yellow leaves on seedlings and fertilizing

liv2learnMay 4, 2007

I have a few dozen tomato seedlings under fluorescent lights inside. They are in their first potted-up stage and are in 3" peat pots and yogurt cups. The soil is a mix of sterile seed starter and sterile potting soil. I have fed them with a 1/2 strength fish emulsion/liquid seaweed mix. After they were potted up, they grew well, but now they are showing some yellowing leaves and some purple on the leaf undersides. I am concerned. Some of what I have read says this may indicate not enough phosphorus, but I am not sure. I water and then let the soil dry out, which is accelerated by the peat pots which wick away moisture very quickly. I probably wouldn't use the peat next year.

Some of the plants could use another repotting into 6" pots, but I don't have any this size. They've been hard to find. Also, if I repotted all the tomatoes into larger pots, I won't have enough room for all of them under the lights. I do have the option of a small, portable plastic greenhouse (plastic film over two racks) that a friend gave me. I could use this outside during the day and take it in at night. This is big enough to house all the tomatoes and would not require the fluorescent lights.

What is the best course of action? Is 1/2 strength fish emulsion too much/not enough? These plants need at least two more weeks before they can go outside. Thanks.

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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

As we have discussed here several times the purple cast to the leaves and veins can be ignored. We all have them. :)

There are several possible causes but none of them harmful to the plant and they always recover once planted in the garden. Trying to identify which of the many causes it might be usually results in doing more harm than good.

The yellow leaves, assuming you are talking about true leaves and not the cotyledons (it is normal for them to turn yellow and eventually fall off), is almost always a result of excessive water. If you feel you are not overwatering - you are overfeeding ;) - then perhaps your soil mix is not draining well. Peat pots do retain water more than plastic and keep the roots damp even when the surface soil appears dry. So try going easier on the water, ok?

Need to be transplanted - many of us use the 16 oz. plastic cups you buy at the grocery with holes drilled in the bottom. They work fine. This time you could try leaving out the potting soil and just use the soilless mix - it drains better.

Lastly - the fertilizer - keep in mind that fertilizing is a stressor to plants and 1/2 strength (depending on it components) is still too strong for seedlings. As you will read in many of the posts here young tomato plants don't need near the feeding that most of us try to cram down their throats. We do it because it makes us feel good but the plants would just as soon we'd lay off it and let them do their own thing...which they do quite well. ;)

    Bookmark   May 4, 2007 at 6:43PM
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Hope you don't mind me chimming in on your post liv2learn...but I've had an issue with yellowing leaves also.

One thing that is different for me, then what digdirt is saying....I find that I am having trouble with my 'plastic' containers retaining water. To the point where some of my plants are just so waterlogged. I caught this happening a little too late! But on the other hand, the plants that I have in peat pots seem to not get enough water unless I absolutely drench the pots with water. The peat pots seem to soak it all up.

I am also growing under lights and I have a fan circulating continuously.

On another note, I have read that the stalks and leaves having a purple hue is an excellent sign of healthy strong plants.

I can't wait to plant outside! I feel like I'm losing the battle when it comes to maintaining the correct moisture.

Good luck Liv2learn!

    Bookmark   May 4, 2007 at 7:17PM
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digdirt, thanks for answering my newbie questions. Although I have planted tomatoes in the past, this is the first time I am raising them from seed indoors. Yes, it is the true leaves that I am seeing turn yellow. The cotyledons did turn yellow and some are falling off, but I assumed that was normal for them. I find it difficult to maintain the moisture level when growing inside in the peat pots. Like mrs. growop, I find that the peat sucks the moisture out of the soil and away from the plants. The pot stays moist while the soil is bone dry.

Certainly some of the plants are too tall and need to be repotted to something larger. I will check into the plastic cups. When I repot, I'll be using fresh sterile starter mix so do I need to fertilize or not? Is there enough nutrition in the soilless mix to last the plants for three more weeks? The mix I use has no fertilizer added. (It's not Promix or something like that.) The fish emulsion/seaweed combo I used was Neptune's Harvest and it is a 2-3-1 formula.

Finally, lighting. Not everyone is going to fit back under the lights, so some of them will have to go in front of windows and hope for the best.

    Bookmark   May 4, 2007 at 7:40PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

I'm not a big fan of peat pots but I have used them and they will work and many use them quite successfully they say. The secret to watering success with them is to wait to water until the pot itself dries out - or at least most of it. The soil and roots are in contact with the pot and they draw moisture from it even if the soil appears dry. That is why eventually the roots will grow right through the pot. So as long as the pot is still moist they probably don't need water.

Drainage problems, like plastic pots that don't drain well, is almost always caused by the soil mix used, not the container itself (unless you happen to have one with no slits in the bottom. ;) Unless you use a light, well draining soilless mix you will have drainage problems and the plant problems that it leads to no matter the container used.

As to feeding - you'll hear both sides. Some use a soilless mix with fertilizer added like MG potting mix, some make their own soilless mix and add a bit of timed release fertilizer to the mix, and some make or use a soilless mix and add some compost to it.

Personally, while I add some compost to my mix for leafy greens and a few other veggies, I don't feed any of my tomato seedlings anything - ever - never have - until they go into the garden and then the planting holes get well-amended as they are planted. They get started and grow on in either Jiffy mix, Metro mix, or my homemade peat/vermiculite mix whichever I have available. Been doing it that way for over 40 years.

