I remember seeing that on some of the lettuce we grew last year in my Horticulture class. I don't know if we found out what it was, but I'm pretty sure we didn't even worry about it.

do you have your lights on 24/7 that will cause it as will a shortage of phosphorous, i had the same problem about 6 weeks ago , i used a product that the nusery gave me called fertilome blooming and rooting soluable plant food
9-59-8 it had a high phosphorous number and the purple in my my plants gradually faded to yellow the a nice dark green . hope that helps you . or take your plant to the nearest nursery they are very helpful.
jim

I have left them on overnight a couple of times, Jim. Not on purpose, but just forgot to turn them off. Thanks for the info! Did the nursery say it was detrimental to the plants?

no , the nursery at first thought because they were chocolate peppers they might have a purpleish tint naturally so he took it in the back and asked someone .
mine were much darker purple than yours , the leaves were all curled up and the stems were dark purple, i thought they were going to die , but after i added the fertilizer they gave me they went from purple to yellow to green , now the stem is all that has a slight bit of purple in it , they all look very healthy now , mine was caused by nutrient deficiency , because i still leave my lights on 24/7 , i wanted to see if it was the lights or fertilizer deficiency . prior to adding the high phosphorous fertilizer i hadn't added any fertilizer since they were planted , this was the first year i ever had my plants turn purple .
jim

I'm going to get some seaweed/fish fertilizer today. I think the Neptune's Harvest version is 2-3-1. I don't want to give them a huge boost of anything because they don't show signs of any sickness except for the purple, but if it is a phosphorus deficiency maybe I can take care of it with a general fertilizer. I haven't fertilized the peppers or the tomatoes yet. The undersides of my tomatoes are a little purple as well.

Here is a link that might be useful: Gumshoe Gardener

Hmmm...well, I'm using Mel's Mix for my plants, with a well rounded blend of composts. The plants are all on a heat mat, so the soil temp isn't low. Would the air temp make a difference? It is cool in the basement where I have the plants. I let the mix dry out before I water, so I'm pretty sure it isn't a case of too much water. The purple is in the centers, not the edges.

The fertilizer I'm going to use doesn't have a huge amount of P compared to N & K, so I wouldn't call it a 'bloom-booster'. But a previous poster said his local nursery recommended a 9-59-8 fertilizer for a similar problem, and it helped. I'm not going to get that strong of a fert though. And I'll cut the recommended dosage down on the fish/seaweed as well since the plants are still in containers.

Thank you for your input and explanation the science behind the color change, I learn something new here every day.

In order for a plant to benefit from extra P it has to be deficient in soils. Based on the amount of N supplied, 9-59-8 fertilizer has 39.3 times more P than the plants could ever utilize. There is NO way anyone can justify using a fertilizer for container culture with that much P. People attribute reactions to erroneous causes and commit logic errors all the time. It's illogical, especially in the face of proven science, to think that supplying 40 times the P a plant needs could somehow benefit the plant.

The next 3 paragraphs are from another post of mine, so if it seems a little odd as far as being directly on topic, please take that into account:

If nutrient availability is unbalanced - if plants are getting more than they need of certain nutrients, but less than they need of others, the nutrient they need the most will be the one that limits growth. There are 6 factors that affect plant growth and yield; they are: air water light temperature soil or media nutrients. Liebig's Law of Limiting Factors states the most deficient factor limits plant growth and increasing the supply of non-limiting factors will not increase plant growth. Only by increasing most deficient nutrient will the plant growth increase. There is also an optimum combination/ratio of the nutrients and increasing them, individually or in various combinations, can lead to toxicities.

When individual nutrients are available in excess, it not only unnecessarily contributes to the total volume of solutes in the soil solution, which makes it more difficult for the plant to absorb water and nutrients, it also often creates an antagonistic deficiency of other nutrients as toxicity levels block a plant's ability to take up other nutrients. E.g., too much Fe (iron) can cause a Mn (manganese) deficiency, with the converse also true, Too much Ca (calcium) can cause a Mg (magnesium) deficiency. Too much P (phosphorous) can cause an insoluble precipitate with Fe and make Fe unavailable. It also interferes with the uptake of several other micro-nutrients. You can see why its advantageous to supply nutrients in as close to the same ratio in which plants use them and at levels not so high that they interfere with water uptake. I know IÂm repeating myself here, but this is an important point.

What about the high-P "Bloom Booster" fertilizers you might ask? To induce more prolific flowering, a reduced N supply will have more and better effect than the high P bloom formulas. When N is reduced, it slows vegetative growth without reducing photosynthesis. Since vegetative growth is limited by a lack of N, and the photosynthetic machinery continues to turn out food, it leaves an expendable surplus for the plant to spend on flowers and fruit. Plants use about 6 times more N than P, so fertilizers that supply more P than N are wasteful and more likely to inhibit blooms (remember that too much P inhibits uptake of Fe and many micro-nutrients - it raises pH unnecessarily as well, which could also be problematic). Popular "bloom-booster" fertilizers like 10-52-10 actually supply about 32x more P than your plant could ever use (in relationship to how much N it uses) and has the potential to wreak all kinds of havoc with your plants.

I'm not sure if it's mentioned in the text above, but that much excess P unnecessarily raises the level of EC (electrical conductivity) and TDS (total dissolved solids) in the soil solution, which makes it more difficult for the plant to take up both water and the nutrients dissolved in the water. I could expand on that point, but I don't think it's necessary. Excess P also interferes with the uptake of Fe and Mn, and raises soil/soil solution pH.

.... ball's in your court, but I'd hate to see you go to a high-P fertilizer thinking it will solve your ills.

