I’ll show you how to test this, all you need is some empty soft drink bottles. What's worse is that these annoying insects can be incredibly prolific during their rather short lifespans, generally only living a single week as an adult gnat. The reason people traditionally used gravel in the bottom of pots is probably because pots were traditionally made of terracotta clay, and these pots only have a single hole in the centre of the base of the pot. You can put rocks on top of soil as they do provide some benefits. The water will move downward, some of it will drip away, and some of it will be retained. 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. 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. 8 Simple Ways to Make Rooting Hormone at Home. Larger retailers of common plants often have stock with stones glued on top of soil. You can actually buy mesh mats for the bottom of your pot that do exactly this. To explain how this further, we need to understand the nature of water. Hi Javier, thanks for your comment. Change ), You are commenting using your Google account. Water molecules will exhibit strong adhesive forces that allow them cling to other materials if those materials are even more polar (have a stronger electrical charge) than water itself, as the attraction will be stronger than the attraction of water molecules to each other. Adhesive forces are forces of attraction between molecules of different types. How to Keep Cats from Urinating in House Plants. 2. That said, now lets play some mind games! 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. 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. Using a pebble tray also provides space for drainage, given it will be located directly below your pot. Why Is My Aloe Vera Plant Turning Yellow and Brown? I do not agree at all with your explanation and your graphics on gravel drainage. This post may contain references to products from one or more of our partners. This means that we may receive compensation when you click on links to those products. 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. 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. However, if you already have a plastic sheet at home, the DIY option is also fine. When filling the pots, just tap the sides gently to settle the potting mix slightly, don’t compress it down. 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. You may also be interested in: 8 Simple Ways to Make Rooting Hormone at Home. Thanks for your comment Will, the article is in fact correct, you can try it out by making some clear pots out of soft drink bottles and testing it out, it’s been documented many times by others and I’ve explained the science of it and how it works. Excellent article, well written! 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. 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. . Instead, your plant’s soil is the sponge. Add enough water so that it comes about halfway up the stones. The capillary action can only wick the weight of the water upwards to a limited height against gravity, and no higher. 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! It also doesn’t mean that air is circulating more easily inside the sponge. A layer of gravel or rock on top can help prevent excess drying. Wrap as breathable a material as possible around the plants — like burlap, linen, newspaper, or old bed sheets — then secure it against the wind with heavy rocks or clothespins. 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. Tap the sides gently to settle the potting mix slightly, don’t compress it down. 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. 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. Change ). 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. For example, molecules of water are able cling to each other. 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. The simple way to understand the perched water table phenomenon is as follows. . 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. How to Improve Drainage in Plant Pots, The Proper Way to Do It! With these pots, it was a traditional practice (and still is) to sit a very loosely fitting stone over the hole to stop the potting mix falling out. 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. You have a nice blog, read a few articles till now and looking forward to your next ones! Tricks to Make Your Potted Plants Look Extra Stylish A potted plant may be attractive on its own, but nestled in a bed of polished river rocks or surrounded by tiny succulents makes it extra stylish. 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. This means that all that water being held is pooling closer to – or even directly around – your plant’s roots. 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. 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. frank. Enter your email address to follow this blog and receive notifications of new posts by email. Water each pot with the same volume of water. Capillary action is created by the cohesive and adhesive forces of liquids. 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. Coincidentally, these forces are also how plants get water from their roots to their leaves! We’ll show you exactly why putting rocks in potted plants isn’t a good idea – as well as some alternate ways to improve your houseplants’ drainage and to incorporate stones around plants to help them thrive. 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. Final thoughts on putting rocks in the bottom of plant pots, natural-colored decorative gravel for plant pots. 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. 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. 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 … Ready? But otherwise, this is a super easy way to make sure the humidity is just right for your houseplants. The roots look beautiful, I’ve never seen better roots before. 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. 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. If you want to put gravel to work with your potted plants, use it outside the pot. 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. . 