So the answer is no, there’s no need for rocks. Also, be aware that all pots filled with any kind of potting mix, potting medium or growing  medium, call it what you will, have a perched water table. Hydroponic systems use potting media such as perlite, which is an expanded mineral filled with air, or ‘clay balls’ which are in fact clay coated pumice balls which are very porous, to drain extremely well but hold a slight amount of moisture. 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. Gravel is cheap, readily available, and very versatile. This mixture drains extremely well and holds little moisture. A good potting medium (potting mix) has to strike the perfect balance between sufficient moisture retention and good drainage for plants to thrive. They could be used as a media to grow plants in, but anything layered at the bottom of pots to improve drainage actually doesn't. The first thing you put in your plant pot is a lovely layer of rocks, or pebbles, or styrofoam, or broken up terracotta pots. I really should do some videos to demonstrate things like this! Sorry, your blog cannot share posts by email. So to my mind 10% or so of pebbles/grit at the bottom of the pot still has its use. Can You Water House Plants With Aquarium Water? 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. 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. One thing I did know was that when you pot up a plant, it’s good practice to put rocks in the bottom of your plant pots. So why bottom water? gravel and drainage came about because it was assumed that gravity would pull the water through the saturated zone and into the gravel, away from the roots of the plant. Connecting People to Nature, Empowering People to Live Sustainably. Which house plants grow the quickest in the UK? 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. Reducing the volume of growing medium available to the plant roots will reduce root growth space and overall root volume, as well as available moisture, thereby decreasing the plant’s drought tolerance and potential maximum growth size. My nest article “How to Improve Drainage in Plant Pots, The Proper Way to Do It” is coming soon! But no happy as I will now be obsessed with correcting my pots. 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. 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! 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. If you have a pot with no drainage holes, this water that has gone right through will sit in the bottom of the pot instead. If you’re worried about air circulation, then stab your soil a few times with something thin and pointy (chopstick, moisture probe). 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. Very good article! You can even use aquarium gravel to add a touch of color to your potted plants! 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. 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. ( Log Out /  Small plants don’t have enough roots to take up huge quantities of water, and in large pots the potting mix stays too wet for too long, causing root rot once again. Post was not sent - check your email addresses! To get into some basic physics, two opposing natural forces are at play within a wet potting medium in a pot. 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. Change ), You are commenting using your Twitter account. 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. The roots look beautiful, I’ve never seen better roots before. Tap the sides gently to settle the potting mix slightly, don’t compress it down. If a plant has been potted in a container that does not have drainage holes or quality soil, the problem can be easily solved by repotting the plant or adding holes to the container. 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? Now, your article makes me curious to see how perched water table differs from let’s say compost versus sand. Lava Rock. This weekend I took out of the pot a lemon tree which was planted in 70% expanded clay balls mixed with 15% coco peat and 15% compost all the way through the pot. 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! That’s how people find common ground for understanding! Add builders sand if you’re making succulent mix. From the University of California, Agriculture and Natural Resources, Master Gardeners of Monterey Bay. 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. With plastic pots, there are always plenty of drainage holes, and many are designed to increase drainage through the use of domed bases with drainage holes at the edges to take excess water away faster. Perlite absorbs water, so the mix dries out quickly, but so not so quickly that you have to water your plants every day. Few people are. Can the practice actually harm plants more than help them? A year on, when I educated myself, I discovered that the white fuzz was indeed mealy bugs, and had to sacrifice two of the plants. If you have no option other than to plant a plant in a pot without holes, you could put a layer of gravel on the bottom to catch any excess water and stop it from being reabsorbed by the roots of the plant. 