Repotting Myths Busted

Gardeners make repotting more complicated than it needs to be and in the process, they have created all kinds of myths about the process. It’s time to simplify repotting and bust the myths around it.

Myth #1: Don’t Repot in Winter or When Plants are Dormant

Many believe that our tropical houseplants go dormant in winter but that is another myth. Their growth may slow down but most do not go dormant.

The belief is that dormant plants can’t handle the shock of being transplanted. Firstly, when transplanting is done correctly it does not shock the plant very much. Secondly, the stress is much less when a plant is growing slowly i.e. dormant. If you repot when the plant is growing well you will do more root damage and stress it more.

It is best to repot plants when they are growing more slowly but most will do just fine at any time of year.

Myth #2: Don’t Use a Large Pot

Online gardening advice is almost unanimous. You should “pot on” using a pot that is one size larger, or one to two inches wider.

The North Carolina Extension Gardener Handbook has this to say, “Choosing larger containers is beneficial, as they do not dry out as quickly and require less frequent watering. ”

Wow! That is the exact opposite of common gardening advice.

Think about plants in nature. They are almost always growing in the equivalent of a humongous pot. The truth is that plants grow well in any pot that has enough room for its roots. You can move them to a large pot.

However, a larger pot contains more soil and therefore stays wetter. If you are the type of gardener that overwaters, then a small pot might be better for you – but the plant does not care provided it gets watered correctly. Larger pots also take up more space and cost more to fill.

Another related myth is that plants grow faster in a big pot – that is also not true. Plants are genetically programed to grow at a certain rate. Better light, adequate water and temperature, and more fertilizer can speed up this process a bit, but it’s mostly driven by genetics. The plant does not even know they are in a pot so why would it affect the growing process?

Myth #3: Used Potting Soil Should be Discarded

Potting soil does not get old and it does not need to be replaced unless there is a specific problem with it.

Replacing it because of a pest rarely works. The same pest from another plant quickly finds the new soil. Some people replace it because it grows mushrooms, but they are a sign of healthy soil, not old soil. You are also unlikely to get rid of a disease by changing the potting media.

Growing with hard water can result in a buildup of white salt crust on the surface of the soil. In that case, scrap off the top inch, discard it, and reuse the rest of the soil.

Epiphytic plants, such as orchids, should be repotted with fresh media. They naturally grow in air and their roots rot easily when the media breaks down. For more on repotting orchids, see this video link.

With a few exceptions, there is no good reason for replacing used potting soil and it can be used for many years.

Myth #4: Don’t Fertilize After Repotting

I have never understood the rationale behind this suggestion, except that some potting soil contains fertilizer so you don’t have to add more.

Plants need fertilizer right after being planted. If you use new media and it contains fertilizer you do not need to add more. But how long does this fertilizer last? When should you start fertilizing? You have no idea unless you test the EC value. For that reason, I usually start fertilizing right away.

If you are reusing potting media, start fertilizing right away.

Myth #5: Add Drainage in the Bottom of the Pot

This advice has been around for a very long time, in part because it seems to make so much common sense. Stones or pot chards on their own drain very well, so putting them at the bottom of a pot should increase drainage. In recent years this has been called a myth but new science suggests that it might actually work.

This all has to do with something called a perched water table. Water does not move easily from small soil particles to the larger-sized stones. It will saturate the lower level of soil, before moving lower to the drainage material.

Even though adding drainage material in the bottom of a pot might work to reduce the amount of water in the soil, it may still not be your best option. To better understand this see Should You Use Drainage in Your Pots?

For an in-depth discussion of this topic, see my video, Understanding the Perched Water Table.

Myth #6 : Mist Your Plant After Repotting

Repotting can do some root damage which means plants have a hard time getting enough water. Some people suggest misting the plant for a few days to increase the humidity around the leaves.

Misting does not increase the humidity around the plant for more than a couple of minutes, so it is not worth doing. If you did a lot of root damage, put the whole plant in a plastic bag or some other kind of container. The moisture from the soil will increase the humidity in the bag.

This is rarely required. Most plants will do just fine even if a few roots are cut off. Just keep it well-watered and out of direct sunlight.

As an aside, pebble trays do not increase the humidity around the leaves either.