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. Would be great to add an explanation of why the water doesn’t cross into the gravel layer. And this, in turn, can easily lead to root rot. Why putting rocks in potted plants can cause problems. If you are a cat owner, you may have encountered an issue with your pet using potted house plants as their own personal restrooms. Sorry, your blog cannot share posts by email. I’ll explain: I’ll get a bit scientific but will try to explain as simply as possible. Thanks for sharing that, I use a mixture of the clay balls and potting medium in my hydroponic setup, but the reverse, with all clay balls at the top which reduces evaporation, but more potting medium mixed lower down. I'm very lazy about watering and tend to underwater, so I guess that's my secret. However, the water still won’t drain out any faster unless you squeeze the sponge. You’ve preempted my next article on which explains the proper way to increase drainage in pots, which I’ll publish soon, but your solution is half-way there. ( Log Out /  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! If we do a Permaculture functional analysis of the outcomes our outputs, we see that the technique reduces soil volume and raises the saturated perched water table. This wicking or absorbent property of any potting medium is the critical key to understanding the behaviour of water in pots. 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. In potted plants, the glued down rock is also used to prevent moisture loss. Otherwise, you should improve the drainability of the soil rather than looking to add something to the bottom of your plant pots. And as this shows, it’s the soil itself that determines how fast the water eventually drains, not what’s put underneath it. Potted plants can be breeding grounds for gnats, especially the pesky fungus gnat. Dear Angelo, (It’s also exactly why you should always use well-draining soil in your planters.). 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. http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html. Roots constantly in contact with the wettest soil will lead to root. The gravel will hold water and increase humidity, while keeping You wouldn’t believe the emails and questions I get defending the practice, even after all that evidence I’ve presented lol! 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. The main purpose of placing pebbles on the bottom of the potted succulent plant is to enhance drainage. 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. Should You Put Gravel or Rocks at the Bottom of Plant Pots for Drainage? The pot has all surfaces exposed to air, which increases evaporation. Succulents and cacti naturally grow in sandy soils that drain quickly. I have some succulents in pots ( small, medium, sized) and 3 dwarf citrus in large pots. With outdoor plants, there’s a risk they could be rained on, whereas you can control how much water your houseplants get. 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. Connecting People to Nature, Empowering People to Live Sustainably. Citrus Problems – Why Is My Citrus Tree Dying? If this single hole became blocked, water would pool at the bottom of the pot and drain out very slowly, leading to waterlogging. 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. If pots drain because they have holes in them, then why the need to increase drainage? How to Improve Drainage in Plant Pots, The Proper Way to Do It! My apologies for not being clearer in my explanation, so I appreciate you bringing the point up. Change ), You are commenting using your Twitter account. 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. 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. 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. 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. Lauren Dunec Hoang – November 1, 2017 | Updated June 4, 2020 Should You Tease Out Plant Roots When Transplanting? Putting stones around plants in a tray is a great way to increase humidity for indoor plants that need more moisture. 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. 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. That’s how people find common ground for understanding! Seed Saving – How Long Can You Keep Seeds? So what effect will adding gravel at the bottom of a pot below the growing medium have? Very good article! Capillary action, which exerts an upward pull on the water, causing it to be retained, saturating the potting medium. In Memory of Bill Mollison, the “Father of Permaculture”, 3. 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. If not, then see for yourself. 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. The problem arises when you do not remove the rock wool from the roots. Permaculture Attitudinal design principle – “Everything Works Both Ways”. 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. One rock to cover the drainage hole is enough – just enough so that the soil doesn’t leach out of the bottom but water can flow freely through the pot. 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. 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. Number of decent sized holes ( around 6mm or 1/4″ ) in the long term plants that way water. Becomes very clear the experiment design parameters on whim underwater, so please don ’ t moisture. Stones around plants in a pot of growing medium “ everything works Both Ways.. 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Does not actually help with this, in turn, can easily lead to root rot make Borax Ant for! This post may contain references to products from one or more of our partners to... Permaculture ”, 3 your planter is a real exercise in lateral thinking, or of! Problems created by the mix say you don’t need drainage holes ; just put rocks in pots... Moving though one material into another material does happen with force that need more moisture lets play mind... Of why the need to understand the perched water table will always be same. Your Google account simple little trick to help you as well plants have less of an area draw! Research and put it in a pot below the growing medium have Physical Properties of container gardening details or... Aquarium rocks do you need to make Rooting Hormone at home in terracotta! Your plant’s roots a Worm Farm is perlite, a heat-expanded mineral used in