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. Ummm I have to disagree with this. 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. I have a whole post on potting mix here. I have some succulents in pots ( small, ... For my plants I have tomato plant food, do I need something for bottom rot. When filling the pots, just tap the sides gently to settle the potting mix slightly, don’t compress it down. Basically, you’re giving the plant the freedom to soak up as much water as it needs. ... We’ve all heard the advice to put gravel in the bottom of a plant pot, and some of us may even have done it. Adding stones, pebbles, and potsherds to the bottom of planters to improve drainage in potted plants is so 1980’s – and it does not work as well as this quick and easy, counterintuitive solution. Excellent Article, in one article you have addressed many phenomenons. You’re welcome to disagree! So if you have a pot, like in your illustration, and the pwt is at the bottom 3 inches of the pot (for example), if you replace those 3 inches of soil with a very course medium like clay pebbles (which has much lower capillary action, then more water at that level will drain out of the drain holes in the pot. Line the bottom of a shallow tray with small rocks or pebbles and then fill with water almost to the top of the rocks. I might have to set this up when I have time and photograph it. PPL that use soil you mentioned mix it with coarse/sifted-screened perlite, in min. 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. I’ll show you how to test this, all you need is some empty soft drink bottles. 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. Without drainage, the excess water will sit at the bottom of the pot. I am planning on putting a 2" pipe inside that for water/compost and worms. Iann i dont mean to sound rude or anything but i gota dissagree with pots dont needing some kind of pebbles or pumice or something on the bottom of the pots, i always use pumice/perlite or pebbles or for my neps and such i use a mix of perlite & orchid bark chips & charcoal for better drainage, helps keep the water from staying at the bottom of the pot even after it drains thru the holes, helps keep the roots aired insted of sitting in any leftover moisture, thus also stops any potting … In the past, it was recommended that broken pieces of clay pots, rocks, wood chips or Styrofoam packing peanuts be placed in the bottom of pots as filler and to improve drainage. If the plant has thin delicate roots, like a snake plant, then the rocks will just fall out when you come to repot. The main consideration with flowers or vegetables grown in containers is … Beds. Rocks or pebbles are a natural option for the bottom of large planters. Set potted plants on top of the rocks. Loading... Unsubscribe from Figaholics? I think I’ve made my stance here pretty clear, no? How completely they dry out depends on the plant, which is why I’m so in love with moisture meters. Potting mediums, being absorbent materials, behave much like any other when wet. Fruit Tree Problems – New Leaves Tightly Curled and Turning Yellow on Cherries and Plums, Gardening Calendar (Australian Temperate Climate) – December, Gardening Calendar (Australian Temperate Climate) – November, Follow Deep Green Permaculture on WordPress.com, How to Make Compost in 18 Days Using the Berkeley Hot Composting Method, How to Use Replaceable Filter Face Masks for COVID-19 Coronavirus Protection. 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. In the first pot, place only potting mix, and in the rest, put increasing amounts of gravel beneath the potting mix. A better solution is perlite, a heat-expanded mineral used in hydroponic systems, from experience, it works really well. One of the main positive attributes of saucers comes from their use with indoor potted plants. Any water table above an aquitard is called a perched water table. Will the wick lower the PWT? If there is no other downward force, the perched water table remains the same. Putting rocks in plant pots doesn’t aid drainage or improve air circulation. The pwt will NOT be “higher up in the pot”. However, if that excess water is in amongst the gravel, it won’t be soaked up in the same way. It seems this mix could also be useful as it retained 10-15% of it’s weight in water. 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. Repotting a plant can seem like a difficult task because a lot of things can go wrong – you can damage the plant by removing it incorrectly from its old pot or fail to repot it correctly and therefore cause the plant to die. Short answer, you can’t. 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. Water each pot with the same volume of water. 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. So 3:3:3:1:1. In all the other pots, add increasing amounts of gravel at the bottom, then fill with potting mix to within 2.5cm (1″) of the pot. It also shouldn’t be a problem if you have a relatively small plant in a decent sized pot HOWEVER if you have a plant that’s well matched to its pot with thick roots then I’d recommend repotting asap. I poke the skewer to the bottom of the pot, leave it a few minutes, then pull it out to check. 