Saving sickly tomato seedlings, a mini case study.

I've had these seedlings under lights and on heat mats for 4 week. I was surprised how slow they were growing and then they took a turn for the worse.
I' mtrying to get to the bottom of my problem and untimely save as many of them as I can.
As you can see in the photos below they are looking pretty sorry for themselves.
I reached out to this forum and have had great help in understanding what was going on and what could be the probable causes.

In the photos you can see examples of purpling leaves and stems, browning leaves and 'leggy' seedlings . An all round sorry mess.
Why did this happen? I jumped on google 'purple tomato seedling leaves' everything pointed to nutrient deficiency. Not enough phosphorus.
How can you fertilize such small seedling, why are they deficient?
It wasn't until I posted on this forum that I was informed that purple leaves doesn't just mean nutrient deficient. It could be a whole host of things. Their too cold, over watering and under watering seemed to be the most common suggested causes.
The purpling of leaves is just a stress response.
This made me rethink my diagnosis, maybe there was something else going on.
I remember that I had introduced fans to the seedling a few weeks into sowing them. This change in conditions caused me to dry out my seedlings one time, I lost a few to this.
What I think happened is that I over compensated with the watering and gave them too much.
In my panic I moved the seedling out into my newly constructed cold frame. The weather was heating up and I'd had good success with other seedling in it. Some had already  out grown the tomato's.
I think the shock of been moved out into almost full sun too quickly also had a part to play in the sorry looking seed tray.

Any how, another gardening lesson learnt.

To save them I've repotted them in 4" pots.
I've buried them as deep as I can so they can grow new roots from the stem hairs. This should also give them some extra support.
All information I have found recommends reporting after they have at least 2 true leaves. Most of mine only have 1, some have 2 but they are very small.
I thought I'd risk it, desperate times call for desperate measures.
Upon repotting I noticed quite a few of the stems were pale and shriveled at soil level. This reenforces my belief that they were over watered.
Something else to note, I repotted them a few days after I took the first pictures and although they still don't look great by any means they looked a little more healthy. New leaves were green and I haven't lost any more since loosing a few when I first moved them out into real sun.

Heres the fun part. I'm experimenting with my potting mix.
I've divided the seedlings up as evenly as possible into two groups.
One group got potted up into 1:1 good quality homemade compost, coconut coir. With perlite and vermiculite added to get the consistency right
The other group got 1:1:1 the same compost, coir, top soil with perlite and vermiculite.
I know there is a chance of introducing dieses with the topsoil but there could also be benefits.
The plants final home will be in 10gal grow bags with a mix of the topsoil and compost and probably some other organic matter. My topsoil is really sandy but it's all I've got. It needs organic matter to hold the water in it and stop it from caking so much.
My theory is that by potting up with some of the topsoil I'll be getting the plants used to there final homes conditions faster and also maybe adding minerals the plants can't get from compost alone.
I will keep this post updated with photos.
Let's see what happens 🙂

Hi James, I think you are on the right track and some of the seedlings are already showing improvement after repotting.

The so called seedling starting mix is mostly for covering seeds which are sown in regular potting mix. It has very little nutrients and watering quickly washes them away. The purple coloring in the stems and back sides of the leaves are normal for tomatoes but stunted growth means the seedlings didn't get enough nutrients, not just phosphorus.

Given the small size if the original cell, nutrients should infiltrate readily to the roots after repotting. But if you have some seedlings to spare and want to experiment switching out potting medium completely, you could gently dislodge the old potting mix off the root. Take the chance to observe the root development as well. Then fill a pot half way with new mix, tilt it side way and make a slope of the mix. Lay bare roots on the surface and fill in the other half. Set the pot upright and water to settle the potting mix. Fill up more if necessary. In this way, root damaging is minimum and you get to see how the potting media affects growth more clearly.

May Lotito wrote:Hi James, I think you are on the right track and some of the seedlings are already showing improvement after repotting.

