SeedlingsTurning Purple

christacharlene(6)March 15, 2014

My tomato seedlings are 5-7 days old. The stems and some the veins on the leaves have turned purple. I have been googling like crazy to find out what happened. From what I have read the consensus seems to be that tomato seedlings are not able to absorb phosphorus from the soil when the temperatures are too cool, so they develop a phosphorus deficiency. The day before yesterday it was pretty cold outside and I didn't turn on the heat in my house the entire day or that night either so I am thinking that is what did them in. Maybe?

Anyhow, I am keeping my house warm now. What else should I do? Should I fertilize them (very diluted of course) with fish emulsions or bone meal? Or do I just leave them alone and hope they recover? I especially would like to hear from anybody that has had this issue and if you did have this issue, what did you do about it and how did your plants turn out?

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keith100_gw(NY 5A)

I had just about the same deal last year. My plants were started in my basement on seed mats doing well, but when I shut the mats off after germination 4days later the temps dropped to hi 40's in my basement. Growth slowed tremendously and the purple you described appeared. I did 2 things , 1st I put cardboard and a towel over the window above my seed station, there was a considerable draft. I secondly extended my chains on my lights so I could get the lights right down next to the tops of my seedlings as they are supposed to be. If memory serves me on the third day after the adjustments I was convinced they were getting better and it wasn't just my hopeful thinking . They then came back to a nice good green color and did well. I'm guessing you will be fine . Good luck! Keith

    Bookmark   March 15, 2014 at 9:03AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Purpling of seedlings when young and small is common, almost normal one could say and most ignore it. Lots of discussions here about it.

It does them no permanent harm and they outgrow it as they develop and age and develop more roots.

It is made worse by too cool temps - ideal is 60-65 - so cooler than that needs to be avoided/corrected if possible. That can affect their ability to absorb P but again it is due to their young root development. There is no long term harm to the plant and trying to "fix" it with fertilizers only makes things worse. Leave them alone and they will recover as long as the ambient air temps are maintained.

And for future reference: if fixing it with fertilizers was needed bone meal or fish emulsion would not work. You'll want to do some research in various fertilizers and how they work and don't work when growing seedlings.


    Bookmark   March 15, 2014 at 10:15AM
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Thank you for both for your advice. The seedlings are near my sliding glass door so I am going to make sure my curtain stays shut at night and I did throw a blanket over top of the grow light last night (after I turned it off) to protect them from any drafts. It is good to know that your seedlings recovered, Keith!

I have been starting my seedlings indoors for 10 years and this is the first time I have had this problem. For now I will leave them alone and skip the fertilizer. I am keeping my house warmer too. I won't be planting them outdoors until the begining of May so I do have some time to restart them if need be but hopefully it doesn't come to that!

I will certainly do some research on fertilizers and how they work and don't work when growing seedlings but Bone Meal and Fish Emulsions are high in phosphorus and seemed like a obvious possible solution to give them a little boost. My knowledge of fertlilizers is definitely limited though as I only occasionally use any kinds of fertilizer.

    Bookmark   March 15, 2014 at 11:19AM
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carolyn137(z4/5 NY)

If the purple color is really bothering you I've found it's best to use either diluted fish or seaweed emulsion as a foliage spray.

Since theproblem is usually lack of P uptake via the roots, no sense using a general fertilizer as applied to the whole plant since it's a root problem, foliage spray circumvents that, and both fish and seaweed have lots of P which is easily taken up by the leaves.

Most of thetime I just ignored the purpling, but I do know that it can bother others.


    Bookmark   March 15, 2014 at 11:47AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

but Bone Meal and Fish Emulsions are high in phosphorus and seemed like a obvious possible solution to give them a little boost.

The issue is that bone meal, why high in P, is very slow acting. It usually takes an average of 4-6 months for it to be effective and that is assuming there is an active soil food web to convert it to a useful form. That active soil food web is absent in soil-less container mixes seedlings are grown in.

