How do drainage material and perched water table affect your plant? That’s a great question. You may be asking what a perched water table is and I am going to attempt to explain it the best I can. I do know that drainage material in the bottom of a pot, whether it has a drainage hole or not, is NOT necessary. I see many people on social media sharing that they use pebbles in the bottom of the pot for “drainage”. It may work for them, but isn’t necessary. It will be detrimental to the potting medium’s drainage capabilities and your plant’s health. It’s true.
Perched Water Table
A perched water table happens in every container whether it has a drainage hole or not. Without a drainage hole and drainage material added, the perched water table occurs above the drainage material. This shortens the soil column that the roots could be growing in without being too wet. With drainage material removed, the perched water table moves to the bottom of the container giving the roots more room to grow above the table. Does that make sense?
The picture below is my attempt to give you a visual of this concept. Between the rubber bands is the perched water table and more water has collected there than above the rubber bands. It is hard to see with the glare on the plastic pot. (This pot does have drainage holes.) The bottom layer is the “drainage material” or pebbles and as you can see there is very little water in the pebbles because it is residing in the potting medium above it, thus the name perched water table. By removing the pebbles, the perched water table would move to the bottom of the pot, giving the roots more area to grow without possibly becoming waterlogged. Waterlogged plants are deprived of oxygen, their roots will rot, and the plant may die.
The height of the container makes a difference as well. All containers have the perched water table at the bottom of the pot, so a taller pot allows more area for the roots to spread out. The shorter pot will have the same amount of perched water table, taking up more of the pot.
That is the reason that when you have a plant in a large pot, what is going on in the top of the pot isn’t what is going on in the bottom of the pot. You may put your finger in the pot and think the plant needs water, yet the potting medium at the bottom of the pot may still be moist. That’s why it is good to use a dowel to determine if the bottom area of the potting medium is dry. If the dowel end is moist, don’t water the plant yet and check again in a few days.
No Drainage Hole, No Drainage Material
If you decide to pot into a container without a drainage hole, omit the drainage material allowing for more root growth, as the perched water table will be closer to the bottom of the pot.
Drill a Hole in the Pot
The best thing to do with a pot without a drainage hole is to drill a hole so that the water can drain out. It is super easy with a diamond-tipped drill bit. I do it all the time and have only broken one pot, but only the bottom making a super huge drainage hole, so I could still use it.
If you don’t want to drill a hole or plant directly into the container, use your container as a cache pot or “hide a pot”. Leave your plant in its utilitarian grower’s pot and set it into the cachepot. Remove the plant to water it, let it drain, and return it to the cachepot. This is the best scenario for the health of your plant if you don’t want to drill a hole.
Drainage material in a pot raises the perched water table, giving your plant less room to spread out. The raised water table may affect your plant in that its roots have no place to go except into the moist soil. Some feel the drainage material is preventing the moist soil but isn’t.
I hope this explains a bit more about why you don’t need pebbles in the bottom of your pot. If the pot has a drainage hole or not doesn’t make a difference. Use the pebbles for a pebble tray to raise the humidity or as a top dressing. Please, don’t put it in the bottom of a pot.
Have a great week, plant friends!
Hi Lisa. Thanks for this. It’s very helpful! I had (have?) a problem with fungus gnats. I can’t seem to entirely eradicate them because some of my plants won’t like drying out. I did get the sticky yellow papers and changed some of the soil. Both of these have really helped. I put horticultural charcoal in the bottom of some of my pots (all have drainage holes) to help prevent fungus. What do you think of that practice?
Letting them dry down a bit more is great, changing the soil, and sticky cards are all good practices. I have never used charcoal but I don’t think it will help with the gnats.
Checkout SmartPlantTray.com for a great drainage solution.