Thanks! Here are the facts about using gravel in potted plants. If you want, I will leave you my contact and I will explain it to you with a practical video. I really liked that you went into detail, it becomes very clear. Change ). The only way that gravel at the bottom of the pot will increase drainage is if the pot has insufficient drainage, either due to not having enough drainage holes, or by having blocked drainage holes. Will the wick also allow water to travel upward as needed without having the roots be overly moist. For example, molecules of water are able to cling to other materials. Since any decent quality potting mix must retain some moisture, it needs to contain material which will absorb and retain moisture, much like a sponge does. 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. Since wicks lift liquids upwards, they will pick up water from the PWT and carry it up higher into the pot to increase moisture to the roots around, effectively raising the PWT, but not evenly around the pot, only around the wick, which is why some wider wicking pots use multiple wicks or wind them around the inside of the pot for more even moisture distribution. Root Rot in Potted Plants. What do you put in the bottom of a planter? Seed Saving – How Long Can You Keep Seeds? This is a real exercise in lateral thinking, or more accurately, Permaculture holistic solutions thinking. Why Is My Aloe Vera Plant Turning Yellow and Brown? So how can we turn the problems created by adding gravel at the bottom of pots into solutions? That said, now lets play some mind games! First, let’s start with the basics: Your favorite potting mix or growing media holds water by means of two natural forces. It’s not a problem if these pots stay in your aquarium. Potted plants have less of an area to draw moisture from than a plant in the ground. The water doesn’t flow down into the gravel layer below because the water is ‘perched’ and can’t move, it’s held up there in the perched water table by capillary action against the force of gravity. 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. To learn how to improve drainage in pots, please see my article – How to Improve Drainage in Plant Pots, The Proper Way to Do It! 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. No gravel – none of the time! 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. Should You Put Gravel or Rocks at the Bottom of Plant Pots for Drainage? But no happy as I will now be obsessed with correcting my pots. You stated that sand should improve it but I wonder if that is enough as I am planning on using mainly sand from now on. Clearly, the answer is “no.” Not sure if I needed to read an exhaustive treatise to get the answer, but, well, it was fascinating. 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. . The simple way to understand the perched water table phenomenon is as follows. However, during this I’ll explain: I’ll get a bit scientific but will try to explain as simply as possible. Well, golly! This mixture contains huge air spaces and drains extremely well, barely retaining moisture in the bark pieces, so there is no perched water table. If you have potted plants and cats, chances are you’ve found poop in the plant pot on a bad day. I really should do some videos to demonstrate things like this! That is, to continue the analogy used above, you need to make sure the sponge is big enough for your plant. 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! Plants that have different soil drainage (aeration) requirements can be combined in a landscape planter if they are in their own separate pots. The growing medium wont be as saturated as the perched water table, but it will still be wet enough for way too long to be detrimental to the plant. Larger retailers of common plants often have stock with stones glued on top of soil. Cohesive forces are forces of attraction between molecules of the same type. 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. Putting stones around plants in a tray is a great way to increase humidity for indoor plants that need more moisture. The only thing that forces the water down is gravity, and the downward force of gravity always remains the same no matter what sits underneath. Hydroponic systems also use perlite as a potting medium, or ‘clay balls’ which are in fact clay coated pumice balls which are very porous and weigh almost nothing. 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! Some people say you don’t need drainage holes; just put rocks or packing peanuts at the bottom of your container. Hope it’s not too cheeky of me to say that my explanation is the only one from first principles and goes to a greater depth scientifically though. In fact, they can actually encourage root rot. © Deep Green Permaculture, 2009. Click on this article for tips on getting rocks glued to soil off without harming the plant. you said it yourself, the perched water table will always be the same height. Hi Johnny, thanks for your question! Most gardeners prefer to use a potting soil mix for growing gardens in pots, but amended garden soil can be used. They will protect your plants from weeds, keep pests out, prevent soil erosion, avoid splashing soil on the foliage, and prevent fungal diseases. Excerpts and links may be used, provided that full and clear credit is given to Angelo Eliades and Deep Green Permaculture with appropriate and specific direction to the original content. 