Container Soils and Water Movement in Containers (long post)

The following is very long & will be too boring for some to wade through. Two years ago, some of my posts on another forum site got people curious & they started to e-mail me about soil problems. The "Water Movement" article is an answer I gave in an e-mail. I saved it and adapted it for my bonsai club newsletter & it was subsequently picked up & used by a number of other clubs. I now give talks on container soils and the physics of water movement in containers to area clubs.

I think, as container gardeners, our first priority is to insure our soils are adequetely aerated for the life of the planting, or at least, 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. Soil is the foundation all container plantings are built on, and aeration is the most important block in the foundation. Since aeration and drainage are inversely linked to soil particle size, it makes good sense to try to find soil components with particles larger than peat and that will retain their structure for extended periods. Pine bark fits the bill nicely.

The following hits pretty hard against the futility of using a drainage layer in an attempt to improve drainage. It just doesn't work. All it does is reduce the amount soil available for root colonization. A wick will remove the saturated layer of soil. It works in reverse of the self-watering pots widely being discussed on this forum now. I have no hands-on experience with these growing containers, but understand the principle well. There are potential problems with wick watering that can be alleviated with certain steps. Watch for yellowing leaves with these pots. If they begin to occur, you need to flush the soil well. It is the first sign of chloride damage.

Since there are many questions about soils appropriate for containers, I'll post by basic mix in case any would like to try it. It will follow the Water Movement info.

Water Movement in Soils

Consider this if you will:

Soil need fill only a few needs in plant culture. Anchorage - A place for roots to extend, securing the plant and preventing it from toppling. Nutrient Sink - It must retain sufficient nutrients to sustain plant systems. Gas Exchange - It must be sufficiently porous to allow air to the root system. And finally, Water - It must retain water enough in liquid and/or vapor form to sustain plants between waterings. Most plants could 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 movement 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 pot than it is for water at the bottom of the pot. 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, 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. It will stop rising when the GFP equals the capillary attraction of the fibers in the paper.

There is, in every pot, what is called a "perched water table" (PWT). This is water that occupies a layer of soil that is always saturated & will not drain at the bottom of the pot. 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 equal the GFP; therefore, the water does not drain, it is "perched". If we fill five cylinders of varying heights and diameters with the same soil mix and provide each cylinder with a drainage hole, the PWT will be exactly the same height in each container. This is the area of the pot where roots seldom penetrate & where root problems begin due to a lack of aeration. From this we can draw the conclusion that: Tall growing containers are a superior choice over 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. Physiology dictates that plants must be able to take in air at the roots in order to complete transpiration and photosynthesis.

A given volume of large soil particles have less overall surface area in comparison 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 PWT is lower in coarse soils than in fine soils. The key to good drainage is size and uniformity of soil particles. Large particles mixed with small particles will not improve drainage because the smaller particles fit between the large, increasing surface area which increases the capillary attraction and thus the water holding potential. Water and air cannot occupy the same space at the same time. Contrary to what some hold to be true, sand does not improve drainage. Pumice (aka lava rock), or one of the hi-fired clay products like Turface are good additives which help promote drainage and porosity because of their irregular shape.

Now to the main point: When we use a coarse drainage layer under our soil, it does not improve drainage. It does conserve on the volume of soil required to fill a pot and it makes the pot lighter. When we employ this exercise in an attempt to improve drainage, what we are actually doing is moving the level of the PWT higher in the pot. This reduces available soil for roots to colonize, reduces total usable pot space, and limits potential for beneficial gas exchange. Containers with uniform soil particle size from top of container to bottom will yield better drainage and have a lower PWT than containers 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 in the soil for water to be attracted to than there is in the drainage layer.

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 are now employing 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, insert a wick into the pot & allow it to extend from the PWT to several inches below the bottom of the pot. This will successfully eliminate the PWT & give your plants much more soil to grow in as well as allow more, much needed air to the roots.

Uniform size particles of fir, hemlock or pine bark 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 rapidly break down to a soup-like consistency. Bark also contains suberin, a lipid sometimes referred to as nature’s preservative. Suberin is what slows the decomposition of bark-based soils. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains.

