I have found that each ingredient used in a more gritty medium retains a different or slightly different amount of moisture, depending on various factors. Numbers are not my thing, so without bringing math or percentages into the discussion, I begin by soaking the pine bark fines, akadama, or any other moisture retentive ingredient I'm using overnight in a covered container before mixing my medium. I then get rid of any extra water that hasn't soaked in. For all intents and purposes, the coarse perlite I use doesn't retain enough moisture to make note of, in my opinion. But beginning with moistened pine bark and akadama, I can ensure that the roots of any freshly potted plants will not dry out too quickly, but also won't have too much moisture to deal with. When I water, especially when using the addition of fertilizer, I use deep saucers to catch the excess, then reuse that a second time to make sure the plant has been adequately watered. Once I'm sure the plant is sufficiently watered, I dump the saucers. I never want to leave them soaking when the process is done. Using a more porous mix means watching moisture content more closely, and most likely watering more often than if one were to use what passes as potting soil sold in bags. But the extra effort is very worth it! I continually read tags, instructions, and hear people say things like "water once a week" or things of a similar nature... when the truth is, I only water my plants as they need it. I only drink liquids when I'm thirsty... why would a plant be much different? :-) There are many substitutions as ingredients go... turface, cherry stone, lava rock, perlite, pine bark, akadama, etc... some can retain moisture, others not... and at differing rates. I sort of tailor make my medium based on factors such as pot and plant size, plant type and needs, the climate or micro-environment it will be kept in, etc. Happy Gardening!

I'm not sure how much container growing you've done, but after a while you develop a sense of what's happening below the soil line. E.g., if I'm watering a plant in a gallon of medium and it's nearly dry, I can usually predict within an ounce or so, how much water it will take to saturate the soil (so water starts to run out of the drain hole). In your case, you should be able to consider how wet or dry the soil is, what the soil volume of the pot is, and about how much water it will take to moisten (as opposed to saturate) the medium. Next time your plant needs water, you might need to fuss a bit by adding the water slowly enough that hydrophobic tendencies don't thwart your effort to moisten the medium, but pay attention to how much water you're applying. I'd guess that in a water-retentive mix, it might take 12 oz of water to rehydrate a gallon of medium so it's moist instead of wet. By simply paying attention to what you're doing, it should take only a couple of waterings to get a feel for the difference between too much and just enough. Honestly, unless you enjoy being passionate about trying to make everything as perfect as possible, you're probably wringing your hands too much. You know I said that in a friendly way because there was nothing critical about it. If you're having fun - that's what matters. If you're creating stress by trying so hard, I'm just trying to let you know it doesn't have to be stressful. Al

It would seem to me that the diapers would pull moisture out of the soil mix, which is exactly the opposite of what you want them to do. And I doubt they would release any of that moisture easily and even less so to plant roots. And I cannot envision how they wouldn't adversely affect drainage, unless you chopped them up into little pieces. So, although I have not tested this personally, I would think they would produce a result that is the exact opposite of what you want. Why not just use the beads or gel? At least these get dispersed uniformly throughout the soil and plant roots can actually access the moisture. They still have an ability to compromise good drainage however.

Al: Apologies again for having diverted from the main topic. TomH: Nice to meet you too. From your profile it is not evident to me that you have been around in GW for a long time. The first comment in your profile is only a couple of months back. But I will take your word for it. Perhaps you created a new ID. I have also read many papers and thanks for the links to various pubs that you posted. We all read and interpret in various ways. It took me a while to go through the articles. I like to understand the whole context of an article when I read them. Mostly it was informative for me and I hope my analysis below is useful to some. It is long but could not help that. But I would like to start with couple of observations I have. A. All the research is done under lab or greenhouse conditions. In greenhouse like conditions every aspect of growing plants can be controlled. Outdoors plants are subjected to vagaries of nature outside our control. B. Published properties of soil mixes are always initial conditions. None talk about long term properties under real life conditions where the soil is subjected to the elements, undergo degradation and growing plants. All organic material will undergo degradation including peat and bark. As they degrade, the soil properties become worse with time. Let me state first that both peat and perlite have some nice properties just like other components have certain good properties too. Similarly they all have downsides too. In the hands of an expert, many types of mixes can be made to work, especially in well controlled environments. My reluctance to use peat or any other component is solely due to its particle/pore size. If peat came in little balls of 2-6 mm range I would have no trouble using it as the organic component of my mix. I will go through some of your linked publications and provide my thoughts on how I interpreted those. Article 1: