Home Improvement Expert Danny Lipford

Garden Myth: Gravel in Pots and Containers

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Planting container pot with gravel in the bottom.
                            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.
  • Pouring water into sponge.
            Soil is like a sponge.

  • 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.

Gardening Tip

If you’re worried about soil washing out of the bottom of your pot, put a paper coffee filter, a piece of screen, or a shard of pottery over the holes before adding dirt. Usually, though, drainage holes are small enough that this isn’t a problem.

How to Use Gravel with Potted Plants

If you want to put gravel to work with your potted plants, use it outside the pot. Put a layer of gravel in your plant’s drainage tray, or down inside a decorative planter, then sit your plant pot on top. The gravel will hold water and increase humidity, while keeping your plant’s roots up out of the puddle.

Putting plastic pot with plant inside ceramic container.
        Gravel comes in handy when sitting a plant inside a decorative planter.

Gravel in Non-Draining Pots

The best type of flower pot has drainage holes in the bottom, and you should always shop for pots that drain. But for pots that don’t have holes, some people put gravel in the bottom of the pot, to create a sort of internal “drainage tray” to collect water under the dirt. Some people are able to get this to work, but it can cause problems, including:

  • Overwatering: You can’t see the gravel, so how do you know how much water is down there? If water builds up, the soil will turn into a soggy mess, and your plant will be on the fast track to root rot.
  • Poor Growth: Water, nutrients, and air move through soil using capillary action, sort of like a straw. If you plug the bottom of a straw, it stops working, and when you plug up the bottom of your plant’s soil (by trapping it in a non-draining pot), it stops working, too.
  • Disease: If you’ve ever opened a container that’s been in your refrigerator too long, you’ve learned firsthand what happens when moisture and organic material are trapped in a space with no air flow. A moldy mess!

Further Information

Julie



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22 Comments on “Garden Myth: Gravel in Pots and Containers”

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  1. Olafur Says:
    December 17th, 2010 at 5:55 pm

    The gravel is used as a drain for pots so the water dont pool
    up in the bottom of the pot, some times the dirt or moss do cluck up the drain holes on the pots. also do sterilize the gravel and dirt before using, there are inzect eggs and pezt you need to get rid off. better safe then sorry ;)

  2. topkick Says:
    July 30th, 2012 at 1:46 pm

    soil usually clogs the hole at the bottom of the flower pot,so its must to use gravel bed around 1 inches thick beneath the soil just to make a good drainage system!
    P.S.-that`s not a myth!

  3. OC Gardener Says:
    October 19th, 2012 at 6:49 pm

    It is a myth. Gravel at the bottom creates a perched water table. It does not improve drainage. If you want water to drain well, put a piece of screen over the hole. Don’t use gravel! If you don’t believe this article, look up perched water table. You will learn about this in any botany or horticulture class.

  4. Sam Says:
    November 4th, 2012 at 10:23 am

    OC Gardener is correct. Any time you have a fine material over a course material, with an abrubt change between the two, you will have a perched water table. If soil is “clucking up” the bottom of your pots the screen is key. This could cause a problem if your potting mix is not up to par. Fine clays can accumulate and settle in the bottom of the pot. So make sure your potting mix is properly proportioned. Some plants will thrive in a wet environment, but you will know that you have a perched water table when you try to grow a plant that requires very well drained soil.

  5. Richard Says:
    January 4th, 2013 at 3:50 pm

    What if you place a 2″layer of pebbles in the the bottom of the pot with a screen over that separating the the soil from the pebbles. Wouldn’t that create more surface area to drain (less likely for the drain hole to clog) and faster drainage than the single drain hole. I have done that for years and it seems to work fine.

  6. RetiredHydrogeologist Says:
    April 25th, 2013 at 5:49 pm

    The gravel or sand is to keep the drainage holes from clogging, as Olafur and topkick noted. A coffee filter works as well.