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 to death because they cannot obtain sufficient air at the root zone for the respiratory or photosynthetic processes.

To confirm the existence of the PWT and the effectiveness of using a wick to remove 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 & allow to drain. When the drainage stops, insert a wick several inches up into the drain hole . Take note of how much additional water drains. This is water that occupied the PWT before being drained by the wick. A greatly simplified explanation of what occurs is: The wick "fools" the water into thinking the pot is deeper, so water begins to move downward seeking the "new" bottom of the pot, pulling the rest of the PWT along with it.

Having applied these principles in the culture of my containerized plants, both indoors and out, for many years, the methodology I have adopted has shown to be effective and of great benefit to them. I use many amendments when building my soils, but the basic building process starts with screened bark and perlite. Peat usually plays a very minor role in my container soils because it breaks down rapidly and when it does, it impedes drainage.

My Soil

I'll give two recipes. I usually make big batches.

3 parts pine bark fines
1 part sphagnum peat (not reed or sedge peat)
1-2 parts perlite
garden lime
controlled release fertilizer
micro-nutrient powder (substitute: small amount of good, composted manure

Big batch:

3 cu ft pine bark fines (1 big bag)
5 gallons peat
5 gallons perlite
1 cup lime (you can add more to small portion if needed)
2 cups CRF
1/2 cup micro-nutrient powder or 1 gal composted manure

Small batch:

3 gallons pine bark
1/2 gallon peat
1/2 gallon perlite
handful lime (careful)
1/4 cup CRF
1 tsp micro-nutrient powder or a dash of manure ;o)

I have seen advice that some highly organic soils are productive for up to 5 years. I disagree. Even if you were to substitute fir bark for pine bark in this recipe (and this recipe will far outlast any peat based soil) you should only expect a maximum of three years life before a repot is in order. Usually perennials, including trees (they're perennials too, you know ;o)) should be repotted more frequently to insure vigor closer to genetic potential. If a soil is desired that will retain structure for long periods, we need to look to inorganic components. Some examples are crushed granite, pea stone, coarse sand (no smaller than BB size in containers, please), Haydite, lava rock, Turface or Schultz soil conditioner.

I hope this starts a good exchange of ideas & opinions so we all can learn.

Al

Al,

What do you use for wicking materials?

A product called magic cloth or magic mop works very well. It is a super-absorbent man-made chamois (100% rayon). Cut in strips, it absorbs & moves water quickly. I've also had good luck with the woven plastic ties that are used to keep citrus bags (oranges, grapefruit) closed until we buy them. Both are effective.

Wicking away the PWT is helpful in many cases, but not a cure-all for soil that drains poorly. It is especially helpful when plantings are young & roots have not colonized the lower portions of the container. Later, when the plants have developed to the point that they need more frequent watering, simply remove the wick & more water is available to the plant after each watering.

Al

Al, fascinating discussion about water movement in containers. Thanks so much for taking the time to post it here for us.

Pen

If the pot insists on staying soggy and the time for transplantingmoving the plant is wrong, would it help to add some Hydrogen Peroxide to the water to add some oxygen to the soil?

Yes, if you're familiar enough with its use & recommended concentration(s). Though it is also helpful in a healthy root environment, it is most valuable when there are root issues like poor aeration or one of the rot fungi beginning to increase in #'s.

H2O2 has an extra O atom (compared to H2O) in an unstable arrangement. It's the extra atom that makes it useful in horticultural applications. Generally, we're not concerned with aerobic forms of bacteria normally occurring in container media or on roots, but various fungi & poorly aerated soils are often a problem.

Since H2O2 is an unstable molecule, it breaks down easily. When it does, a single O- atom and a molecule of water is released. This O- atom is extremely reactive and will quickly attach itself to either another O- atom forming stable O2, or attack the nearest organic molecule.

Many disease causing organisms and spores are killed by O, the free O- H2O2 releases is extremely effective at this. H2O2 can help eliminate existing infections and help prevent future ones. The free O atom can destroy dead organic material (i.e, leaves roots) that are rotting and spreading diseases.

