Some people say you don’t need drainage holes; just put rocks or packing peanuts at the bottom of your container. 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. 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. . 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. In fact, they can actually encourage root rot. From the North Willamette Research and Extension Center, Oregon State University, Physical Properties of Container Media. The gravel will hold water and increase humidity, while keeping The pwt will NOT be “higher up in the pot”. Plant pots fail to drain because the capillary action that suspends the water in the soil is stronger than gravity. It might need a better explanation, although you do well as always. © Deep Green Permaculture, 2009. Potting Mix acts like a sponge and will not release water until it is saturated. Enter your email address to follow this blog and receive notifications of new posts by email. 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. 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. Succulents and cacti naturally grow in sandy soils that drain quickly. 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. You’re welcome to disagree! If you have pots without drainage holes and they’re made from a material that means you can’t add any, you have to be very careful about not over-watering. 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. If you have a large planter, it can take a lot of potting soil to fill it completely. But rocks serve no useful purpose in planters, and as you have seen, only put them at risk of root-rot. 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. Capillary action, which exerts an upward pull on the water, causing it to be retained, saturating the potting medium. How to Improve Drainage in Plant Pots, The Proper Way to Do It! 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. You may also be looking for how to weigh down plastic planters if you feel that yours are too top-heavy and could tip over if they’re just filled with soil. 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. Coincidentally, these forces are also how plants get water from their roots to their leaves! To keep dirt from washing out of pots, put a large rock or something similar over each drainage hole, like broken pottery, a coffee filter or a cheesecloth. Most gardeners prefer to use a potting soil mix for growing gardens in pots, but amended garden soil can be used. 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. 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! I’ll show you how to test this, all you need is some empty soft drink bottles. 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 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. This is a proper controlled experiment, so please don’t go changing the experiment design parameters on whim! I have some succulents in pots ( small, medium, sized) and 3 dwarf citrus in large pots. A better solution is perlite, a heat-expanded mineral used in hydroponic systems, from experience, it works really well. I really should do some videos to demonstrate things like this! 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. 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Add enough water so that it comes about halfway up the stones. Growers of Cymbidium orchids use an orchid mix which is composed mainly of  coarse 20mm (3/4″) composted pine bark pieces. 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. you said it yourself, the perched water table will always be the same height. 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. 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. 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. Root Rot in Potted Plants. The problem would be even worse in glazed terracotta pots, which don’t seep moisture from their sides and stay wet longer. Post was not sent - check your email addresses! 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. 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. Make sure you check on the water from time to time so you can refill it when the water level drops. One of the problems gardeners encounter often is unknowingly planting a tiny plant into an overly large pot. With outdoor plants, there’s a risk they could be rained on, whereas you can control how much water your houseplants get. http://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html. Gardening Questions #002 – How Many Trays to Use When Starting a Worm Farm? Now that we understand how the forces of adhesion and cohesion within liquids create capillary action, leading to the formation of a perched water table at the bottom of an absorbent medium, we can see that it won’t have any effect on these forces in any way at all. For example, molecules of water are able to cling to other materials. Even if you balance it on some gravel for house plants, these won’t help the sponge dry out any faster. 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. Change ), You are commenting using your Twitter account. The more absorbent the potting medium, the taller the perched water table will be. 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. The reasons for this vary, but the practice can be damaging to the plant in the long term. Potted plants can be breeding grounds for gnats, especially the pesky fungus gnat. This means that, when looking for what to fill a large planter with, you can use any of the following: Putting pebbles on top of potted plants can help to prevent evaporation and avoid soil washing away when you water your plants. 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. 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. Tap the sides gently to settle the potting mix slightly, don’t compress it down. Wait till all pots drain well, this will depend on the type of potting medium used and the volume of the containers. This would make a great classroom experiment. Putting rocks on top of potted plants is a perfectly acceptable method to cover the soil decoratively. 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. For example, molecules of water are able cling to each other. Here are the facts about using gravel in potted plants. Put rocks on your soil! Wonderful informative and well written article-thanks‼️, Thank you for this enlightening article. 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. What about putting rocks on top of potted plants? 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. Final thoughts on putting rocks in the bottom of plant pots, natural-colored decorative gravel for plant pots. But otherwise, this is a super easy way to make sure the humidity is just right for your houseplants. From your experience stated I am guessing you’ve probably grown lots of plants in containers with very different requirement. Think of it like this: if you soak a sponge, it will hold on to its water. Thanks Ben! 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. 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? Welcome to Deep Green Permaculture – Connecting Pe…. 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. I really liked that you went into detail, it becomes very clear. The capillary action can only wick the weight of the water upwards to a limited height against gravity, and no higher. Nearly all plants prefer a natural wet-dry cycle, as that’s what they experience in nature. 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. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. Place the pot on top of the rocks – and that’s basically it! Do you need to put rocks in the bottom of plant pots? Gravity is self-explanatory, it’s the ever-present force on this planet which pulls everything down! This is the principle by which wicking pots work, as explained in my article DIY Self-Watering Pots and Mini Wicking 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. Adhesive forces are forces of attraction between molecules of different types. 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. 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. If you want, I will leave you my contact and I will explain it to you with a practical video. 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. My apologies for not being clearer in my explanation, so I appreciate you bringing the point up. 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. You have a nice blog, read a few articles till now and looking forward to your next ones! Cactus and succulent growing mediums for pots are a coarse, open mixes made with some organic matter to retain a little moisture, and plenty of gritty material such as crushed quartz or other crushed rock, which act like a sandy soil and lets water pass almost straight through. The simple way to understand the perched water table phenomenon is as follows. 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. Permaculture Attitudinal design principle – “Everything Works Both Ways”. You can actually buy mesh mats for the bottom of your pot that do exactly this. Dear Angelo, They are put in the plant for several reasons: 1) aesthetic- they look nice 2) to keep your cats from pooping in your plants- … What can I put in the bottom of my indoor planter for drainage? 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. 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. 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. 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. 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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. 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. But no happy as I will now be obsessed with correcting my pots. You do not need to put rocks in the bottom of plant pots as they do not help with drainage or air circulation. That is not right. Excellent Article, in one article you have addressed many phenomenons. This means that all that water being held is pooling closer to – or even directly around – your plant’s roots. 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. Water moving though one material into another material does happen with force. That’s how people find common ground for understanding! 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. Water each pot with the same volume of water. However, during this 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. So how can we turn the problems created by adding gravel at the bottom of pots into solutions? Plants that have different soil drainage (aeration) requirements can be combined in a landscape planter if they are in their own separate pots. You can put rocks on top of soil as they do provide some benefits. 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. 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