Chilis come in various breeds and they have different sizes. There's couple of things to consider in pots: Pot size and pot type.
When choosing a pot, first thing is to determine how big the plant grows naturally. If you just have a bunch of seeds or seedlings do some research online. Simple way is to search in google for the variety, for example: hainan yellow chili height
The first few search results will tell you that hainan yellow habanero will grow about half a meter tall (fatalii.net and wikipedia).
What if you have another breed, for example Carolina Reaper? Googling will reveal that "The Carolina Reaper can grow to a height over 4 feet tall." (chilipeppermadness.com). That's about 1.2 meters.
You can find height estimates for different chili types here:
Small and big chilis will need different size pots. Let's put some estimations here for pot sizes based on my personal experience:
Large chilis (growing taller than 1 meter)
Seedling pot: 5 Liters soil capacity
Mature plant pot: 20+ Liters soil capacity (or even up to 40L)
Smaller chilis (growing less than 0.5 meter tall)
Seedling pot: 1 Liters soil capacity
Mature plant pot: 10 Liters soil capacity
These are rough estimates, not the absolute truth. You will find that some people will argue for smaller or bigger sizes. The purpose here is to give an outline that allows you to choose a pot that doesn't get you in trouble. You'll be fine with these sizes.
A common problem that growers face is growing plants in pots that are too small. This will limit how large the plant can grow.
Some facts about pot size:
Each plant has a genetic tendency to grow to a certain maximum size. Grower can regulate plant size with pot size and by pruning the plant. (read more about bonsai chilis and pruning in later articles)
Pot size has a tremendous effect on maximum plant size. A small pot will prevent a plant from reaching its genetically determined maximum size.
A plant will regulate its size autonomously. When roots extend to the maximum capacity of the pot this will show up as reduced growth of the foliage and branches. Small pot = small plant.
The following video shows the tremendous effect of pot size on plant size:
Obviously, if you want a lot of harvest you need a large plant. Consequently you will need a big pot. When in doubt, go for bigger ones! Everyone wants to get maximum yields!
The next thing you need to determine is what kind of a pot you buy. There are many different kinds on the market. The following list isn't exhaustive but should get you started:
Plastic / clay pots
Cheap and easy to find. Mid-size pots are easy to stack. These are handy for growing the seedlings into a small chili plant of perhaps 30cm height. After small plants are transplanted to bigger pots these pots are easy to put away for storage.
Watering happens typically from the top and water drains down through the soil. Some nutrients will be lost with the excess water. Top watering may cause the plant to grow roots heavily at the top layers of the pot, and not grow deep roots.
Water these pot types only when the top soil is dry to the touch. Poke your finger 1cm deep in the soil. Does it feel dry? If it does then it's time to water the plant. You want the roots to go deep!
Make sure you only get pots that have proper drainage, e.g. holes at the bottom. Root aerination is important to prevent root rotting. If there are no holes in the bottom get a drill or hot screwdriver and make some holes!
Some growers prefer clay pots, but I have never personally figured out any big difference between clay and plastic.
Handyman tip: You can also buy a stack of cheap plastic buckets for a dime and make holes at the bottom. This will work just as well. And you can probably find nice coloured buckets that way!
Below: cheap plastic buckets make a good mid-size pot. Here I'm experimenting with an idea where the inner bucket has holes at the bottom while the outer bucket does not. There's 2cm layer of leca balls in between, providing same functionality that self watering pots do. I discarded this design later as wasteful eventually although I feel it kind of worked. Simplicity is better - just a simple pot with holes at the bottom will do the job just nicely!
Self watering pots
These pots typically have a small water reservoir at their bottom, and a watering system. The water is added through a pipe to the bottom. Typically there's a tester stick that you can use to determine when it's time to add water to the reservoir.
After adding water the soil pulls the water up by osmosis principle from the water reservoir.
Plant will grow roots down deep in the soil to pull in the water it needs. There is very little risk of overwatering because excess water will be deposited in the reservoir space.
This pot type is especially good if you've got an environment where you can't water the plants often. I have excellent experience from office environment where company has bought a number of self watering pots for ornamental chilis. The plants are watered only once per week by filling up the water reservoir and they do really well in the office!
Growing bags are my personal recommendation for large mature plants.
First of all, bags are easy to store, handle and move around. They can be stacked, stored in a small space, transported, bought online easily. They cost very little. Most of them can be bought from amazon or other online stores. They come in many colors and styles and can really spice up the look and feel of your garden.
Second, the bags are made from fibrous material and they naturally provide the best possible root aerination. This means the risk of root rotting is as minimal as it gets.
Using bags will naturally prevent plants from becoming "root-bound". Root-bound happens when plant's root reach the edges of a (plastic) pot and start circulating the edges. When the plant grows larger the circle-shaped roots will slowly strangulate it. In a growing bag the roots sense that the soil at the edge of the pot is dry and they will not reach the edges, and hence, they won't start circulating the pot edges.
The only flipside for growing bags is that they will have a moist bottom at all times. You can't really have them indoors unless you put a large plate under them. But for growing outdoors they are the best!
Here's a maturing Charapita Chili in a pretty 20Liter bag!
Railing pots are usually long, rectangular pots with about 10-15 liters capacity. They often come with an adjustable railing attachment and support. You put the support on the balcony railing and the pot is attached on it. It's best to install the pot inside the balcony rather than outside. You don't want it to fall down on anyone.
Most people use balcony railing pots for ornamental plants because they like how flowers look. Chiliheads will be thinking of putting something hotter there instead!
I have excellent experience from growing small-size chili varieties in railing pots. They are pretty when they flower, and very pretty when they make colourful peppers. Check out this list of small sized chili plants http://www.reimerseeds.com/Peppers-by-Plant-Height.aspx
I wouldn't put more than two plants per railing pot because of space constraint and rather small soil capacity.
Image below shows small size bullet chilis (thai padi variant) in a railing pot:
Before you hurry up buying pots and soil, please exclude rough gravel / stones / pot shards / leca balls from your purchases!
Common gardening myth says you should put some rough material at the bottom of the pot to increase drainage and prevent root rotting. This is far from truth! The truth is that adding coarse material to the bottom of pots will increase the chances of root rot.
Just fill the pots with ordinary potting soil and you'll be just fine!
Happy potting moments!
(Image below: a young transplanted Carolina Reaper in a 20Liter growing bag)