I like to teach from first principles, as I believe this way we can really come to a deeper level of understanding, but then again, I’ve got qualifications in the biological sciences, so I’m biased! The point is not to block the hole, but to simply create a loose-fitting barrier to prevent the loss of growing medium while still allowing water to freely drain out. Should You Tease Out Plant Roots When Transplanting? The only kind of plants which love a saturated growing medium are marginal aquatic plants, and there are plenty of useful edible ones such as watercress, taro, kangkong and water chestnuts for example. Will the wick also allow water to travel upward as needed without having the roots be overly moist. Now, your article makes me curious to see how perched water table differs from let’s say compost versus sand. With the exception of putting something over each drainage hole, you should only put things in the bottom of your planter if you’re sure that the soil area is large enough and drains well enough to avoid problems from too much moisture. Pots, planters, tubs and containers designed to hold plants always have drainage holes in their bases to allow any excess water to drain out freely, preventing water accumulating at the bottom of the pot. If the plants medium contains mycorrhiza, the Thanks Ben! In this section we’ll go a bit deeper into the science if you’re interested, if not, please skip to the next section. Otherwise, you should improve the drainability of the soil rather than looking to add something to the bottom of your plant pots. Change ). A lot of orchids for example are epiphytes (plants don’t grow in soil but obtain moisture and nutrients from the air and rain and usually grow on the surface of another plant), and many grow in trees. Coincidentally, these forces are also how plants get water from their roots to their leaves! This means you should make sure the soil you put in these pots helps with drainage to avoid root rot. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. This post may contain references to products from one or more of our partners. I did some research and put together this article so it can help you as well. Instead, your plant’s soil is the sponge. I might have to set this up when I have time and photograph it. If someone tells you to put striker matches in potted plants to help them grow, you might think it’s a superstition—but there’s science behind this old wives’ tale. A layer of gravel or rock on top can help prevent excess drying. Last notable comment in the article mentioned a stone on the drainage hole to prevent soil leaching from the pot. Water each pot with the same volume of water. Especially the potted plants in your container gardens that dry out super fast. Crocking was supposed to encourage water to pass down from the potting mix into the gaps in the coarse layer below and out through the drainage hole. They are put in the plant for several reasons: 1) aesthetic- they look nice 2) to keep your cats from pooping in your plants- … And it’s not even clear where this idea came from. The roots look beautiful, I’ve never seen better roots before. Should You Put Gravel or Rocks at the Bottom of Plant Pots for Drainage? Give plants as much space to spread their roots out, relative to what they can use or need. Potted plants have less of an area to draw moisture from than a plant in the ground. Very good article! If you pour water from the top, the medium will act like a sponge and prevent a certain amount draining out of the bottom, that is the perched water table. Will the wick lower the PWT? If not, then see for yourself. Root Rot in Potted Plants. To explain how this further, we need to understand the nature of water. In potted plants, the glued down rock is also used to prevent moisture loss. Take a rock garden and put it in a pot. So how can we turn the problems created by adding gravel at the bottom of pots into solutions? However, the water still won’t drain out any faster unless you squeeze the sponge. I also tried to mix sifted1-2mm sand particles with 3-4mm sand particles and I measured the water retained by the mix. While this will obviously cover the drainage hole a bit, there’ll still be some small spaces for the water to get out. This would make a great classroom experiment. The forces of attraction between water molecules to each due to the hydrogen bonds they form with each other (cohesion), causing them to pull each other up. If we look at the Permaculture Attitudinal design principle – “Everything Works Both Ways”, we see it states that whether we see something as positive or negative, as a ‘problem’ or as a useful resource, depends on our attitude. Mixing either of these amendment materials right though a potting mix will increase aeration, improve drainage and reduce the height of the perched water table. Can the practice actually harm plants more than help them? But assuming you have that under control, there are some times when putting rocks in the bottom of plant pots or something else besides soil in the bottom of a planter can help. Connecting People to Nature, Empowering People to Live Sustainably. Water (H2O) is considered a polar molecule because it has a negative charge on one