Stems keep breaking

[DeepWater]

A few weeks ago I added a few plants to the aquarium. Following guidance from the master, I left the dark red ludwig in the packing foam and plastic cup.  As can be seen, every stem has broken off within an inch of the soil level.  Why does this occur?

I jammed several of the floating stems into the rocks, however part of the concern is that several were very limp.

[MattyM]

I've had hit or miss success with stem plants. Couple of ideas:

1. You can try some root tabs in case it's a nutrient thing (and Easy Green if you aren't already), and/or
2. Float the stems until they start to grow roots, and try planting again. 
3. Get a small terra cotta pot, and try putting a different substrate in it.

Some stem plants I had to give up on, no matter how much love I gave them they just didn't like something about my water - even the so called "easy" ones. 

[Rube_Goldfish]

Ludwigias have given me trouble where I've had good success with limnophila, bacopa, and rotala, so sometimes a plant just doesnt like your tank. Have you had any luck with any other stem varieties?

@MattyM has some good suggestions above, especially the floating them part. What is the stocking? Anything that might uproot plants?

[DeepWater]

Thanks