Written by: Jenelle Schafer
You buy a cute plant in a cute pot and, after awhile, the pot is still cute, but the plant, not so much. While light, temperature and humidity all play a role in the health of a plant, the success of a houseplant largely depends on the right conditions for the roots. Roots need water, air, and suitable space to grow; all of which are determined by what kind of growing media the roots are in and how it is potted. Hopefully, this repotting guide will give you an idea of how to keep your plant happy and cute, and maybe even find a cute pot too.
When does my plant need to be repotted?
There are a couple of ways to determine when to repot. If your plant is top-heavy and the stem & leaves start to teeter the pot making you afraid it's going to take a dive off a shelf in the middle of the night, then a larger pot, or perhaps a wider bottomed pot is needed. While watering, if you notice the plant dries out quickly, then it probably needs to be in a larger pot where the increased volume of media can retain water longer. Conversely, if you have a plant in a pot where it doesn't seem to fill out the pot and it takes a long time for the media to dry out, then sizing down might be necessary to meet the plant's current size. Lastly, pay attention to how the roots are filling out the pot. Are roots coming up out of the soil? Is there a lot of roots coming out of the pot's drainage holes? If you have a plastic pot, can you feel the roots pushing against the pot walls? Is the plant root-bound? In these situations, repotting is probably the best option for the plant's health.
What growing media should be used?
Whatever growing media you use, it should function to accomplish a few things. It should provide support so the roots can stabilize the above ground portion of the plant. It should provide aeration for the roots, which leads to good drainage. It should also have water holding capacity so roots can access water when needed. And lastly, growing media should have nutrient holding capacity. Different plants may require these functions in different proportions. For example, succulents will need a potting mix with lots of drainage and aeration, but only needs the mix to provide a little bit of water holding capacity. Now, unless you have a large amount of growing media components on hand, you probably aren't going to be mixing your own potting soil and will buy a mix formulated by a company. This is totally fine, but I'll walk you through common potting mix components and what you should look for in a mix.
One common question I get asked about repotting is "How come I have to buy potting soil and I can't just use soil from my garden?" Natural soil is very heavy. Compared to a potting mix, soil has a very high bulk density, but with containers it is ideal to have a low bulk density. While the soil in my garden drains well and my vegetable plants are just fine growing in it, the same soil in a container just doesn't have the same drainage properties. So most of the time, with containers and pots, we end up using a soil-less media. Ironic that we commonly call it potting soil since there's usually no soil included.
The main component of most soil-less mixes is sphagnum peat moss. Peat moss is light weight, which provides good pore space & aeration, yet is extremely absorbent of water. It can actually hold up to 20 times its weight in water! However, when it is dehydrated~ which it usually is when it is packaged~ it actually acts hydrophobically; it doesn't absorb water. For this reason, when you repot, you need to rehydrate the peat moss in the potting mix by adding warm to moderately hot water to the mix. The warmer water gets absorbed right in to the moss, but cold water will bead up and roll off, leaving the peat moss as dry as it was before.
Another common ingredient is perlite. Perlite is volcanic material that has been heated at a very high temperature causing it to become porous. Perlite is very light weight and contributes to good aeration and drainage in potting mixes, making it a great complement to the high water holding capacity of peat moss. Sand is another ingredient that allows a potting mix to have good drainage and aeration. However, sand is a much heavier component than perlite, so sand should only be used in certain situations regarding potted plants. For instance, a large plant that may be top heavy could benefit from a heavier media. Lots of cacti potting mixes also have a sand component as well as a perlite, but usually will have a smaller amount of peat moss so that succulent-type plant have plenty of drainage in the growing media. One note of caution about sand: not all sand is the same. If you are mixing sand into your own media, use a horticultural grade sand, otherwise, instead of well drained, your potting soil could become concrete!
Two more media components that you may encounter in potting mixes are coir and vermiculite. Coir is made from the middle, fibrous shell of coconuts that is ground up into a fine texture. Coir has a high water holding capacity, comparable to peat moss, but has low aeration and needs to be combined with another component to improve the drainage of the mix. Vermiculite is made from mica-type material that has been "popped" at a high temperature causing it to expand. Vermiculite hits a lot of functions as a growing media component. It is light weight, has good water holding capacity (500% its weight), provides good aeration and drainage through its porosity, because of its chemistry, vermiculite is able to hold nutrients for roots to access.