Reduced O levels and high temperatures encourage both anaerobic bacteria and fungi. When plants growing in soil are treated with H2O2 it will break down and release O into the area around the roots. This helps stop the O from being depleted in the water filled macro-pores until air can get back into them. High O levels at the roots will encourage rapid healthy root growth and discourage unwanted bacteria/fungi.

I know it comes in several different strengths. I'm thinking 3%, 5%, 8% and 35% solutions. Cheapest is 35% which you dilute (to 3%) by mixing 1:11 with water. Plastic or glass is best to store it in, & the container should be opaque to prevent light degradation. If three-liter pop bottles are available in your area they are ideal for mixing and storing H2O2. Once you have it mixed at 3% (or start with 3%) mix it at the rate of 1-1/2 tsp/gallon of water as a cutting dip & up to 2-1/2 tsp/gallon to water containers with on a regular basis. Start at the lower concentration and increase concentrations gradually over a few weeks.

H2O2 in high concentration is a powerful oxidant & will bleach skin white & oxidize almost anything it contacts - quickly. This includes living plant tissues, so be careful with it if you use it. A solution that's too strong can kill any organic molecule it contacts.

Al

Al, can you tell me how to insert a wick into an already potted plant. I'm going to use some strips of terry cloth, so it will be like inserting a noodle. --Thanks

Bacteria colonizing the pot bottom will quickly munch through the cotton fibers, causing it to rot to pieces in no time. Better to use a synthetic shoelace or a tie from an orange bag. I bet a strip of pantyhose would work, too.

Fold in half over the end of the blade of a straight-slot screwdriver or similar. Push up into drain hole several inches. It will remove most or all of perched water, but remember - it's not a cure for lack or aeration. ;o)

Al

Al, thanks. I had read on another site that terry cloth or any type of cotton was a good wicking material. But I believe you. I don't buy oranges by the bag, so I'll try shoelaces.

Explain to me why removing the excess water would not solve the aeration problem. I'm going to start adding H2O2 (thanks for the formula) to the container water, but I have far too many containers to think about repotting all of them.

Another question: I have some herbs growing very happily in a round, shallow planter. I'm sure the roots are all in the PWT, but this is the second year those herbs have been growing in it, and they are really doing well. I have curly parsley, flat parsley, chives, rosemary and basil, all doing great. You think maybe the pot is so shallow that evaporation is preventing saturation? These plants tend to droop if I don't water daily, so I know it's drying out quickly.

And another question: I have an R/O system in the house. Would it be worth the trouble to collect filtered water from the indoor tap to water all the outside containers?

Thanks for all your help. I read all your posts with great interest.
......Pen

Thanks, Al. All of my plants are in containers, and trying to keep this one barely damp, this one dry, and that one moist is very difficult as I can't handle a hose so my DH has been doing the watering. I am wondering if it might solve at least part of my problem if I water them a couple of times a week with the water containing H202, giving the roots shots of oxygen.

You started this thread by saying your comments could be boring. NOT! I found it fascinating, and I really think that my plants will be healthier, thanks to you.

Dotti

Excess water: If soil is retaining too much water, it's a sure bet that macro-pores are virtually non-existent (compaction). Removing the water in the PWT will not resolve the compaction issue to any great degree. It really depends on how good (or bad) your soil is.

Please don't think I'm suggesting you repot anything, or even change what you're comfortable with. I only offered the information so those that don't have much knowledge of soils or water movement could start putting things together & perhaps incorporate some of the things they learn, not just from me, but from discussions following the post as well. ;o)

Herbs: Yes, I think you nailed it. In building my soils, I try to consider things like container size, how many plants, sun/shade, etc. and make the soil so it will need watering once per day in the hottest part of summer. As long as you provide nutrients & don't allow the plant to dry completely, a soil that requires watering daily will outperform soils that can go two days, three days, or even longer between waterings. Technically, evaporation isn't preventing saturation, it still occurs, but roots that are in saturated soil, but dry inside of a day (on a regular basis) will show little in the way of ill effects from the temporary lack of aeration. Extend the time to a day & 1/2 in the hottest part of summer, & one of the root rots are likely to take hold. Funny part of that is, the plants will wilt & you'll be tempted to over-water, which only compounds the problem.

