Container Soils - Water Movement and Retention III

continued from: http://davesgarden.com/community/forums/t/719569/

I'm posting this continuation of a thread originally posted in Jun of ‘07 out of consideration for those who find it takes a considerable amount of time to load because of its length. It has garnered much more attention than I ever imagined it would, and has been great fun - a wonderful catalyst in the forging of new friendships and in increasing my list of acquaintances with growing interests similar to mine. The same information was posted on a competing forum site in '05. Still very active, it has received the attention of just under 1,500 posts as I write.

The forum and email exchanges that stem so often from the subject are, in themselves, enough to make me hope the subject continues to pique interest and the exchanges provide helpful information. Most of the motivation for posting this thread again comes from the participants’ reinforcement of the idea that some of the information provided in good-spirited collective exchange will make some degree of difference in the level of satisfaction of a considerable fraction of the readers’ growing experience. It is difficult for me to talk about the thread in an objective manner without a few taking it as my being boastful, but if I may be brief, I will just say there have been enough growers who have expressed the opinion that the information in the thread has been pivotal in their progression as container gardeners for me to finally bring myself to say that I feel the information is valuable.

This thread is not about recipes, though they are widely discussed, it is about concepts and a way of approaching gardening in containers that varies from what we might consider current convention. I'll let the success stories and enthusiasm in the previous postings, and likely this one, speak for themselves.

I'll provide links to the previous threads at the end of what I have written - in case you have interest in reviewing them. Thank you for taking the time to look into this subject - I hope that any/all who take the time to read it, find something interesting and helpful in it. I know it's long, but I hope you find it worth the read. Most of all, I hope it stimulates discussion and questions. Please excuse the lengthy introduction, which I'll conclude by thanking everyone who has shown interest and participated in the discussions. I'll look forward to your input and questions.

Al

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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’ll 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

The original thread:
http://davesgarden.com/community/forums/t/527353/

The second thread:
http://davesgarden.com/community/forums/t/719569/





This message was edited Feb 2, 2010 4:36 PM

Thanks, Al!

By the way, if you remove about half of the asterisks (***********) it will allow the thread to be viewed w/out having to scroll back and forth. In other words it will keep the page more compact and more easily read.

Thanks for all your help. I read every word!

Shoe

Marilyn,

Those "self-watering" pots and the like are very expensive and not very effective. On effectiveness first --it will be YOUR-self who waters them. Just because you put in an extra quart or gallon doesn't mean they won't dry out. Even if the extra water provides the proper moisture level consistently --let's assume it does-- if you are lulled into thinking you don't have to water, you got trouble.

I also think that Al will say a.) the better use of the pot-space the devices occupy, at the bottom of your pots, is best used as more space for soil in which roots can grow, with proper watering and b.) these things don't change the laws of physics --you'll still have a PWT level, it'll just be higher up in your pot by the exact depth of the water level in the device.

On expense --for the price of two of those pots, $25, you can put together a simple irrigation system that will let you water all your plants in a couple minutes each day. For the price of five or six, you can put one together with an automatic timer that provides two different timing/amount patterns.

Overall, with proper watering (by and or by irrigation), you and your plants will be better off with good soil to the bottom of your pots instead of an expensive, hidden reservoir where roots could otherwise be growing.

I read this before but found it refreshing to find again and gave me some more food for thought.

Good! - it's supposed to be thought provoking. ;o)

Al

Al,
Searching for pine or fir bark online (having had no success finding it locally), I came across a website selling fir bark by the 2 cu ft bag. They offer several sizes. The "fine" is 1/16 to 3/16, whereas "small" is 3/16 to 3/8 inch. I ordered small. Was that the right choice, do you think? This is for making up your last recipe, for woody plants. Thank you.

This message was edited Jun 5, 2010 6:54 PM

Either will work well if you're using the granite and screened Turface. The mix tends to take on the physical properties of the two ingredients closest in size. I use 1/8-1/4, but I think that if I could get it, I would choose the fine, 1/6-3/16 as a better choice for my purposes, probably yours, too; but don't be disheartened - it's going to work fine, and you'll be well pleased.

You've decided on a fertilizer regimen?