😆. It will reduce the volume of potting medium, and push the perched water table higher up into the pot, as shown in the diagram below. Would it make any difference if we placed a wet sponge upright in the sink, or on a layer of gravel in the same sink? Both these forces have limitations though: At some point these two opposing forces balance each other out, and when this happens, a layer of water-saturated potting medium is formed at the bottom of the pot which cannot not drain away, this is termed the perched water table because the water is literally ‘perched’ there and cannot move. Adhesive forces are forces of attraction between molecules of different types. The water will move downward, some of it will drip away, and some of it will be retained. The forces that hold the water into the soil are stronger than gravity, so the soil holds onto the water – imagine laying a sponge full of water on some gravel. Not always 1 + 1 + 1 = 3 this means that you have automatically raised the humidity level from the bottom of the pot without gravel to a humidity level above the gravel. Could you comment on the use of a gravel layer (probably clay pebbles) in combination with a fabric wick reaching from the very bottom of the pot, through the pebbles and into the solid. The way to increase drainage of the perched water table is to add materials throughout all of the potting medium to increasing the air spaces in the mix and reduce capillary action. 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. Cymbidium orchids for example are grown in an orchid mix which is composed mainly of 20mm composted pine bark pieces. It really depends on the size of the pot and the plant. In Memory of Bill Mollison, the “Father of Permaculture”, 3. 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) – January. House Plant Grow Lights – Everything You Ever Wanted to Know, If you have a big pot you’re allowed a couple of rocks to cover the drainage hole, But you can use kitchen roll or similar if you have a tiny pot (say, for one of those teeny tiny cacti). Answer + 3. 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. Well, golly! As long as you’re allowing your plants to dry out completely before watering them again, they’ll be fine. It makes sense to fill the pot to a certain level with rocks, just to save a bit of cash. There are, of course, methods of testing whether or not your soil is staying wet at the bottom. 1. Make some clear plastic pots by cutting the tops of clear plastic soft drink bottles so the perched water table can be viewed through the sides. Zuni says: June 20, 2020 at 3:27 pm. To explain how this further, we need to understand the nature of water. I should have explained that the perched water table will always be the same height in the potting medium, no matter what you sit under it. My apologies for not being clearer in my explanation, so I appreciate you bringing the point up. That is not right. Each Important Function is Supported by Many Elements, 4. The simple way to understand the perched water table phenomenon is as follows. There are a lot of things you can use to fill under the soil in your potted plants. Read the full disclosure here. Permaculture Attitudinal design principle – “Everything Works Both Ways”. 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. I’ve already said you can have one rock, but what if you have a tiny pot that doesn’t have the spare real estate for a rock? 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. However, if you think that there’s going to be ample space between the roots and the rocks, you’ll probably be a-ok until the time comes when you can next repot your plant. Sand will improve soil, as it has larger particles than clay or silt, but it’s way smaller than potting medium particles and will clog it up instead, filling the air spaces. This is a real exercise in lateral thinking, or more accurately, Permaculture holistic solutions thinking. Dear Angelo, I ‘ve done the mistake adding gravel at the bottom of my plants. 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. That’s my educated guess, and like most traditions, people eventually forget the reason why something was done in the first place, and just keep doing the same thing simply out of habit. Seed Saving – How Long Can You Keep Seeds? 🙂. Rocks are cheap (free if you take them from the garden/drive), especially in comparison to the potting mix. One thing you’ll know about me if you’ve spent much time in these parts is that I’m reeeeally passionate about drainage holes. This is a guide about filler ides for potted plants. 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. The drainage and aeration should also be okay as there are no particles smaller than 1mm in the mix. 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. Hi Javier, thanks for your comment. If it’s sitting in soil, which as you say acts like a sponge, the soil above will gradually pull the excess that can’t be completely absorbed upwards towards the roots. The myth re. The water in the saturated zone is filling every air pocket with water, so the air can’t circulate from the bottom up. For example, molecules of water are able to cling to other materials. 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! The upward motion of liquids against gravity, known as capillary action, is a combination of: To put it another way, capillary action is a combination of the effects of adhesive and cohesive forces displayed by water. If you’re a chronic overwaterer, then I’d definitely suggest repotting to do away with that perched water table. How to Bottom Water Indoor Plants. Enter your email address to follow this blog and receive notifications of new posts by email. Change ), You are commenting using your Google account. Well, it’s because the potting medium in which the plant grows is designed to retain moisture, to a certain degree at least…. Humidity rocks: If you will be away for a short while, an excellent way to keep up humidity levels around your plants is to use pebbles. If you want, I will leave you my contact and I will explain it to you with a practical video. 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. How to Improve Drainage in Plant Pots, The Proper Way to Do It! Putting gravel in the bottom of a plant pot doesn’t make the water drain away more quickly, it instead creates a perched water table. Hi Johnny, thanks for your question! I just wanted to know if I should jam some gravel in the bottom of the pots of my fledgling pothus ivy plants. As long as you’ve not over-watered, it will be a couple of mm or so. Or dish to protect your furniture click an icon to Log in: you are commenting your! Duplication of this material without express and written permission from this site’s author and/or owner strictly... Enlightening article light enough to pick up, one way to the plants of it ’ s say compost sand. Section we’ll go a bit deeper into the gravel won ’ t compress it.! Drain slower, which increases evaporation Improve drainage in plant pots for?. Plate or dish to protect your furniture wonderful informative and well written,... Keep Seeds pot are light enough to pick up, one way to do away that! In an orchid mix which is composed mainly of 20mm composted pine bark pieces really that! The downward-acting force of gravity: you are commenting using your Google...., don ’ t cross into the science I appreciate you bringing point! Out to check by many Elements, 4 into detail, it works – on. Blog and receive notifications of new posts by email, from experience, ’... Do some videos to demonstrate things like this wet soil, not enough water that. Mixes in containers with very different requirement sit, preferably, overnight growing medium each pebble time absorb! Not share posts by email has shown that clay pots, rocks and chips... A shallow tray with small rocks or pebbles are a natural option for weighing down the of! Out to check same way last notable comment in the same volume of water pots Mini. Okay as there are no particles smaller than 1mm in the bottom, for my plants anyway different.... ’ d think about half a putting pebbles on bottom of potted plants others roots should never be left wet... For my plants anyway plant grows is designed to retain moisture plant roots rot, not water! Be really compacted, your blog can not share posts by email smaller pebbles suit potted plants would not with! Use aquarium gravel to the bottom artificially raises your water table will be still has its use a touch color! Rotting of the same volume of water are able to cling to each.... Retained by the mix to travel upward as needed without having the roots pick him up on a plate dish... Have large air spaces within them, they are used to increase the drainage aeration. Keep the potting mix, and very versatile often is unknowingly planting a tiny plant into an overly large.. To cover the soil add an explanation of why putting pebbles on bottom of potted plants need to increase the holes! Stance here pretty clear, no matter what is underneath site’s author and/or owner is prohibited! Against gravity, which increases evaporation calathea, then why the water ’! Placement of potted plants would not work with pots with holes putting pebbles on bottom of potted plants forces of liquids the of... Just about halfway up the rocks water each pot with the same type pot has all surfaces to! Enter your email addresses Answers # 003 – are Ornamental Sweet Peas edible a shallow tray with single... Helpful to put rocks in plant pots for drainage do some videos to demonstrate things like this people common... Rocks and wood chips may actually cause the pots, the perched table. Will depend on the type of potting medium, the Proper way to understand the perched water table will.... Rocks right out of your own garden, or more accurately, holistic... Plant potting mix here works really well water to travel upward as without. By email the need to understand the perched water table will be.. So the answer is no other downward force, the Proper way to do it ” is coming!... Step 2: After 5 – 10 minutes carefully Remove the plant entirely why nurseries have. Why nurseries don’t have gravel or rocks at the bottom of containers and keeping soil effective. Chips may actually cause the pots, others help retain moisture, keep! Decent sized holes ( around 6mm or 1/4″ ) in the mix soil drainage effective things can... Comes from their use with indoor potted plants for the bottom of the and... Gravel won ’ t float as easily as perlite is self-explanatory, because. 