Water: Tough question w/o knowing particulars. Do you have municipal water? know the pH of it? Alkalinity level (it's different from pH in case you wondered)? Find out? What kind of soil are you growing in? My first inclination is to say yes, it's worth it, especially if you're as particular about your containers as I. If you find the pH of your water is higher than 8.5 at any time, it would be worth it. Our water here is surface water from Lake Huron, which is usually lower in pH than ground water. After obtaining an analysis from our municipal supplier, I discovered that our water ranges from a pH of around 8.1 all the way to 10. I remember how I struggled 10 years ago before I acquired a reasonable working knowledge of soil chemistry. I think I would have problems with the pH of my water if I hadn't paid attention to business & learned ways to work around nutrient problems. If I had the opportunity - I'd try it for a couple of months on at least a portion of my containers. It could make a huge difference, or non - no way to tell w/o looking into it more or experimenting. ;o)

Good growing.

Al

After seeing Al's post on another website, I tried the wick in some big tomato pots that gave me all kinds of trouble last year, with the watering and the soil in the bottom turning sour.

I have 5 pots, and tried to test the theory that if one wick is good, then TWO must be better. in fact, don't see any difference between the pots based on the number of wicks....

thanks, Al.

Michael

Hi, Mike! Good to see you! Decided to take you up on your invitation & come over to Dave's to hang out. Still learning how this site works, but am enjoying it very much. Thank you for your consideration. ;o)

You're accurate in your thinking that multiple wicks are no better than one. Also, when considering only drainage & discounting any evaporative benifit that multiple drain holes offer, there is no advantage in having multiple drain holes in pot bottoms as long as the container bottom is level.

This gives me an opportunity to offer a tip on how to improve drainage during periods of prolonged rain (if your soil drains slowly). Under these conditions, drain holes at the container bottom and close to the outer edge are helpful and will allow you to tilt your container to improve drainage (technically, it's not improving drainage, only taking advantage of physics to drain unwanted water from container soil). When a container is tilted, the perched water table remains at the same depth. If we take an example of the PWT at 4 inches in a container, if we tilt the container at a 45* angle, the PWT shifts so that it is horizontal and 4 inches from the lowest point of the container. If you picture this in your mind, you will see there is much less saturated soil at the container bottom. I employ this method frequently on recently planted material with no roots in the container bottom to take up excess water. I also use it on bonsai material that doesn't appreciate wet feet (pinus, juniperus, etc). To prove its effectiveness, water a container thoroughly & wait for water to stop draining from drain hole. If you tilt the container (even with the hole at the center) substantial additional water will drain from your container(s). In imagining this picture, you can now see why some holes near the edges on problem containers can be helpful. With holes in the center only, there is a "dead" area between the drain hole and container edge/bottom that cannot drain when containers are tilted.

Take care.

Al

Al, I use municipal water and it is very hard. I would guess the pH is very high, but I'm going to call and find out. Thanks for that suggestion.

I am still full of questions, and so happy to find someone to answer them. I hope you don't get tired of answering them.

Please talk to us about size of container vs. size of plant and root mass. I think I've already learned enough from you to know the answer: too big leaves too much soil without any roots to take up water and perched water content is greater. ???

Also please comment on the following potting experience: I purchased 24 little hosta divisions with small leaves and roots ('Golden Tiara') and proceeded to pot them up in small clay pots to grow them out. Well, I ran out of small pots toward the end and put the last 6-7 eyes crowded together in a slightly larger pot. That was about 8 weeks ago. Today, the crowded hostas are growing vigorously, and the individually planted ones have grown very little by comparison. The leaves on the crowded ones are at least 5-6 times larger than the single ones. The difference is beyond significant. The difference is huge. Do you think that this is a soil saturation issue, or is there perhaps some other phenomena at work? I would have thought the result would be just the opposite. ???