https://www.researchgate.net/publication/327992532_A_RESEARCH_ON_THE_INFLUENCE_OF_POROSITY_ON_PERLITE_SUBSTRATE_AND_ITS_INTERACTION_ON_POROSITY_OF_TWO_TYPES_OF_SOIL_AND_PEAT_SUBSTRATE The authors refer to 1:1 to 2:3 air:water porosity needed for a good mix. From the table that would require perlite fraction to be 50-70%. So it would take that much of perlite to make peat a good soil. Using bulk density to calculate total porosity is a bad method. That is why the authors have a very high total porosity of 90% of pure perlite. To me the results are very suspect. In fact there are many articles out there that say that total porosity of perlite is around 75%. Eg https://journals.ashs.org/horttech/view/journals/horttech/17/3/article-p312.xml They state total porosity of perlite is 74%. If you look at Table 1 you will see that the authors state that 60% perlite with peat air porosity is a meager 13% and water porosity is a whopping 59%. No where close to 1:1 or 2:3 ratio the previous paper suggested. Which one do I believe? The authors in the second paper cited air porosity needed is 10-20% again very different from the previous one. Bark+Peat: https://oregonstate.edu/dept/nursery-weeds/presentations/nw_ag_phys.pdf Before anyone says bark will rob nitrogen - easy to solve - apply more N. On pages 50-53 the author compares bark+peat mixes. Shows that bark by itself has better water holding and air porosity than perlite. By adding small amount of peat to bark one can alter these characteristics. One can achieve much better properties than by adding perlite to peat. Article #2: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/perlite. You used this reference to bolster your support of perlite based on this sentence I presume: "Perlite is probably the medium ingredient having the highest air-filled porosity." Probably it is. Is the air that is trapped inside perlite available? Likely not since bulk of it is a closed cell structure where the air is permanently trapped. Eg: http://www.perlite.com.eg/Download/Agricultural_Perlite.pdf. Quote: "Horticultural Perlite particles have a closed cell structure with multiplicity of tiny crevices on their surface. These crevices trap water and hold it against drainage and evaporation, yet making it available to plant roots on demand" Perlite's contribution to holding air and water is entirely dependent on the surface properties. That is why using bulk density to calculate total porosity (as Article #1) did is such a bad idea for perlite. Size matters too. Large perlite particles have relatively small surface area compared to the volume. So these mostly occupy space. Smaller it gets there is more surface relative to volume and becomes more useful for plants. Too small (less than 2mm or so) perched water will become a problem. "So it’s more complex than simply reducing all potting materials to their particle size as you both are doing, as if bark & perlite were both marbles with the exact same characteristics (you used that exact analogy last year)." An analogy by definition means similar and not necessarily exact but significant. In science, analogies are frequently used to convey complex ideas in a more accessible form. It would be foolish to assume that they are exactly the same thing. I use them in my engineering classes just like the sponge analogy earlier to illustrate what perched water is. You want to delegate particle size considerations as a lesser consideration but your own references delves on that topic as I will point out later. In fact, all decent publications talk about particle sizes in a neutral fashion. Some better ones resort to visuals and analogies. Article #3: https://journals.ashs.org/hortsci/view/journals/hortsci/44/3/article-p781.xml on nitrogen immobilization Really?? The article is about comparison of woody substrates against peat and pine-bark. They clearly mention that it is a routine procedure to use extra initial charge of nitrogen to counter the effect in pine bark. That is a common practice. Apparently, according to the article, that does not work so well for woody substrates like sawdust and others. They use PB for an intermediate data point like all good scientists should. Otherwise comparison of sawdust against peat will be completely lopsided. You see peat also consumes Nitrogen - so it also decomposes and degrades. Means the particles will become smaller. Bark decomposition will also have the same effect. But I can always start with larger bark as a portion of the mix. Article #4: https://journals.ashs.org/horttech/abstract/journals/horttech/8/4/article-p481.xml on root medium properties and your contention that peat moves water 2.5 times better. The above article, you referenced, actually talks about a number of topics and quite revealing. You based your conclusion based on the fact that peat "loses" water to evaporation at 2.5 times than Pine bark. Is that a good thing? Don't you want your medium to retain water as much as possible so that it is available to the roots? You are making your own conclusion that evaporation decreases the impact of perched water (indirectly admitting that perched water is present and needs to be dealt with). Whereas the authors conclude it is a negative. Quoting them "Thus, the water holding capacity of peat compared to other is offset in part by evaporation ... ". Later, "Evapotranspiration can be reduced by placing a barrier over the surface ..." In several places in the above article the authors talk about the impact of particle size. Page 482 in section: Particle size and Pore Space Distribution. Notice how the discussion does not mention peat or bark till the end. That is because the basic physics applies to any medium. The section "Settling" on the same page talks about compaction issues in peat based media. Next page section "Moisture release characteristics", the last para on the page. Quote: "Of the organic material peat held the most water ... but plants grown in peat took the shortest time to wilt. Pine bark held 30% less water ... pine bark went 80% longer to wilt ..." In