Al

Thanks again for all the info, Al. If you aren't a teacher, you should be! You really have a knack for explaining very technical things so that a layperson can understand. Thank you for taking the time.

Like I said above, I'm not using one of those bloom-booster ferts. I have a fish/seaweed fertilizer that is 2-3-1. I diluted it to half strength and used it as a foliar spray last night. The peppers still seem strong, but their growth seems to be a little slow. So using some general fertilizer might give them a little boost. I'm not worried about overdoing it with those small numbers at half strength. I checked them this morning and all is well. Judging by some problems with my brassica leaves turning red as well, and that the plants I treated with fertilizer look great compared to the ones I didn't, I'm pretty confident there may be a P deficiency in my homemade mix. But I don't want to overfertilize or fertilize unnecessarily. That's why I cut the dose in half. Being a new gardener, this is all a massive experiment for me. While I would hate to lose my pepper plants, I'm also curious to see how different environmental factors contribute to the health of the plants. So let's call this a science project!

The peppers don't look any better after the fertilizer treatment. But they're not dead, so I guess that's a good thing! I have new pics on my blog if anyone is interested in seeing the pepper massacre in progress...

IMHO you need more than a half-dose of 2-3-1 from the info presented. Cutting it in half is like giving you a half of a celery stick in place of dinner after you skipped lunch.

The adage 'feed weekly, weakly' is appropriate and for seedlings I cut a 10-10-10 in third to half; not the best formulation but too cheap frugal to buy a specialty fert for every task. Nonetheless, yours should be in the ground soon and supplemented with your preferred granular fert and they'll hopefully start being happy.

Dan

Interesting, thanks Dan! It never occurred to me that the half dosage recommendation would be meant for stronger fertilizers.

I'm having the same problem with my Thai chili peppers. I brought the seeds back from Thailand and started them in peat pellets. After they were in the ground for about a week I started to notice the lower leaves turning purple. Some are completely purple, some just the veiny areas in the middle of the leaf.

The stems have turned completely dark purple.

I live in South Florida so I know cold soil is not an issue. But, it has been quite windy for the last 5 days, with 15 to 25 mph winds, which is a little unusual for this time of year.

Think this might be a phosphorous deficiency ?

Doug

I like to use compost tea for mine.

I'm working thru the same problem with multiple varieties of bell pepper I'm growing under lights for the last 6 weeks. What I'm learning is:
Young/New leaves light green with purple veins is due to nitrogen deficiency.
Mature/old leaves and petioles purple due to phosphor deficiency.

My new leaves are N deficient *AND* my old leaves are P deficient which I conclude as a lack of any fertilizer. Since I hadn't been fertilizing with anything this would make sense.

Commercial growers use a ratio of 2.3:1:1.9 of NPK for peppers so my fert solution is inorganic for immediate uptake till the plants look more "normal." Calcium Nitrate plus Potassium Nitrate(stump remover) plus a touch of bloom booster for some P. Mix your own using: http://users.hal-pc.org/~menendez/hydrocal.html

While I also have seaweed/compost fertilizer in my arsenal, it will take too long for the organic nutrients to break down and become available so inorganic is the cure.

I'll post back as the plants hopefully improve!

Guys, I'm glad to see I'm not the only one with this particular problem. Well, not glad for you, but glad that it's not something completely unheard of. I sprayed and bottom watered my plants with fish/seaweed a couple days ago and I'm hoping this will help. They're still surviving, which is a good sign anyway. Sparkgap, thanks for ruling out the possibility that they are too cold in the basement. I really thought that was a big factor.

Weekly, weakly.

I can't say I've ever had purple lvs on peps with this adage.

Dan

I had a similar problem with tomatoes and peppers last year, but mine was caused by a nitrogen deficiency. I used worm tea, but it sounds to me like either case will be solved with your light fert.
Wow Al! That's all, just wow.

What's really going on is that your peppers are going through tiny stages of shock. My peppers always get a purple vein along some leaves right before they blossom. Plants need a lil stress now and then to promote growth. Don't worry about it. But I will say water on a CONSISTENT basis.

And stay away from fertilizer that has uneven NPK. You want a good balance like a 10 10 10 or 12 12 12. Don't be hoodwinked by these blossom bloom high phosphorus cuz you will stunt or even stop your growth entirely.

Old post, I know, but for the sake of those who will read this thread in the future, it needs to be said that plants never "need" stress. Stress is limiting and inhibits the plant's ability to realize as much of its genetic potential as possible. There are times that a grower might choose to subject a plant to stresses that result in something the grower prefers, but from the perspective of the plant, stress is never a good thing. As far as stress promoting growth, that idea is about as far from reality as can be.

Watering shouldn't be consistent in the sense that intervals between waterings are uniform. Plants should be watered on an "as needed basis". In a perfect world, plants would be watered immediately prior to the onset of drought stress. This maximizes the length of time the plant has to grow in a medium where no water is held between soil particles, which maximizes air porosity.

1:1:1 ratio (balanced) fertilizers (12-12-12, 20-20-20, ....) are not a good choice for any plant in a container, and almost never for plants in gardens/ landscapes. There is no plant on earth that uses equal measures (by weight) of NPK. For gardens and landscapes, a soil test determines what fertilizer program is appropriate. Anything else is just a SWAG. For containers, a fertilizer with a 3:1:2 ratio (24-8-16, 12-4-8, 9-3-6 are all 3:1:2 ratios) is almost always appropriate. Reason: The average plant uses about 6x as much N as P and about 3/5 as much K as N. 3:1:2 ratio fertilizers provide macronutrients at almost exactly that rate.

High-P fertilizers provide so much phosphorous, that calcium, iron, zinc, and copper quickly become unavailable, and it can cause the plant to take up too much magnesium (acts as a synergist).

Al