Thanks again for sharing your knowledge.
.....Pen

Container size - Very small plants can be grown in very large pots with very fast soil, but even plants in small pots can suffer from a slow soil. Roots are not eternal, even in ideal soils. They die & regenerate at an amazing rate. The older roots are, the tougher they are & more impervious to cultural extremes. The all-important fine hair roots are always the first to succumb to adverse conditions - too little/too much water, too hot, too cold, too much or too little of this/that. This slows plant development drastically. I often get mail asking why "my plants aren't doing anything - they're not growing - just sitting there." In most cases, maybe 80 - 90%, the problem can be traced to root issues & a slow soil.

I'm not sure what you meant about "too big leaves"? As plants grow, the roots are always able to support foliage unless something occurs to upset the balance of roots:shoots. This can occur from mechanical injury, temperature extremes, pathogens, or lack of water. Most often, in containers, it's too much water. Roots deprived of 02 begin to die within hours. This is why roots are often unable to penetrate the lower parts of containers with slow soils. Without seeing the size of the pot/plant combo & gaging how highly aerated your soil is, I can't say what's ailing the hostas. My guess is that you're correct in thinking there are root issues with the small plants in individual pots. It's not unreasonable to think that the plants in the crowded pot are able to use up the water that saturates a smaller amount of soil much faster. This allows air (O2) into the soil, which is needed for proper root metabolism and kills root rot pathogens . When next you water, another charge of fresh air is drawn into the pot as water is used.

Plants that are crowded into a pot can exhibit what appears to be normal growth for quite some time, but here is what occurs: Roots occupy an increasingly higher percentage of the container. Soil in the root mass becomes very compacted, or roots themselves become a part of soil structure & soil is washed from roots out drain holes. Watering/nutrient supply becomes an issue in both cases. As roots continue to grow against each other, there is a girdling effect going on, nutrient flow is disrupted & often specific parts of the plant will suffer or die. The most reliable way to determine if your plant needs a repot is by noting extension. E.g., in trees it is easy to determine. If you look at leaf bundle scars, you are able to see exactly what branch extension is from year to year. When extension is decreasing - repot. Immediately, you will see an increase in branch extension in the coming year, & if soils are good, it's likely in the second year as well. In the third year it is likely the extension will diminish, indicating a repot is again needed. Through the whole cycle, leaves are likely to appear perfectly healthy, so try not to allow healthy looking leaves to deter you from a needed repot. More herbaceous plants exhibit similar lack of extension while sporting healthy looking leaves, but it a little more difficult to detect.

Al, dunno where "too big leaves" came from. Probably some sort of edit error. Thanks, you answered my question.

Al...whew! what a wealth of information...thank you! Ken

WOW AL! Thanks for all the great info,you sure know your stuff!!
;) Joelle

Very good post! I had wondered why the excess water comes out of the containers when you tip them. Never been much on a drainage layer in the bottom, I use a very light mix because of the climate I live in.

Very good thread!

11th commandment............"Honour Thy Soil"........for sure! great thread, Al!..........Elaine

As you can see, I'm no fan of "drainage layers" in container bottoms. Not only are they ineffective, but often detrimental.

I'll argue the science regarding why not to use them and why they do not improve drainage, but never argue when the reasoning is to lighten containers or economical (as in cannot afford to buy enough soil to fill containers).

Thank you all for the kind words - much appreciated.

Al

Al
Thankyou for the technical information. You have explained the science very well and I sure didn't understand the why's till now.
I have been using the peanuts to take up space and keep things light. I learned my lesson the hard way by trying to move a way too heavy pot.
Thanks again.
Ann

This was fascinating and I learned a lot. But am a little overwhelmed. I have a lot of containers that I fill at the bottom w/overturned pots to keep them lighter. But, can you distill your information to what you think are the most important points, given that parameter?

I just can't quite wrap my mind around all the info and then figure out exactly what to put into practice. However, I am doing away with the drainage layer in my smaller pots. It will be a pleasure to not purchase and wrestle the bag-o-rocks.

Thanks for your postings.

Hi, tapla-- and welcome to DG!

Yours is the explanation I've heard of potting mix/soil/drainage/aeration.

Thanks so much for sharing all the detail.

