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. This would make a great classroom experiment. This post may contain affiliate links. 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. As I already mentioned, you just need one rock, to keep the potting medium in the pot. From your experience stated I am guessing you’ve probably grown lots of plants in containers with very different requirement. Excellent Article, in one article you have addressed many phenomenons. Rocks are cheap (free if you take them from the garden/drive), especially in comparison to the potting mix. Rocks for Plants, Succulents, Fairy Garden Big 3lb Bulk Bag – 5mm Tumbled Crushed Natural White Stone Pebbles for Decorating Bonsai Trees, Zen Garden, Succulent Plants 4.4 out of … 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. The problem would be even worse in glazed terracotta pots, which don’t seep moisture from their sides and stay wet longer. Few people are. There are only two forces at play on water in a pot of growing medium. 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. The more absorbent the potting medium, the taller the perched water table will be. In the first pot, place only potting mix, and in the rest, put increasing amounts of gravel beneath the potting mix. In this section we’ll go a bit deeper into the science if you’re interested, if not, please skip to the next section. The pwt will NOT be “higher up in the pot”. 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. 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. 1:1 ratio. The main consideration with flowers or vegetables grown in containers is … 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. That said, now lets play some mind games! If you’ve read this far, and still aren’t convinced that putting gravel at the bottom of a put just pushes the perched water table up, but doesn’t improve drainage, then I have two diagrams and two direct quotations from authoritative sources to illustrate the point: Hopefully that’s convincing! Capillary action is created by the cohesive and adhesive forces of liquids. 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