A Tale of Two Seedling Trays

Question: Hello!

This is my first time starting seeds indoors in earnest and I planted two trays. One filled up with tomato plants and the other has peppers and some cherry tomatoes. I used seed-starting soil in new trays, had the plastic covers on for at least a week (more like 10 days for the second tray), watered with a spray bottle for the first week or two, and have had a fan on the seedlings since taking the covers off. The only difference between the two trays is that one had a heating mat and the other did not. (Well, the trays themselves are slightly different too.)

The tomatoes have all germinated and seem to be doing fine, but the pepper tray is a total failure. Germination has been between 20-50% and even the seedlings that have come up are weak and seem to be dying I've only two viable plants (cherry tomatoes) out of the 40 that were planted.

Any ideas on what might have happened? Is it too late to try again?

responder: Amy J. Extension Master Gardener - HC Replied March 27, 2023, 10:22 PM EDT
response: Several things may have occurred with your second tray of seeds. 1. Lack of heat without the heat mat may have caused lesser growth and conditions for “damping off”. This is a condition whereas soil is cooler and supports the growth of pathogens that reduce the health of the seedlings., 2. The pepper and cherry tomato seeds were not viable., 3. Lack of consistent moisture during the early growth stages.  You do not mention what type of light you are using. Seedlings generally require artificial lights. In the early growth stages the light should be about 2” above the seed trays.  You have ample time to try growing another batch of peppers and tomatoes. Throw away the current soil, cleanse and dry the tray and use new seed starting soil. I would recommend you use the heat mat and keep consistent moisture throughout the seedling stage. Below is a link with many details on seed starting.   https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors

responder: The Question Asker Replied March 28, 2023, 8:38 AM EDT
response: Ah, I should have mentioned the LED lights I have over them. Each tray has its own light. The only differences between the two trays is that the one that failed had the heating mat under it and it’s more of a cardboard tray while the other one is plastic. And seed viability seems unlikely as there were four different varieties of seeds in that tray. I’ve treated both trays essentially the same except I left the cover on the failing tray longer since they weren’t coming up as well as the other tray.From the three reasons you provided it sounds like inconsistent moisture is the most likely. Might the combination of the cardboard tray and heat have dried it out too much? I watered both trays with a spray bottle to keep it moist under the covers and have been keeping up with a drink from a watering can daily since the covers came off. On Mar 27, 2023, at 21:22, Ask Extension <<personal data hidden>> wrote:

responder: Amy J. Extension Master Gardener - HC Replied March 31, 2023, 7:56 PM EDT
response: Water is likely the issues. Cardboard does not hold moisture as well. If it was on the heat mat it would also dry out more rapidly.

responder: The Question Asker Replied March 31, 2023, 10:17 PM EDT
response: Thank you. I will watch that more closely this second time around. Wish me luck!— JulieOn Mar 31, 2023, at 18:56, Ask Extension <<personal data hidden>> wrote: