Sometimes one leaves a potted plant in the care of people who then proceed to overwater your plants. If rot ensues, you may be forced to repot the whole plant which can be messy, and tricky if it's a largish tree.
What are other ways to remediate a pot with excessive water in the potting mix?
I guess the trick is to do it in a way that doesn't hurt the plant. Decreasing the humidity should help dry it out, but might harm your plant. Increasing the heat might help and hurt in the right way.
Without repotting it, my first idea is to increase the evaporative surface. Since you can't make the pot bigger, my idea (untested) is to stick some type of wicking material into the soil. You could use something like paper towels or an old t-shirt, depending on the size of the pot.
The thought is based on the wicking method of watering some plants. If you haven't seen them, search "plant soda bottle wicking" The water wicks from a reservoir, through a wicking material like cotton, hemp, etc... into the soil as it dries, so it always has a steady supply of water. If you applied the same principle in reverse, you could poke a small, yet deep, hole and use a chopstick to press the material down into it. Then firm the dirt around it. Leave the rest of the material hanging in the air. As the water wicks from the dirt into the fabric, it'll drastically increase the evaporative surface the water has to evaporate from. This includes the bottom, so make sure it's exposed as well. You could blow a fan across this material to help speed the process.
Because of the wicking effect, it'd help pull excess water from all over the pot.
Again, this would only be if you thought your plant was in mortal peril. I've had plenty of plants that accidently got over watered and I've simply let them drain and not watered them again until they needed it with no ill effect. It's just one idea I had that might work in a dire situation where you don't want to repot.
Depends how heavy and large the rootball is - certainly, the pot, if possible, should be stood on a rack or support with holes in it off the ground to assist rapid draining. If its possible to extract the plant from the pot, then removing it and standing it on lots of newspaper will wick the water out more quickly, and also allows for inspection of the roots for signs of root rot. If that's seen,then the soil should be removed, carefully, and any mushy roots clipped out, followed by repotting.
Generally, though, root rot occurs from consistent waterlogging rather than occasional overwatering, and if stood on a rack or something similar, water drains and evaporates fairly quickly, particularly during the growing season.
We know that when you have soil in a container, the water gravitates to the bottom so that there's a gradient of water content in the soil from lowest at the top to highest at the bottom.
For any particular soil mix, the height of the perched water table is the same regardless of the shape of the container.
Having more holes in the floor of the container doesn't necessarily help with drainage as we can see from this extreme example from Air-pot
where the bottom is just full of holes. Water is kept inside the pot on account of capillary forces and a perched water table can exist as mentioned above.
So, feeling the soil at the top of the container tells you little about how much water your roots are sitting in at the bottom of the container. You have to be able to feel the soil at the bottom or use a moisture probe that reaches deep into the soil.
One way to drain moisture from a pot, as mentioned in another answer, is to insert wicks into the soil. Since the water is at the bottom, the wicks have to be inserted from underneath into the soil. Capillary action from the tighter weave of the wick can then draw water out of the container.
Since the perched water table is at the same height regardless of shape of the container, another way is to double pot the container. By sitting the pot into another with the same mix, we are effectively converting it into a tall container, and the perched water table moves into the second pot. This assumes that you have large enough holes at the bottom to make enough contact between the soil in both pots.
Since gravity determines where the water sits, it occurs to me that you could invert the container if it's of a suitable size. You could pack the top with more of the same potting mix and hold it down with a mesh so that it doesn't all fall out. The perched water table would then move to the "top" of the container, and this would pull in fresh air to the "bottom" aerating the roots. You still have the problem of removing the water which could be done by wicks but this would sound like the fastest way of moving the water away from the bottom roots and to provide air.
