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A given volume of large soil particles has less overall surface area when compared to the same volume of small particles and therefore less overall adhesive attraction to water. So, in media with large particles, GFP (remember the weight of the water column pushing down on water lower in the pot is the Gravitational Flow Potential) more readily overcomes capillary attraction. They simply drain better and hold more air. We all know this, but the reason, often unclear, is that the height of the PWT is lower in coarse media than media comprised of primarily fine particles. The key to good drainage is size and uniformity of particles. Mixing large particles with small is often very ineffective because the smaller particles fit between the large, increasing surface area which increases the capillary attraction and thus the water holding potential. An illustrative/ rhetorical question: How much perlite should we add to pudding to make it drain well?

I already stated I hold as true, the grower's medium choice when establishing a planting for the long term is the most important decision he/she will make. There is no question roots are the heart of the plant, and plant vitality is inextricably linked in a hard lock-up with root vitality. In order to get the best from our plants, we absolutely must maintain roots in a healthy state.

If we start with a water-retentive medium, we cannot effectively amend it to improve aeration or drainage characteristics by adding larger particulates. Sand, perlite, Turface, calcined DE ...... none of them will work effectively. To visualize why sand and perlite can't change drainage/aeration, think of how well a pot full of BBs or would drain; then think of how poorly a pot full of pudding would drain. Even mixing the pudding with perlite and BBs at a 1:1:1 ratio in a third pot yields a mix that retains the drainage/aeration characteristics and PWT height of the pudding. It's only after the BBs/ perlite becomes by far the largest fraction of the mix (80-95%) that aeration begins to improve. At that point, we are growing in BBs/ perlite amended with a little pudding .

We cannot add coarse material to fine material and improve drainage or the ht of the PWT. Use the same example as above and replace the example of pudding with play sand, peat moss, or a peat-based potting medium - same results. The benefit in adding perlite to heavy (water-retentive) soils doesn't come from the fact they drain better. The fine peat or pudding particles simply 'fill in' around the perlite, so drainage and the height of the PWT remains roughly the same. All perlite does in heavy soils is occupy space that would otherwise be full of water. Perlite simply reduces the amount of water a medium is capable of holding because perlite is not internally porous. IOW - all it does is take up space. That can be a considerable benefit, but it makes more sense to approach the problem from an angle that also allows us to increase the aeration AND durability of the medium. Adding ping pong balls which are full of air adds how much aeration to a bucket of soil? It would actually reduce aeration. That is where Pine bark comes in, and I will get to that soon.

If we wish to profit from a medium offering superior drainage and aeration, we need to start with an ingredient or ingredients as the basis for your medium that already HAVE those properties by ensuring that the medium is primarily comprised of particles much larger than those in peat/ compost/ coir/ sand/ topsoil ….., which is why the recipes I suggest as starting points all direct readers to START with the foremost fraction of the medium being coarse particles. From there, if you choose, you can add an appropriate volume of finer particles to increase/ adjust water retention. We do not have that option with a medium already extremely water-retentive right out of the bag.

I fully understand that many might be happy with the results they get from using a commercially prepared soil, and I'm not trying to twist any arms to convince anyone to change anything. My intent is to make sure that those who are having trouble with issues related to their choice of soil, understand why the issues occur, there are options, and what they are.

We have seen that adding a coarse drainage layer at the container bottom does not improve drainage. It does though, reduce the volume of required to fill a container, making the container lighter. When we employ a drainage layer in an attempt to improve drainage, what we are actually doing is moving the level of the PWT higher in the pot. This simply reduces the volume of soil available for roots colonization. Containers with uniform particle size from top of container to bottom will yield better/ more uniform drainage and have a lower PWT than containers using the same medium with added drainage layers. The coarser the drainage layer, the more detrimental to drainage it is because water is more (for lack of a better scientific word) 'reluctant' to move downward because the capillary pull of the medium above the drainage layer is stronger than the GFP. As mentioned, the reason for this is, there is far more surface area on particles for water to be attracted to in the medium located above the drainage layer than there is in the drainage layer, so the water 'perches'. I know this goes against what most have thought to be true, but the principle is scientifically sound, and experiments have shown it as so. Many nurserymen employ what are termed the 'pot-in-pot' or the 'pot-in-trench' method of growing to capitalize on simple science to be rid of the limitations associated with PW.

If you discover you need to increase drainage, you can simply insert an absorbent wick into a drainage hole & allow it to extend from the saturated medium in the container to a few inches below the bottom of the pot, or allow the wick to contact soil below the container so the earth acts as a giant wick, pulling all or most of the perched water from the medium in the container (see images in the OP). Eliminating the PWT has much the same effect as providing your plants much more medium to grow in, as well as allowing more, much needed air into the root zone.

