Container Soils - Water Movement and Retention forum: Container Soils - Water Movement and Retention

 
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Imagetapla
Feb 3, 2010 4:44 PM CST
Name: Al
5b-6a MI
Container Soils - Water Movement and Retention - (A Discussion About Soils)

As container gardeners, our first priority should be to insure the soils we use are adequately aerated for the life of the planting, or in the case of perennial material (trees, shrubs, garden perennials), from repot to repot. Soil aeration/drainage is the most important consideration in any container planting. Soils are the foundation that all container plantings are built on, and aeration is the very cornerstone of that foundation. Since aeration and drainage are inversely linked to soil particle size, it makes good sense to try to find and use soils or primary components with particles larger than peat. Durability and stability of soil components so they contribute to the retention of soil structure for extended periods is also extremely important. Pine and some other types of conifer bark fit the bill nicely, but I will talk more about various components later.

What I will write also hits pretty hard against the futility in using a drainage layer of coarse materials as an attempt to improve drainage. It just doesn't work. All it does is reduce the total volume of soil available for root colonization. A wick can be employed to remove water from the saturated layer of soil at the container bottom, but a drainage layer is not effective. A wick can be made to work in reverse of the self-watering pots widely being discussed on this forum now.

Since there are many questions about soils appropriate for use in containers, I'll post basic mix recipes later, in case any would like to try the soil. It will follow the Water Movement information.

Consider this if you will:
Soil fills only a few needs in container culture. Among them are: Anchorage - A place for roots to extend, securing the plant and preventing it from toppling. Nutrient Retention - It must retain enough nutrients in available form to sustain plant systems. Gas Exchange - It must be sufficiently porous to allow air to move through the root system and by-product gasses to escape. Water - It must retain water enough in liquid and/or vapor form to sustain plants between waterings. Most plants can be grown without soil as long as we can provide air, nutrients, and water, (witness hydroponics). Here, I will concentrate primarily on the movement of water in soil(s).

There are two forces that cause water to move through soil - one is gravity, the other capillary action. Gravity needs little explanation, but for this writing I would like to note: Gravitational flow potential (GFP) is greater for water at the top of the container than it is for water at the bottom. I'll return to that later. Capillarity is a function of the natural forces of adhesion and cohesion. Adhesion is water's tendency to stick to solid objects like soil particles and the sides of the pot. Cohesion is the tendency for water to stick to itself. Cohesion is why we often find water in droplet form - because cohesion is at times stronger than adhesion; in other words, water's bond to itself can be stronger than the bond to the object it might be in contact with; in this condition it forms a drop. Capillary action is in evidence when we dip a paper towel in water. The water will soak into the towel and rise several inches above the surface of the water. It will not drain back into the source, and it will stop rising when the GFP equals the capillary attraction of the fibers in the paper.

There will be a naturally occurring "perched water table" (PWT) in containers when soil particulate size is under about .125 (1/8) inch.. This is water that occupies a layer of soil that is always saturated & will not drain from the portion of the pot it occupies. It can evaporate or be used by the plant, but physical forces will not allow it to drain. It is there because the capillary pull of the soil at some point will surpass the GFP; therefore, the water does not drain, it is perched. The smaller the size of the particles in a soil, the greater the height of the PWT. This water can be tightly held in heavy (comprised of small particles) soils and perch (think of a bird on a perch) just above the container bottom where it will not drain; or, it can perch in a layer of heavy soil on top of a coarse drainage layer, where it will not drain.

Imagine that we have five cylinders of varying heights, shapes, and diameters, each with drain holes, and we fill them all with the same soil mix, then saturate the soil. The PWT will be exactly the same height in each container. This saturated area of the container is where roots initially seldom penetrate & where root problems frequently begin due to a lack of aeration. Water and nutrient uptake are also compromised by lack of air in the root zone. Keeping in mind the fact that the PWT height is dependent on soil particle size and has nothing to do with height or shape of the container, we can draw the conclusion that: Tall growing containers will always have a higher percentage of unsaturated soil than squat containers when using the same soil mix. The reason: The level of the PWT will be the same in each container, with the taller container providing more usable, air holding soil above the PWT. From this, we could make a good case that taller containers are easier to grow in.

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 soils with large particles, GFP more readily overcomes capillary attraction. They drain better. We all know this, but the reason, often unclear, is that the height of the PWT is lower in coarse soils than in fine soils. The key to good drainage is size and uniformity of soil 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 question: How much perlite do we need to add to pudding to make it drain well?