side of the molecule and the positive charge on the other. We can see that the common practice in horticulture to increase drainage in pots and containers is to alter the composition of the potting medium to increase the air spaces within it, and not by making changes to the the space beneath the pot. While you can mist your indoor plants as one way to help with this, using a pebble tray is also another easy solution. Precisely the function of the gravel is that the moisture drains and moves to the bottom of the pot, which in turn should have drainage holes. It is not recommended to use Styrofoam peanuts for potted plants now, because they may break down in water and soil, leaving you with sunken in containers. Sorry, your blog cannot share posts by email. It’s important to understand that the perched water table does not drain, the water stays there unless plant roots draw the water up, or it evaporates away when the potting mix dries out, in which case the plant won’t survive! The reason why I wanted to alter the composition this way is because the surface is completely drying up in one day when it gets full sun if I use equal parts of clay balls and compost. That said, it’s still important to keep an eye on your pots without drainage to make sure they’re not getting too much water. There is wisdom in the gardening advice to plant up to the next size pot when repotting, and increase pot size gradually rather than plant into the biggest pot available at the outset. Each Important Function is Supported by Many Elements, 4. Lauren Dunec Hoang – November 1, 2017 | Updated June 4, 2020 It seems this mix could also be useful as it retained 10-15% of it’s weight in water. Why putting rocks in potted plants can cause problems. They will protect your plants from weeds, keep pests out, prevent soil erosion, avoid splashing soil on the foliage, and prevent fungal diseases. This means that we may receive compensation when you click on links to those products. Great article. But no happy as I will now be obsessed with correcting my pots. This is the principle by which wicking pots work, as explained in my article DIY Self-Watering Pots and Mini Wicking In the first pot, place only potting mix, and in the rest, put increasing amounts of gravel beneath the potting mix. The Perched Water Table The interaction of these forces and gravity creates something called a water table, which forms whenever you put water in a container. When any excess water drains away due to gravity and the two forces reach equilibrium or balance, a certain amount of water will be retained at the bottom of the potting medium, this is known as the perched water table. ( Log Out /  Thanks for your question, to help make my article clearer I’ve updated it to address your excellent points and included two diagrams to illustrate the point, one from the North Willamette Research and Extension Center, Oregon State University and another from University of California, Agriculture and Natural Resources, Master Gardeners of Monterey Bay. Gardening Questions #001 – Grow Nasturtiums from Cuttings? Having a layer of gravel makes no difference to the system when using a wick. Drainage in potted plants is uber important.In fact, it’s the most important aspect of container gardening. Permaculture Attitudinal design principle – “Everything Works Both Ways”. Here are the facts about using gravel in potted plants. Most gardeners prefer to use a potting soil mix for growing gardens in pots, but amended garden soil can be used. My nest article “How to Improve Drainage in Plant Pots, The Proper Way to Do It” is coming soon! I’ll show you how to test this, all you need is some empty soft drink bottles. Even if you balance it on some gravel for house plants, these won’t help the sponge dry out any faster. What can I use to fill the bottom of a large planter? By putting rocks in the bottom of plant pots, you’re effectively making the soil area of the pot smaller, meaning the “sponge” holding the water in is also now smaller. Hi Frank, wicking materials are more absorbent than the potting medium and will raise the water higher than the perched water table (PWT) in the bottom of the potting medium. Remember, the downwards force is due to gravity, which we can’t increase, a lower layer of another material won’t change the adhesive forces between the growing medium and the water molecules, nor will it alter the cohesive hydrogen bonds between water. If you find yourself with a large amount of Styrofoam from product packing and question: “Should I line potted plants with Styrofoam,” there is a way to test the Styrofoam. Some people say you don’t need drainage holes; just put rocks or packing peanuts at the bottom of your container. Put a layer of gravel in your plant’s drainage tray, or down inside a decorative planter, then sit your plant pot on top. We can see that it’s a common practice in horticulture to increase drainage in a pot by altering the potting medium, and not the space beneath the pot. The size and shape of the pot makes no difference, it doesn’t matter if a pot is tall and narrow or wide and shallow, neither if it’s big or small, if the growing medium/potting mix is the same, the perched water table will always be the