Have a good Memorial Day. Remember those who gave all.

Al



Al

Remember them.

I'm running a bit late here, but I had to say thanks so much for the revised edition.

This is valuable information that should be given to every garden center worker, plant magazine editor, & garden forum (LOL), to stop the "old wive's tales" concerning container culture. (Such as using pot shards for "drainage", using crazy materials on the bottom of pots to save potting soil, or "recycling" medium by just adding a bit of new to the old. Aiee!)

And many, many, thanks for making the science behind it understandable to the layperson too. That's no easy task !

This message was edited Jun 1, 2010 7:33 AM

Al,
This container soils part III should probably be a sticky like the other two, otherwise it disappears and is hard to find. Is that something you do, or the folks at Dave's Garden?

As for fertilizer regimen, I'm doing a mix. In the pots that are far from the house that I water by hose, I'm using continuous release pellets. In the pots nearby, I put in a small sprinkle of pellets as a safety margin but will add liquid Dynagro 7-9-5 also (on a sadly erratic schedule). I know that isn't the right nutrient proportions (I can't remember what you said is the best balance, and that post isn't as easy to find as the soils post) but I haven't, so far, found the Dynagro that you recommend.

My ginkgo bonsai was repotted this spring with your woody plant mix. I've been amazed at how well it retains moisture--it doesn't seem like it would, by the look and feel of the mix--but it does. I'm currently watering it about every 3-4 days. (I use a rock on the soil to tell when it needs watering. If the soil under the rock is dry, I water.) The plant is thriving. I only had enough for a few plants with the "good" mix that I did right. Then I ran out of pine bark and substituted what I could get locally and used that mix for a number of Japanese maples, and that is better than the potting soil I used to use, but not as good as the pot the bonsai is in. Hence my order for properly graded fir bark online, despite the fact postage costs as much as the bark!

This message was edited Jun 1, 2010 7:47 AM

I'm not sure how one gets a thread to become a sticky - never done it before. I've had others ask if it was ok if they write admin & request it (sticky) if the information seems valuable enough. I think that's how all the threads I have as stickies got to be that way, but some of them just showed up one day, stuck to the top of a forum .....

About the bark - if you have any places near you that sell orchids and orchid supplies, you might check with them for the prescreened fir bark. I get to CHI quite frequently, and I'll often take my truck and pick up 10-20 3 cu ft bags @ around $17 each, but you could also screen uncomposted pine bark & use the fines in the 5:1:1 mix for veggies & flowery stuff.

I prefer fertilizers in the 3:1:2 ratio for almost everything I grow in containers. It provides nutrients in as close to the ratio plants actually use, which allows you to keep TDS/EC (basically salts level) at the lowest levels possible w/o nutritional deficiencies - a decided advantage. Some examples of 3:1:2 ratios include MG, Peter's, Schultz, others in granular soluble 24-8-16 - MG liquid 12-4-8 - Dyna-Gro's Foliage-Pro liquid 9-3-6 (preferred).

I often look for the thread about fertilizing containers too, but it's hard to find with the search function not working. I'll try again.

Al

Yes, I've been using the 9-3-6 on virtually all my containerized plants for the last several years, and I can say it's performed better than any fertilizer I've ever used. It really does take all the guesswork out of supplying your plant's nutrition.

Pirl was kind enough to let me know in a D-mail that the search function is now alive and well, so here is the link to the thread about fertilizing containerized plants:

http://davesgarden.com/community/forums/t/783660/

Take care.

Al

I copy and paste the good threads and info right into my blog, so I can find it later.

Al,
It turned out the people at Roberts Flower Supply hadn't yet shipped my bark and kindly substituted the finest grade for the "small" grade. It arrived today and it is GREAT. I'm so pleased. I now have all ingredients in place to make a decent-sized batch of the woody mix. The funny part is they included a printed catalog with my order, and wouldn't you know it, they also carry the Dyna-Gro Foliage fertilizer. If I'd only realized, I could have had them add that to the box and probably wouldn't have paid any more postage...oh well, next time.

Too bad about the fertilizer/shipping thing, but like you said ..... next time! ;o)

Take care.