    If you want a water reservoir to protect the plant from drying out, put some sand in the bottom of a pot (with no bottom holes) and make drainage holes in the side of the pot near the top of the sand. When the soil is saturated, water will drain into the sand, fill the reservoir, and drain out the side when the reservoir is full. As the soil dries out, soil moisture will move upward from the sand into the soil by capillary action, at least until the moisture content reaches an equilibrium.

    A perched water table forms when the fine-grained layer in beneath the coarser-grained layer, not the other way around.

  7. Trina Says:
    April 4th, 2014 at 4:48 pm

    I put Spanish Moss in the bottom of my pots to keep soil from spilling out the drain holes. Sometimes I use fabric pot scrubbers to cover the holes as well. I hope it works out okay since this is my first time doing it…if it doesn’t then I will have to try the coffee filters.

  8. the man Says:
    April 8th, 2014 at 12:31 pm

    the purpose of rocks in the bottom of the pot is not only to drain water off the bottom of the soil, but to help air get in to the roots. Plus if you have straight soil in the pot, then all the water setting in the bottom of the pot makes your plant un-happy. because it will have or get root rot from all the water, and you can drowned it out. I say put some rocks in the bottom, and mix some in your dirt so that it will resemble a more natural growing environment. plus mix in a little bit of sand to help keep the soil lose and workable for when you might have to aerate the roots. plus it will help keep the soil broke down for the plants to get the nutrients from the soil. if you use a good potting soil it probably will have sand in it. just read the label to see if it is in there. if not then just use a little bit of sand because it is already a good soil that is pretty well broke down. however, if you use just plain ol dirt then you may want a little more sand in it and work it over real good mixing it so the dirt won’t pack down and become hard. if the dirt gets to hard then water and air will have troubles penetrating to the plants roots.

  9. Gina Says:
    April 8th, 2014 at 7:13 pm

    Hi,
    Can you help? I have a sandstone planter situated along the width of my swimming pool. The planter has been waterproofed and a series of drainage holes have been placed along the back wall of the planter (close to the bottom). Could you please tell me if this is OK and how should I proceed? What do I have to do to get the planter ready for planting?

    Kind regards
    Gina

  10. Peter Says:
    May 15th, 2014 at 1:41 am

    We are beginning to plant vegetables in long colorbond planter boxes. There is no holes in the bottom so I need to drill some in the plastic base. The sides are corrugated colorbond. Instead of using filters as mentioned, what if I put a rubber mesh doormat in there, and then soil over that?? Will that act as an airator and drainage, and allow soul to natural breathe & drain thru the bottom??

  11. Chris Says:
    May 17th, 2014 at 11:19 pm

    All my potted plants I drill holes into the sides the plants seem to love it

  12. Dennis Ellard Says:
    May 28th, 2014 at 6:33 pm

    Serial plant killer here. On the typical self watering plastic container the holes in the base only line up correctly in one configuration. Why? Is it for the purpose of connecting only one or two of the holes to allow for airflow and better drainage? Thank you

  13. jac Says:
    May 31st, 2014 at 11:58 am

    Your opinion concerning covering the base of a tree
    with stone chips. It’s about 10 inches thick up the trunk.

    I think this could damage the roots..cut off oxygen and
    moisture. There’s conflicting opinions here about this.
    Thanks
    jac

  14. Kathleen Says:
    June 9th, 2014 at 12:10 pm

    Hi. is it safe to use florist spong on the bottom of containers with vegetables growing???

  15. Sherri Says:
    June 14th, 2014 at 10:48 pm

    We have 14 very large concret culverts 4 & 5. Ft. diameter , 2ft to 6ft tall. We filled them half full with native dirt then filled the top half with good planting soil. Irrigation is a bubbler at each. All but one is doing great, it’s the largest, at 5x6ft. The water just pools & won’t drain. It’s open at the bottom, sitting on native dirt. Only the one is having trouble. irrigation pipe is not broken. Any ideas to get it draining.