The so called seedling starting mix is mostly for covering seeds which are sown in regular potting mix. It has very little nutrients and watering quickly washes them away. The purple coloring in the stems and back sides of the leaves are normal for tomatoes but stunted growth means the seedlings didn't get enough nutrients, not just phosphorus.

Given the small size if the original cell, nutrients should infiltrate readily to the roots after repotting. But if you have some seedlings to spare and want to experiment switching out potting medium completely, you could gently dislodge the old potting mix off the root. Take the chance to observe the root development as well. Then fill a pot half way with new mix, tilt it side way and make a slope of the mix. Lay bare roots on the surface and fill in the other half. Set the pot upright and water to settle the potting mix. Fill up more if necessary. In this way, root damaging is minimum and you get to see how the potting media affects growth more clearly.

Do you think that would speed up recovery? I'll give it a go and compare to the ones I've already potted up. I've still got a couple of trays to pot up and I'm all for experimenting.
I was trying to disturb the roots as little as possible.
Some seedlings came out of their cells with all soil intact, holding the shape of the cell. I'm assuming the roots on these seedlings were well developed. Some seeding came out with very little soil and I felt slight tearing when I carefully removed them. I'm assuming these roots weren't doing so well.
It was mostly the weaker looking seedlings that did this.
Maybe I misused the seedling soil mix. It didn't even seem fit for the purpose you described ether though. There were quite large sticks and bark chunks in it. I didn't get the cheap stuff so I was unpleasantly surprised. Definitely happier with my own mix.
I do have a question about that though.
I was doing one block of coconut coir, 2 cups perlite, 2 cups vermiculite and a handful of organic worm casting.
It works well but I was considering putting 2 handfuls of worm castings to help the seedlings with nutrients after their true leaves come in.
I intend to pot them up as soon as possible, after 2 developed true leaves come in.
Would I make the mix too rich by adding the second handful? Would it just be wasteful as the plants only really need nutrients after their true leaves come in?

Hi James,
You had some issues with your seedlings, got some ideas from here, acted on them, took pictures, and then came back and reported your success. So often we on Permies will offer advice and suggestions without any closure to whether they tried it or whether they were successful. So you just made my day :)

The shriveled stem sounds like damping off. Often from too much water and/or not enough air flow. That happened to me one year on two flats of tomato seedlings. I did exactly what you did. I re-potted them deeper. It took a little while for them to get settled in, but once they did, they were fine, and I went on to get a bumper crop of tomatoes that year. Keep in mind that while tomatoes can be somewhat picky, they can also be very forgiving because you can bury them deeper and they grow fast :)

PS - Instead of a second dose of worm castings, could I suggest adding 1 part compost? The other stuff you put in your mix is lacking nutrients as has been mentioned. Some compost would help out a lot.

It's strange an expensive and supposedly higher quality seed starting mix would have large bits like that. Noted that the sellers of soilless potting mix are expecting customers to use the products with liquid fertilizer and watch the watering schedule closely. If you add good quality compost it will help with holding the nutrient too. Don't worry about adding too much, probably the plant will just grow faster and you need to repot again sooner. Tomatoes are forgiving and responsive when you give them what they need.

Matt McSpadden wrote:Hi James,
You had some issues with your seedlings, got some ideas from here, acted on them, took pictures, and then came back and reported your success. So often we on Permies will offer advice and suggestions without any closure to whether they tried it or whether they were successful. So you just made my day :)

The shriveled stem sounds like damping off. Often from too much water and/or not enough air flow. That happened to me one year on two flats of tomato seedlings. I did exactly what you did. I re-potted them deeper. It took a little while for them to get settled in, but once they did, they were fine, and I went on to get a bumper crop of tomatoes that year. Keep in mind that while tomatoes can be somewhat picky, they can also be very forgiving because you can bury them deeper and they grow fast :)

Thanks for the feedback. I really appreciate the knowledge I get from permies, I wish I could share more of what I'm doing. Life is very busy though. I'll see this case study through to the end though.
These photos are a good example of quite a few of the seedlings.
It's not the only problem I had though, I think there were a few things going on.
I've got results with the seedlings I potted up. I'm going to wait until a week to take photos and share.