In simple terms: Plants that expire because of drainage problems either die of thirst because the roots have rotted and can no longer take up water, or they suffer/ die because there is a volume of air in the root zone insufficient to insure normal root function, so water/nutrient uptake and root metabolism become seriously impaired.

To confirm the existence of the PWT and how effective a wick is at removing it, try this experiment: Fill a soft drink cup nearly full of a water-retentive medium. Add enough water to fill to the top, being sure all the medium is saturated. Punch or melt a drain hole in the bottom of the cup and allow the water to drain. When drainage has stopped, insert a wick, or even a toothpick into the drain hole. Take note of how much additional water drains from the cup. Even touching the medium with a toothpick through the drain hole will cause substantial additional water to drain. The water that drains is water that occupied the PWT. A greatly simplified explanation of what occurs is: The wick or toothpick 'fools' the water into 'thinking' the pot is deeper than it is, so water begins to move downward seeking the 'new' bottom of the pot, pulling the rest of the water in the PWT along with it (because water sticks to itself). If there is interest, there are other simple and interesting experiments you can perform to confirm the existence of a PWT in containers, and I can expand later in the thread.

I always remain cognizant of these physical principles whenever I build a medium. I have not used a commercially prepared medium in many years, preferring to build or amend one of my 2 basic mixes to suit individual plantings. I keep many ingredients at the ready for building soils, but the basic building process usually starts with conifer bark and perlite. Sphagnum peat moss plays a secondary role in my container media because it breaks down and compacts too quickly to suit me, and when it does, it impedes drainage and reduces aeration.

Size matters. Partially composted conifer bark (pine is easiest to find and least expensive) works best in the following recipes, followed by uncomposted bark in the smaller than 3/8" range. Bark fines of pine, fir or hemlock, are excellent as the primary component of your media. The lignin (it's what makes woody plants woody) contained in bark keeps it rigid and the rigidity provides air-holding pockets in the root zone far longer than peat or compost mixes that too quickly break down to a soup-like consistency. Conifer bark also contains suberin, a lipid sometimes referred to as nature's preservative. Suberin, more scarce as a presence in sapwood products and hardwood bark, dramatically slows the decomposition of conifer bark-based media. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains - it retains its structure.

Note there is no sand or compost in the media I use. Sand, as most growers think of it, can improve drainage in some cases, but it reduces aeration by filling valuable macro-pores in a medium. Unless sand particle size is fairly uniform and/or larger than about BB size, I leave it out of anything I grow in.
Compost is too fine and unstable for me to consider using in any significant volume as well. The small amount of micro-nutrients it supplies can easily be delivered by one or more of a number of chemical or organic sources that do not detract from drainage/ aeration.

The basic blends I use:

The 5:1:1 mix:

See dry 5:1:1 mix in the center below. The bark products at 3, 6, and 9 o'clock are ideal for the 5:1:1 mix. The bark at top/ below is prescreened fir bark in 1/8 - 1/4", and what I use for the gritty mix.

5 parts pine bark fines, dust - 3/8 (size is important)

1 part sphagnum peat (not reed or sedge peat, please)

1-2 parts perlite (coarse or all-purpose, if you can get it – not super-coarse)

garden lime

controlled release fertilizer (if preferred)

Big batch:

2-3 cu ft pine bark fines

5 gallons peat

5 gallons perlite

2 cups dolomitic (garden) lime

2 cups CRF (if preferred)

Small batch:

3 gallons pine bark

1/2 gallon peat

1/2 gallon perlite

4 tbsp lime (or gypsum in some cases)

1/4 cup CRF (if preferred)

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~ page 3 ~

I have seen advice that some highly organic (practically speaking - almost all container media are highly organic) container media are productive for up to 5 years or more. I disagree and will explain why if there is interest. Even if you were to substitute fir bark for pine bark in this recipe (and this recipe will long outlast any peat/ coir/ compost based medium) you should only expect a maximum of two to three years life before a repot is in order. Usually perennials, including trees (they're perennials too) should be repotted more frequently to insure they can grow at as close to their genetic potential (within the limits of other cultural factors) as possible. If a medium which will retain its structure for long periods is desired, we need to look more to inorganic components. Some examples are crushed granite, fine stone, VERY coarse sand (see above - usually no smaller than BB size in containers, please), Haydite, lava rock (pumice), Turface, calcined DE, and others.

For long term (especially woody) plantings and houseplants, I use a superb medium which is extremely durable and structurally sound. The basic mix is equal parts of screened pine bark, Turface, and crushed granite.

