Expert Issues Warning For Gardeners Who Put Rocks at the Bottom of Their Planter: 'If There Is...'

The basic nature of water is to fall due to the influence of gravity. When sprinkled inside plant pots, the water usually seeps down to the bottom of the container and runs down, leaking through the drainage holes, unless there’s something to hold it. All the water that is still inside the container gets sucked upwards by the plants in the process of “capillary action,” explains Science World. Somewhere between this downward pull of gravity and the upward pull of capillary action, the thirsty plants get hydrated. Some gardeners like to scatter gravel, pebbles, and rocks at the bottom of the plant pots to maintain this balance.

However, most of the time, these solid objects layered on the soil bed end up waterlogging the plants, perching the water table, as this Reddit post also explains. And plants, they don’t like to have “wet feet.” In an interview with The Spruce, Laura Janney, gardening expert and founder of The Inspired Garden, explained why putting rocks at the bottom of the plant pots could be doing more harm than good to your plant’s roots. "The last thing you want to do is put any sort of rocks or gravel in the bottom of your container. Instead of helping with drainage, a layer of rocks, or any different material that is not absorbent, creates a zone of saturation that slowly creeps toward the top of your container,” Janney explained. 

A cluster of rocks, settled at the bottom of a plant, can cause the water level of the container to rise. This excess water can damage the plant's baby by causing root rot. "Rocks or no rocks, if there is water sitting in the bottom of a planter, the plant is in danger of root rot. This health issue isn’t caused by the substrate, rocks or soil, but rather it is caused by standing water,” Ruth Carll, Rutgers State program leader for consumer horticulture, told the digital home improvement outlet. Besides drowning the plants, this water can release enormous quantities of salt in the container, fostering a toxic environment for the roots as well as for the rest of the plant body.

This is also one of the reasons why gardeners should keep a check and empty the planter if there’s a pool of stagnant water collecting at its base. Adding a layer of rocks also makes the soil shallower, which would further slow down the drainage. “The idea that rocks create a barrier between the soil and sitting water isn’t accurate; since most potting mixes are made of fine particles that act like a sponge when the particles are together, these fine particles will filter down between the rocks and pull any sitting water up to the plant roots,” Justin Hancock, a horticulturist at Costa Farms, told Real Simple.

Meanwhile, Carll recommended that if one still wants to put rocks at the bottom soil, they should do that only for the reason of covering the drainage holes. A good idea, she said, is to buy a planter that already comes with drainage holes. If the holes aren’t there already, one can drill their own drainage holes. Alternatively, gardeners can add a layer of activated charcoal at the bottom.