Myth #7: Visible Roots Mean You Need to Repot Urgently

This may or may not indicate a root bound plant. Tip the plant out and have a look at the roots. If there are a lot of circulating roots it might be time for a larger pot. A single long root coming out of the bottom is not a reason to repot. You can just cut the root off if it bothers you.

On orchids it is quite common to see roots outside of the pot.

Myth #8: Plants Should Always be Repotted into a Bigger Pot

That may be true in some cases but not all. It depends on the plant and your goals for it.

You can keep a plant in the same size pot for 50 years. A smaller pot will limit plant growth and you may need to remove excess roots and leaves when you report, but you don’t always need a bigger pot. My wife’s Anthurium has been in the same pot for about 30 years. When it gets too tall, I cut the bottom section off (including most of the roots), and pot it up. It is now lower in the pot and it starts growing all over again.

I never pot orchids in anything bigger than a 6″ pot. They don’t need it and I don’t have space for large pots. My largest streptocarpus are in 4″ Dixie cups and none get a bigger pot. That size pot can give me 50 flowers at one time. When they no longer fit the pot, they get divided and part of the plant gets repotted in the same old pot.

If you are trying to grow larger plants, they will benefit from larger pots.

Myth #9: Don’t Remove Existing Roots

This is generally a good idea, but there is nothing wrong with removing some roots. Roots regrow very quickly and removing some won’t significantly harm the plant.

If the plant is very root-bound, it might actually be good for the plant to remove some because a root-bound plant becomes very hard to water. All the water runs down the outside of the root ball and the center of of it stays completely dry. Such a plant will benefit from some root pruning since it allows you to water the soil properly.

Myth #10: Repotting Should Be Done Every Year

That is a rule that is almost never right. Instead of following it, learn to understand your plants and let them tell you when they need to be repotted. Provided the plant is growing well and the roots are not completely root-bound, it does not need to be repotted.

Orchids are a special case. Their media breaks down in about 2 years, so it is a good rule to repot every two years.

Most potting media lasts for many years and does not need to be replaced every year.

Myth #11: Sick Plants Should be Repotted

This is a tricky one. In general, a sick plant won’t benefit from being repotted. The extra stress is only going to stress the plant more and if a plant is doing poorly, new soil and root disturbance is not going to help.

However, if the plant is sick because of the root conditions or the soil that is in the pot, then repotting will help the plant. For example, old potting media may be staying too wet for your watering practices, and repotting in fresh media may help that problem.

A plant that was potted in the wrong media for your growing conditions might do poorly in your hands. A change of media to one that more closely matches your watering habits and your environmental conditions will help the plant recover.

For example, you can grow orchids in sphagnum moss and many purchased plants are growing in it. But it is difficult to get the watering just right and therefore many new gardeners and even experienced growers like myself do much better with a different media. I repot new plants in sphagnum as soon as I get them to put them into a drier mix which more closely matches my watering habits.

Myth #12: Newly Purchased Plants Should be Repotted Right Away

In most cases that is a bad idea and serves no purpose but there are a few situations where it is a good idea to do this as soon as you bring a new plant home.

Why is it a bad idea? Moving a plant from one location to another is stressful for the plant. Temperature, light, humidity, type of water, and type of fertilizer are all suddenly different. The plant does not really need another stressor. Let the plant settle in for a couple of months and then decide if it needs to be repotted.

Most purchased plants are in fairly new potting media and it does not have to be changed.

There are also situations where it is a good idea to repot right away or soon after the plant settles in. If the potting media is very different from that of your other plants you are more likely to either over water or under water the new plant. Repotting into soil that you are familiar with can be good for the plant.

For example, I have purchased garden plants that were in a shredded wood material and my outdoor potted plants are in a clay/compost mix. I’d like to water them all at the same time so I usually repot the new plant into a soil I know.

I suggest you do not repot unless you have a very good reason for doing so.

Myth #13: Potting Soil Should be Sterilized

Potting soil is never sterile even right after you sterilize it. As soon as it is exposed to air, your hands, or plants it is contaminated with microbes.

There is one reason for heating soil. Some people claim they find fungus gnats in bagged potting media – I am not sure how true that is, but if the bag has a hole in it or it was previously opened, it is possible. Heating such soil will kill fungus gnat eggs and larvae.