conclusion section pg 484. Quote "In transplant production media water is never a limiting factor ... Instead aeration is the primary concern" They go on to describe three methods to increase aeration. The very first method is to increase particle size but admit cannot be done since they are stuck with using medium with fine particles because it makes it easier to quickly and uniformly fill the pots. A business decision. The second is to increase container height so that the saturated soil (perched water) is way below. Nurseries do not like that apparently. So they opt for the third method - saturate with water and then use a combination of heating, ventilation and air flow. Only possible in a greenhouse. Perhaps this where the rapid evaporation loss of peat is useful to greenhouse operators. The authors did an excellent job of convincing me that I should be ultra careful about using peat in my containers. Thanks for the link. Article 5: https://books.google.com/books?id=d1v5pAmhYXEC&lpg=PA53&pg=PA125#v=onepage&q&f=false I am astonished how you want us to believe evaporation is a good thing and then link an article which says exactly the opposite. Quote: "High peat mixes rapidly lose water ... A mulch of bark ... greatly reduces the loss. These last few points indicate that high peat mixes are generally inferior in physical properties to mixes based on best composted pine bark. The best way to use peat is to use in small proportions to increase water holding capacity." The above quote basically provides more justification for Al's 511 mix of bark, perlite and peat. "In the US, mostly Canadian peat moss is used. This can absorb up to 8 times it’s weight in oil (here is the science), and up to 20 times or more it’s weight in water (here is the science), and blonde peat, which I love, even higher." I stand corrected. But isn't very high water retention a problem also in soil mixes? Article 4 above thinks so and greenhouses have to employ specific water management procedures to counter that. "Water evaporates out of the top of a pot of peat-based soil at 2.5 times the rate of pine bark (here is the science p 484 ¶ 2; more science p 125 #3). The method it moves is irrelevant, as long as it is leaving the pot. Another way to say the same thing is that water festers down in bark’s perched water table for days longer than in peat’s (you & I both know why Al talked about overturned pots up above). This movement of water makes perched water tables not a serious problem for peat. So peat actually does have a very unique structure with multiple kinds of porosity & water transfer mechanisms, to which the laws of physics do seem to apply differently." Do not know where to start but here it goes. Laws of physics (or more generally science) always apply the same way - that is why they are called laws. Every material has a complex and unique structure. You want to depend up evaporation loses as a mechanism to control perched water? How is that going to work out outdoors. Hot dry days will dry out the soil fast. Cool rainy days will keep the container saturated. Properly mixed mixes has very little perched water - so nothing to control. I do not have to worry about vagaries of nature saturating my containers. On the other hand I can always water when needed because that is completely under my control. Even if it means watering daily during hot dry spells. Ballasts (overturned pots) are a great way to deal with saturated soil but why bother when I can make mix that does not have saturated water zone or is extremely small. First you tell me that peat holds a great deal of water and convince me that is a good thing. Then quickly followed it by how fast it loses water and that is a good thing too !! Complex indeed. I would rather have a mix that has consistent moisture levels throughout the soil instead of dry zone at top and wet zone at the bottom. Article 6: https://www.sciencedirect.com/science/article/pii/S0009254116301243: Nice paper on peat. But I do not see how it is relevant except to state that it is complex. Plus it will take me a while to understand most of the paper. If you have a better analysis I will love to hear. Article 7: http://www.dnr.wa.gov/Publications/ger_b44_peat_reasources_wa_1.pdf to support that peat has unique cell walls that resist compaction under high pressure. I wonder how the industry compresses and bags them in those 3 cu ft bales? I would have thought, instead, it would be a good argument to state that peat will spring back to its original shape easily when allowed to - because of its cell structure. Article 8: https://books.google.com/books?id=d1v5pAmhYXEC&lpg=PA53&pg=PA123#v=onepage&q&f=false The fact that peat has unique properties is already established. It is a tenuous argument that peat does not compact when your own referenced article (4) above says it needs to be avoided. In fact, if you look up nursery manuals they will precisely detail how to fill pots with peat based mix to minimize compaction related effects. "Fortunately, you also said directly that adding perlite eliminates compaction." I said it prevents and does not mean it will not compact. "Do you see the Alocasia on the left in this photo? It’s been 21 years in that same pot of peat-perlite-pumice-compost (including 4 years dormant!) It is still uncompacted and drains freely. The soil has lost about 1.5” of height in that time. Very acceptable and not at all a problem." Nice plant. Guestimating that the pot is 10" high - so a 15% loss in volume for 1.5 inch drop in soil level. Pumice and perlite will not collapse. So let us say half of it is peat and compost - so it collapsed by 30% !!! Peat does have two properties that are truly great. One is its superior ability to release most of the water it holds. Thus roots do not have to fight as much to extract the water from the media. Second is its superior ability to hold and release nutrients. By adding a small amount of peat to a bark-based mix allows one to take advantage of that.