Light to the roots stresses and confuses the plant, which produces hormones partially according to how light hits it.
Algae also needs light, and is likely to grow in your soil if the container is clear.
For small seedlings, I have used plastic cups with no apparent problems BUT and this is important, as soon as you see roots visible, transplant into something lightproof.
Take a bottle of black spray paint to your milk jugs (outside only). Problem solved.
stinkyattic Reviewed by stinkyattic on . clear cups i was reading the shot glass thread and some one said it might be damaging to the roots if the light got on them. is this the case and if so what actually does it do im growing mine for veg in clear paint mixing cups and then im gonna flower in milk jugs also clear. thanks in advance for the info! Rating: 5