus are said to be more prone to being leggy. So, some people keep their seedlings low on phosphorus on purpose for that reason. (Or keep them colder, which makes phosphorus less available.) Phosphorus is important for leaf size, flowering and plant maturity, too.

If the leaves weren't actually getting damaged, another possibility would be that it's a high anthocyanin variety (a blue tomato).
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Re: Purple undersides of tomato leaves

#7

Post: # 1862Unread post Greatgardens
Wed Dec 18, 2019 8:32 am

A little update... The plants look quite a bit better. Only the seed leaves still have any significant amount of purple. They look like they will be "toast." I did two things. Fertilized with weak blue water twice. Took out one of my T-8 daylight bulbs and replaced it with a regular Gro-Lux (not wide spectrum). When I start plants in March, I'll add some bone meal as suggested, and probably add a bit more perlite to the Burpee mix. But for now, it looks like I caught the problem in time, and all the true leaves will be fine.

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Re: Purple undersides of tomato leaves

#8

Post: # 1892Unread post Growing Coastal
Wed Dec 18, 2019 10:35 am

Nice when you can turn things around like that. Good for you!

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Re: Purple undersides of tomato leaves

#9

Post: # 1921Unread post GoDawgs
Wed Dec 18, 2019 11:28 am

I'm glad they're better! I was going to post that I water my seedlings now and then with half strength "blue stuff" water starting when the second set of true leaves appear and don't have any problems with that discoloration.

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Re: Purple undersides of tomato leaves

#10

Post: # 2517Unread post Tormato
Sat Dec 21, 2019 11:48 am

Many years ago, a T'ville member recommended to add a pinch of bone meal to seed starting mixed. It completely cured the purple undersides of leaves, for me. The rest of the story is that he was a deer hunter, and cooked/charred his own bones. He sent me about a pound of his meal. The package arrived with a small leak. And, I recommend wearing gloves when handling bone meal.

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Re: Purple undersides of tomato leaves

#11

Post: # 2621Unread post Greatgardens
Sun Dec 22, 2019 4:40 am

Thanks for the anecdote of your experiences. But I'm curious -- why the gloves? All the commercial products are steamed which would kill any blood-borne bacteria. Along the same line, do you recommend gloves for handling potting mix? I'm not nay-saying your recommendation, but I'm curious what you're trying to protect against.
-GG

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Re: Purple undersides of tomato leaves

#12

Post: # 3340Unread post Daphne
Fri Dec 27, 2019 9:30 am

I have purple leaved seedlings every year. I think it's the cold, but I honestly don't really mind because they always grow up to be healthy, well rooted plants.

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Re: Purple undersides of tomato leaves

#13

Post: # 3356Unread post Tormato
Fri Dec 27, 2019 12:57 pm

Greatgardens wrote: Sun Dec 22, 2019 4:40 am Thanks for the anecdote of your experiences. But I'm curious -- why the gloves? All the commercial products are steamed which would kill any blood-borne bacteria. Along the same line, do you recommend gloves for handling potting mix? I'm not nay-saying your recommendation, but I'm curious what you're trying to protect against.
-GG


It may be nothing to worry about. But, better safe than sorry. Many years ago, when there was a slight panic with chronic wasting disease, and other like things, it was recommended to wear gloves and dust masks while handling animal by-products.

Sure, commercial products are steamed, but in the efficiency of their mass production. How does one absolutely know there is no cross contamination with starting and ending product, and what that product was to begin with? And no, I am not a worry wart. ;)

As for potting mix, vermiculite has been banned in some areas, therefore might not be in your mix. I have no problem handling it. Breathing its dust is another thing.

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Re: Purple undersides of tomato leaves

#14

Post: # 7299Unread post Greatgardens
Wed Jan 22, 2020 5:19 am

Update: As I mentioned, I made two changes that appeared to have corrected my "purple problem." I fertilized with blue water and changed one of my 6K daylight fluorescent bulbs to a T8 regular Gro-Lux bulb. After a week or so, the purple faded away. Today, I found a YouTube video comparing HID vs LED vs T5 Fluor. lights growing peppers. Both the LED and the T5 plants had a definite deep purple color in the leaves. A couple of years ago when I was using LED daylight bulbs, I lost several plants after turning purple. I'm even more suspicious that the lighting is a major factor in this issue. Here's a link to the video:

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Re: Purple undersides of tomato leaves

#15

Post: # 7313Unread post bower
Wed Jan 22, 2020 8:18 am

The trouble with LED is that unless they are specifically designed to combine multiple frequencies for plants, the basic LED sold for shop lighting or house lighting is one single frequency of light. Even though it may look the same to our eyes, it is not the same for plants at all, and is nothing like the natural light from the sun which spans far red to blue and UV. Fluorescents OTOH do have a range of frequencies present, even if they are designed for one frequency output or another. I had a similar experience with 'warm white' LED shoplights, produced strange leaf colors - especially tomatoes and peppers did not do well under them at all. They are okay for greens - brassicas and lettuce seem to grow fine under them. But I would not put tomato seedlings under those again. You pretty well have to get LED's that are designed for plants, or expect wierd results. :?
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Re: Purple undersides of tomato leaves