What will be your next topic? I must be sure to tune in!

Linda - if the inserted pot is conical in shape, there will be soil that occupies the space between the two container walls. This soil will act as a wick and drain the PWT from the soil above the overturned pot. You can also achieve the same results by growing in a shallower or smaller pot and using a wick to remove most excess water in the PWT.

Wicks are also great when they are employed to temporarily chance the container physics. Fill a container to near the top with soil and add a plant. If the soil remains wet for too long. because of an out of balance relationship between container size/ plant material size/ soil choice, you can insert a wick in the drain hole to help remove the extra water until roots have colonized the entire container. Then, simply remove the wick to extend periods between watering.

I spend lots of time on another container gardening forum site and help lots of people from all over develop soils for their container needs. This weekend, I have received at least 12 e-mails about soils. One was from Brussels and another from Antwerp. Whatever I write and whenever I'm asked to distill something or pick the most important point to consider in container growing, it is ALWAYS, without fail, that: In order for your plants to grow at full potential, you must insure drainage and aeration will be guaranteed in your soil as long as you intend the planting to remain viable. In container culture, you can change all the primary cultural requirements (light, water amounts, nutrient supply, temperature, etc.) but you can do little or nothing about drainage/aeration after the planting is made. Air (at the roots) is just as important as water to plant vitality.

Tabasco - Thanks for the welcome. I think I've been around since last Jun or Jul, but have kept a pretty low profile. Why don't you pick a topic you're wondering about & we'll all talk about it. I sure don't know everything, but I might be able to contribute something. ;o)

Al

Al, am sure glad you are posting again. I mainly lurk, but I watch this thread like a hawk. I have learned so much. Just keep talking, and I can keep on learning. LOL Dotti


P.S. I learn answers to questions I didn't even realize I had yet. Thanks

This message was edited Mar 12, 2006 9:40 PM

Hi, Al,

First, I think you can say 'GW' and 'gardenweb' on this site. (At least I do!) (-: And name any other site, too.

And I read your (interesting) posts over there, but, I don't post there because I was once 'bounced' and would rather be here anyway.

Well, I am doing experiments with my Amaryllis in pots--nothing conclusive since I am not scientific--and may have a few concepts to discuss (after I kill them all!)

And I am getting ready to create a raised bed for vegetables and I found your thread on your new raised bed and will study that and no doubt have questions about that.

And we are talking about the soil conditions for Siberian Iris (not in containers) on the Iris Forum and I am wondering about your potting mix concepts and how they might relate to garden soil... maybe Siberians don't really like all that compost but would prefer some sand...?

Do you know how a lay person/amateur finds out about Soil Science on the Web? Is their a University/Ag School that specializes in it with a good web site? Lots of different opinions among the random web sites...

My garden is very muddy today and I am worried about it.

Thanks again.

I'll go right down your post & comment on what I can. It's funny you'd mention Amaryllis. Up-thread, I mentioned a discussion with a grower in Antwerp. Chef Michel. Of course it took me a couple of messages to determine that Michel was Michael and not Michelle, but I'm off the track now. I bring this up because a good part of the discussion was about the Amaryllis he was growing in a passive hydroponic set-up. It was really interesting & the plants looked perfectly healthy. He had maters, peppers, and lots of other interesting things in a set-up he made himself. A handy guy.

Raised beds are very close to growing in the garden, but with better drainage, so much of what you learn about container growing will not apply. You can use a soil in raised beds that would drain far too poorly to even consider in containers. You can also take good advantage of compost and sand if it pleases you because it will not impact drainage aeration like it does in containers.

Of all the Irises, siberica is one of the easiest to grow. They are like potatoes or blueberries in that they really like water, but won't tolerate wet feet. A fast draining soil that you can water often will keep them from rotting. A tomato fertilizer or one with a low N content is a good choice.

"Do you know how a lay person/amateur finds out about Soil Science on the Web?" Read read read, then pay attention to what you are seeing in your own plants & what they are trying to tell you. I have no formal education other than HS, but my interest in bonsai and container culture has kept me studying whatever I find about soils and plant physiology for a good number of years. I also seek out educational opportunities through the several plant-related/garden clubs I belong to and travel to various functions that offer good speakers. I always go with a list of technical questions that have been bothering me & am persistent enough to usually get them answered.

