Leaves of tomato seedlings in starting mix yellow from start

Question

I started tomatoes indoors under CFLs like I have for years, but this year every one of my tomatoes have yellow sickly-looking cotyledon/first leaves and are taking forever to develop their first true leaves. I don't remember ever seeing this color predominate the way it is this year.

I have them in Burpee Seed Starting mix in paper carton cell trays sitting on a wicking mat stretched over a board and draped down the sides, pulling moisture up from a reservoir below. This keeps the mix consistently moist by wicking action.

I germinated them at 85 degrees soil temp and then once they were all up let them drop to 65 degrees (ambient temperature in that part of the house). Could that be too much of a drop for seedlings?

My well water here might be a bit on the high pH side, possibly as high as 7.0. It has no chemicals and has not been softened. Well, I guess I do sometimes mix a bit of warm water with the cold in the reservoirs, and that is softened, so maybe there's a residual salt in there? Any chance that's the culprit? And the Burpee starting mix does say it has some food in it, so it could be an excess of fertilizer salts too soon for such tiny seedlings?

My lighting is a shop tray with four 48" 32W T8 flourescents @ 6000-7000K, hung a few inches above the plants. These have worked fine in the past. They always end up a bit spindly at planting time but the plants have always stayed green.

Other ideas?

Answer 1

Notes about your Light Source

You wrote that you are uaing CFLs. I think you mean "Compact Flourescent Light Bulbs".

Most light bulbs, in general, do not produce the correct color of light for plants. Instead of "incorrect color of light" we could talk about "incorrect spectrum of electromagnetic radiation".

Plants leaves contain a green chemical substance known to scientists as chlorophil.

Chlorophil absorbs energy more readily from ured and blue light than other colors. I reccomend red and blue light emitting diodes over compact flourescent bulbs.

Even better than red or blue light emitting diodes, would be natural sunlight. Using electricity to power electric lighting usually involves burning fossil fuels a long way from your home.

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Distance between top of the dirt and bottom of the Dirt

By "dirt" I refer to the growing medium or seed starting mix.

I have grown seedlings for more than 15 years.

When the plants are sickly, it usually is because the plastic pots, or paper-based cell trays, or growing vessels, are too small.

If all of the dirt I wet, the roots of the plants rot, or get damping off desiease.

The bottom the the dirt layer should be wet.

The top of the dirt should be dry.

If all of the dirt is wet or all of the dirt is dry, then the seedlings die.

I reccomend increasing the distance between the top of the soil and bottom of the soil.

Taller pots work better than short pots.

If the distance between the bottom of the growing vessels and the top of the growing vessels is more than 6 inches, then the bottom of the growing vessels can be sopping wet while the top is dry or slightly damp.

If most of the water is not touching the plant roots, then the roots will not rot.

Most paper cell trays are not tall enough to ensure that the bottom can be soggy and sopping wet without the plant roots rotting.

If you try to let teeny tiny cell trays dry out, then whole thing will dry out instead of only the top 2 inches of soil.

If each seedling cell is smaller than a baseball, then the tomatoes will always be either too wet or too dry. I reccomend big pots, wet at the bottom, and dry at the top.

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PH : sour acidic soil versus bitter alkalyne soil

You wrote that your well water here might be a bit on the high pH side, possibly as high as 7.0.

7.0 is neutral. 7.0 pH is the ph of water. The ph of water, also known as dihydrogen monoxide, is a good PH for plants. A pH level of 7.0 is not sour acidic and not bitter alkaline.