We have seen that adding a coarse drainage layer at the container bottom does not improve drainage. It does though, reduce the volume of soil 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 to colonize. Containers with uniform soil particle size from top of container to bottom will yield better and more uniform drainage and have a lower PWT than containers using the same soil with 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 make the downward transition because the capillary pull of the soil above the drainage layer is stronger than the GFP. The reason for this is there is far more surface area on soil particles for water to be attracted to in the soil 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 the pot-in-pot or the pot-in-trench method of growing to capitalize on the science.

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 soil in the container to a few inches below the bottom of the pot, or allow it to contact soil below the container where the earth acts as a giant wick and will absorb all or most of the perched water in the container, in most cases. Eliminating the PWT has much the same effect as providing your plants much more soil to grow in, as well as allowing more, much needed air in 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 starve/"suffocate" because there is insufficient air at the root zone to insure normal water/nutrient uptake and root function.

Bark fines of fir, hemlock or pine, are excellent as the primary component of your soils. The lignin 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 soils. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains.

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 garden soil. Add enough water to fill to the top, being sure all soil is saturated. Punch a drain hole in the bottom of the cup and allow the water to drain. When drainage has stopped, insert a wick into the drain hole . Take note of how much additional water drains. Even touching the soil 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. If there is interest, there are other simple and interesting experiments you can perform to confirm the existence of a PWT in container soils. I can expand later in the thread.

I always remain cognizant of these physical principles whenever I build a soil. I haven't used a commercially prepared soil in many years, preferring to build a soil 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 plays a secondary role in my container soils because it breaks down too quickly to suit me, and when it does, it impedes drainage and reduces aeration. Size matters. Partially composted conifer bark fines (pine is easiest to find and least expensive) works best in the following recipes, followed by uncomposted bark in the larger than 3/8" range.

Note that there is no sand or compost in the soils I use. Sand, as most of you think of it, can improve drainage in some cases, but it reduces aeration by filling valuable macro-pores in soils. Unless sand particle size is fairly uniform and/or larger than about ½ BB size I leave it out of soils. Compost is too unstable for me to consider using in soils. The small amount of micro-nutrients it supplies can easily be delivered by one or more of a number of chemical or organic sources.

My Basic Soils
5 parts pine bark fines
1 part sphagnum peat (not reed or sedge peat please)
1-2 parts perlite
garden lime (or gypsum in some cases)
controlled release fertilizer (if preferred)
micro-nutrient powder, other continued source of micro-nutrients, or fertilizer with all nutrients - including minors

Big batch:
2-3 cu ft pine bark fines
5 gallons peat
5 gallons perlite
2 cups dolomitic (garden) lime (or gypsum in some cases)
2 cups CRF (if preferred)
1/2 cup micro-nutrient powder (or other source of the minors)

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)
micro-nutrient powder (or other source of the minors)

I have seen advice that some highly organic (practically speaking - almost all container soils are highly organic) container soils 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 based soil) 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 vigor closer to their genetic potential. If a soil is desired that will retain structure for long periods, we need to look more to inorganic components. Some examples are crushed granite, pea stone, coarse sand (see above - usually no smaller than ½ BB size in containers, please), Haydite, lava rock (pumice), Turface or Schultz soil conditioner, and others.

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

1 part uncomposted pine or fir bark
1 part Turface
1 part crushed granite
1 Tbsp gypsum per gallon of soil
CRF (if desired)
Source of micro-nutrients or use a fertilizer that contains all essentials
I use 1/8 -1/4 tsp Epsom salts per gallon of fertilizer solution when I fertilize (check your fertilizer - if it is soluble, it is probable it does not contain Ca or Mg.

Thank you for your interest.

Al
ImageHorseshoe
Feb 3, 2010 6:31 PM CST
Name: Horseshoe Griffin
Efland, NC
And in the end...a happy beginning!
Am I glad to see you here, Al!

Thanks for posting your info/knowledge!

Shoe
Imagetapla
Feb 3, 2010 7:31 PM CST
Name: Al
5b-6a MI
Thanks, shoe. Still working on it - trying hard to find the time. Glad to see you - and thanks for saying hey!