Don't worry about the mud in the garden. God has it under control and your worrying will not help. ;o) Resist the urge to work the soil until you find that when you pick up the soil and squeeze it in your hand, then release it, it crumbles like chocolate cake. If you say that would/could never happen, you have work to do and it looks like organic matter.

Al

A 5 year old soil from a raised bed. Notice the tilth.

tapla, am glad to see you are still here as this thread started so long ago. I have a question concerning using hydogen dioxide in killing the spores of certain fungus. I had a bad outbreak of pythuim last fall in the pansies ( this pythium was resistent to the fungicide Subdue-which I had never seen before , but know it can happen because we all use Subdue first when treating pythium and phytopthera.) and was looking at various ways of treating it. I used Oxidate as a drench (its 27% and the treatment was 64 oz/50 gal water). I was not impressed with its ability or lack thereof in killing the spores because the pythium kept on going and there was already a treatment of Truban as well as Subdue-all full strength-so it had help in the soil to start with. I was also isolating like crazy. I was told that this hydrogen dioxide only had the ability to kill spores on contact on top of the soil, or on any part of the plant above the soil. That once it was put in the soil, it lost its ability to kill-that the particles of the soil compromised its killing potential. So it would be useless with pythium or phytoptherea as they are down in the soil. What do you think-have you any knowledge or experience treating these fungus with hyrogen dioxide? Would love to hear from you about it. Thanks

tapla,

thanks for your reply. i'm looking forward to trying some new things this season. keep posting so we can keep reading!

Terry - I have never read anything scientific on this question. I have asked scientists about the use of H2O2 as an anti-fungal, and a temporary soil oxygenator for O2 stressed roots. Their replies were something along the lines of what you alluded to above, but not that it was a soil-surface sterilizer only. My observations (though purely anecdotal) do not support that either. H2O2 is probably considered a topical because it reacts with (oxidizes) the first organic molecule it contacts. Common sense tells us that a portion of the chemical, mixed with water, will perc through the soil before contacting other molecules.

I have used H2O2 to water my indoor plants during the over-winter period for nearly two years now. I use 1 oz of 6% solution I have diluted from 35% food grade per L. of tap water. I have observed no problems with rot fungi during that period, even in plants where soil conditions would cause me to expect a problem to come calling (some plants are over-wintered, badly in need of repots due to lack of time on my part) collapsed & soggy soil being one. I also have noticed better growth and vitality, increased resistance to insects, and better color. Given some of the shallow containers my plants are in (shallow containers have a very high % of saturated soil and are more difficult to keep rot and soil-insect free) I should expect some rot issues and soil-insect presence, but have noted none, unlike in past years.

I cannot attest to whether H2O2 might be effective in eliminating an infection of either pythium or phytopthera, but it appears to have effectiveness at preventing fungal spread. Again, this may well be scientifically refuted, and what I observe may have basis in another cause/effect relationship. I'm usually quite careful about what I attribute things I observe to, but I am comfortable in my belief that including H2O2 in my watering program is compatible with and an aid to my growing methodology.

Best I can do - wish I could help more, Terry.

Al

Thanks Al for your considered reply. Am thinking that I should at least water my houseplants with it-as much as I underwater them, they need a break!
It was a plant pathologist that gave me the info about not being effective in the soil. I guess I should assume that it makes a better preventive than a solution if I get pythium or phytopthera.
All comes back to watering huh? I tell people that its the hardest job in the greenhouse, and the most important.
Thanks again
Terry

Terry - My interest in container gardening is an outgrowth of my pursuit of bonsai. An interesting story: Those that travel to Japan to pay to serve as apprentices of bonsai masters are always relegated to what seems to most to be the very menial task of watering - only. The masters recognize that learning exact watering techniques is a prerequisite to achievement in bonsai. Only after many months of practicing watering under watchful eyes is the apprentice allowed to progress to the more "glamorous" tasks that include handling the master's trees. Watering along with the related aeration and drainage are extremely important to container culture, as you know.