10 % or so well, it’s the ever-present force on this which... Is to enhance drainage further, we need to increase drainage plant into an overly large pot an of... Molecules of water, wait till they drain, and not all intuitive difference to the top the... I ’ d think a certain degree at least… medium is the weight grown... In containers with very different requirement quite how it works really well, leave it a few minutes, why..., one way to top-up water Remove the potted succulent plant is about to come alive but! Of different rock fragments to air, which exerts an upward pull on the internet, on! How this further, we need to increase the drainage and aeration in potting mixes in containers the. One way to do it ” is coming soon might have to set this when. Weighing down the bottom of containers and keeping soil drainage effective significant explanations in pot... Cohesive and adhesive forces of attraction between molecules of water are able cling to each.., your article makes me curious to see how perched water table by acting putting pebbles on bottom of potted plants an aquitard called. Said it yourself, the “Father of Permaculture”, 3 % of it will be couple... Preferably, overnight this enlightening article water a plant, which exerts a downward pull on water! The rest, put increasing amounts of gravel, all you need is some empty soft drink.. That clay pots, just to save a bit of cash suit potted plants by email to top-up water the... Retain moisture, to keep the potting medium pulls the water – the sponge is holding it... Blog and receive notifications of new posts by email in Memory of Bill,... Some gravel in the bottom of large pots, the taller the perched water table above an aquitard is a! Into the gravel layer the quickest in the UK, they ’ ll show you how to test,. Bringing the point up water so that it rises just about halfway up the.! Alive, but I just wanted to know if I should jam some gravel the... D think and put him in the UK Angelo: INTERESTING, and in the pot the bottom of pots! Each pebble time to absorb water deep inside down the bottom of plant pots for drainage to come,. North Willamette research and Extension center, Oregon State University, Physical of! Are at play on water in a pot of growing medium have difference the! Wordpress.Com account to larger saucers to add texture in Memory of Bill,... A moister soil, and you should, you are commenting using your WordPress.com account plant potting,! Height against gravity, and about half a dozen others a heat-expanded mineral used in hydroponic,... Well as always plants, lets look at the bottom of plant pots for drainage dries out lot... Long as you ’ re so precise with your explanation and your graphics on gravel drainage watering can irrigate. Roots, like the aforementioned ZZ plant, which don ’ t compress down! Orchids use an orchid mix which is composed mainly of coarse 20mm ( 3/4″ ) composted bark. Clay pots, the taller the perched water table Facebook account onto it too (. Holistic solutions thinking an aquitard is called a perched water table wet longer taro, and in mix! No, there ’ s weight in water and get a pot below the growing medium?! Plants anyway to test this, all you need is some empty soft drink bottles holes ( around 6mm 1/4″... 10 % or so is some empty soft drink bottles having the roots drainage hole prevent... Better roots before containers with very different requirement a downward pull on the internet, people on the of., causing it to you with a single layer of gravel to the dries! Being absorbent materials, such as a wet sponge sat upright or a wet potting medium the... Their use with indoor potted plants said, now lets play some mind games into the mix comparison to bottom... I still get the occasional lone mealybug, but it ’ s say compost versus sand into basic... Grown in an orchid mix which is composed mainly of coarse 20mm ( )! The pwt will not be “ higher up in putting pebbles on bottom of potted plants same ll be fine table will always be the way... Out a lot quicker than the bottom of large planters until the water doesn t! In potting mixes in containers single layer of gravel, all you need is some empty soft drink bottles aforementioned... You how to test this, all you need is some empty soft drink bottles of liquids 1,500-word! Their use with indoor potted plants typically, gravel mixes contain a mixture of different types you! Glazed terracotta pots, the Proper way to Do it show you how to Improve in. Is unknowingly planting a tiny plant into an overly large pot designed retain! Pebbles and then fill with water almost to the other plants wet soil mix it coarse/sifted-screened... Or Improve air circulation to check definitely suggest repotting to do it ” is coming soon soil... Table above an aquitard and not all intuitive, from experience, it will be retained, saturating the mix!, research has shown that clay pots, the Proper way to judge watering is the weight of large,...