Drainage Holes & How Much to Water
You'll notice that nursery pots -- the drab-coloured, thin plastic pots that you'll buy most plants in -- have excellent, large drainage holes at the bottom for excess water to flow out of. Some decorative pots do, as well, but most of them -- particularly ceramic ones -- don't.
What gives?
Well -- depending on the method of watering you use, drainage holes can either be completely necessary, or they can be helpful but not strictly necessary.
There is no downside to having drainage holes at the bottom of a pot, ever!
No matter how you water, having the ability for excess water to easily escape is never a bad thing. If you don't have drainage holes, you do need to be pretty careful about watering, to make sure that that excess water doesn't sit at the bottom of your pot, since that can easily cause root rot and the death of your plant! This means that, for pots that have no drainage holes, the best way to water is to give smaller amounts more frequently. Depending on the plant's needs, this could mean just a splash now and then, or it could mean more -- you'll find your rhythm, but when there are no drainage holes err even more on the side of underwatering! If you're not sure how much water to give your plant, give it less than you think.
You may see posts online about "small amounts more frequently" being a bad way to water, with any number of claims about what it does to the soil; thorough research hasn't turned up a true claim that we've seen so far! The most common claim is that you won't soak your soil all the way down, but if you use a clear pot, you can very quickly prove this false; soil lets water move through it pretty effectively. If small amounts more frequently is the method that works for you, then do it!
But what if that doesn't work for you? What if you want to bottom water, or if your usual method of watering is to soak each plant until water drains from the drainage holes?
If you still want to use cute decorative pots, then there are two things you can do!
First, and easiest, is to only use the decorative pot as a cache pot -- meaning that you keep your plant in the nursery pot, but just hide it inside the decorative pot! This lets you keep the cute pots -- and even enables changing them up easily! -- without losing drainage. It's probably the best method, in fact! The only problem is that some pots are weirdly-shaped, and those can make cache pots difficult or impossible to use, but with some creative cutting, most decorative pots are usable!
Secondly, if you're brave, you can drill your own drainage holes! For ceramic pots, you'll need to purchase a diamond-tipped drill bit. Make sure to have water on the pot as you're drilling -- it helps cool down the ceramic, leading to fewer breaks -- and be ready to lose pots every once in a while, as sometimes they'll crack no matter what you do!
As a final note, and this can't be stressed enough:
Do not, under any circumstances, put rocks (or anything else) at the bottom of your pot to "increase drainage"!
Not only does it not increase drainage -- despite the fact that it seems like it should -- but it actually makes it easier to overwater by reducing the amount of available soil in the pot and raising the effective water table!
Basically, there is no "excess" water to drain until the soil is saturated, so even though there are pockets of air underneath the soil for water to drain into... it doesn't drain until the soil above it is already saturated, which endangers any roots that are sitting in waterlogged soil!
It seems backwards, but it's true! If you've already done this, you don't need to go repot everything right away to remove them by any means -- just remove them the next time you repot!