When it comes to root health, pots with gas permeable walls carry the day. Terra cotta clay pots are better than plastic or vitrified clay pots and fabric pots are better than terra cotta clay. The reason is greater gas exchange through container walls and the fact that an increase in gas exchange comes with an increase in evaporative water loss, which can be a lifesaver when using water retentive media. There will still be a PWT in these pots, and for any given medium it will the same ht in a pot with rigid sides as in the fabric or air pots at container capacity. Container capacity is a measure of how much water the grow medium in a pot or container holds at the moment it has stopped draining after having been watered to the point of complete saturation. The ht of the PWT and how long it affects root function is usually key/critical in determining what opportunity a plant will have to realize as much of its genetic potential as possible (within the limiting effects of other cultural influences). The factor that most affects the ht of a PWT is the size of the particles from which the medium is made. So, reducing the duration of PWTs limitations increases the opportunity for plants to realize a greater measure of their genetic potential. But wait! There's a more important consideration. If you place your fabric containers directly on the ground/soil, from the perspective of hydrology it changes the fabric container to a raised bed; this, because water is free to move through the fabric between the grow medium and the earth, with the earth acting as a giant wick. This means, because of the increase in the force of adhesion in the mineral soil beneath the pot (due to a mineral soils much larger o/a surface area on a per volume basis), water in the soil will be pulled downward with enough source to overcome the capillarity holding it perched in the container. As long as you don't place the fabric container on coarse sand, peastone, or other large particles, the earth will likely pull all perched water from most media one is likely to use in a container. I've mentioned this and the fact that healing in your pots situating them directly on top of soil turns them into raised beds. the only caveat being it's essential that there is a 'soil bridge' so there is continuity of the soil column between the soil (earth) and the grow medium in the container, through the drain hole(s), so water doesn't have to jump an air gap to exit the container. This applies more to pots with rigid walls and is not a factor when discussing fabric containers. Al

Hi! I'm glad this thread is still alive despite it being 10 years old! :D Just what I need—I've had a Calathea Zebrina for almost 6 weeks. A week after getting it, leaves started turning yellow, browning, and shriveling up. I was able to asses that it lacked humidity and fixed it with a humidifier on it's 5th week with me. Since then, leaves stalled their yellowing but I'm down to two good leaves. Now on it's 6th week with me, I noticed one of the good leaves started browning from the bottom (near the stem). Not sure what else to do! I've been keeping the soil moist, checking it everyday. I have the humidifier going nearly 24/7 for a week now. Should I be patient and wait for new growth? Should I do something to jumpstart it? I watched a video on Youtube where someone put a bag over her Calathea and it rejuvenated after 3-4 weeks. Does that help? The seller of the plant suggested I put a few pieces of osmocote to encourage growth, but I'm afraid of fertilizer burn. I just really want to save her. Thank you! Some notes that might help: • 53-65% Humidity at night or when the air conditioner is running (with humidifier) • 70-95% Humidity during the day with humidifier • 2.5-3 meters from my North East facing window, it has bright indirect light • It's beside a Fishbone plant and an Adansonii • I live in a city of a tropical country -J

I've been meaning to get to this post. Just a little late weighing in as usual. First, as to "natural": I don't feel that this is a helpful term. As far as emulating nature, that of course is helpful up to a certain point. We know that orchids can be quite specific as to their light and temperature requirements. We have also learned over the centuries that in cultivation, orchid plants respond well to tweaking in certain respects. Losing sleep over using just the right fertilizer may be going a bit far, but it doesn't make sense to me to naysay the investigation of methods that make our plants bigger and better just because they don't receive these attentions in nature. I do think these pursuits are best left to more experienced growers however. Beginners absolutely should be encouraged to keep their culture straightforward lest they miss the forest for the trees. As far as organic media, obviously success varies widely with other cultural considerations besides light. The relative heat that the light source transmits for one, consistently high or low humidity, for another, the type of pot, and the efficiency and consistency of air movement all affect the efficiency of a given potting media. My own experiments have followed Howard's predictions. I was attracted to a dry, inorganic media because I tend to worry overmuch about watering. In mediums that combine absorbant with non-absorbant materials, I have experienced uneven drying under my warm HID lights. The one orchid I still have in aliflor - though it certainly could be doing worse, demands water at least every other day. And during growing season - I'm thinking of increasing to every day. The backbulbs are just a bit too shrunken for my liking. That said, the plant is strong, the root system seems excellent from all I can tell and the current pb is producing two new growths simultaneously. There is no perfect medium, but there may be the perfect medium for ME or for YOU. I'm still searching for mine. John :>)

