Pepper Seedlings Turning Yellow UPDATE

I posted a couple of weeks ago about how my once healthy pepper seedlings were starting to turn yellow. They started out a rich green, then developed purple spots on the leaves and then started to turn yellow.

I did some research and found a variety of reasons why this might happen. Luckily most of the reasons were not disease related.

 Possible causes:

- Watering with chlorinated water.

- Over watering causing nutrient deficiencies or excess nitrogen absorption.

- Too much light (from florescent lights indoors) causing a phosphorus deficiency.

Purple spots on leaves and the stem is usually a sign of a phosphorus deficiency.

Yellowing leaves are usually a sign of a excess nitrogen.

I decided to leave most of the plants alone and see what happened over time. With these plants I stopped watering them until the soil was dry. Then I only watered with non-chlorinated water. I filled a jug with tap water and then let it sit out overnight so that the chlorine would evaporate.

I chose 3 plants as test subjects to see if a different treatment would make a difference. I removed the 3 plants from their pots and examined the roots. They looked healthy  but the soil felt pretty waterlogged. I carefully  shook most of the soil off of the roots and replaced it with new dry soil. The plants were watered with regular strength liquid kelp (made with non-chlorinated water). Before this watering the seedling had only been watered with 1/2 strength liquid kelp. I only gave the plants enough liquid to dampen the soil. Then they were set under the lights and were not watered again until the soil was very dry.

No changes were made to the lighting set up.

After the first week all of the plants had leaves that were drying up and falling off, but also showed some new green growth on top.

After the second week (now), I am starting to see a big difference between the 2 groups of plants

Plants left alone:

- bottom leaves dried up and fell off.

- new leaf growth on top, but all of the leaves remained pale, curled and upright

The test subjects:

- bottom leaves dried up and fell off.

- at the beginning of the second week new healthy leaves formed and plants appear to be on the mend.

Because the test subject plants seem to be a success I repotted the remaining plants today and gave all of the peppers a drink of regular strength liquid kelp.
Hopefully they will all return to normal or at least be on the road to recovery in time for planting.

UPDATE 5/2/2012: I only bottom water my seedlings. Instead of watering by pouring water into the pot from above, instead fill a tray with water and allow the plants/ soil to absorb the water. This will help prevent the nutrients from being washed out of the soil.