Another thing you commonly see in potting mixes is Mycorrhizae. Mycorrhizae is a beneficial fungal organism that makes connections with roots and improves a plants ability to intake water and nutrients. If you notice thin, white threads in potting soil, that would be the Mycorrhizae.
What pot is right for my plant?
The most important thing a pot needs is drainage holes. Without drainage holes, the plant roots are going to sit in moist media where there isn't enough oxygen for the root cells to function properly and they are at a high risk of developing a root or crown rot. So, I either make sure I have a tray under the pot that water can drain into, or I use the pot-in-pot method. I'll put the plant in a plastic nursery pot with drainage holes and then set it inside a more decorative pot, without drainage holes, and then after watering, I can empty the pot with the excess water so the growing media can dry out before the next watering. You can use cups, bowls, baskets and other thing to set the pot in and then you get both a happy plant and a decorative pot.
When you are choosing the container you are going to repot the plant in, it is best to use the next size pot. This is another reason why using nursery pots is helpful, as they have somewhat standardized sizes~ 2.5", 4", 6", 1 gal, 1.5 gal, etc. Be careful of jumping a plant up to a pot that is much larger than the previous one. While the roots will have more room to grow, the growing media may take longer to dry out between waterings.
Repot a Spider Plant with me!
I have a spider plant (Chlorophytum comosum) that needs repotting because it dries out in 2-3 days, there are some roots coming out of the drainage holes and because it gets dry often, the tips of the leaves are brown & dry. I'll walk you through each step as I repot my spider plant.
First, I am going to get my growing media ready. It is dry media so I need to pre-moisten it with warm water and make sure clumps are broken down so the media evenly absorbs the water. I know the media is moist enough when I can take a handful of the media, squeeze it into a ball and it stays in the same shape when I open my hand. If there wasn't enough water, the media wouldn't be able to hold its shape, and if there was too much moisture, water would drip out of the media when squeezed.
Then, I am going to remove the plant from its original pot. As you can see, it's pretty root bound, to the point where the root ball might be so restricted that new roots won't be able to expand into the new growing media. So, I am going to trim the root ball a bit so that the new roots will grow out into the new potting soil by shaving off the sides with a serrated knife. Roots are much more resilient than the above ground portion of the plants, so while you want the plant to retain a good amount of roots, you definitely don't have to use kid gloves on them.
Next, I am going to get my potting soil in the new pot. The original container was a 4" diameter pot and I am transitioning it to a 6" diameter pot with drainage holes and a drip tray. I am going to use the same potting mix to fill the entire container; I won't put rock or gravel at the bottom of the pot on top of the drainage holes. Water moves through soils texturally; it will saturate one texture of media before it drains down and saturates the texture below it. This can slow down drainage, which is not what we want when a plant is in a container. So, it is best to make sure the media is consistent in the whole container. While I add potting soil to the bottom of the container, I will tap the pot against the table to settle the media down without compressing it. This should keep the pore spaces in the media open enough so that water and air are available to the roots while they grow.
Once I think there may be enough potting mix in the bottom of the pot, I set the plant in to see what height the crown sits at. Ideally, the top of the root ball, or the crown of the plant should be at the same height in the pot where the top of the potting soil should be, about 0.5 to 1 inch from the top of the pot. This space should be able to hold water without overflowing the pot until it drains down through the media. Once the plant is situated, I start adding soil around the sides of the root ball. While doing this, every little while, I may tap the soil down, like before, and firm the media around the root ball. Now I want to ride a fine line with this. I don't want to compact the media, but I do want to make sure the root ball won't shift and tip over time. The way I do this is my sticking my fingers down into the media vertically so that I can press some of the media down but also leaving some uncompressed. I'll keep doing this until the potting soil level on the sides of the root ball is even with the crown of the plant.
The last thing to do when repotting is to "water the plant in." You should add enough water so that it drains out the bottom. Sometimes, the potting media will settle in after watering leaving the soil level uneven. In this case you can easily rectify it by adding more media to the top of the pot. By watering the plant in you can also make sure the media and the pot will drain properly and that the plant will be in an ideal environment to continue growing and thriving. Happy re-potting!
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