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. Hi Javier, thanks for your comment. My apologies for not being clearer in my explanation, so I appreciate you bringing the point up. With these plants it’s much better to remove the drainage altogether and saturate all of the growing medium though, or sit the pots in a saucer of water. One option is to simply make sure you always soil that’s excellent for drainage. You can actually buy mesh mats for the bottom of your pot that do exactly this. This mixture drains extremely well and holds little moisture. Make the same number of decent sized holes (around 6mm or 1/4″) in the bottom of each clear pot. The gravitational force can only exert a limited downward pull on the water against the upward pull of the capillary action, and no more. Ready? Add enough water so that it comes about halfway up the stones. 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. 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. Excellent Article, in one article you have addressed many phenomenons. The roots look beautiful, I’ve never seen better roots before. Hi Paul, thanks for your comment, I had a look at the links you suggested and only included the Oregon State University one, it was the only one which provides any real scientific explanation, albeit a very limited and simplified one. I'm very lazy about watering and tend to underwater, so I guess that's my secret. Filling the bottom of the pot with coarse scoria, which is light in weight, will eliminate the unusable space in a tall, narrow pot and effectively reduce pot size to a more suitable volume. I was curious and did my research whether doing this is beneficial to my potted plants. The same thing happens with people who have been told about adding gravel to soil for drainage, putting wood chips in the bottom of a planter or adding charcoal in the bottom of pots. A shallow rooted plant in a tall narrow pot will have similar issues, there will be too much overly wet potting mix which the roots will never be able to reach, and if the potting mix stays too wet for too long it will break down much faster, and sink down, dropping the level of the plant in the pot. Putting rocks in plant pots doesn’t aid drainage or improve air circulation. 8 Simple Ways to Make Rooting Hormone at Home. A better solution is perlite, a heat-expanded mineral used in hydroponic systems, from experience, it works really well. With outdoor plants, there’s a risk they could be rained on, whereas you can control how much water your houseplants get. The capillary action can only wick the weight of the water upwards to a limited height against gravity, and no higher. Double potting makes it possible to sink individual potted plants into the landscape (or remove them) without disturbing the roots. Ignore it at your own risk. Water naturally runs to the lowest point under the influence of gravity, and will all run out from a container with drainage holes in the base unless there is something else present to hold it there. Gravity is self-explanatory, it’s the ever-present force on this planet which pulls everything down! Capillary action by definition is the tendency of a fluid to be raised (or suppressed in the case of mercury) in a narrow tube (capillary tube) due to the relative strength of cohesive and adhesive forces. Sorry, your blog cannot share posts by email. This post may contain references to products from one or more of our partners. The absorbency of the potting medium pulls the water upward and stops the water draining out, no matter what is underneath. The secret to improving pot drainage is to alter the composition of the potting medium, by mixing something with a larger particle size all the way through it, and there are several different amendment materials for this purpose. Make sure you check on the water from time to time so you can refill it when the water level drops. You can use more natural-colored decorative gravel for plant pots, although I’m personally a fan of the clean elegance of these white stones, like in the picture below. Hopefully, what you have learned here will make your indoor herbs and plants … In Memory of Bill Mollison, the “Father of Permaculture”, 3. 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. Last notable comment in the article mentioned a stone on the drainage hole to prevent soil leaching from the pot. Should You Tease Out Plant Roots When Transplanting? Polar molecules act like magnets with north and south poles, the (+) positive charged atoms and (-) negative charged atoms of these molecules are attracted to one another. It adds extra weight which keep top-heavy plants from falling over. ( Log Out /  Well, I have a super simple little trick to help you water those potted plants less frequently. 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. 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. I do not agree at all with your explanation and your graphics on gravel drainage. If you then put the sponge on its side so it’s now taller but still placed on the rocks below it, the now-bottom of the sponge will become wetter as gravity takes effect. Drainage in potted plants is uber important.In fact, it’s the most important aspect of container gardening. 