Al

"Roberts Flower Supply"????? Why didn't I find them before????

Okay, thanks for the link, anyway. I can stop throwing away two-thirds of every bag I buy, after sifting out the stuff I want!

Holy smokes! They're literally 3 miles away from my home, and I've never heard of them. Time to drop in.

http://www.orchidmix.com/

This message was edited Jun 5, 2010 2:17 PM

Puddle, I grew up in Elyria, Oberlin, and Lorraine, till age 11. I remember going to North Ridgeville and grandma talking about it all the time but don't know why. She was a gardener too. I got it from her. Funny how when she moved here to the desert from Ohio, she thought the desert land she lived on was land that nobody had pulled weeds. She lived on some people's property that was 5 acres of Caleche soil and hard pan. One day she was out there looking like death and said Dawn will you please help me pull these weeds. I was 18 or 19 and said Oh no grandma I have to go somewhere, but laughed that she had mostly hand weeded 5 acres herself and did not know it would come back next year again. I get weepy thinking of that day. I wished I had helped her or offered to come back when it was not so hot to help her later.

Hi, guys. Please don't think your input and comments aren't welcome, because they are, but if we could just try to keep them focused on the subject - so others reading through the thread for information don't have to sort through the OT conversations. Thank you.

Al

Sorry.

Mr. tapla/Al: where are u? Haven't seen very recent posts... I really appreciate all your info and expertise.

In both 5-1-1 and gritty mix: does using FoliagePro 9-3-6 eliminate the addition of lime and/or gypsum? I don't seem to grasp this aspect of the mixes. I'm using containers for a number of cacti/succulents and may try some fall veggies - brussel sprouts, kale, maybe others.

Also, in a thread regarding repotting, I think, a pre-bonsai plant, you had a picture showing the wick and screen setup in the bottom of the pot; what is the crosswise piece of what looks like clothes hanger wire?
TIA--mg

I only come around when someone else has comments or needs help - always avoid bumping my own threads. ;o)

I tried several plants this year with only FP, using the gritty mix, and they seem fine, but the 5:1:1 mix should be limed to bring pH up. The pH of the gritty mix is higher than the pre-limed 5:1:1 mix, which was the reason for using the gypsum as a lime source and Epsom salts as the Mg source (they don't raise pH). When using fertilizers that DO NOT contain Ca and/or MG, it's important that you take measures to make them available, so read the labels.

If you're still confused, let me know & I'll go into detail.

The wire is like a staple pin-stitch made from a scrap of bonsai wire that goes through the mesh & outside of the pot to hold the mesh securely in place.

Al

Thanks, Al. Man, I hate to belabor the topic, but ... I needed more grit and in the interest of time/money/gas, etc. bought some MannaPro (no size info that I could find) and it's generally larger than gran-i-grit. I've screened it thru 1/4 (most went thru), then 1/8 (and got a good amount there) and then insect/tea strainer to get rid of the tiny stuff. The 1/4-1/8 seems larger than the gran-i-grit -- ok to use it in gritty mix?

Also, I've mixed two 5-gal. buckets of 5-1-1 using bark, peat & turface (to avoid perlite) and it seems awfully "fine". I did read your post regarding leaving out peat in a situation like this, but it's now that I my mix may be too fine -- what would you suggest to add at this point? I will most likely be making more 5-1-1 in the future, mainly for SWC of some fall veggies. Thanks again, Al; you're a very patient man!
Mary

Hey, Mary! Thanks for your interest.

They should have a smaller size grit that would be more appropriate. I use #2 cherrystone, which tends to run a little larger than grower size in the Gran-I-Grit. I'd say it's about 3/32 - 3/16. You can use larger, but here's the deal. When you use disparate sizes in your material, it has more of a tendency to separate, and the soil takes on the characteristics of the two ingredients that are closest in size. IOW you can use large grit, but if you bark is also large, the soil takes on (primarily) the characteristics of the bark and grit.