My goal with tomato seedlings is to get a small, sturdy plant with a great root system that is not yet blooming when it is garden time. Adding fertilizer to seedlings defeats that goal. It stimulates blooming and top growth and you end up with tall, skinny plants with widely spaced leaves and stems and poor roots. It stresses the plant because it's roots can't support all that top growth. Now plants that were maybe started way too early, have already been transplanted a couple of times, and are already well past the normal garden transplanting size? Yeah, they will need some feedings, but standard 6 pack or 4" pot seedlings - nope. ;)

But it sounds like you have enough plants to try it both ways and see which works best for you and let me know.

Can't help you with the light problem except to suggest buying one of the cheapo shop light fixtures that Wal Mart carries for the overflow. They run a total of $12 including 2 bulbs here and work great. Good luck.

    Bookmark   May 4, 2007 at 9:08PM
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Thanks for your reply. I already have four shop lights set up on two racks and it will be hard to convince hubby that we need more. ;-) Not all the tomatoes are outgrowing their containers; only some of the five varieties I tried are doing so. The majority are 3-4" in size, so not too large yet. I could mound up some more soil against the stems in some of the pots since the soil has sunk down a bit.

I've let the all the pots dry thoroughly. The peat pots are now quite dry and light. A couple of the plants were starting to look wilted, so I gave them a water - no food. I'll follow this strategy for the remainder of their indoor time unless they start to look worse. The new leaves are now mostly looking green. A few plants of two varieties are the more yellow of the bunch. Overall they are hanging in there. Now if we can get through the next two weeks or so in a healthy state, the weather *should* be good enough for transplanting outdoors.

    Bookmark   May 5, 2007 at 8:36PM
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timmy1(6a ri)


Not trying to disagree but...

Tomato seedlings require between 50-75 ppm N/ 25-50 ppm P/ and 50-100 ppm K plus micros.

You can starve them until you set them out but it's like anything else in nature, the weak and hungry will get disease faster than the strong and healthy.

    Bookmark   May 5, 2007 at 9:20PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

No problem timmy1 - Like I said above there are all sorts of opinions on how to grow tomato seedlings and what or what not to feed them. All we can do is offer our opinion and tell what works for us. So ask 50 people and you'll get 50 different answers because there simply is no way to control for all the inherent variables in the process.

But the two things I am sure of is that (1) tomato seedlings are a lot tougher than most of us give them credit for, and (2) there are no absolute "requirements" when it comes to growing them. All the differing opinions and approaches posted on this forum would seem to support me on those 2 points.

So, if it works for you...go for it. ;-)

    Bookmark   May 5, 2007 at 10:21PM
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When I used to grow veggie seedlings indoors, they would look punk, with yellowing leaves and reddish purple on underneaths, signs that outside I would see as undernourishment [lack of nitrogen and phosphous, respectively]. Yet the usual fertilizers weren't helping, even harmful. I came across a crazy sounding idea that worked great ! Sprout water. I made alfalfa sprouts for eating; they need rinsing several times a day, so instead of pouring the rinse water down the drain, I saved it to water the seedlings with. In no time they had great color and vigor.

    Bookmark   May 21, 2007 at 7:29AM
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That makes some sense since alfalfa is used as a green mulch.

Once I transplanted all the seedlings into 16 oz. cups and sunk down the stems even further, they grew like weeds. The stems got thick and the leaves turned a nice green shade. Well, I learned my lesson there. :-) The weather is finally nice enough today to put them all out for an hour or so, with the hope that next week (first week of June) will be transplanting time.

    Bookmark   May 21, 2007 at 10:25AM
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I had the same situation. I cut back the water, and sprayed the plant leafs with a light mist containing water and epsom salts. The plants greened right up.

    Bookmark   May 21, 2007 at 12:16PM
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This is the first time I've tried to grow tomatoes from seed, and it's difficult figuring out what could be wrong and how to fix it. Three different varieties have been under a grow light since sowing, and are now 8-12" tall ~ they've been transplanted into larger pots once.

Here's what's happening. Some curled leaves and some yellow leaves. There are a few that look just fine and strong; some that have 10% yellowing on leaves that look otherwise healthy; some that have 80% or more yellowing leaves (kind of striped with yellow, the plants look OK except for the yellowing); some that look good except for some curl in the newer, topmost leaves. Some leaves fell off of the yellow ones, or looked dead so I pinched 'em off.

I may have watered too much... and unfortunately, I also added fish emulsion (2 Tablespoons to 1 gallon of water) which, after reading this, appears to be way too much fertilizer for them.

So the next time I watered them, I made sure they were pretty dry and just used plain water and soaked them good. I've always avoided getting water on the leaves.

I also didn't have much air circulation going on, when they were under the grow lights. I also think the grow light may've been too close to the leaves. Additionally, they were really close together under that one grow light. After reading this, it occurred to me that they might need more room. I guess tomatoes need elbow room and fresh air, just like everything else :-)

Today I am setting them outside in a large cold frame, plenty of elbow room, and there's a light bulb installed (to keep it a bit warmer inside the cold frame).

The tomatoes don't look like a lost cause, yet. I'm hoping they will recover in their new environment. I'm praying they don't have a fungal disease.

Wish me luck... and oh, any comments or advice would be really appreciated.

Bigtomato ~ what does the epsom salts do?

    Bookmark   April 22, 2011 at 6:53PM
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Thanks all for the helpful comments on here. My Roma's looked puny and yellow so i decided to search. i think I am over watering. All my other plants are nice, green and growing, including other tomato varieties, but the flat of Roma's is not doing much. I use recycled materials for my pots, but have drainage holes, etc. Anyhow, great advice. thanks!

    Bookmark   April 2, 2012 at 9:25PM
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