I guess you might say it's a pet peeve of mine. I've have this discussion with lots of people over the years who think a few inches of gravel in the bottom of a flower pot will lead to a well drained root zone. In soil physical terms, it creates a perched water table, meaning water won't move into the gravel until the soil is completely saturated. This is how a USGA green is constructed and was done so to conserve water. However, sand doesn't hold on to water like a quality potting soil mix. Our old bunkers at HCC behaved similarly. If you recall, they were overly compact to the point the where difficult to play from (prior to last year when we topped off the bunkers with a different sand that didn't play well either). The sand over- layed a courser textured soil (gravel in this case) which created the perched water table. The opposite of a perched water table is a temporary water table created when a courser textured soil over lays a finer textured soil. This is the case with our fairways, where a clay soil has been topdressed over and over with coarser sand. The result is a soil where water moves through the upper portion of sand but is temporarily held up by the finer textured soil and will only drain as fast as the underlying soil will allow it to. This article does a nice job explaining this is simple terms.
Garden Myth: Gravel in Pots and Containers
Flower pots don’t need gravel in the bottom.
I’ve always been told to put a layer of gravel in the bottom of a flower pot before planting. Is this really necessary?
Actually, it’s a myth, but it’s one that even I believed for many years. The common belief is that a layer of gravel in the bottom of pots will improve drainage and keep the soil from spilling out, and besides, that’s how we’ve always done it, so it must be right.
Here are the facts about using gravel in potted plants.
Why Gravel Doesn’t Improve Drainage
The gravel myth is based on a mistaken idea that it will increase drainage. Follow my logic here and see if we can debunk this idea:
- Gravel vs. Soil: Gravel does drain water – obviously, water runs through gravel faster than soil. However, the opposite is also true: soil holds water better than gravel.
- Soil Acts Like a Sponge: Water won’t run out into the gravel, or out of the pot, or anywhere, until the soil is saturated. If you don’t believe me, try laying a sponge on top of a pile of gravel, then pour water into the sponge. Does the gravel make the sponge drain faster? No, the sponge fills up, and it won’t drip until it can’t hold another drop.
- Not Enough Soil: Just like with a sponge, water naturally settles toward the bottom of the soil. But because you’ve partially filled your pot with gravel, that soggy soil bottom is now higher (and closer to your plant’s roots). Basically it’s like having a smaller pot!
- Poor Results: So, you end up with an unhappy, crowded plant sitting in too wet soil, and you’ve wasted valuable pot space with gravel that’s doing no good.
Drainage Made Easy:
Your plants will be happier if you uniformly increase the drainage of the soil itself. Choose high-quality potting soil that is well draining. And if your plants need even more drainage, instead of putting gravel in the bottom of your pot, try mixing in perlite, PermaTill, or organic matter into your potting soil to increase drainage throughout the pot.