[Not snotty here. ;o)] I'm not selling you on a soil, I'm selling you on a concept. That is, on 'a' soil that has very good aeration for the life of the planting. How I got there took a lot of consideration & experimenting. The ingredients I use are the best I've found at what they do for the soil, but I realize there will always be the need for substitutes, and tinkerers trying to improve on the soil to suit their purposes, which is actually what I intended. I wasn't pushing the recipe, rather, the concept. If you understand the concept & what all the different ingredients (can) bring to the table, you should be able to fix any problems. I'm also usually around to help where I can.

Suggestion: If you find the larger grit makes for too little water retention, adjust the amount of grit:Turface, keeping the bark fraction at no more than 1/3 of the o/a mix. Try 4 Turface, 3 bark, 2 grit, or something similar. Play with it until it suits you. Some are tempted to leave the Turface unscreened to increase water retention, or even add in peat or similar. This eliminates the very reason the gritty mix works so well and reintroduces a PWT to deal with. The soil is made with the water retentive screened Turface and grit that holds no water, other than what it holds in its surface, so you adjust water retention w/o having to deal with a PWT.

The peat is in the 5:1:1 mix to adjust water retention. If you feel the soil you made is too fine & will support too much perched water, then add more bark & perlite to what you have, along with a small fraction of lime. After you've used the soil for a year, you'll be able to tell what you need to do by simply looking at the bark you have to work with. Small bark with lots of fines requires little or no peat, while a larger bark, especially if it's pretty fresh, might require more peat than a 5:1:1 ratio.

I didn't name the soil, others did - both of them, so the 5:1:1 and the 1:1:1 ratios are just my initial guidelines. The recipe gives you a starting point ....... a fledgling bird - the wings come with understanding the concept. ;o)

Al

I've repotted two plants that I put in a mix that turned out to be too coarse. My bark was pretty large and I had no peat initially. Had to take the plants out (one was a bamboo, the other a ming aralia), mix in some peat, and try again. Sound like you are saying it would have been better to add more turface. In any case, things seem to be going better now, I'm not finding the leaves all curled within a day of watering.

I don't know what your mix was, but if it was a variation of the gritty mix, it probably would have been better to increase the amount of screened Turface, rather than add the peat. FWIW - I have about 250-300 plants in some minor variation of the 1:1:1 gritty mix, and I don't have issues with water retention, though I do have to water more frequently than if I was using a bagged peat-based soil.

It's always better to get the job done with some consistency. IOW - if you mix sand with boulder-size marbles, you won't have a very good soil from the perspective of physical properties, no matter what ratio of sand:marbles you use, but if you were mixing screened Turface & crushed granite - you get a consistent mixture that stays mixed and that you can vary to adjust water retention.

Your problem sounds like it was related directly to the size of the bark. Reducing the size of the bark would increase water retention and make any peat or Turface you might add more effective.

Al

Al, thanks so much for your input and guidance, especially on adjusting the mix ratios. I just get so frustrated with attempts to locate the ingredients; turface and grit are less of a problem tho my sources are 50-100 miles in opposite directions! The pine bark is the main problem; a big box store website advertised "soil conditioner" but when I got there it was not to be had - they were now selling a "landscape mix" (which I bought) and it turned out to be something I'm not sure I can use. When I lived in the Carolinas it was easier to buy products 'cause the nurseries had displays of their soil amendments and I don't remember so many pre-mixed products either. I thought I had located a source of bark, what they call "regrind" and not composted BUT (you know there'd be a but) they sell only large quantities and if I remember correctly, delivery only, and the place is 350 miles from me........

I've got the screening fairly covered: 1/2, 3/8, 1/4, 1/8 and my trusty tea strainer. You know I'll be back as more questions come up -- right now I'm gonna repot a jade plant and an agave that didn't seem to like what I thought they needed to be planted in (my opinion, of course) and see how they like the gritty mix. Thanks again, Al. You're so very knowledgeable!
Mary

I hope this is not too off topic... I've read through these threads over the past year or so but I don't remember this coming up, I apologize if someone has already asked but...

I have a lot of plants in containers and I believe I have a good soil mixture but I am constantly battling weeds in the pots. I try to pull them always when I see them but it seems like a never ending battle. The pots that are topped off with gravel don't have AS big of an issue but its still an issue. I know that part of the fight has to be in the lawn in general but I tell ya these weeds are just having a hay day in my pots. Any words of wisdom for me?