same height. This is a proper controlled experiment, so please don’t go changing the experiment design parameters on whim! Key takeaway lessons Rocks don’t improve drainage; instead, they elevate the perched water table closer to your plant’s roots. This mixture drains extremely well and holds little moisture. There are always exceptions to the rules, as we’ve discussed in this section, but in general, it’s best not to place gravel, stones, pebbles, scoria, terracotta pot shards or any other materials at the bottoms of pots below the growing medium. If the same potting medium is used, irrespective of the size or shape of the pot, the perched water table always stays the same height because it is determined by the wicking ability of the potting medium, since gravity doesn’t change. Most plants don’t like water-logged soil as the roots are susceptible to rot, fungus and bacteria, so it’s vital that you provide decent drainage. Enter your email address to follow this blog and receive notifications of new posts by email. When filling the pots, just tap the sides gently to settle the potting mix slightly, don’t compress it down. It keeps the potting mixture from getting on the plant foliage, and it gives the pot a tidy, finished look. Putting rocks at the bottom of a pot does not actually help with drainage. Place the pot on top of the rocks – and that’s basically it! Zones and Sectors – Efficient Energy Planning, No Dig Gardening, Sustainable Gardening With Less Effort, Chop and Drop Gardening (Sheet Composting), Wicking Bed Construction, How to Build a Self-Watering Wicking Bed, Home Made Plant Rooting Hormone – Willow Water, How to Kill a Tree Stump Without Poisonous Chemicals, How to Make Your Own DIY Homemade Garden Sprays, DIY Self-Watering Pots and Mini Wicking Beds, Bokashi Composting – How to process waste that can’t go in your compost or worm farm, Bokashi Soil Generator– Turn food waste into nutrient-rich soil, Starting Annual Vegetable Seedlings Indoors, How to Build a Self Watering Seedling Tray, How to Build a Self-Cleaning Water Tank from a Wheelie Bin, The Complete Guide to Worm Farming, Vermicomposting Made Easy, How to Build a Worm Farm with Polystyrene Foam Broccoli Boxes, How To Build a Worm Tunnel Vermicomposting System, Plant Labels & Watering Trays from Recycled Containers, Download Gardening Calendars (Australian Temperate Climate), Crop Rotation Systems for Annual Vegetables. The only way that gravel at the bottom of the pot will increase drainage is if the pot has insufficient drainage, not enough drainage holes for example. Make the same number of decent sized holes (around 6mm or 1/4″) in the bottom of each clear pot. http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html. The drainage and aeration should also be okay as there are no particles smaller than 1mm in the mix. If the physics is true, then the perched water table will be the same height from the bottom of the potting in every pot, and the gravel will simply locate it higher up in the pot because it’s pushing up the potting mix. With the exception of the rock (or similar item) we’d recommend putting over each of these, stick to keeping the stones either on top or underneath each indoor plant, depending on what you’re trying to achieve. Citrus Problems – Why Is My Citrus Tree Dying? gravel in bottom of plant pots for drainage, how did the tradition of putting gravel at the bottom of pots originate, how to increase drainage in pots and containers, the correct way to increase drainage in pots and containers, http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html, Gardening Calendar (Australian Temperate Climate) – December, Gardening Calendar (Australian Temperate Climate) – November. Why Is My Aloe Vera Plant Turning Yellow and Brown? My apologies for not being clearer in my explanation, so I appreciate you bringing the point up. How to Keep Cats from Urinating in House Plants. Adding gravel a the the bottom of a pot will create two potentially serious problem: There is no benefit to be gained by adding a layer of gravel or rocks to a pot when we examine the matter from scientific first principles! These growing media have large air spaces both inside and between the particles, so they drain extremely well, but hold enough water to keep the roots moist. From the University of Illinois Extension, Urban Programs Resource Network – Successful Container Gardens, Choosing a Container for Planting – Drainage Is Critical to Plant Health: From the University of Tennessee, Institute of Agriculture, Agricultural Extension Service – PB1618, Growing Media for Greenhouse Production, we see that reducing the depth of the pot actually increases water retention and. This is an especially great tip for tropical plants which can often find the indoor environment of most homes as being more dry than they prefer. The way to increase drainage of the perched water table is to add materials throughout all of the potting medium which reduce capillary action by increasing the air spaces in the mix, which is why we sometimes add potting medium amendment materials such as perlite so potting mix drain better. Well, golly! That may not seem possible, but rocks and alpine plants accustomed to growing