The importance of adding drainage materials to the bottom of houseplant pots is a long-held gardening myth. Photo: Kallihora, depositphotos

By Larry Hodgson

Question: Why don’t nurseries put gravel in the bottom of their houseplant pots anymore? Every time I buy a houseplant, I have to repot it to add a drainage layer at the bottom. You’d think nurseries would do this so the plants can grow well.

Leila

Answer: If nurseries don’t put a drainage layer of gravel, pot shards or clay pebbles in the bottom of the pots of the houseplants they sell, it’s not out of laziness or lack of concern about their client’s success with the plant. They don’t do it because it’s considered poor horticulture!

The idea that a drainage layer at the bottom of a pot with drainage holes was of any use to the plant was debunked years ago. Already by the 1950s, many tropical plant producers had stopped putting a drainage layer in the bottom of the pot, claiming it left the plants subject to rot. Then studies by the late Bonnie L. Appleton of the Polytechnic Institute and State University’s College of Agriculture and Life Sciences back in the 1980s, notably, showed plants grew better in pots that were filled with potting soil right to the base … and that such pots actually drained more efficiently than pots with a drainage layer. A drainage layer pushes the “perched water table”—a zone that tends to remain overly moist—up, reducing the space for roots to grow and function properly, cramping the plant and possibly causing its slow demise.

And even in terrariums and pots with no drainage holes, water tends to accumulate in the so-called “drainage layer”, then migrate up into the root zone due to capillary action where its continued presence leads to rot.

Illustration showing pot with drainage layer with a big X superposed over it.
A drainage layer is at best a waste of time; at worst, it can kill the plant. Ill.: Claire Tourigny

The next time you buy a houseplant, you may need to repot it for various reasons (maybe it’s overgrown, the pot is too tight, the plant needs a change of soil, etc.), but certainly not in order to put a drainage layer in the bottom.

When it comes to drainage layers, just bury that idea!

7 comments on “Drainage Layer Woes

  1. Good advice. Does this apply to outdoor pots too?

  2. Surprising how long this practice has continued. I usually put a piece of newspaper or a small piece of fine weave wire screen on top of the hole in the pot to prevent the soil from running out. The paper disintegrates by the time the roots fill in.

    • I like your idea of using newspaper. I usually use landscape fabric for the same purpose and sometimes punch holes even in the fabric (where the drainage holes) are.

      But landscape fabric does not biodegrade or if it does, it takes a very long time to do so — and I’m not sure it is a good practice.

      Last year I bought plants through a plant share that had newspaper liners at the bottom and I liked the idea. I also made many, many newspaper pots using a pot maker for tomato seedlings that I sold for charity. Interestingly, the more layers of newspapers there were, the less well the pots held together (so I had to use scotch tape, which I thought was counterproductive to the whole newspaper thing. The ones that held their “pot” shape best and didn’t need scotch tape were formed from one layer of newspaper. Sometimes even those were hit and miss – maybe I just need more practice).

      I might still poke some holes in the newspaper that’s used to line pots.

      And might experiment with a flour-water glue to reinforce newspaper pots.

  3. Cheryl Shenkle

    I set my Orchids on top of a layer of pebbles in a plant tray, which is set on top of a wider container full of pebbles to capture all extra water. That keeps the roots safe while collecting all extra water in a humidity tray full of pebbles. I have to water heavily to keep the humidity tray full, but the roots only get what I pour on to them directly and all excess drains away immediately. No mess and the orchids have much more humidity without fuss.

  4. Since we used to grow many acres of horticultural commodities, I am pleased that it is not so complicated.

  5. Pingback: How to Repot a Cactus Without Getting Jabbed – Laidback Gardener

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