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. You might have to check if your plant needs water differently, since you can’t see, or may not easily be able to touch the potting soil. I might have to set this up when I have time and photograph it. 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. Should You Put Gravel or Rocks at the Bottom of Plant Pots for Drainage? However, the water still won’t drain out any faster unless you squeeze the sponge. First, let’s start with the basics: Your favorite potting mix or growing media holds water by means of two natural forces. Gravity, which exerts a downward pull on the water, causing it to be drained away through the drainage holes. Absorbent materials, such as a wet sponge sat upright or a wet bath towel hung from the line, behave the same way. Putting rocks on top of potted plants is a perfectly acceptable method to cover the soil decoratively. Should You Tease Out Plant Roots When Transplanting? With outdoor plants, there’s a risk they could be rained on, whereas you can control how much water your houseplants get. No gravel – none of the time! 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. Here is a simple experiment that can be set up to determine whether adding gravel at the bottom of a pot improves drainage or not. 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. Using a pebble tray also provides space for drainage, given it will be located directly below your pot. 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. Or perhaps it was simply something passed down from one plant owner to the next. 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. Now, we’re not talking about squeezing your plants here (although feel free!). 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. While you can mist your indoor plants as one way to help with this, using a pebble tray is also another easy solution. 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. 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. 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. The gravitational force can only exert a limited downward pull on the water against the upward pull of the capillary action, and no more. 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. That is, when people ask why put rocks in potted plants, they usually have some idea that this will help with drainage. Unfortunately, however, the concept that you need to put rocks in the bottom of your planter is a complete myth. Excellent Article, in one article you have addressed many phenomenons. But otherwise, this is a super easy way to make sure the humidity is just right for your houseplants. 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 … 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. Final thoughts on putting rocks in the bottom of plant pots, natural-colored decorative gravel for plant pots. 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. Cymbidium orchids for example are grown in an orchid mix which is composed mainly of 20mm composted pine bark pieces. This would make a great classroom experiment. Add enough water so that it comes about halfway up the stones. The gravel will hold water and increase humidity, while keeping From the University of California, Agriculture and Natural Resources, Master Gardeners of Monterey Bay. I’ll explain: I’ll get a bit scientific but will try to explain as simply as possible. Welcome to Deep Green Permaculture – Connecting Pe…. . 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. Take a rock garden and put it in a pot. Why should I not put rocks in the bottom of my planter? 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. 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. Combining plants with differing requirements. 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. Hopefully, what you have learned here will make your indoor herbs and plants … 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. I also tried to mix sifted1-2mm sand particles with 3-4mm sand particles and I measured the water retained by the mix. To explain how this further, we need to understand the nature of water. I also appreciate your efforts in providing significant explanations in the comments section. And it’s not even clear where this idea came from. (It’s also exactly why you should always use well-draining soil in your planters.). http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html. Potted plants can be breeding grounds for gnats, especially the pesky fungus gnat. The capillary action can only wick the weight of the water upwards to a limited height against gravity, and no higher. Too much water and plant roots rot, not enough water and plants dry out. What about putting rocks on top of potted plants? 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. It’s a common idea that a lot of so-called gardening experts mention as being critical for making sure that your plant’s soil is able to drain enough moisture. Cohesive forces are forces of attraction between molecules of the same type. 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. 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. Simply take your plant saucer and add a single layer of pebbles, which can include either small decorative stones or simply some small rocks you find outside. . 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, because this leads to root rot, which can kill a plant. Place the pot on top of the rocks – and that’s basically it! Wonderful informative and well written article-thanks‼️, Thank you for this enlightening article. 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. If you have a large planter, it can take a lot of potting soil to fill it completely. 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. Well, it’s because the potting medium in which the plant grows is designed to retain moisture, to a certain degree at least…. 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. Change ). 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. Sorry, your blog cannot share posts by email. 