Al
Imagevalleylynn
Feb 5, 2010 12:04 PM CST
Name: Lynn
Dallas, OR zone 8
Just found this one Al. I am doing the happy dance for sure. I have come to the right place. : )
Lynn
Imagetapla
Feb 5, 2010 4:02 PM CST
Name: Al
5b-6a MI
So glad you think so, Lynn. Smiling Can't wait for the fun/conversation/questions to start! Hurray!
Imagevalleylynn
Feb 7, 2010 6:01 PM CST
Name: Lynn
Dallas, OR zone 8
What mix would you use for semps & sedum Al. I have many of them I would like to start putting into pots.
Imagecoconut
Feb 7, 2010 6:44 PM CST
Name: Melissa E. Keyes
St. Croix, U.S. Virgin Islands
Zone 11
What about using shavings, either cedar or pine, that is sold for rodent litter?

I don't have access to pine bark.

Melissa
Melissa

Imagetapla
Feb 7, 2010 9:45 PM CST
Name: Al
5b-6a MI
Lynn - I would definitely use this for anything you think will be in the soil for more than a year:
1 part uncomposted pine or fir bark
1 part Turface
1 part crushed granite
1 Tbsp gypsum per gallon of soil
CRF (if desired)
Source of micro-nutrients or use a fertilizer that contains all essentials
I use 1/8 -1/4 tsp Epsom salts per gallon of fertilizer solution when I fertilize (check your fertilizer - if it is soluble, it is probable it does not contain Ca or Mg.

You'll find that your houseplants love it. I post a lot over on GW, and there are 100s of people over there using it, and I've been using it myself for around 20 years. I've yet to find anything that works better or is more forgiving of grower errors.

Melissa - Cedar isn't good for soils because it contains terpenoid and phenolic biocompounds known to be allelopathic (inhibit growth) to many other plants. While pine and fir BARK are excellent as the primary fraction of container media, pine shavings and hardwood shavings or bark are not good choices. The wood shavings are mostly cellulose, so they break down very quickly, this causes N immobilization (robs N from the medium) and the rapid decomposition generates a considerable amount of heat during the composting process (same reason your compost pile 'heats up'), which can also cause much more harm than you might imagine.

Probably not a lot of pine trees growing in your neighborhood, huh? Smiling Are there any operations in your area that cater to the orchid growers? If so, they would be a likely source of the bark like you see at the top of the pic below, which is perfect for the gritty mix recipe I just posted.

Al

Thumbnail by tapla

Imagecoconut
Feb 9, 2010 2:58 PM CST
Name: Melissa E. Keyes
St. Croix, U.S. Virgin Islands
Zone 11
Al, thanks, I'll shop around.

Melissa
Melissa

Imagevalleylynn
Feb 16, 2010 6:32 PM CST
Name: Lynn
Dallas, OR zone 8
Al , what is Turface? And is the above recipe for sedum & semps?
Imagetapla
Feb 16, 2010 7:52 PM CST
Name: Al
5b-6a MI
Turface is a calcined (baked at high temperature until it is ceramic-like) clay product that holds moisture and nutrients very well. The soil in the picture below holds no perched water, yet it still holds good amounts of moisture inside the Turface and bark. The result is a highly aerated soil that is extremely long-lasting and root healthy. It's very forgiving and offers a wide margin for grower error, unlike peat based soils that have inherent problems. I have been growing all my houseplants (succulents and cacti, too) and other long term plantings in this soil for years. Well over 100 people from GW are using and loving it as well. This post is well over a year old, but you can see how people feel about it: http://forums2.gardenweb.com/forums/load/contain/msg11134158... There are many more threads like it at GW.

Here's a picture of the soil:

Thumbnail by tapla

Imagevalleylynn
Feb 16, 2010 10:09 PM CST
Name: Lynn
Dallas, OR zone 8
That just looks like sedum & semps would love it. Where do I get Turface? I am going to go get the fixings and plant the new semps & sedums that are coming in April. I also have a bunch of them out in the gardens that are going to need replanting and potting. I am really excited about trying this. Also what is CRF and where do I get that?
Thank you Al.
Imagetapla
Feb 17, 2010 7:15 AM CST
Name: Al
5b-6a MI
For Turface, try this link. http://turface.com/ (See: Find a Distributor) If you don't see what you need, check out the Ewing Irrigation link because all their stores carry it. Also, the John Deere link opens another locator, and they sell Turface MVP under their name 'Allsport'. If you need more help, let me know. You can likely find the bark at entities that cater to orchid growers, - ask for 1/8-1/4" fir bark. If you get stuck on the granite part, let me know & we'll figure something out. Remember that the size of these ingredients markedly affects how the soil performs, so if you're serious about building the gritty mix - stay in touch for help. ;o)

Good luck!!! I promise that once you try it, you'll love it. Oh - btw, I suggest that you invest in a jug of Foliage-Pro 9-3-6 fertilizer by Dyna-Gro. Alternately, any of the granular soluble fertilizers (like MG, Peter's, Schultz, ....) 24-8-16 fertilizers, or MG liquid 12-4-8 (yellow jug) are ideal for almost all the plants you're likely to grow (note that these are all 3:1:2 ratios). You can find more technical detail in the 'Fertilizer Program' thread on this cubit if you're interested.

