Basic Houseplant Care: Repotting Versus Potting Up

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When it’s time to repot, should you increase the size of the pot? Photo: Hall’s Flower Shop and Garden Center

Repotting. Potting up. They’re the same thing, right?

Not quite. 

Repotting is a more generalized term. It means moving a plant to a new pot. There is no implication of pot size. 

Potting up specifically implies moving the plant into a larger pot. And that’s not always what you want to do.

Pot Size Is Linked to Growth

This young African violet may need to be repotted into a larger pot in only a few months, but once it reaches its full size, it will probably be happy in a 6-inch (15-cm) pot for the rest of its life. Photo: SueLee Charron

Potting up (moving a plant to a larger pot) tends to encourage it to grow faster and become larger. It’s the sort of thing you do to a younger plant, sometimes more than once a year. For example, you’d want to start a stem or leaf cutting in a small pot, but as the cutting grows into a plant, it will need more space, so you’d move it into a larger one, perhaps only a few months later. And likely a larger one again the following year. But as it attains the size you want, you reach a pot where giving it a larger pot is no longer worthwhile. 

Perhaps it has already reached its full size and will grow no further. That would be the case for an African violet or a cyclamen, for example, also many orchids. So, no need to pot up. But you’d still need to change the soil. So, you’d repot into a container of about the same size.

Once a houseplant has reached about the size you want, there is no reason to repot it into a bigger pot. Photo: http://www.costafarms.com

Another possibility is one you run into most often with larger houseplants, especially indoor trees. There is practically no limit to how large these will become, but there may be limits on how large you want them to grow. If your dieffenbachia or ficus is already as big as you’d ever want it to be, or nearly so, you wouldn’t want to repot it into a larger pot: that would just encourage it to become even bigger. Instead, you could repot into a pot of the same size and slow it down. 

I have plants that have been in the same size pot for more than twenty years. Two examples are a huge, bulky croton that I certainly don’t want to see grow any larger and a money tree (Pachira aquatica) that is nearly up to the ceiling. Yes, I could replant these giants into bigger pots, then prune them back when they go into a growth spurt, but why bother? Essentially, I’m underpotting them: repotting them into pots smaller than they would like, and that nearly stops their growth cold. Neither of these two plants has grown to any noticeable degree in twenty years. 

Essentially, underpotting is the equivalent of bonsaiing your plants: using pot size to keep their growth to a minimum, as bonsai masters do.

Repotting to Change the Soil

The main reason for repotting a young plant is to give its roots room to grow. But the main reason for repotting a more mature plant is to change the soil. 

You can see minerals salts building up on the side of the pot. Photo: garden.org

Over the years, mineral salts tend to build up in potting soil: minerals from tap or spring water, from fertilizer, etc. And as they do, they become toxic. When minerals in the soil around the roots are more concentrated than in the plant itself, water begins flowing out of the plant rather than in, leaving it in a constant state of drought stress. By unpotting the plant, then removing most of the old contaminated soil before repotting into fresh soil, you give the roots a new lease on life.

I find that I can get away with repotting small to medium-size plants (ones I don’t want to see grow, that is) every 2 to 3 years. Big ones in big pots can hold out for 4 to 5 years. Or you can try top-dressing and delay repotting even further. Read the article, If You Can’t Repot, Top-Dress for further information on that technique.

Clean Pot Needed

Clean the pot to remove mineral salt buildup … although cleaning inside the pot is more important than cleaning its outside.. Photo: saigonpotteryfinearts.com

Do either thoroughly clean the pot before reusing it (minerals build up on the pot surface as well as in the soil) or, more logically, repot into a new or clean pot. (That way you can take your time and clean the old pot later.) And it can be a pot of exactly the same dimensions.

So, you decide. If you want your plant to grow, pot it up. If you want to limit its growth, yes, do remove the old soil, but repot into the same size pot, thus keeping it underpotted. Simple, isn’t it?

Repotting is best done in early spring, just as the plant begins a new growth cycle. And it can be carried on throughout the spring and summer if that’s more convenient. It’s best not to repot houseplants when their growth is at a standstill, usually from late fall through winter.

Underpot to Keep Indoor Trees Under Control

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Do you really want your indoor trees to reach the ceiling? Photo: apartmenttherapy.com

Indoor trees are marvelous things. They give you the feeling of being in the great outdoors even while you’re in your own living room. They provide shade, making reading easier, they help purify the air and they perk up your décor like nothing else. But they do tend to get big over time. Ficus, scheffleras, money trees, corn plants and other indoor trees just want to keep growing. In nature, some can reach 50 feet (15 m) or more in height. That’s just not possible indoors. So, what’s an indoor gardener to do?