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. From the North Willamette Research and Extension Center, Oregon State University, Physical Properties of Container Media. Nearly all plants prefer a natural wet-dry cycle, as that’s what they experience in nature. Why putting rocks in potted plants can cause problems. 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. Find out more here. © Deep Green Permaculture, 2009. 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. 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. There are only two forces at play on water in a pot of growing medium. 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. How to Make Borax Ant Bait for Indoor and Outdoor Use. It depends upon your growing medium. 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. 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 mixture drains extremely well and holds little moisture. This is a proper controlled experiment, so please don’t go changing the experiment design parameters on whim! You may also be interested in: 8 Simple Ways to Make Rooting Hormone at Home. In fact, they can actually encourage root rot. How to stop To figure out what’s best for plants, lets look at the science! 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. So what effect will adding gravel at the bottom of a pot below the growing medium have? Very good article! Gravity is self-explanatory, it’s the ever-present force on this planet which pulls everything down! It prompted me to look around. What can I use to fill the bottom of a large planter? 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. 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. Food for the thought! But rocks serve no useful purpose in planters, and as you have seen, only put them at risk of root-rot. One option is to simply make sure you always soil that’s excellent for drainage. Dear Angelo, 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. The main purpose of placing pebbles on the bottom of the potted succulent plant is to enhance drainage. So how can we turn the problems created by adding gravel at the bottom of pots into solutions? The problem would be even worse in glazed terracotta pots, which don’t seep moisture from their sides and stay wet longer. How to Keep Cats from Urinating in House Plants. Permaculture Attitudinal design principle – “Everything Works Both Ways”. 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. 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! 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. Well, I have a super simple little trick to help you water those potted plants less frequently. 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. They will protect your plants from weeds, keep pests out, prevent soil erosion, avoid splashing soil on the foliage, and prevent fungal diseases. Put rocks on your soil! 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. They are put in the plant for several reasons: 1) aesthetic- they look nice 2) to keep your cats from pooping in your plants- … If you are a cat owner, you may have encountered an issue with your pet using potted house plants as their own personal restrooms. 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. Some plants require extremely well draining potting mixes in containers. However, if you already have a plastic sheet at home, the DIY option is also fine. Especially the potted plants in your container gardens that dry out super fast. You can put rocks on top of soil as they do provide some benefits. There’s also the added benefit that it can look really beautiful, giving your indoor plant a tidy, “finished” look. And these spaces will be way too small for the dirt to wash out. 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. Capillary action, which exerts an upward pull on the water, causing it to be retained, saturating the potting medium. 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. 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. What do you put in the bottom of a planter? 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! My nest article “How to Improve Drainage in Plant Pots, The Proper Way to Do It” is coming soon! If this single hole became blocked, water would pool at the bottom of the pot and drain out very slowly, leading to waterlogging. Give plants as much space to spread their roots out, relative to what they can use or need. The simple way to test this is to make some clear plastic pots by cutting the tops of clear plastic soft drink bottles and making the same number of holes in each, so the perched water table can be viewed. 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 reason for wanting to improve drainage in pots is because most plants don’t like having ‘wet feet’, otherwise known as waterlogged roots, … The roots look beautiful, I’ve never seen better roots before. 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. Larger retailers of common plants often have stock with stones glued on top of soil. While this will obviously cover the drainage hole a bit, there’ll still be some small spaces for the water to get out. This means you should make sure the soil you put in these pots helps with drainage to avoid root rot. 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. frank. Putting rocks in plant pots doesn’t aid drainage or improve air circulation. The reason why I chose expanded clay balls is because they don’t float as easily as perlite. 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. Putting rocks at the bottom of the pot doesn't change that. Put a layer of gravel in your plant’s drainage tray, or down inside a decorative planter, then sit your plant pot on top. The white rocks in potted houseplants are aquarium rocks. If not, then see for yourself. 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 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. 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. Practice can be damaging to the plastic to allow water to drain out how prevent... When people ask why put rocks in plant pots action is created by the cohesive and adhesive are! S best for plants, the Proper way to understand the perched water table be. Of growing medium that drain quickly means that all that water being held is pooling closer to – even. 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