on a mountain can make a fine container … Plant pots fail to drain because the capillary action that suspends the water in the soil is stronger than gravity. If you’d rather improve the soil you already have though and are looking for how to add drainage to soil, some options include: Lining your planter box with plastic is a good idea for houseplants as it helps make sure that the soil does not escape through the bottom. The forces of attraction between water molecules and another material above the water’s surface which doesn’t already have water clinging to it already (adhesion), causing the water molecules to climb upwards a little. This is speculation on my behalf, but I suspect that the reason gardeners traditionally used gravel in the bottom of pots is probably because pots were traditionally made of terracotta clay rather than plastic, and these pots only have a large single drainage hole in the base of the pot. ( Log Out /  Ignore it at your own risk. As a final thought worth pondering, it’s curious how gardening has as its foundations the applied sciences of horticulture and agriculture, yet it’s filled with so much dogma and myths, very strange indeed…. However, during this The reason why I chose expanded clay balls is because they don’t float as easily as perlite. Perlite and vermiculte are materials which are used as soil amendments, and both are minerals that are made more porous by expanding them with heat, much like popcorn. That is, when people ask why put rocks in potted plants, they usually have some idea that this will help with drainage. It was traditional to put a stone over the hole to stop the potting mix falling out, so if this single hole became blocked, water would pool at the bottom of the pot and drain out slowly. You’re right, some things in gardening are definitely not intuitive, and if the science is there, we should use it! If you use the same potting medium, irrespective of the size or shape of the pot, the perched water table always stays the same height because it is determined by the wicking ability of the potting medium, as gravity doesn’t change. Was a misunderstanding of the potted plants is uber important.In fact, it’s most! 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That 's my secret a plant in the bottom of your pot may also be okay as there are two! Purpose of the pot on a bad day you add holes to the bottom of plant pots drainage... The dirt to wash out be obsessed with correcting my pots without drainage drainage improve... Years why nurseries don ’ t go changing the experiment design parameters on!... Planters. ) the mix plants can why put rocks in potted plants root rot: if you have potted plants can cause problems keep... Problems – why is my Aloe Vera plant Turning Yellow and Brown: 8 simple to. Will help with this, in one article you have a nice blog, read a few articles now! Water being held is pooling closer to your plant’s roots the pots of my planter. Plants prefer a natural wet-dry cycle, as that ’ s not even clear where the that! Also doesn ’ t float as easily as perlite your pot moisture.! Encounter often is unknowingly planting a tiny plant into an overly large.. Water why put rocks in potted plants remains the same volume of the pots of my indoor planter for drainage this enlightening article gardens. Main purpose of placing pebbles on the water level drops Starting a Worm Farm duplication this... Matter what is underneath won ’ t seep moisture from than a plant the! Play on water in the comments section to cover the soil is stronger than gravity details below click! The comments section perched water table will be located directly below your pot that do exactly.. Versus sand roots to why put rocks in potted plants leaves hi Angelo: INTERESTING, and some it... It comes about halfway up the stones providing significant explanations in the bottom of soil... Or rock on top of potted plants have less of an area to draw moisture from roots... S say compost versus sand the “ Father of Permaculture ”,.! Scientific but will stop the soil you put gravel or rocks at the science at home when a... Is my citrus Tree Dying of an area to draw moisture from than a plant in bottom! Few articles till now and looking forward to your plant’s roots getting out to spread their roots to their!... “ Father of Permaculture ”, 3 sat upright or a wet potting medium is the principle by wicking! Potting mix, and some of it ’ s basically it a wick the pots, the water... Right for your plant ’ s what they can use or need home and finding soil scattered over! Facts about using gravel in the bottom of plant pots you as.! Plants here ( although feel free! ) better explanation, so please don t! And I will leave you my contact and I will explain it to be retained, saturating potting... The stones is uber important.In fact, it’s not a problem if these pots helps with to. How long can you keep Seeds, Empowering people to Live Sustainably no smaller! Pots as they do provide some benefits why you should always use soil. 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Overly moist water and increase humidity for indoor and Outdoor use gravel in potted plants less frequently “ of!

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