This is a real exercise in lateral thinking, or more accurately, Permaculture holistic solutions thinking. It depends upon your growing medium. 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. It’s not a problem if these pots stay in your aquarium. If you want to put gravel to work with your potted plants, use it outside the pot. 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. Well, it’s because the potting medium in which the plant grows is designed to retain moisture, to a certain degree at least…. 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. How to Make Borax Ant Bait for Indoor and Outdoor Use. You’re right, some things in gardening are definitely not intuitive, and if the science is there, we should use it! Overwatering a potted plant can cause root rot, a disease that results in the slow death of the plant. . Coincidentally, these forces are also how plants get water from their roots to their leaves! 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. 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. Excellent Article, in one article you have addressed many phenomenons. A better choice is placing a coffee filter in the pot to contain the soil. Gardening Questions #002 – How Many Trays to Use When Starting a Worm Farm? 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 size and shape of the pot makes no difference, it doesn’t matter if a pot is tall and narrow or wide and shallow, neither if it’s big or small, if the growing medium/potting mix is the same, the perched water table will always be the same height. This is the principle by which wicking pots work, as explained in my article DIY Self-Watering Pots and Mini Wicking 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. 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. Why should I not put rocks in the bottom of my planter? 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. Give plants as much space to spread their roots out, relative to what they can use or need. Why putting rocks in potted plants can cause problems. 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. 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. You can actually buy mesh mats for the bottom of your pot that do exactly this. 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. It's best to avoid using plastic or vinyl sheets alone to protect plants from frost, since these materials can trap condensation inside, which can freeze and damage the plant. I have wondered for years why nurseries don’t have gravel or the like in the bottom of their pots. A good potting medium (potting mix) has to strike the perfect balance between sufficient moisture retention and good drainage for plants to thrive. I just wanted to know if I should jam some gravel in the bottom of the pots of my fledgling pothus ivy 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. Very good article! 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. 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. 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. 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! ( Log Out /  In general, it’s not necessary to put rocks in the bottom of plant pots. Water (H2O) is considered a polar molecule because it has a negative charge on one side of the molecule and the positive charge on the other. 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. Water moving though one material into another material does happen with force. 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. 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. 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! It seems this mix could also be useful as it retained 10-15% of it’s weight in water. In the first pot, place only potting mix, and in the rest, put increasing amounts of gravel beneath the potting mix. Permaculture Attitudinal design principle – “Everything Works Both Ways”. Crocking was supposed to encourage water to pass down from the potting mix into the gaps in the coarse layer below and out through the drainage hole. It is not recommended to use Styrofoam peanuts for potted plants now, because they may break down in water and soil, leaving you with sunken in containers. This post may contain references to products from one or more of our partners. Last notable comment in the article mentioned a stone on the drainage hole to prevent soil leaching from the pot. Instead, your plant’s soil is the sponge. There’s also the added benefit that it can look really beautiful, giving your indoor plant a tidy, “finished” look. The others were without any real explanations, so I didn’t include them as a I only link to authoritative sources, so I hope that’s okay. 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. If pots drain because they have holes in them, then why the need to increase drainage? Putting rocks in plant pots doesn’t aid drainage or improve air circulation. I like to teach from first principles, as I believe this way we can really come to a deeper level of understanding, but then again, I’ve got qualifications in the biological sciences, so I’m biased! The white rocks in potted houseplants are aquarium rocks. The capillary action can only wick the weight of the water upwards to a limited height against gravity, and no higher. Capillary action, which exerts an upward pull on the water, causing it to be retained, saturating the potting medium. To figure out what’s best for plants, lets look at the science! And these spaces will be way too small for the dirt to wash out. First, let’s start with the basics: Your favorite potting mix or growing media holds water by means of two natural forces. Drainage Holes There may be conflicting advice about how to keep your container garden plants from drowning. Great article. Thanks Elizabeth, that’s an excellent idea! 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. 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. 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. 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? 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. Potting Mix acts like a sponge and will not release water until it is saturated. 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. While this will obviously cover the drainage hole a bit, there’ll still be some small spaces for the water to get out. 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