I have lots of problems with oxalis - particularly Oxalis corniculata - the little creeping one with purplish foliage and tiny yellow flowers (if you let it get that far) , Euphorbia maculata (spotted spurge), and Sagina subulata (pearlwort/Irish moss).

I usually just pull the spurge, which comes up roots & all - and doesn't grow back unless it's already seeded out, so pull it when you see it. Sometimes, I pull the pearlwort, but other times I'll spray a little premixed Round-up (or similar) into a small cup & use a small paint brush to daub a little solution on the plants. I always use this technique on the oxalis, as it usually does no good to try to pull it because even if you get the taproot, there are usually stolons & rhizomes left behind in the soil that develop into new plants.

I guess you'll need to develop your own strategy, based on how tenacious the weed is, but keep after them & be sure to get them out of your containers before they seed or get a strong hold. "The price of freedom is eternal vigilance" T.G.

Al

Yes that is truly what you have to do. I try pre-emergent in the late fall and then if any sign of it shows, I use q-tips to brush on the stem of the unwanted creature. I am using this method in my mixes now, and having success, but having troubles finding the right size particles as well.

A couple of days ago on August 30th I re-planted my Colorado blue spruce dwarf weeping variety called 'the blues' into the same 20 x 20 container, but I used a 3 part mix of 1 part potting soil (sphagnum peat moss, perlite, starter charge, dolomitic limestone, calcitic limestone, wetting agent), 1 part lava rock and 1 part pine bark fines to make the soil fast draining. In August we had 9.14 inches of rain which was above average and the potting soil in the container stayed very moist which caused the tips of the blue spruce to turn yellow from too much water since they don't like wet feet. Thankfully the last few days it has been hot, windy, and mostly dry and the forecast calls for more dry weather. It has only been in it's new soil for a couple of days, but it already looks better and hopefully it thrives. I still have it on the east side of the house so it only gets morning sun, but once it gets cooler I will move it to the south side of the house so it can get full sun. Does this sound like a good soil mix for a dwarf blue spuce in a container? (I originally received and planted the spruce a month ago using just potting mix).

It SOUNDS like it should work ok, but w/o some idea about how large the bark & pumice were, it's hard to be any more specific than to offer an encouraging word. ;o) Is the bark on top (in the pic) part of the soil, or is it mulch you added after planting?

Al

Thanks Al. The potting soil, lava rock, and pine bark I mixed thoroughly for the container soil and added a top layer of the same pine bark. The size and type of pine bark and lava rock:

http://www.lowes.com/pd_87940-66882-87940_0_?productId=3044731&Ntt=mulch&Ntk=i_products&pl=1¤tURL=/pl__0__s?rpp=30$Ntt=mulch$identifier=

http://www.lowes.com/pd_2568-66882-2568_4294857240_4294937087?productId=3028785&pl=1¤tURL=/pl_Bagged%2BRock_4294857240_4294937087_?rpp=15$No=0

The lava rock I would say to be half dollar size and smaller pieces and the pine park was mostly quarter size and smaller pieces and very thin. I hope I used the right material.

The bark and pumice are extremely large for a soil. You want the particles to be around 1/8" or so. The object is to use a mix of soil particles large enough to minimize or eliminate perched water, yet small enough to maximize retention of water that doesn't perch. IOW - you want your soil to hold as much water as possible w/o it perching.

Your plant will probably grow ok, but my concerns are that the potting soil will separate because of the particle size disparity and end up on the bottom of the container, and because of the very large particle size that you'll have trouble keeping the soil moist, particularly the top 2/3.

Al

After I re-planted I kind of had that thought in the back of my mind about the potting soil separating. I wouldn't think it would separate very easily using drip irrigation, but rain storms are another story. I will keep an eye on it and see what happens for now, but I'm thinking I might have to re-plant sooner than I would have needed to if I would have found more ideal products for my specific application.

Good luck! At least now you know what to look for so you can head it off at the pass if necessary. ;o)

Al

Semps on a board:

Al

Semps on a rock:

Al

More semps on another rock: