I've probably potted thousands of plants by now! It's crazy to think about. In the shop, specifically? The number might be in the hundreds; but overall? It's thousands for sure. That's all to say: I'm pretty well-versed in the art of getting my hands dirty. I've got a few tricks up my sleeve- and, well, quite a bit of soil up my sleeves too.
When's the Time?
First thing's first. When do you do it? It's nothing seasonal, despite what the internet may say. Yes, there's more sun in summer, and plants grow faster because of that. But to say that regular houseplants are dormant in winter? that's a pretty common exaggeration. They're growing! Just not quite as much.
So if it's not about the time of year, how on Earth are we meant to know when to do it?
Don't worry, it's simpler than you might think. It's a one sentence answer, in fact.
I repot my plants when the soil starts drying so quickly that keeping up with the watering becomes inconvenient.
Ok, well, maybe there's a tiny bit more to it than that. Sometimes I'll repot new plants the day I get them to get them into more familiar soil and to check on their roots. New plants you buy are usually in way too much dirt or way too little. The internet will say to wait, but it's really not necessary.
Sometimes I'll repot plants to group then together and save space. Sometimes I'll remove 1/3 of the roots and put a plant in a smaller container because it's cuter that way.
Why Repot in the First Place?
It's not a nutrient thing- there are better ways of addressing that type of issue. It's more about the soil's ability to be a good sponge for what you need. If you just watered your fern two days ago, and come home to it wilting: you'll either have to water daily, or go for a repot.
Over a very long span of time, soil breaks down into liquid and gas. It decomposes with the help of tiny little bugs and bacteria and whatnot. When the soil dissolves into the water, the plant eats it! Well, at least that's part of what happens. If your pot has holes and you water at the sink, you'll definitely be losing some soil that way as well.
The other, probably more significant part, is the plant giving the soil a good squish. The roots branch and grab and hold onto the soil pretty tightly. This kinda compresses it and flattens the pores- the tiny holes where air and water used to live. Think of, like, a sponge that's been vacuum-sealed- or a piece of bread that's been steamrolled. Not so airy now!
With the pockets all squished out, there's really not much space for the water to hang out. People call it "rootbound" when it gets to that point. That's when you might end up with some issues. You'll be watering extra often to keep up, since the dirt sponge has lost its holes! A lot of the times, in pots with holes, the water won't even be able to absorb. You'll have to water gradually over a few hours, or soak the bottom of the pot in a water tray. It gets pretty inconvenient.
But Some Plants "Love Being Rootbound"!
Wait, before we go into the repot tutorial, have you ever heard something like this? "<plant name> loves being rootbound!" What gives, man? Isn't being rootbound a bad thing? Isn't that what I just said?
Plants that "like being rootbound" are plants I "pot small". I don't know if "potting small" is an actual term, but it's what I tend to call it. Anyways, the love of bondage shared by these plants is more-so an issue of vulnerable roots. These plants are adapted to their soil drying quickly. If the dirt stays soggy for more than three days or so? They get mad about it- yellow leaves and brown squishy roots. The roots basically drown in the water and suffocate to death. Roots actually breathe oxygen, just like us! Still, the lists of plants that "enjoy being rootbound" aren't the most accurate things in the world. Even making a list of my own was pretty tricky, so I made several! These are some of the weirder plants. Most plants are somewhere between the two extremes and aren't as picky. Plants with thick stems, leaves, or roots are a lot more tolerant of soil that dries quickly. Plants that don't have anywhere to store extra water will struggle a lot more. They can go crispy or drop leaves if the dirt dries up!
Plants that Like their Soil to Dry Extra Fast
Most Cacti (not holiday cacti or mistletoe cacti)
Plants that Freak out If Their Soil Dries Completely
It's Just Water?
Wait, but if roots love oxygen so much, how do people root their plants in vases of water? It's adaptation! First, it's good to mention that oxygen travels 32 times as fast in plain water, when compared to waterlogged soil. That's a huge difference! In soil, you also end up with a bunch more microorganisms. These microorganisms will readily decompose a dying root if given the chance.
The cool part is that plants can actually react and adapt to water when they're planning out their new roots. If the plant knows its stem is all soggy, it'll grow its next roots with bigger tubes for airflow, a thicker waxy coating, and smaller pores. The roots become a scuba pack! Roots grown in soil don't have these properties, so they won't be able to handle those extra wet conditions. That's why overwatering is bad, but growing a plant in water from the get-go is fine. Still, hydroponics is a whole entire complicated science in its own right.