tapla said... "Ideal pH for container gardening is about 1 whole number lower than growing in mineral soils" Again, you've simply thrown out another statement un-tethered to anything... I know, I know you intended it to be that way... but why? I've no idea. As far as water holding capacity... you choose to present it based upon weight where dried peat is going to be much lighter than an equal volume of coir and so appear to hold more water but to my thinking basing water holding capacity on volume would likely be more relevant for the gardener (in either container or in soil). This I've done myself and am quite sure coir is going to expand far more with a given volume of water. Water holding capacity is important provided air pore spaces remain equivalent... however perlite, pumice, or vermiculite is so often suggested as an addition with peat potting mixes to make one wonder why the need for these components... likely to maintain the air pore spaces due to compacting as the peat degrades and thus collapses within one growing season, its lignin content notwithstanding (btw, coir has significant lignin content as well, especially considering percentage of weight). And as every gardener knows, maintaining the air pore space is critical for healthy root development and growth of a good many plants (but not all plants however). Holding luff then is the important feature and not necessarily lignin content. Again, a simple comparison study would prove out which material best maintains adequate air pore space over time... so could you point me to one or more of these studies? I don't know the answer but would definitely like to see some studies conducted that could enlighten me on this subject. Until then, I've got to say the jury is still out... there's lots of theory out there but empirical evidence is what's called for to solve this particular inquiry. tapla said "Allelopathy - High levels of phenolic compounds known to be present in coir ... can profoundly affect root morphology, limiting length, number, and size of all orders of roots" From the foregoing statement I gather you're saying that coir has an allelopathic effect on ALL rooted plants? and thus you cannot and/or need not supply a list of affected plants... is this a correct reading of what you're meaning to infer? I'm surprised that this allelopathy of coir is not mentioned on the Internet somewhere... or at least from the simple yahoo search I've done so far. I'm so intrigued by this new piece of information that I'm going to take it from a theory and try to come up with empirical evidence of it by planting some radishes in dixie cups... a half dozen in a 50/50 with peat/soil and another half dozen in 50/50 with coir/soil... the soil will be the same (coming from my garden to supply the micros and biology) and then water the same amount each day with one teaspoon of Jack's Classic into a gallon of water. In approximately two weeks I'll wash the soil mix off the roots and compare. Do you see any complicating factors I should be aware of before beginning this little experiment? I'm excited. (BTW, the reason for radishes is merely speed of germination and the roots will not swell if I end the experiment too soon... I don't have the time or patience to carry on anything that's going to take more than 2 weeks at the most to complete... also I already have everything I need to do this in the shed right now). EDIT: In my search for allelopathic connection between phenolic compounds and plant root growth I came upon these tidbits from two separate sources... make of them what you will but they sure seem to complicate matters with previous claims of allelopathy of coir over peat... "Once the coir is freed from the fiber it goes through a maturation process to stabilize the product and this can take up to 6 months. During this process salt, tannins, and phenolic compounds are removed. It is buffered, washed and calcium nitrate is added to displace sodium and balance the pH." "Sphagnum and the peat formed from it do not decay readily because of the phenolic compounds embedded in the moss's cell walls." So does that mean peat too is allelopathic to plant roots? If so, then its a wash and I'd be wasting my time conducting the simple radish experiment? Final UPDATE: Okay I give up... After a single search I've already found several references to peat and peat bogs as being allelopathy to the germination of certain plants... I'm going to call the allelopathy claims against coir and peat a wash.