Garden Myth: Houseplants Need a Drainage Layer

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No, houseplants don’t need a drainage layer. Source: Claire Tourigny, laidbackgardener.blog

Old myths die hard and one myth that refuses to die is that houseplants need a “drainage layer.”

It used to be believed that you had to put a layer of gravel or pot shards at the bottom of any pot, both those of houseplants and container plants, to improve drainage. I did this for years … until I ran out of gravel one day and potted up a few plants without adding the drainage layer. Since they did just as well as those with a drainage layer, I simply stopped adding one. One less step, one less expense, equally good results! It worked for me.

Years later, I learned that a drainage layer can even be harmful to plants! If there is too big a difference between the size of the soil particles and that of the drainage layer, the water collects in the soil just above the gravel and stays there until there is no remaining air space, i.e., until the soil is saturated. Only then does excess water drain away. As a result, a drainage layer can leave plant roots soaking in water and actually lead to rot!

Japanese bonsai masters obviously knew the truth hundreds of years ago. Bonsais grow under very extreme circumstances (small pots, severe root pruning, etc.) and need both thorough watering and yet perfect drainage. So what the masters do is put the finest soil at the bottom of the pot, medium-texture   soil in the middle and the coarsest soil (but not gravel!) on top. Bingo! Water flows out like a sieve!

The Proof Is in the Pudding

Still don’t believe me? (When people have been doing something all their life and are suddenly told it was a waste of time and energy, they’re generally unwilling to believe the information.) Try this!

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Commercially grown houseplants have no drainage layer when you buy them. Why would they suddenly need one when you repot them? Source: seeyouinthegarden. com

Unpot any greenhouse-grown plant you have on hand and take a gander. Where is the drainage layer? There isn’t one. That’s because professional horticulturists abandoned this old technique ages ago. Studies showing that drainage layers are a waste of time go back a century! Yet many people still add one.

Still not sure? Here’s another way of looking at it. Almost every flower pot has at least one drainage hole, if not more, right? (If it doesn’t, either you shouldn’t be growing anything in it or you should be using it as a cachepot!) Do you really think that surplus water would stay forever in a pot with a hole in the bottom?

To Keep the Saucer Clean, Just Add a Filter

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A filter in the bottom of the pot will keep the soil in and the saucer clean while still letting excess water drain out. Source: laidbackgardener. blog

What you might want to add to the bottom of a pot is a filter. It could be a piece of screen, newspaper or paper towel, a coffee filter, an old rag, etc., as long as it entirely covers the drainage hole(s). You choose! That way, when you water and excess water flows out, no soil will flow through and dirty your saucer, only water.

(You don’t have to use a filter. After the plant has “settled in” and its roots have filled the potting mix, no further soil will flow out. Besides, unless the pot has really large drainage holes, only a smidgen of soil actually ends up in the saucer: not enough to make any difference to the plant. But still, if you like clean saucers…!)

Next time you repot a houseplant, therefore, just add a simple filter, then fill its pot with your favorite growing mix from bottom to top. Sometimes gardening really is incredibly simple!20180227A.jpg

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