May Lotito wrote:It's strange an expensive and supposedly higher quality seed starting mix would have large bits like that. Noted that the sellers of soilless potting mix are expecting customers to use the products with liquid fertilizer and watch the watering schedule closely. If you add good quality compost it will help with holding the nutrient too. Don't worry about adding too much, probably the plant will just grow faster and you need to repot again sooner. Tomatoes are forgiving and responsive when you give them what they need.

Is it a risk to start seedlings with compost in the mix? Due to soil bourn diseases I guess? It was my gut instinct to use compost but from my research online I was put off.
I make my own compost out of all sorts. I've got different piles. One of lots of food scraps (no meat or cooked food), egg shells, coffee grounds, old straw mulch etc.
One leaf mulch, wood chips pile
A well composted cow manure pile
Annnd a new about 8 ton pile of cow manure mixed with lots of straw!!! This needs to sit a while
What I'm lacking is top soil. I live on very rocky ground.

From my direction I am more concerned about what isn’t in  commercial potting soil than I am about what is in my compost.

here are some suggestions that might help .put in sun, if threat of night time freeze is past where you are put them outside, water with miracle grow for tomatoes, dont overwater, dont move them out of those trays till the roots bind up all the soil of each cube.

these are just suggestions but you might experiment to find out what works best for you

James, I have to guess that the reason for your experience with your seedlings has to do with the soil, the small cells  the seedlings are in, and that they have not been warm enough.

Tomatoes are an odd plant in that they like really warm temperatures when they are germinating. Heat mats help a lot. The red color of your seedlings tell me they have been too chilled. What are your temps for them, day and night? They definitely don't like being colder than 50 at night and germinate best in the 70s and 80s range.

Second odd thing is that they love lots of room for their roots. My friends and I have experimented with uppotting them to gallons instead of 4" pots once they have a couple sets of true leaves, and they perform way better going directly into gallons. Bury them deep in the gallons - as deep as you can, and they will grow roots all along the buried stem.

Lastly, the soil. I have experimented with using my own compost and garden soil to grow seedlings and failed miserably. All sorts of wierd pests, fungus gnats, damping off and failure to thrive. I even tried baking the soil in the oven for an extended period of time to sterilize it. I expect there's a way to do it that that works, but I now buy seed starter mix and my experience is night and day better. A little goes a long way because I just use it either in the little 1" cells like you have or as a topping on potting soil for bigger seeds planted in bigger pots.

Good luck and thanks for sharing!

Do you see improvement in the first batch of repotted seedlings after a week? If you have extra seeds, start some more in 2" or even 4" pots as backup. With warmer weather and bright sunlight,  those will catch up quickly.

May Lotito wrote:Do you see improvement in the first batch of repotted seedlings after a week? If you have extra seeds, start some more in 2" or even 4" pots as backup. With warmer weather and bright sunlight,  those will catch up quickly.

Results!!!

Here's the photos 10 days after re-potting, drastic improvement for the majority of the seedlings. Only the weakest didn't make it or are still stunted.

I can't tell a difference between the compost and topsoil, compost mixes. Both have strong plants equal in size and both lost weaklings.

A couple plants do have something going on with the leaves. Not sure what that is. It's the last two photos.
The blue tray is compost, red tray compost, top soil.

If you're relatively new to tomato planting, one of the most common mistakes is overwatering. Many of the suggestions for soil improvement on here are very good and having photos is very helpful, but overwatering is assumed to be the death of seedlings.

One thing I haven't seen mentioned here that we use at my commercial nursery is cinnamon.

If you notice that the stems near the soil level are spindly, weakened and floppy, (known as damping off), sprinkling a little cinnamon over the soil kills the bacteria responsible in the soil and they can recover ONCE watering is backed off . It doesn't kill off all soil bacteria so is safe for the soil.

A little cinnamon goes a long way so don't over sprinkle. Buy cinnamon that does not have flours or bulking agents added and is just pure cinnamon. Hope this helps.