Roots do not need to keep growing the whole time a plant is alive in order for it to live happily and grow. The only thing that is needed for a plant to live happily is all its conditions being met.
To avoid all argument in this thread I will ask this question alone.
When people transplant a plant such as this, It gives the plant more access to nutrients in that new soil and it continues growing correctly again as it once was.
But this is Not NEEDED and an absolution as most people growing marijuana seem to think.
Leaving the plant in that same small container and increasing the amount of nutrients that you feed it @ that time should be perfectly fine for that plant to be ok and start growing again once you knock out the plants deficiency.
Issues that come from growing in small pots are ALWAYS due to plants not getting enough nutrients to grow with.
What happens is this, You start a plant in a small container, it grows just happily. Eventually the roots suck out all of the nutrients in the soil where they have grown to and it becomes deficient in nutrients enough that it stops growing as it once was.
I have seen it over and over again and Im tired of the Myth/rumor being spread on these kinds of forums, namely this one so much.
Cannabis plants raised right indoors will NOT get "root bound" when its roots fill the pot.
Air-pots are a more costly growth system, especially when compared to other seed starting solutions. But they offer a small pot that is about a quart in capacity, and not as expensive. So you could use this for your larger seedlings that will be allowed to mature quite a bit before planting outdoors.
NET CUPS: Net cups were developed for use in hydroponics. These basket shaped cups have open slits in the sides and bottom. The openings allow plant roots to grow freely into rooting medium, nutrient solution or even into highly humid air!
In particular, air-pots are great for growing healthy perennials like herbs and even trees. Perennials are permanent fixtures in your garden that you want to keep for many years. But planting a root bound tree in the ground gives it a horrible start in life. It stunts plants and ultimately leads to increased death rates.
Video: Seed Starting Containers:
10+ Ideas for Vegetable Gardening
Such systems are very common and cheap to implement. They devote only a small amount of potting media to any given plant. But seedling trays are most useful in a nursery or greenhouse application. They may not be the best solution in a small scale home environment.
RENEWABILITY: Some seed starting solutions may seem simple and affordable at first glance. But a few of these systems are designed in a way that you’ll have to come back, year after year to buy them again and again. This is something worth considering. Would you prefer a reusable product that you can clean and use again next year?
The first and more important thing to bear in mind is that when it comes to seed starting, there is no perfect, single solution. What’s the best seed starting container? The answer to that question will depend upon the factors that are most important to you:
DRINKING CUPS / FOOD CONTAINERS: If you are brand new to gardening, you might not have many materials on hand. Starting from scratch can be daunting. And it can be quite costly. But it doesn’t have to be that way. Recycling containers is a free way to acquire some seedling containers without spending a penny!