Transplant Tomatoes Stunted

This is my first time growing tomatoes from seed, but I'm running into a problem with stunted growth and have no idea what the cause is. I purchased a fancy starting mix with coconut coir, worm castings, azomite, humus, and some fungi, which was a dry mix which expands as you add water. It was a great mix as it held water well. The seeds sprouted fabulously, only the wild cherries were a little slow and feeble. Our garden wasn't ready to be planted as soon as we hoped, however, so the seedlings had to stay in their trays for about a month and a half. They grew true leaves and got about 6 inches tall, but never got any taller. I transplanted them into the garden in their little biodegradable seedling cups right into the soil, and piled up some of the seedling mix  around them for better water retention and nutrition. It's been 2-3 weeks, but they haven't grown any new leaves and haven't increased in size. Granted, our nights have been a bit cool, this Spring is definitely the coolest I've ever experienced in Texas, so I blame it on that, but I'm just about to start over and plant tomatoes again from seed right into the garden. The same thing is happening to many other seedlings, like basil, melissa, and malabar spinach. When I transplanted the seedlings, I also planted some seeds directly into the garden, like lettuce, sunflower, beans, zucchinis, etc., and they are doing great.

Maybe I kept them too long in the seedling cups? Maybe they're just expanding their roots right now? Should I wait longer? Should I amend with something? I have not done any soil testing, but this is a new garden with a purchased soil with balanced nutrition mixed in with native soil, and all the other plants grown from seed are doing fine.

Maybe it is the biodegradable cups they are in. I read somewhere that they were not recommended due to them breaking down very slowly when put in the earth and the roots, therefore, are kind of stuck in there. Perhaps try digging into the soil and peel away the cups from the plant roots and see if the plants take off. Good luck, I hope they end up making it!

Hello Tatiana!

As Anna has said it could be those containers causing the plants to be root bound in the cups, and it sounds like the extra time spent in those containers may have had them root bound before even planting them. Maybe try hers suggestions of gently removing the pot, them replanting, but keep some in the pots for a control group to help identify the exact issue.

It sounds like you had a good soil mix the plants obviously liked originally. So the only other potential issue I can think of to cause that is water quality. Mineral and or hard water salts quickly build up in small containers, and those salts quickly alter pH in addition to potential salt stress and or burn. So if the plants are root bound in the containers and the pH in their little containers is to alkaline, they may just stagnant for unusually long periods of time, untill they can get some roots out of the container and start fresh building root mass.

(FYI) If your not using rain water, I would investigate your water quality to test for TDS PPM, plus make sure there's no water softener system used in any water for plants. Some municipal water processes will even use water softeners. Water softener salts are very bad for plants, but hard water often from wells is usually the culprit. If you have any soil from those containers the plants are struggling in, you could also test the pH, and that will help give you data to further confirm the results of any water testing to see how the potential mineral build up have effected your soil.

You can get TDS (total dissolved solid) meters, that measure PPM (parts per million) for around $15, and pH test kits for around $10. That way in the future you'll know how to approach watering without issues. If water is a contributing factor, and rain catchment isnt an option, a sink side reverse osmosis system will provide you with abundant high quality water for container watering. I got one from APEC for about $300, because it was cheeper for me in the long run, and since water quality is the difference between success and failer especially when growing in containers, it was more cost effective.

Hope that helps!

If you've planted tomatoes before then there's nothing new except those pots. Assuming the transplants you've been buying in past year came in plastic.

R. Steele, I think that must be it! We have very hard well (pumped from 300+ ft) water and have a water softener, and I was watering the seedlings with the softened water. We were planning to get a rainwater capturing system eventually, but after just having built the garden we kinda can't do much else for a while. I think I'll try to salvage whatever tomatoes I can and reseed everything else. Thank you!

Try digging up the tomato's that are in the peat cups and removing them from the cups.  I found that those cups are problematic to good growth.  I started tomato's in late Feb they went from seedling tray to six pack to three inch pots.  I've planted a few into my final containers for the season, but my "extras" are still in three inch pots and are growing well and a few are starting to form blooms already.  I also water with softened water up to the point that it warms up enough that I can drag my two hundred feet of hose from the house to the  shop/garden/greenhouse area.  When I can water from the hose I am able to bypass the water softener.  So far I've never had any troubles that can be traced back to the salts in the water.  My softened water only registers about .02 EC (100ppm total dissolved solids) on my Blue lab EC meter.