#16

Post: # 7322Unread post MissS
Wed Jan 22, 2020 9:13 am

Thank you so much for posting this. I often see people asking about which type of light to use for starting their seeds. This shows some significant findings and is worth some of us doing further investigation.
Nice video.
~ Patti ~

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Re: Purple undersides of tomato leaves

#17

Post: # 7342Unread post Growing Coastal
Wed Jan 22, 2020 10:32 am

Bower wrote: Wed Jan 22, 2020 8:18 am The trouble with LED is that unless they are specifically designed to combine multiple frequencies for plants, the basic LED sold for shop lighting or house lighting is one single frequency of light. Even though it may look the same to our eyes, it is not the same for plants at all, and is nothing like the natural light from the sun which spans far red to blue and UV. Fluorescents OTOH do have a range of frequencies present, even if they are designed for one frequency output or another. I had a similar experience with 'warm white' LED shoplights, produced strange leaf colors - especially tomatoes and peppers did not do well under them at all. They are okay for greens - brassicas and lettuce seem to grow fine under them. But I would not put tomato seedlings under those again. You pretty well have to get LED's that are designed for plants, or expect wierd results. :?
When I worked in a tomato house, long before LED was ever a thing, we used fluorescents plus incandescents to grow tomato seedlings. They worked well. I did the same at home with great results. Much easier these days with so many lighting options out there. Now I've got some T5 led plant lights. They seem very expensive compared to old style but power usage is so much lower.

My two little micros got very purple all over! The seed starting mix obviously has almost no fertilizer at all.

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Re: Purple undersides of tomato leaves

#18

Post: # 7356Unread post pepperhead212
Wed Jan 22, 2020 11:58 am

This last season I got some really cheap ($16.95 then, $19.95 now, so still cheap) LED lights from Harbor Freight - a single 4' 5,000k bulb, with 5,000 lumens, 30,000 hrs., in each "shop light". Not quite as much light as two of the T8 bulbs (3,240 lumens each) I use for my seedlings, but I did an experiment for a few of my tomato seedlings - ones I had 2 of, so I could compare them. I had 2 of the LEDs about 5" apart, and a tray with tomatoes just 3 across, and they did great, not getting leggy at all, and growing about the same height, with about the same # of leaves as the ones in the florescent trays. But, they all had leaves with the purple undersides! The tops were also a darker green. Nothing different happened when these plants were grown next to each other, out in the garden, so I didn't think much about it again, until I saw this post.

I also had a few other plants under these lights, just to see, but tomatoes were the only ones that looked different.
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Re: Purple undersides of tomato leaves

#19

Post: # 67135Unread post Setec Astronomy
Wed Apr 06, 2022 6:48 pm

Ok, I've got this purple leaf/stem problem. I have 30+ tomato seedlings of about 25 different varieties, and there are 2 that are bad enough that I'm getting some leaf curl, that are the same variety. There aren't too many threads on this topic here, but I found a bunch at T'ville and in one of them, Fred Hempel suggests that it could be too much or too little light, water, or fertilizer.

I'm sure it's not too little light, but it could be too much--I have this new really bright T5 LED setup (note above about LED's perhaps being more problematic with this). Could be too much fertilizer (been using 1/2 strength Neptune's Harvest Tomato & Veg, perhaps too often). The watering...I haven't let them get so dried out that they wilt, but I haven't been putting a ton of water in, either.

So how do I figure out which is the problem? I have moved up the lights a little, switched back to plain water, just sprayed some epsom salts (at 1/2 tbsp/gallon) on the leaves of the two bad ones. I have been using softened tap water...whenever I have mentioned that in previous threads I seem to get half the respondents saying "you can't do that, you have to use distilled water!" and the other half saying "that's fine, I never have any problems doing that".

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Re: Purple undersides of tomato leaves

#20

Post: # 67147Unread post Shule
Wed Apr 06, 2022 8:06 pm

@Setec Astronomy
Can you show us a picture?

What kind of softened water do you have? Some uses sodium to soften; some uses potassium chloride; some might use other methods. The sodium kind would likely be more of a problem. If it's potassium-based or something, that would probably be better.

Extra sodium will make the plants act like they have more water than they do. So, they won't wilt as easily in drought, the roots will rot more easily with less water. Stuff like that. How much sodium is in the water is a matter of concern.

Excess potassium shouldn't hurt the plants at all, but the chloride might (you'd probably need a lot of it, though). Plants with a lot of potassium will be really strong/tough. It helps with disease/pest-tolerance, fruit size, and other things. So, if you're softening with sodium and can switch it out for potassium chloride, that could possibly help.

What's the temperature in your growing environment?

My guess is the problem is the softened water (especially if it's the sodium-based kind of soft water).

If you didn't have soft water, though, and your fertilizer didn't have a phosphorus-bias, I would guess the plants were just cold, and in need of the nutrients needed to help them withstand the cold better (which are phosphorus, and probably calcium, too). Epsom salt and excess nitrogen might compete with the calcium, I'm guessing. If your pH is too high, that can also make the phosphorus seem low (the pH of your water also matters, if it's high).

Low sulfur might also be an issue.

I've never heard of too much light making tomatoes purple. If it did, I doubt it would be a bad thing (probably just anthocyanin). I could be wrong, though, as I don't grow under high powered lights (I use outdoor sunlight).
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