Plant growth is based on a lot of factors that aren’t necessarily correlated to being inside or outside. Plants have a few specific requirements to grow. They need water, nutrients, light, and carbon dioxide.

Water can be supplied by a human to a plant regardless of whether it is kept inside or outside but being outside since water isn’t a resource that is difficult to come by. The same goes for nutrients. Plants get their nutrients though the soil they are planted in, so if a farmer prepares by planting with enough fertilizer, then the plant should be fine whether it is inside or outside. A problem arises when you consider how large the plant will grow. The larger the plant, the more room it will need to grow, and the more soil/fertilizer it will require. Unless you are willing to set aside a large area of your home, then larger plants would be better suited to grow outside. Since plants need sunlight to grow it would seem best to keep them outside, but if you are willing to purchase specialized light bulbs that mimic the sun then you could grow the plant indoors.

Also, you could keep the plant by a window, but be warned: the sun may not enter through the window throughout the entire day. Lastly, plants need carbon dioxide, a gas from the air, in order to grow. While carbon dioxide is present everywhere, it is actually more concentrated inside homes than it is outside. This is because humans produce carbon dioxide by breathing so a lot of it gets trapped indoors.

In conclusion, with enough time and energy spent into the set-up you could grow plants faster indoors than outdoors. Take a look at greenhouses, they are specially created indoor environments meant to grow plants faster. This question is really interesting because even though it is possible to grow plants more quickly inside, it requires a lot of preparation in advance in order to achieve the desired outcome.

It depends! Plant growth depends on how much light the plant receives for photosynthesis and how many nutrients are in the fertilizer. Some plants, like orchids, will actually die in direct sunlight so they grow faster inside. Yet other plants, like sunflowers, need direct sunlight to grow really fast and perform better outside.

Some plants can't grow inside, because they need more light or different temperatures. The light is especially a problem, because there's a lot less light indoors than outdoors, even when the sun is shining indoors. Only a few plants are 'indoor plants.'

Here's an article that gives a lot of useful info:
outdoor and indoor plants

Some plants can only grow indoors, if you live in a place that gets cold, and the plant can't grow in a cold place. But plants growing indoors don't have as much space to grow as plants growing outdoors in the ground.

Greenhouses are usually hot and humid, for plants will grow better when it's hot and humid.

Here's an experiment done by a student who studied a cactus and another plant, with 1 indoors and 1 outdoors, for 6 days:
plants growing

Thanks for the great question!

Plants need three different things to grow: sunlight, a gas called carbon dioxide (which you produce when you breathe out), and water from the ground. In the wild, plants are stuck with whatever is around. But humans can move plants indoors and change how much sunlight, carbon dioxide, and water the plants get.

In your home, plants may not grow as fast as they do outside because there is less sunlight. However, you may have heard of greenhouses, which have walls and roofs made of glass. The glass lets light in, which then heats up the room. The heat cannot get out of the room, and so everything in the greenhouse gets hot. So plants inside a greenhouse can grow faster than plants outside because they are being cared for by humans in ways that we know makes them grow fast.

Thanks for the great question,

Depends on the plant - some plants grow best with more light, some with less light. Too much light can damage a plant. Plants that grow best with less light tend to grow better inside than out, while other plants grow better outside. Generally, if a plant normally lives in the shaded understory of a forest, beneath the trees, it probably will grow better as an indoor plant, while plants that live away from trees, or that reach the forest canopy (like trees themselves) will grow better with more light outdoors.