The gritty mix:

1 part uncomposted/ screened pine or fir bark (1/8-1/4")

1 part screened Turface

1 part crushed Gran-I-Grit (grower size) or #2 cherrystone (screen dust out)

1 Tbsp gypsum per gallon of medium (eliminate if your fertilizer contains Ca)

CRF (if desired)

I use 1/8 -1/4 tsp Epsom salts (MgSO4) per gallon of fertilizer solution when I fertilize if the fertilizer does not contain Mg (check your fertilizer - if it is soluble, it probably does not contain Ca or Mg. If you choose to use my currently favored fertilizer (I use it on everything), Dyna-Gro's Foliage-Pro in the 9-3-6 formulation - no need to use gypsum or Epsom salts in the fertilizer solution.

The ingredient screens I use when needed:

If there is interest, you can search for 20-some other threads on the same topic that reached the maxim number of posts allowed.

If you feel you were benefited by having read this offering, you might also find this thread about Fertilizing Containerized Plants helpful.

If you do find yourself using media you feel are too water-retentive, you'll find some Help Dealing with Water Retentive Soils by following this embedded link.

If you happen to be at all curious about How Plant Growth is Limited, please follow the link.

Finally, if you are primarily into houseplants, you can find an OVERVIEW of the BASICS, which should provide help in avoiding the most common pitfalls encountered by houseplant/ container growers.

As always - best luck. Good growing!! Let me know if you think there is anything you think I might be able to help you with.

If you have found value in my effort and feel like saying 'thanks', please consider clicking on my user name that appears at the top of all my posts (tapla Original Author), then click the "Follow" button. I would appreciate it. The reason I ask relates to the idea that an increase in the number of people following someone helps to solidify their 'credibility'. It follows that as their perceived credibility increases, the more likely it is they will be able to help others help themselves. I'm not looking for fame or fortune; rather, I try to help because I've found I can quickly summarize the most important things I've learned over the last 30 years, saving folks a LOT of time/effort. Feeling like I've made a positive contribution to someone's growing experience or growth as a gardener is a reward in itself, and over time has become a natural extension of my own growing experience.

Al

Yes I did read all three! 👀 Although this post is about container water principles it gives me hope that when/if I decide to plant potted tree to ground, our heavily river-rock filled ground soil won't guarantee a death for the tree!

Do you have a thread on "transplant shock" you can share? Is the shock more.due to poorly arranged new environment, or to the frail soul of the plant roots?

Al, FYI, the link to your user page leads to a Page Not Found notice, but clicking on your user name at the top of the post works fine.

Do you have a thread on "transplant shock" you can share? Is the shock more.due to poorly arranged new environment, or to the frail soul of the plant roots? At some point, we all harbored a dread of disturbing or damaging the roots of or plants for fear it would do calamitous damage with a visit from the grim reaper immediately subsequent. The truth is, roots are very forgiving of most of the indignity we might choose to heap on them, so long as we are actually ready to perform the root work and use good judgment. A key element of repotting all common houseplants save succulents/ cacti is keeping the roots wet for the entire duration of the repotting session. I'm pretty sure I've provided you links that will go into more detail about how to proceed with the work and what results should look like. Again, you don't need to be as aggressive as I am about repotting. The appearance of the root systems of trees destined to become bonsai specimens is critically important to the appearance of the composition. Flat roots that radiate evenly and outward from the trunk are highly desirable for bonsai. A hobby grower can remain unconcerned about the appearance of the surface roots and trunk flair, so you needn't spend time/ effort at developing flat root systems. Notice how evenly the roots are spaced and how they radiate outward on this maple:

This tree has been layered off of it's original roots. See the thick wire in both images. That is a tourniquet, the job of which is to provide a 'dam' which blocks the downward flow of nutrients and a growth regulator (auxin) to the old root system.

Here is another tree (Korean hornbeam) on which I'm setting up a layer because it's roots are so unattractive:

As occurred with the maple above, the new root system will grow from the circular holes above the plastic zip ties. When the new roots have grown to a suitable stage of maturity, I will cut through the trunk just below the ring of holes, which will be treated with an insoluble rooting aid. Actually, this is an old image and the work of re building the root system has already been successfully completed.

So, the only time roots can be considered "frail" is when the plant is struggling due to cultural stress or injury or disease pathogens. Root regeneration requires a good deal of energy. If the plant's energy reserves are near nil and conditions are such that the plant is unable to make enough food/ energy to rebuild the root system, it wouldn't bode well for the plant. Ideally, we should complete the regular repotting required to keep plants at the peak of vitality before they decline so far they need to be snatched back from the edge of oblivion.

I'm not sure there IS such a thing as transplant shock. If there is, it is related to the damage roots sustain during transplanting. If you buy a plant which has been growing under 50% shade cloth and transplant it into the landscape in a full sun site, only to have it burn, you can't consider that or similar errors to be TS.

