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"How did you get them to grow so tall even for clones in a beer plastic cup?"
After cloning I let them veg under a 125W 10,000K HO florescent until I need them, sometimes 30" from the light. I've got a Skunkberry and a Northern Lights clone that are 2 years old, not topped or trained, and are 10"- 14" in height. I just neglect them until they're wilting, and hardly ever feed them.
The high Kelvin light helps keep the nodes close, even when the plants are far away.
I don't know if that's what let's me grow such tall plants in a 20 oz cup, but it's pretty easy as long as you really don't care if they live or die. I had a 2'+ Kali Mist, about 8 months old, that was veggining fine in a beer cup, I only switched to a 6" pot so I wouldn't have to water so much. Gives another concentration of roots too. The BOG method of transplant.
"I wonder if mine can grow that tall as well."
Yes, but you don't need to if you have the space and a powerful enough light. The plants will grow better in a larger pot. I always use a 5 gallon bucket for flower, just so much easier for watering.
"That way I don't need to change pots I'm growing mine in a 5 quarts bucket. Tell me if that's good."
Veg or flower? That's 1.25 US gallons - great for veg and you can flower good plants in a pot that small, but it's going to be a lot of work. 5 gallon buckets makes life easier
(if you ph ballance all nutes and water, and do not over feed).
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