Houseplants don't have a hard and fast rule about when to repot, but there are a few tell-tale signs to look out for that will indicate your plant needs fresh soil or a larger pot. Alternatively, refreshing soil involves adding fresh soil without disturbing a plant's roots. In this blog I will cover the difference between repotting and refreshing, signs it's time to repot, how to choose a pot, repotting in practice, and some further considerations to keep in mind when repotting your plant.
Repotting vs. Refreshing
As a plant grows, it's roots uptake nutrients and water from the soil. In turn, over time that soil can become nutrient-deficient and begin to shrink (just as wet soil swells, roots pulling water from the soil compacts it). Fresh soil can replenish nutrients and essential soil microbes (bacteria, fungi) that are incredibly important for plant health, growth, and development.
Repotting does not always mean going up or down in pot size, instead it is the process of removing old soil and replacing with new soil. The plant is removed from it's existing pot, the roots are jostled and massaged to shake out the old potting soil, the plant is placed back into a pot (maybe of different size), and covered with fresh soil. This process loosens and aerates the roots, provides much-needed air pockets in the soil, and restores nutrients.
On the other hand, refreshing a plant's soil involves replacing the top layer of soil or adding fresh soil to the existing pot, without disturbing the roots. This is incredibly helpful if soil is lost over time through the drainage hole (especially in a very airy potting mix like my aroid/hoya mix) or if the soil has shrunk away from the sides of the pot. I will generally refresh the soil of my houseplants annually (in the spring when they also come outside for their first springtime patio shower!).
Signs it's time to repot your plant
You don't need to think of repotting as a scheduled event to perform once a year. Many plants do not need this level of care or attention (in fact, it could be detrimental in some cases). Instead, look for the signs that your plant needs to be repotted.
The plant seems to have lost its luster and pep This may sound weird, but most plant people have excellent observational skills with plants they have lived with for a long period of time. The plant may seem dull and the leaves a bit "blah." If you haven't been fertilizing, or fertilizing infrequently, start with 1/2 strength fertilizer every few waterings and see if that cheers up your plant. If not, your plant may be ready for a repot.
Water pools on the top layer of soil and has a hard time draining down This is a sure sign your plant needs a repot! My monstrous jade plant had water pooled on the top layer of soil for almost two days before I realized it had not drained out. The soil was so tight and compact that water just couldn't work it's way through. We ended up taking a hammer to that pot because it was so tightly packed in!
The plant stops growing If it's prime growth season for your plant and it just isn't growing-- your plant is either short on nutrients or needs more leg room.
The potting soil dries out very, very quickly This could be because it is hot and dry outside, which can cause significant evaporation, but it could also be because the plant requires more water than the potting medium can hold. When repotting, determine if the potting medium is adequately holding moisture (if not, you can amend) or if your plant simply needs more potting medium (and therefore a larger pot).
Roots are coming out of the bottom of the pot This may not always mean the plant needs more room, especially if you use a cache pot/nursery pot system, because sometimes roots simply find a reservoir of water at the bottom of the cache pot. Most of my monstera do this, and I just leave them be.
Roots are busting through the pot Yeah, it needs a bigger pot!
The big 'ole heirloom plant has never been repotted This is a tricky situation-- if you have a very large, very old plant that has never been repotted, it likely needs that nutrient-rich boost and aeration for the roots, but disturbing a plant "set in it's ways" may end up detrimental to the plant itself. If opting to repot a big 'ole plant, try to keep the root disruption at a minimum and keep 3/4 of the old potting mix. A plant with a drastic change in soil conditions after so long may become incredibly stressed, which can be heartbreaking when it has been thriving for so long.
Choosing the right pot
Drainage
I never recommend using a pot without drainage holes unless you are using it as a cover pot/cache pot for a nursery pot that does have drainage. The old "rocks at the bottom" hack is really not great advice because water that cannot flow out of a pot and stagnant at the bottom of a pot breeds lots of detrimental bacteria that can rot plant roots really quick! Many studies provide evidence for this, along with a whole series of detrimental effects of this hack, I'm not just a hater (check out the University of Illinois or Washington State University to start). Water needs to flow in and out easily.
Size matters
Most people are too quick to go up in pot size with their plants. The common belief is that more room for roots to grow will make the plant grow quicker. Unfortunately, too large of a pot can make a plant spend all of it's energy growing roots instead of foliage (the part we really like). Additionally, too large of a pot may be detrimental to roots because they are only able to uptake what is in nearby soil, not moisture deep down into the pot- this leads to root dehydration or rotting, and it can happen quick. In short, the pot size does matter!