  16. Kurt Says:
    July 13th, 2014 at 10:54 am

    My problem is that when the outside pots are watered the soils drains too fast and flows out the bottom very quickly. I use high quality potting soil. The water has started staining the patio area. Just purchased saucers for the pots but they over flow if the plants are given a good watering. I live in Phoenix. Any suggestions to slow the water down from draining out so fast? The soil is not uniformly wet when the drip system is activated. Seems to go straight down and out.

  17. David Says:
    July 16th, 2014 at 10:03 am

    You’re right about saturated water gathering at the bottom. However, when suggesting water under the pot increases humidity you are nurtering another myth. It does only do that in confined spaces, not in ventilated rooms like living areas, greenhouses or outdoors. Get a hygrometer and see for yourself. And the phrase “perched water table” I think is based on a misunderstanding by someone at the gradenweb forum. A water table is the level of water naturally occurring in the ground outdoors. The saturated water area at the bottom of pots doesn’t have a name that I know of, you can call it trapped water, saturated water area, or possibly perched water but without the “table”, although the word perched makes less sense in a pot than outdoors.

  18. Charlie Says:
    August 1st, 2014 at 6:52 am

    Can someone explain if my thinking is correct or why if it is not? I think gravel down the bottom helps drainage because it prevents the drain holes from getting blocked and preventing the soil from becoming water logged. It can allow for more air to reach the roots especially when used in conjunction with side holes at the bottom of the pots. Also i can’t understand any reasoning behind the “perched water table” theory, soil which has adequate drainage will only hold so much water thus will never be “too” wet for the roots and if it is “too” wet then i would think it would be the mixture of soil that was not correct for your particular plant and maybe has a too higher water retention in it rather than it being the gravel below it that could be causing the problem? Maybe even adding more gravel to the mixture of soil would help this further?
    Any explanation or opinion would be very much appreciated.

  19. David Says:
    August 1st, 2014 at 8:51 am

    Gravel at bottom does not improve drainage, and after watering (and a long while after that) bottom layer is saturated with water and oxygen moves 10000 times slower through water than air i e no oxygen that way.

    Main item for getting much oxygen to roots is to have a large portion of pores with relatively large size (100-500um or so) which means the best thing toi do is to add e g gravel size 1-2 mm or at least 0,5-8mm (>8mm is ok but less good since roots will circulate it and thus lessen oxygen uptake). You must also avoid adding much fine grained substance since it will clog the big pores and then youre back at square 0

    “perched weater table” is a funny name since there are no water tables in pots, just outdoors, but the ideas are correct also for pots and the saturated water layer att the bottom is there because of capillary action and surface tension

    You have to go to a university library to get proper info, much confusion in internet forums and books on potted plants, and too complicated matter for forums like this. I am just writing a book on soil, sadly in Swedish though ;)

  20. tony Says:
    August 26th, 2014 at 5:22 pm

    drainage problem developed and plant is dying is there anything i could do to save and rescue the plant ( a pot plenty of holes on bottem but god knows what is preventing drainage could be a paper plate and or all the above) help

  21. uncle cracker Says:
    August 28th, 2014 at 8:40 pm

    I disagree with this article. I have talked to many nursery people and they have told me to use gravel and sand mixed with cow manure and compost. the proper way to actually do it is to mix everything not layer it. This year I used just potting soil and some of my plants never made it out of the bulb stage because they drown. So I mixed sand/cow manure compost mixture, gravel, cactus potting soil and regular soil. I am also going to add an powdered egg shell/coffee used coffee grind mixture and I have drilled several holes in my pots for both air flow and drainage

  22. Ginnae Says:
    October 9th, 2014 at 4:55 am

    Gravel In The Bottom Is Not So Much For Drainage As It Is So That Your Plants Won’t Have Pruny Feet.

    The Gravel Gives The Water A Place To Go So That The Soil Isn’t Sitting In Water To Get Sour, And SoThat It Doesn’t Cause Root Rot.

    If Your Pot Doesn’t Have Drainage Holes It Is Also Recommended That Some Charcoal Be Added To The Gravel To Keep The Water From Going Sour.

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