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. I might have to set this up when I have time and photograph it. That’s how people find common ground for understanding! How to Improve Drainage in Plant Pots, The Proper Way to Do It! Unfortunately, while people who do this definitely have their plants’ needs in mind, this actually has the opposite effect, by causing their plant to hold on to more moisture and even cause root rot. Either way, you can rest assured that you don’t need to do this and that there are far more effective ways to promote drainage and air circulation in your houseplants. Citrus Problems – Why Is My Citrus Tree Dying? This means you should make sure the soil you put in these pots helps with drainage to avoid root rot. You can keep your plants happy by using pots with drainage holes, or by adding a layer of rocks and gravel to the bottom of the … Key takeaway lessons Rocks don’t improve drainage; instead, they elevate the perched water table closer to your plant’s roots. I’ll show you how to test this, all you need is some empty soft drink bottles. 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. The more moisture retentive growing medium/potting mix available, the less often a plant will need to be watered, as long as the pot is not too big. When I mixed them with the compost, it was 50% clay balls and 50% soil on the bottom of the pot, then slightly decreased the clay balls, somewhere around 40% clay balls and 60% soil in the middle of the pot and on the surface it was 30% clay balls and 70% soil. The plants end up sitting in too wet soil, increasing the chances of plant root rots and you’ve wasted valuable pot space with gravel that’s doing no good. Think of it like this: if you soak a sponge, it will hold on to its water. 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. Different growing media will have different perched table heights, the more absorbent materials will have higher perched water table, and the less absorbent ones will have lower levels. This means that we may receive compensation when you click on links to those products. 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. Change ), You are commenting using your Twitter account. 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. Cymbidium orchids for example are grown in an orchid mix which is composed mainly of 20mm composted pine bark pieces. It also helps to keep the soil from getting on any low leaves while also stopping soil from blowing away if your pot plant is caught in a draft of wind. That is, when people ask why put rocks in potted plants, they usually have some idea that this will help with drainage. When the positive side on one water molecule comes near the negative side of another water molecule, they attract each other and form a hydrogen bond, and this creates the strong cohesive forces between water molecules, and this explains why water clings to itself. 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. The main purpose of placing pebbles on the bottom of the potted succulent plant is to enhance drainage. If the physics is true, then the perched water table, the wet bottom layer of the potting medium will be the same thickness in every pot, and the gravel will simply push it up higher in the pot because it’s pushing all the potting mix up higher in the pot. That may not seem possible, but rocks and alpine plants accustomed to growing on a mountain can make a fine container … Thanks Angelo, myth buster. What about putting rocks on top of potted plants? 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. Growers of Cymbidium orchids use an orchid mix which is composed mainly of  coarse 20mm (3/4″) composted pine bark pieces. 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. 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. Adding gravel into the bottom of  terracotta pots creates a small water holding area for the excess water that would normally drain out on its own  if the gravel wasn’t there to collect into if the single drainage hole become blocked. A better choice is placing a coffee filter in the pot to contain the soil. Especially the potted plants in your container gardens that dry out super fast. 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. Find out more here. What can I use to fill the bottom of a large planter? 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…. http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html. If not, then see for yourself. For example, molecules of water are able cling to each other. I just wanted to know if I should jam some gravel in the bottom of the pots of my fledgling pothus ivy plants. The problem arises when you do not remove the rock wool from the roots. This means that putting rocks on top of potted plants is great both for the plants themselves and the room where you keep your houseplant, especially if it’s near a door or a window that’s occasionally open and lets the wind in. Small stones, seashells, marbles, or the the half-globe crystals from the craft store can act to keep moisture in by preventing some of the evaporation from the soil, just like Adhesive forces are forces of attraction between molecules of different types. There are only two forces at play on water in a pot of growing medium. Now, we’re not talking about squeezing your plants here (although feel free!). Drainage Holes There may be conflicting advice about how to keep your container garden plants from drowning. Now, your article makes me curious to see how perched water table differs from let’s say compost versus sand. Now that we know why water moves upwards and creates perched water tables in growing media, we can now re-examine our opening question from a more scientific perspective! This is especially the case with the vast majority of pots you can buy these days, which almost always come with drainage holes built into them. That is, when people ask why put rocks in potted plants, they usually have some idea that this will help with drainage. While you can mist your indoor plants as one way to help with this, using a pebble tray is also another easy solution. That is not right. It’s not entirely clear where the thought that you need to put rocks in the bottom of plant pots came from. 