When a plant gets rootbound in a pot, where did all the soil go?
I swear I’ve had plants so rootbound it’s ALL roots in the pot and NO soil. But where did the soil go? Let's find out...
Surprisingly, the majority of the soil doesn’t really ‘go’ anywhere. Even a fine, dense soil is around 20% to 30% air. Great for plants outdoors. But that's not a good choice for most houseplants. The typical chunky aroid mixes we use for most indoor plants are even higher in air. So a large percent of the soil’s simply been compacted over time as a normal result of actions like watering and the roots growing.
Plants don't literally 'eat' the soil, but that essentially happens also. Some soil will have been slowly broken down over time and absorbed by the plant. Bacteria and fungi break down organic matter in the soil over time, turning it into nutrients the plant uses for growth.
Some is also lost over time when you water, especially at first as the ‘fines’ get washed out. But each time you water, like erosion on a really small scale, a little more is lost.
Also keep in mind roots contained within a pot tend to spread out, down and around, forming a cage-type structure in the pot, trapping soil in the middle where you can’t always see it.
I wish I was one of those people that enoy repotting. I do enjoy the results once it's over! But I’m a shocker for putting off repotting (sorry plants). If you’re anything like me, these 'how to delay repotting' tips are for you...
To delay repotting without a rootbound plant suffering, gently scrape off the top few cms or inches of soil and replace it with fresh soil. The new soil will work its way down into the pot each time you water, helping temporarily replenish nutrients without disturbing the roots. No, it's not a forever solution, but your plant will be happier in the meantime.
The soil level tends to naturally reduce over time, but avoid the temptation to 'top up' lost soil by just dumping more on top. This can lead to the stem rotting and before long it could be goodbye plant!
Instead, if the soil is so compacted the level has dropped considerably, instead slide your rootbound buddy out and add a layer of fresh soil to the bottom to lift it back up (and gain you more time before you can't put repotting off any longer).
Don’t’ starve rootbound plants!
Fertilising rootbound plants is even more important than plants in fresh soil. Old soil and less soil means little to no nutrients left, which can stunt growth and cause deficiencies, or even lead to a plant’s death if left rootbound in soil devoid of nutrients. A plant in old soil or in a pot with more roots than soil, is more reliant on YOU to provide the nutrients it can't get from the soil.