Al

My project this weekend was to be filling and planting my 2 whiskey barrels and 1 ammo box! What a streak of luck that I found this thread and the Big Container Gardening thread first! Thank you all for the invaluable expertise and experience. Looks like a shopping trip first for a drill, screen cloth, wicking stuff, roofing asphalt ... OMG!

I have found this thread to be very useful. I printed it out and have read it several times to absorb the information. Now I have a few questions.

At our summer place we have four large whisky-barrel type containers. Often we are not there for 4-5 days at a stretch, and the plants suffer if there is no rainfall. These are mostly annuals and some tubers (begonias or dahlias), so their roots typically go down less than a foot.

From Al's discussions here, it seems reasonable that, using his mix (recipe above), I could thoroughly soak the medium to increase the height of the PWT to just under the root area and then expect that, over the week, capillary action would pull the moisture from below up to the roots of the plants. This is assuming the mix, and only the mix, fills the pot. All have drainage holes, with optional saucers.

My questions: Would this work? Should I use the saucers? Should I add a wick? Is there any way to prepare the 'system' for a downpour during the week which might alter the level of the PWT?

Also, I was under the impression that the decomposition of wood/bark particles consumes nitrogen. Is this correct, and, if so, does this have any impact on the plant growth? Or does the controlled-release fertilizer compensate for this?

I'm planning to experiment with this over the summer. thanks to everyone participating in the discussion.

Andy

You must use a soil or arrange some means of irrigating that insures your plants will not die from lack of moisture during extended periods between waterings. The PWT will be consistently the same ht when soil is at container capacity (this is the measure of water after soil has been completely saturated and has just stopped draining). You cannot increase the ht or volume of perched water by supplying extra water. During a downpour, the water in the PWT will remain at a consistent ht, or possibly briefly increase in ht during the rain, only to quickly return to its normal ht when it stops. From there, the ht of the PWT will steadily decrease as the plant uses water from the soil or it evaporates, until more water is supplied. Perhaps the use of polymer crystals like Soil Moist would be of some help in your case?

Since all bark is rich in lignan (as opposed to cellulose, like in sapwood), and conifer bark is highly suberized (Suberin is a lipid sometimes referred to as natures waterproofing for trees), it's very difficult for decay organisms to cleave the hydrocarbon chains in conifer bark. As a result, it breaks down very slowly. It is fairly easy to compensate for N tie-up in your bark based soils as long as you are already aware that you'll need supply extra N. I have found it effective to use fertilizers with a higher first number (N) and I especially like supplementing full strength doses of soluble 20-20-20 with a simultaneous full strength dose (in the same water) of 5-1-1 fish emulsion. This has been very effective on woody plants & plants grown for foliage. On blooming plants, I often use a bloom promoting fertilizer like 10-50-10 as long as foliage is nice & green. I generally watch the color of the older leaves on a plant as indication of a need for N. N is a mobile nutrient and they yellow first as the plant robs N from them to translocate to newly emerging leaves.

You will almost surely need to supplement your crf with some sort of additional nutrient program. This is especially true when growing in a fast soil. Try to be sure your soils contain the minors (micro-nutrients) too.

If that didn't answer your questions, please let me know.

Al

Al, thanks for this great information, I make my own potting soil and have thought it was a little "heavy" Your recipe is perfect. In place of the peat moss in your recipe I use my original potting mix which is 1/3 peat moss, 1/3 compost and 1/3 rotted leaves (I have 3 areas where I dump my leaves on a 3-year rotation. These areas have the leaves spread out to a depth of about 2 feet. At the end of the third year I rake off top layer of leaves and use the rotted material underneath in my mix) I have already made and used one batch following your directions and am very pleased with the result. Thanks again. Charlie

Al,

Is the pine bark ok for vegetable soils; or did I miss out on reading about it above?

~* Robin

This message was edited May 27, 2006 2:00 AM

Charlie - I can see where your original mix would be water retentive & hold little air. Soo glad it helped.

Robin - Pine bark is just fine in the mix for veggies.

Al