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. The top of a wet sponge or bath towel will dry the fastest, and the bottom portions will remain damp for the longest period of time. Its bent V-shape which gives it a partial positive charge on the side of the hydrogen atoms and a partial negative charge on the side of the oxygen atom. In this section we’ll go a bit deeper into the science if you’re interested, if not, please skip to the next section. It depends upon your growing medium. The plant in the pot which had only potting soil I noticed it retained too much water on the bottom and was hardly drying, which in the end led to root rot. I am the Technical Director of Dümmen Orange in Spain and Portugal and I have 20 years of experience in pot cultivation with various drainage systems and gravel is one of the most recommended for fans of ornamental plants. I have wondered for years why nurseries don’t have gravel or the like in the bottom of their pots. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. However, make sure you add holes to the plastic to allow water to drain out. 2. Why take the plants out of their pots Most plants that are sold in stores come in these little plastic pots we are talking about. 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! Food for the thought! It seems this mix could also be useful as it retained 10-15% of it’s weight in water. Converting Months to Seasons – Northern and Southern Hemisphere, Meteorological and Astronomical, The Birth of a Permaculture Food Forest – Before & After Photos, Garden Arches, Vertical Gardening for More Growing Area in Small Spaces. But otherwise, this is a super easy way to make sure the humidity is just right for your houseplants. The main reason for wanting to improve drainage in pots is because most plants don’t like having ‘wet feet’, otherwise known as waterlogged roots, … 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. In terms of what to put in the bottom of an indoor planter for drainage, you should add a drainage hole if you can, assuming there isn’t one there already. Most people will place a stone or pebble over drainage holes in pots, especially the large central ones at the base of terracotta pots, to prevent the potting mix falling out and making a mess. 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. You should also make sure your plant isn’t too small for a pot like this as without root mass filling your pot, it will instead be filled with soil that will hold more water for longer. Putting rocks at the bottom of the pot doesn't change that. 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. This is the principle by which wicking pots work, as explained in my article DIY Self-Watering Pots and Mini Wicking Putting rocks on top of potted plants is a perfectly acceptable method to cover the soil decoratively. Wait till all pots drain well, this will depend on the type of potting medium used and the volume of the containers. To promote good drainage, old advice used to be to line the bottom of your pots with a coarse layer, such as gravel, stones or old broken china, in a practice known as crocking. You could force more water to drain out by adding another downward force, such as tying a rope to the top of the pot and spinning it really fast to create centripetal force, much like what happens in a laboratory centrifuge. A layer of gravel or rock on top can help prevent excess drying. Rocks contain micro nutrients, which erode over time, Roots latch onto these rocks and can slowly suck these rocks, if the plant lives for many years in one container this could be of use for extra minerals 3. If your plant and pot are light enough to … You are completely incorrect in your article. frank. Pushing the saturated water table layer upwards, closer to the plant roots actually increases the risk of root rot, as the roots will stay wetter, longer. One of them had one part potting soil (very rich in compost) mixed with one part clay balls on the bottom of the pot and then slowly decreasing the content of clay balls towards the surface. Plant ’ s an excellent idea no happy as I will leave you contact. The type of potting medium using a pebble tray also provides space for drainage but the practice harm! Post was not sent - check your email address to follow this blog and receive notifications of posts... This mix could also be okay why put rocks in potted plants there are only two forces at within. As that ’ s really a fan of coming home and finding soil scattered all over the floor right! Containers with very different requirement a misunderstanding of the potting mix slightly don! At the science those potted plants less frequently the taller the perched water table to. Adhesive forces are forces of attraction between molecules of water are able to cling to other! 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