growing 3 plants in one container (what week should i combine them)?

i been reading about growing 3 plants in the same container recently. i understand the the yield will be better than if you topped a single plant. what im not too clear about is when to transfer the plants from the first container (im going to start them in red party cups) to their 15 gallon Smart Pot container. My plan is to veg them from seed (meaning germenation, seedling, pre veg included in my veg time) for 5 weeks. my question is when is it okay to take them from their first container to their bigger container?

would it be the third true leaves or around the fifth true leaves?

i know how plants do better in a small container for 1-2 weeks so water and nutrients can settle at the bottom of the container and the new plant can use its newly form roots to absorb it compared to 3 tiny plants in a 15 gallon container. im asking for your advice guys! i respect what you guys have to say, and even if you lurk around the rollitup forums and dont usually contribute, i would love to hear your input! serious, i want to learn from people with knowledge and not from mistakes. thank you guys for your time and concern, it means alot!

Soon as roots are ready to transplant.. i.e got roots out the bottom of pot then transplant to larger container.
Sooner the better to allow roots to develope further before flowering.

Placing a small plant in a large container if anything....... is better as less transplanting... there's less shock..... healther plant.
Generally only reason people plant first in smaller pots is due to ease of use. Less soilso less watering etc. Planting your seedlings directly into say a 20L pot instead of a 3L pots for example takes up more room and takes more water.
Basically what i'm trying to say badly is if you got the room and roots are developed transplant soon as possible. In the long run your plants will benefit from transplanting sooner over later.

One downfall to combining plants is if 1 plants get a disease or deficiency it is generally transfered to the other healthy plants also.

should work....never heard of this...5gal of soil per plant aught to work?
i need to research this cause my knee jerk response was one of anger....3 plants to a pot?
Intriguing...

technically you can transplant at any stage...it's all a matter of preference. The trick is to not shock or stress them.
(Go with nice peat starter pots, skip having to monkey with transplants)
in general this seems dependent on your seedlings pot size, since most people say to transplant after rootbound conditions are reached.
i have my own opinion there, but to much data confuses...
herd mentality still produces fine herbage...go with what works, tinker after you are comfy and have a few grows under the ol belt

It's never a good idea to put more than 1 plant per pot IMHO. 15 gal. is a huge pot, so three 5 gal. would be better.
Daniels

bumping for more opinions. thanks to Hillcrest, ChubbySoup, Danielsgb for you info, i'll take it into consideration.

bumping 2.0

use the 20 + gal rubbermaid storage box's

A plant needs to get close to root bound before it's up-canning. It is so it doesn't spend time trying to get a large root system before growing foliage. If you put more than 1 per pot you are asking for problems. 1 will probably be the dominant, while others suffer. 1 may need more nutrients, 1 may need more of a certain nutrient. Cal/Mag is a common deficiency.
Daniels