Fish emulsion (diluted) also has adequate P but the lack of feeder root development on young seedlings makes using it as a soil drench a waste of time. There are no roots yet developed to benefit from it.

Thus the need to first understand exactly how each supplement works and works best rather than just knowing what it contains.

As Carolyn pointed out, foliar feeding of diluted fish emulsion instead can provide some benefit.


    Bookmark   March 15, 2014 at 11:56AM
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Thank you for the explanation Dave. That makes sense.

Carolyn I will definitely try it if they haven't improved much in a week or so, but I think they are already turning around for the better! It is nice and warm in here now and I am going to take precautions to keep them from getting cold. Yesterday 2 of my plants looked like they were on their death throws, droopy and the leaves were curling. I assumed it was because of the P deficiency but maybe it was something else. Either way, they are looking way better than they did earlier this morning and last night.

    Bookmark   March 15, 2014 at 1:24PM
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I had severe purpling of tomato seedlings last year for the first time in over 30 years of starting from seed. The only differences from the past were new brighter lights (6 x T8 bulbs instead of four), and starting them in a new house with a slightly deeper cellar. In addition to the deep purple coloration, the seedlings were so curled that many laid down near the soil surface.

In seeking help, some suggested temperature was the issue, but I measured the temperature and the cellar air temperature was 61ðF, the potting soil temp at the bottom was 67ðF, and at the top 1/4" was 71ðF. The air temperature under the lights at seedling level was 73ðF. These temperatures are fine for seedling grow and I provided a slight breeze from a fan on a timer.

Others suggested it was too much light (didn't know there was such a thing!). The lights were kept 1 to 2" above the seedling tops as usual, but I did accidentally leave the lights on for 24 hrs for two days instead of the usual 16 hrs. I used 5000K lights.

I tried adding small quantities of lime water and fertilizer with no effect.

The good news is the plants eventually outgrew the curling and grew normally except for the deep purple underside of the leaves. Once in the garden they took off and greened up.

Never did find the cause. This year I will try raising the lights a little to about 4" above the plants.


    Bookmark   March 16, 2014 at 10:51AM
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seysonn(8a WA/HZ 1)

Some of my peppers also turned purple. At the tim I was keeping the lights too close (almost touching) and for too long (almost 16 hrs). So, I increased the distance to over 1 inch and reduce ON_TIME to 12hrs. No more purple.

NOTE: this purpleing s different from the one caused by cool soil and ambient temperature.

    Bookmark   March 17, 2014 at 4:50PM
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That's interesting Seysonn. While most people I talked to said there is no such thing as too much light, some others suggested that light was the culprit. Good to know that moving the lights up a bit helped you.

My pepper seedlings also had purple leaf undersides last year, but not as severe as the tomatoes, and they did not have any curling. I also suspected that heat from the lights may have played a role, but the air temperature under the lights was only 73ðF. This year I'll set the new bright lights about 4" above the seedling tops and start them out at 12 hours until they develop true leaves, and then gradually increase the light time to 16 hrs.


    Bookmark   March 18, 2014 at 10:03AM
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seysonn(8a WA/HZ 1)

I think, from what I have learned, plants need a limited amount of TOTAL light for their photosynthesis. Beyond that amount the light has no benefit and in the case of seedling and in the case long sunny summer days, excess light can be stressful.

Most would think that tomatoes would need lots of light, the more light the better. I DON"T THINKS SO. Tomatoes are partial sun, partial shade plants, I read a comment here not too long ago, somebody quoting a German gardener as saying that We consider tomatoes shade plants. There is some truth to that statement.

I have grown tomatoes withe 5 to 7 hours direct sun for years fairly successfully. My point was/is that PROBABLY (?!) 16 hours of light is excessive. !0 hours should be enough. People have grown seedlings on window sills with about 8 hours (+/-) for centuries. JMO

    Bookmark   March 18, 2014 at 4:01PM
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