Here's another view of the plants leaves (notice edges). This picture was taken before I thinned out some plants.

Well, what I decided to do is remove the aluminum foil from the sides of the grow light. I heard aluminum foil helps give the plants more light. But maybe tropical milkweed plants don't care to much for a lot of light. Although they are full sunlight plants. Will see. If anyone knows what might be causing these red spots comments would be great. Thanks :^)

I was actually Just looking for an answer to this. I have the same issue.
I just noticed that my milkweed that was being wintersown had started sprouting. I brought them in and put them under lights. A few of the seedlings are about 3 inches tall. They've gotten the same thing your describing. I wonder what it is.
They are sitting on a black shelf. Lights are about 6 inches away from the lights.
Hmmmmm....
How are yours doing?

I have observed this in a greenhouse and suspect it's normal, just part of the plant's growth. In other words, not pathological.

so jealous of your sprouts!! keep us posted :)

Congratulations on your new seedlings! They look very healthy to me, with great looking, stocky stems. The little seedlings might be old enough now to feed with a heavily diluted liquid fertilizer but that is your call. The only thing I can think of to suggest is to make sure you don't over water as the roots need to be able to breath. Based on your photos, it looks like you're doing a good job in this area.

The bottom leaves in your photos might be the seed leaves (cotyledons) and if so and I am remembering correctly, once the plant draws all the nourishment from them, they die and fall off. Maybe this is what is happening to these tiny lower leaves.

The coloring on the leaf edges is most likely normal. Depending on the variety of Tropical Milkweed you are growing, I've found some exhibit this type of coloring, especially the newer Red/Gold varieties.

Thank you so much for growing milkweed for the Monarchs.

Mary

Hey eddie980 How are your plants doing?
Only a few of the swamp milkweed I have under lights are still getting that Burgundy coloration on the leaves.. I have noticed that when I dont turn the fan on it gets worse..

Have you noticed any difference with things you are doing differently if any?

I have almost 300 swamp milkweed seedlings growing and 6 tropical..

The reddish edges could be a sign of a mineral deficiency. From the looks of the leaf color, your plants may be anemic. If they have strong root systems already, try a half strength dilute mixture of a balanced fertilizer (20-20-20 with trace, or some such) and see if that helps.

I fertilize my seedlings (under grow lights and a heat mat) with a half strength after the second or third set of true leaves emerge.

I currently have seedlings of tropical milkweed under lights and I'm seeing the same coloration. I did use a dusting of rock dust mixed into the potting mix when I transplanted and I feed with a very weak liquid fertilizer. The plants have extremely sturdy stalks and are already putting out side shoots. Thank goodness I read this thread earlier or I would have been looking for a reason for this coloration. From everyone's experience, it appears to be a by product of growing under lights.

Mary

mary, what is your setup? yesterday i bought 4, 4 ft t8 incandescent shop lights. my work/potting benches are 8ft long and 2 ft wide...