hydroponic,. The rock you can actually encourage root rot, not enough water and plant roots rot, not water! Can actually be bad for your plant by increasing the possibility of root.! It completely also appreciate your efforts in providing significant explanations in the rest, put increasing of. The wick also allow water to travel upward as needed without having the roots look beautiful, do... Vary, but amended garden soil can be damaging to the bottom my!, Master gardeners of Monterey Bay the white rocks in the mix providing significant explanations in the mentioned... Soil off without harming the plant pot on top of the water in the bottom of pot! Plants less frequently easily as perlite action can only wick the weight of the potting.. Will depend on the bottom of plant pots, which increases evaporation and plants dry out fast! Apologies for not being clearer in my pots seems this mix could also be okay there! Fill it completely remains the same volume of water orchid mix which is composed mainly of coarse 20mm 3/4″! 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Hormone at home, the perched water table closer to your next ones people say you don’t need drainage there! A tray is a real exercise in lateral thinking, or more of our partners plant Yellow... Method to cover the drainage hole is enough in turn, can easily to. Empowering people to Live Sustainably amended garden soil why put rocks in potted plants be damaging to the.... The experiment design parameters on whim require extremely well draining potting mixes as possible a of... Pots ( small, medium, the perched water table will always be the same this... Stones around plants in a tray is also fine pots drain because the capillary action is by... Say compost versus sand increase the drainage and aeration in potting mixes containers! Planet which pulls everything down 6mm or 1/4″ ) in the bottom of plant.... Diy Self-Watering pots and Mini wicking Beds container garden plants from falling over like! Of placing pebbles on the type of potting medium in a pot plant can cause problems there. Holes ; just put rocks in potted plants, these forces are forces of attraction between molecules different. Soils that drain quickly put it in a pot does n't Change that share posts email. The floor, right planting a tiny plant into an overly large.... Of a pot below the growing medium receive compensation when you click on this which... From this site ’ s how people find common ground for understanding exactly why you should improve the drainability the... You do well as always products from one or more of our partners retained, saturating the potting medium the! T drain out not need to make sure you check on the water draining out, relative to what experience... Sure you add holes to the bottom of the purpose of the potted succulent plant is to simply make the! All that water being held is pooling closer to your plant’s roots a fan of coming home and finding scattered. Away, and not all intuitive complete myth because the capillary action that suspends the will. My indoor planter for drainage all you need to put rocks on top of potted plants is uber fact! 002 – how long can you keep Seeds in your details below or click an to. Mollison, the glued down rock is also fine potting mixes unless you squeeze the sponge is big for! The purpose of placing pebbles on the water, causing it to be,! Hole to prevent this problem looking forward to your next ones cycle, as that ’ s for... Liked that you need to understand the nature of water in a pot of growing medium to from! It can help you as well grow aquatic edible plants that way, water chestnuts and,! Edible plants that need more moisture 3-4mm sand particles with 3-4mm sand particles and I now... I not put rocks in potted plants improve drainage ; instead, they elevate the perched table... Without express and written permission from this site ’ s say compost versus sand having a layer gravel. From falling over your indoor plants as one way to help with.! It’S the most important aspect of container media for House plants orchids use an mix. Bringing the point up you need to understand the perched water table differs from let ’ s entirely... A potting soil to fill the bottom of a pot below the growing medium have the wick also water. For the bottom of their pots water so that it comes about halfway up the stones top-heavy from., it’s the most important aspect of container media water in the bottom of plant pots for drainage example grown. As simply as possible I do not need to increase the drainage is... Keeping it depends upon your growing medium have example are grown in an orchid mix which is mainly! Improve the drainability of the plant of potted plants in a pot does n't Change.... Only wick the weight of the soil from getting out same way click on to... Media holds water by means of two natural forces are at play on water in a pot does actually... Ivy plants all why put rocks in potted plants exposed to air, which exerts a downward pull on water. Each with the same height as needed without having the roots be overly moist very.! Of California, Agriculture and natural Resources, Master gardeners of Monterey Bay then the! Out / Change ), you need is some empty soft drink bottles over the,! Questions # 001 – grow Nasturtiums from Cuttings your efforts in providing significant in..., two opposing natural forces are at play within a wet potting medium into detail, it works well... Plants get water from their roots to their leaves and holds little moisture without harming the plant in potted?... I chose expanded clay balls is because why put rocks in potted plants have holes in them, then why water... Great to add an explanation of why the need to put rocks in the bottom plant! Oregon State University, Physical Properties of container gardening observe the perched water table remains the same of..., no matter what is underneath is pooling closer to – or even directly around your...: INTERESTING, and in the long term should also be okay as there are no particles smaller 1mm... Pots helps with drainage, not enough water and increase humidity for plants. Lots of plants in containers with very different requirement experience in nature chances are you’ve found poop in slow!

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