A Cozy Fit
Ok, ok, so pots. Which one do you pick? Well, if you know anything about my shop, you know I'm super biased. I use various glass or clear plastic containers without drainage holes. This way, I can see what's going on, and don't end up with the overflowing saucer of doom. If the soil is dry, I can see it. Is it's a swimming pool, I can see that too. If the roots are growing, I can see that. If the roots are getting brown and squishy, I can see that too. Ferns can be a little annoying in this type of container, though. Their roots are brown to begin with, and they'll try to grow baby plants anywhere the light reaches. This includes underground, right up against the side of the glass. I've started planting these guys in various ceramic containers instead. Still, no drainage holes!
Just make sure you don't use anything that gets much skinnier towards the top. You'll have a huge struggle trying to get the plant back out later.
So, what about the container size? If your plant is drying so fast that it's getting annoying, you'll want your dirt space to be just an inch larger, in total, than what your plant was in before. That way, it'll dry slower, but not so slowly that the roots decompose. This could be half an inch wider and half an inch deeper, an inch deeper, or an inch wider.
If your plant was rooted in water, you'll want a pretty snug fit for it in its new pot. If your plant is recovering from overwatering or root rot, you'll want a pretty snug fit as well.
Planter shape and design will need its own article. Just keep in mind: the more dirt surface is exposed, the faster it'll dry. This means a wide and shallow pot would dry faster than a skinny and deep one, even if they both contained a cup of soil. Think of it like spreading out paint. The paint that's been spread onto a surface dries way faster than the paint that's been poured into a cup. That's because the paint on the surface is in contact with a lot more air. Same thing goes for soil.
Let's Do This Thing!
Finally, the time comes for the act of repotting itself. I really don't use any tools: just my hands, a bin to catch old dirt, fresh soil, the plant, and its new container. Make sure your plant is in moist soil before you start. Otherwise, things will get pretty dusty.
If the pot is flimsy, like one of those plastic pots plants are usually sold in, you can give all the sides a nice squish. Don't flatten the pot, but don't be super gentle either. You're trying to compress the dirt a little more, so the whole plant/root/dirt block will come out more easily.
If the pot has holes, you can poke through these to help lift the plant out. If roots are coming out of the holes, cut them off. The plant should have more than enough roots to be ok with losing some.
Now, for any plant, regardless of the container it's in, you'll want to lay the whole plant/pot situation on its side in the bin. Hold onto the base of the plant (the area closest to the dirt) with one hand, and hold onto the pot with another. Pull gently, while giving the plant a little wiggle to help loosen it. In most cases, this'll work. In particularly difficult cases, you'll need to cut the plastic pot off of the plant, or create some gaps. Gaps are created by wedging something between the dirt/root block (usually called the "rootball") and the side of the pot. I recommend something flexible like a silicone spatula. Just wash it really good when you're done.
Now the plant should be out of its pot. Usually, most of the dirt stays attached. If most of the dirt falls away easily, you might actually want a container smaller than what you'd used before. Make it snug. If you find out the container you bought is too big or small, you can use an appropriately sized cup or bowl as a temporary home.
If the plant has thick and sturdy roots, you'll be able to remove a lot of the old soil without breaking too much. Plants are ok with losing up to 1/3 of their roots on occasion. You do this kinda like you're trying to untangle a ball of yarn, sticking your fingers in, wiggling them around, pulling things apart gently.
If your plant has thin stringy roots, you'll want to leave the roots be. You'll just break them a lot if you try to get the soil off.
Now, you'll want to put the plant into its new home. Once it's in, you can start adding the soil: poking and pressing on it to get it to go down and fill in most of the gaps. Make sure you cover the top of all the roots. You'll want to leave at least 1/8 inch height difference between the container height and the soil height. This is to make sure you can water the plant without it just overflowing. Leaving more space doesn't hurt. Sometimes I use a container that's too tall for my plant's rootball to fill. I just compensate by leaving several inches of empty space. The soil you're using should be slightly moist so it doesn't get dust everywhere. Inhaling soil dust is no fun. I don't recommend it. After that, I'll water with maybe 1/3 of what I would normally use. So that's maybe 1/9 of the container size? I'm just trying to wet the soil surface to get it all settled. I'll move the container of water or the container of plant around as I'm watering. That way, the water covers the whole top instead of just soaking deeper.
Whew! We did it! The next steps? Enjoy your plant, take a photo maybe, then take a nice nap. The repotting itself is much less of a process than reading or writing a whole article going into depth on it. It'll take just a few minutes, so go for it! You've got this.