Roots should be somewhat snug in a pot for most houseplants You should be able to see a happy balance between root and soil. Roots should have a good inch or so of free space in soil around them, but not much more than that. When you take a plant out of it's pot, if the root ball is extremely compact/tightly wound and you do not see much soil, this is a root-bound plant and it probably needs a larger pot. On the other hand, if your plant's roots have more than an inch of free soil space around them, they are likely in too large of a pot. Check out my very crude drawing to illustrate this point (since I can't get a good photo of roots underground).
Do not look at the size of the foliage to determine pot size Just because a plant's leaf canopy spans over the size of the pot does not mean it needs more pot space. Sometimes we go up in size for practical reasons, such as toppling over with the weight of the foliage, but be sure the roots are guiding your pot size decisions!
When sizing up, pick one size larger If you have a 4" potted plant that you have determined needs something larger, go up 1-2 inches to a 5" or 6" pot, but no bigger. Houseplants do not follow the same rules as outdoor gardening, where we put tiny tomato seedlings in giant felt bags and trees in humongous pots in anticipation of what they will need. Most houseplants take a couple of years before needing to go up in size.
There are always exceptions Remember, there is no hard and fast rule to sizing your plant's pot, because there are thousands of plant species we can keep indoors, and every species has their own specific needs. While a snug fit is a general piece of advice, some plants such as colocasia and alocasia species may like more room in their pot or they will not grow.
Pot material
Plastic and plastic nursery pots This is the least breathable of the pot materials as it does not allow airflow between the soil and the air outside. It therefore holds moisture longer than other kinds of pots.
Glazed ceramic This pot material also retains moisture very well and does now allow airflow between the soil and the air outside the pot.
Unglazed ceramic, concrete These pot types are lightly breathable and dry soil quicker than a plastic or glazed ceramic pot.
Terracotta These pots are super breathable and do not retain moisture for extended periods of time before evaporating water into the surrounding air. They are excellent for plants that need to dry out such as succulents and cacti. These pots are not suitable for plants with delicate root systems because plant roots will attach to the sides of the terracotta pot and can tear during repotting (e.g., hoyas do not do well in terracotta).
Fabric These pots are the most breathable of the pot materials and are constantly drying out. There are specific cases in which fabric can be great, but I have not used them for houseplants- only outdoor vegetables such as peppers and tomatoes.
Net pots If you are interested in hydroponics ("passive" hydroponics is making waves in the houseplant world currently) then net pots are what you'll use as they are intended to be submerged in oxygenated water, delivering the right balance of O2 and H2O to plant roots. They are also great for epiphytic plants kept in high humidity conditions such as orchids, hoya, and rhipsalis.
Repotting
Here is a quick repotting checklist, now that you have read through all of these considerations!
Are there specific signs your plants needs to be repotted, or does the soil need a refresh or some fertilizer instead?
What pot size will you choose?
What kind of pot (material) will you choose?
What kind of potting medium will you use? (This is in my Potting mixes and amendments blog)
The Process
Gently squeeze the sides of the nursery pot to loosen the root ball
Lightly massage the root ball to loosen the roots from the soil- if the root ball is extremely compacted soak in a bowl of water to loosen
Do not rip, cut, or scrub healthy roots!
Place a layer of potting mix on the bottom of the new pot
Set plant into pot
Optional: Sprinkle mycorrhizae onto the roots
Cover with the fresh potting mix
Water thoroughly
I used the same potting medium I always use on my aroids and hoya (made up of bark, organic soil/compost, perlite, and horticultural charcoal). After I repotted I gave it a large moss pole and watered thoroughly. It has done very well!
Other repotting considerations
Transplant Shock
Some plants go through considerable transplant shock if they are repotted in a drastically different potting medium. Transplant shock signs include wilt, limpness, yellowing leaves, and dying foliage. It is best to avoid transplant shock by minimally disrupting the fine root hairs during repotting (never scrub roots!), keeping a similar potting medium to maintain a similar pH and soil ecology, and using a nitrogen supplement such as Super Thrive.
Do not repot stressed plants
Unless you know the potting medium is causing significant stress on the plant, do not pot a plant that is stressed, as it may make it worse. It's better to allow a plant to adjust to it's external environment (light conditions, humidity, temperature, etc.) before adding new soil into the mix.
Try not to overthink it
I know I just wrote a long blog about repotting a plant, but really it will not be detrimental to your plant if you decide to wait awhile before repotting it. Instead, opt to refresh that top layer of soil, and focus on giving your houseplants the appropriate light, water, and pest control- as these three are the top determinants of indoor plant health!
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