Benign Neglect

Once your indoor tree (here, a Ficus benjamina) has reached the size you want, slow it down by no longer potting it into bigger containers. Photo: Julie Deken, pinterest.ca

One thing you can try that requires very little effort on your part is to simply stop potting them up. That is, start leaving them in the same pot year after year instead of moving them to a bigger one every two to three years, as you’ve been told you ought to do. With their roots severely constrained, most trees wisely start to grow more slowly, some putting on almost no new growth worth mentioning, but simply replacing older leaves with fresh ones. 

Severe underpotting has helped keep this nearly 400-year old bonsai small. Photo: Ragesoss, Wikimedia Commons

Underpotting in this manner has been used in producing bonsais, tiny, pot-bound replicas of full-sized trees, for 2,000 years. On indoor trees, you simply apply it at a later stage, when they’ve reached the size you want.

Now, depending on the species, some selective pruning may also be needed, cutting back taller branches to stimulate denser, shorter growth, but by the time a tree has been in the same pot about three years, you’ll find you won’t need much of it. Underpotting will have slowed it down considerably.

Saves Time, Effort and Cash!

Repoting a large plant is a lot of work. Do you really want to do it? Photo: roomfortuesday.com

Besides, repotting a big plant is a major hassle. They’re heavy and awkward to manipulate. Just getting the old pot off without a second pair of helping hands can be a struggle! If you keep the plant in the same pot year after year, you avoid that.

Plus, you save the price of fresh soil and the cost of a new, bigger pot. OK, admittedly, potting soil is not that expensive, but pots—certainly big pots suitable for an indoor tree—certainly can be.

What About Mineral Salt Buildup?

Mineral salt buildup inside a pot. Photo: whav.net

One of the reasons for repotting houseplants has always been to reduce the buildup of mineral salts, deposits caused by the use of hard water and fertilizer that have high concentrations of dissolved substances such as calcium carbonate, sodium, and iron. They’re often visible as a sort of white to yellow crust forming on the inside of the pots and are a sign the potting mix is becoming slowly toxic to the plant. By repotting into a larger pot, thus changing part of the old growing mix and adding fresh, uncontaminated mix around the root ball, you can help alleviate that. 

So, what happens if you’ve stopped moving your tree into bigger and bigger pots. Won’t the mineral salts build up until they kill them?

Not if you try one (or both) of two things: leaching and top dressing. 

In leaching, you pour fresh water over the soil until it drains out the bottom. And keep it up until you’ve applied the equivalent of two to three times the pot’s volume. That will dissolve and carry away much of the minerals. Then you simply throw away the drainage water. 

It’s easy enough to leach a small houseplant in the kitchen sink, but trees may need to be leached outdoors. Ill.: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux

Leaching a tree while it’s indoors is pretty much impossible, though. It’s not as if you can put it in a kitchen sink to leach it as you would for a smaller plant. And it may no longer fit into the shower. I leach my indoor trees simply by putting them outdoors for the summer without a saucer underneath. There, Mother Nature does the leaching by supplying regular downpours. In a drier climate, simply water more than strictly necessary and the leachate will drain off, carrying the excess minerals away. 

Top dress by scraping off the top layer of potting soil and replacing it with fresh mix. Ill.: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux

To top dress, just scrape off the top layer of soil (about an inch/3 cm or so) annually and drop it into the compost pile. That works because mineral salts tend to migrate upwards and mainly accumulate in the top part of growing mix. By removing the top layer of soil, you’ll severely reduce mineral salt buildup … and all that’s left to do is to replace the inch (3 cm) of soil removed with an equal amount of fresh potting mix.

How Long Can You Delay Repotting?

But how long can you keep this underpotting thing going? 

Actually, I don’t know the upper limit, but I have some fairly imposing corn plants and ficuses that haven’t been repotted in 20 years and they’re still doing fine just through leaching them outdoors in the summer and annual top dressing. And remember 400-year old bonsais in their tiny, root-cramped pots. 

I therefore figure there is probably no real upper limit. You can just keep not potting up pretty much forever.

So, slow your trees down by not repotting them, a laidback solution to a common houseplant problem!