Take care.
Al
Imagevalleylynn
Feb 17, 2010 5:16 PM CST
Name: Lynn
Dallas, OR zone 8
Thanks Al. I'll start trying to track down the ingredients.
ImageSeray
Feb 17, 2010 5:46 PM CST
Name: Sherri
Coastal GA
Hi Al

Thanks for the great information. I'm also looking for a semp and sedum mix and that looks perfect. Would you use this in a mini bed as well as a container? I'm planning to use my semps as ground cover and wondered about the depth of the bed and if these ingredients would be appropriate. Is CRF slow release fertilizer?

Thanks

Sherri
Imagevalleylynn
Feb 17, 2010 6:04 PM CST
Name: Lynn
Dallas, OR zone 8
Al, I am so excited. I found a place in Salem (John Deere Landscape) that sells the Turface and the business next door to them has the fir bark. Will be making a trip to Salem tomorrow. Does chicken grit work in place of the crushed granite? And where would I find gypsum? I'm on a roll.
Imagetapla
Feb 17, 2010 7:44 PM CST
Name: Al
5b-6a MI
Lynn - Good job! Smiling Some chicken grit is crushed granite or cherrystone. Either will work, but steer clear of crushed shellfish (oysters/clams ......)

Seray - Because of the physics involved with growing in the ground vs in containers, you won't need the uniform, large particle size that is so important in containers if you are growing in a raised bed. If you are growing semps/sedum in the ground, other than in a raised bed, the bed will need to be well-drained. It's probably a good idea to share a little more info if you want to explore further.

Al

Thumbnail by tapla

ImageSeray
Feb 17, 2010 8:04 PM CST
Name: Sherri
Coastal GA
Thanks Al

Once I get into it I'll ask for detail help. The area I'm planning to put them in drains well. GA sand and clay. I was planning to raise it up a little more with some compost and then add the soil mix on top. Almost like a lasagna bed with the compost on top of the what's there and the soil mix on top of that. The compost would be fairly loose, leaf mold, coir, some perlite, probably some sand. They aren't large areas but they are entryway and I want them to be very happy. Smiling

ImageGreenfield
Feb 18, 2010 10:11 PM CST
Name: Diana
Willamette Valley
Oregon Zone 8a
Just found this cubit today, Al, you are a fountain of knowledge!

I have long been disappointed in the packaged potting soil mixes sold at the big box stores. They are generally composted municipal yard waste, as far as I can tell by the slivers of wood I have found in them. They are too dense, and you are absolutely right about most potted plants expiring from lack of drainage & rotted roots.

Your data above all makes sense and all these years I thought sand was the only thing to add to the potting soil mix to provide extra drainage. We do have easy access to Fir bark in our area and I had never heard of Turface until today, but I am going to give it a try. I'm not sure of a source for crushed granite, but we do have the medium grit cherry stone at our local feed store.

Do you feel that the granite has some micronutrients that are in a small enough form that the plants could take it up, if a person could find crushed granite? I don't have any experience with that, but I do know of people who have used powdered rock dust to feed micronutients to plants.

There was at one time a plant to the south of us that produced Glacial rock powder, I believe it was sold under the name of McKenzie rock dust. I lived and gardened in N. Calif. for many, many years and I knew of organic farmers down there that swore by that stuff. They had it brought in by the truck loads and broadcast it all over their fields. This powder was so fine that it appeared to dissolve in water. I'm thinking maybe rock material any coarser than powder that the nutrients may be locked up in the rock and that the plants could not utilize them, but I could be wrong. I'd be interested in your opinion on that subject.

Also what organic fertilizers would you recommend? I have mainly used liquid fish emulsion and seaweed, but I know there are powdered products such as greensand, rock phosphate, etc. as well. Do you like any of those products?
Imagevalleylynn
Feb 25, 2010 7:57 PM CST
Name: Lynn
Dallas, OR zone 8
Hi Al. Well I finally mixed up my first batch of potting mix. Here is a picture. The fir bark is the smalles I could find, hope it's not to big. Mix is equal parts of the three components. It isn't moistened yet so will probably stay mixed better once it is wet.

Thumbnail by valleylynn

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