If the grower transplants correctly by bare-rooting, correcting problem roots, and back-filling the hole with native soil, there will be a considerable amount of damage to roots, which is why it's best to transplant while trees are in a predictive dormant state if possible. When root damage occurs, growth predictably stalls until the root damage is repaired and the plant's chemical messengers tell plant central the root system has recovered and is now ready to provide for a larger foliage mass.

Al

Thanks LB. I changed it.

Al

Shall someone refresh my memory. How much N tieup occurs as the bark breaks down

Bark, and especially conifer bark, breaks down very slowly by virtue of its inclusion of significant amounts of both suberin, a naturally occurring polyester biopolymer, and lignin, another biopolymer. Both compounds are hydrophobic (repel water), which plays a major part in why hydrocarbon chains of both materials are so resistant to cleavage by fungi and herbivorous organisms of all sizes, a characteristic which significantly limits N immobilization in media based in large part on conifer bark.

While N immobilization does occur, especially when using fresh (uncomposted bark), I have never found it to be a problem unless I drop the ball and allow intervals between fertilizer applications to become a limiting factor. IOW, if you keep up with your plants' N needs by fertilizing at appropriate intervals, it becomes pretty much a nonissue; whereas, you can expect it to be a problem if you don't fertilize at appropriate intervals.

As a basis for comparison, setting aside issues related to water retention, I would be much more concerned about N immobilization if I were using unfinished compost as the primary fraction of a container medium rather than conifer bark because cellulose remaining in the compost is comparatively easy for soil life to break down.

Al

I think the expense of Al's gritty mix is a matter of scale.

My first trial batch was small and the Turface and pine bark were easily ordered from Etsy and shipped to me. I did find cherry stone grit on Amazon and it was $35 delivered.

When I saw how little that made relative to the containers I wanted to fill, I started looking for better deals. As far as pine bark, I ordered a larger amount from BonsaiJack and that seemed to address the expense of that component. I went to the Turface website for the second batch and found a local (Chicago area) dealer where I can buy 50lb bags for $25. Turface has great bulk for little weight, so should stay a moderate cost. The main issue is that sifting the Turface yields only about 1/3 usable material if I want to filter out both the fines and the smaller pieces (see post above). I now found a purpose for the fines/smaller pieces in my rain garden. I then ordered a second cherry stone grit but it is obviously a cost issue because the 50lb weight causes high shipping costs, while its density provides little in the way of bulk.

For this latest batch and going forward, I feel like I hit the jackpot by finding cherry stone grit for $8 per 50lb bag from a farm supply store. It is about an hour one-way drive though, so I am stocking up.

I thought this might be useful for those discussing the higher cost of gritty mix materials. The more your needs, the more you save by searching out the materials in bulk. I am still on the lookout for quantity of screened pine bark though.

Hi guys,

I've been in a long journey to find something as complete with the 3:1:2 ratio like Foliage Pro here in Brazil. Finally, I've found a decent alternative, but I'm not sure about the amount of Sulfur it delivers (maybe it's too much?).

Can you help me to judge? The secondary nutrients' proportion are:

• Ca 1%
• Mg 0,5%
• S 2,4%

For comparison, Foliage Pro has:

• Ca 2%
• Mg 0,5%
• S 0,05%

That's a huge difference.

What about the NPK %s?

Al

In this one NPK %s sound quite good: N 10%, P 3%, K 5%.

It also has all the micronutrients.

I'm also considering another option that's not quite as optimal and doesn't have sulfur, but could be associated with gypsum.

N 8%, P 3%, K 8%, Ca 1%, Mg 1% + micronutrients

The Ca:Mg ratio should be somewhere between 2:1 and 5:1 respectively, but you can increase the Ca level (if ever necessary) and/or S content with gypsum (CaSO4). If any of the nutrients are sourced from a sulfate compound, you won't have S issues unless you get lax when it comes to fertilizing intervals.

On your fertilizer label, is P listed as a weight % of P2O5 (phosphorous pentoxide)?

Al

Nice, so the first fertilizer I mentioned looks quite fit. It has 2:1 Ca:Mg, an almost perfect NPK %, and contain some sulfate.

Ah, and yes, they list P as a % of P2O5. Is it ok?

Looks like your efforts paid off. Strong work!

Al

Thanks Al, for your ever original in-depth post and your kindness :)

I've come to look at spending time here at GW/ Houzz as a natural extension of my own growing experience, and find that helping others get more from their growing experience is almost as rewarding my own growing adventures. Take good care!

Al

You never understand more about what you yourself know as when you have to reduce it to be understandable to those who don't know what you know.

"If you can't explain it simply, you don't understand it well enough." ~ A Einstein