Happy - You should be able to buy or order granular rockwool from any hydroponics supplier. You can buy an absorbent type or a hydrophobic product. Both increase aeration and drainage while only the absorbent type increases water retention.
Al
Container Soils and Water Movement in Containers (long post)
I clearly have to find a local hydroponics store!
Al - I guess the absorbent type is what we'd want to use??
Remember guys (Happy & Pirl), Lynn lives in a very arid region of the country & the need to use a highly water-retentive soil there is going to be far more urgent than where you live.
The soil recipes I suggest are just good starting points. If you intend to build your own soils, you'll need to get a feel for how they will perform and amend them appropriately to suit your plant material and growing habits. It may or may not be appropriate to use absorbent rockwool in your soils, but I am quite certain that you can build a perfectly suitable soil for your area with nothing exotic or hard to come by.
Al
My reason for asking, Al, is that the pots will be in the courtyard and it's probably an effective zone 8 there. I think the heat from the stone would dry out the pots faster than if they were placed in the shade or within gardens, on soil or on grass.
Last summer our little ten day heat wave dried out every pot and only a few plants survived even though I watered them daily.
ok - ;o) Forgive me - hope you have the info you need then.
Al
I have noticed that I need to change the potting medium mixture a bit with the wick method, as the first round of experimental wicks is indeed drying the pots out, which this time of year is good, however when the heat turns up will need to adjust to some of the above recommendations.
I have been experimenting with Lava Sand the past few years, and it has a great capability of moisture retention at certain temperatures. From what I've studied about and observed from it's use is it's ability to facilitate a greater nutrient absorbtion rate by the roots.
Al, any thoughts are experience with such?
Rj
Thanks for all of your help, Al. I really do appreciate it.
You're welcome, Pirl. ;o)
Hi, Rj
By "lava sand", are you referring to zeolite or specifically the product ZeoPro? It's purported to have some kind of extraordinary CEC, but from recent conversations with some whose judgment I trust: "... I didn't see results that made feel I can't do without this." There's nothing stopping you from trying it out & letting us know your findings though.
You may also wish to consider substituting a calcined clay product for any perlite in your soils. Calcined clay aggregates (such as Turface MVP) have an excellent CEC capacity (if it means anything, up to 12 me/100 cc) and 40-50% internal porosity. This translates to good water holding capability (over perlite since it has 0 usable internal porosity) and a whole lotta cation attachment sites @ more than 13 acres of surface area per lb of aggregate.
Build your soils and select container sizes so that you can go at least 24 hours between watering in the heat of summer and when the planting is mature. If you do this, you could well be over-potted early in the grow season when the planting is immature & roots have not colonized the container completely. If such is the case, then is the time to use a wick - until you need to water more frequently than you are willing to. At that point, remove the wick to increase irrigation intervals.
Finer sands will increase water retention and can provide enhanced drainage in some soils, but they generally do so at the expense of aeration. What I consider appropriate-sized sand for hort applications is going to be about 1/2 BB size or larger. I've used screened products: coarse silica, crushed granite, pumice, and Turface all extensively with very good results, but only find them necessary in soils that need to be formulated for extended life.
As far as the sand you refer to "facilitating a greater nutrient absorption rate by the roots, I would have to say that is probably technically not accurate. It may be true that it could prove beneficial by holding onto nutrients that can readily go into solution and then be absorbed by the plant, but it won't likely increase absorption over and above what any adequate nutrient supplementation program would. Plants absorb water and dissolved nutrients when the moisture (matrix) tension of soils is lower than the cellular tension and is probably unaffected by what soils are comprised of (structurally speaking - pH assumed appropriate) so long as air/water/nutrients are present in appropriate ratios.
Al
Been reading all this and this winter I have been bottom watering using nylon rope as a wick material with great success. Too water or not to water this way. Can you address this topic.
This message was edited Feb 13, 2007 6:11 PM
It can be an effective way to water, helping to reduce some of the soil compaction that you find from top-watering and reducing over-saturation at container bottoms. You should be careful about allowing fertilizer salts & dissolved solids in your water from building in soil due to ongoing evaporation (this will be especially evident in the top 1/3 of the soil volume). Top-watering helps prevent this build-up, and you can lessen its effects it by flushing soil with an occasional copious top-watering. Do this by watering well & then returning a little later to flush the soil with water enough to approximately equal the soil volume.
Al
Interesting. Other sources I have read suggest flushing up to 4 times the container volume. I generally flush 3-4 times the container volume about 3 times a year.
Oh - it probably doesn't matter much if you apply that much water, but it does tend to increase compaction, which is a valid reason to water via wicks to begin with. The description I gave is well-supported in bonsai culture, where watering plants is made into a very exacting science, so I'm pretty comfortable offering it up as a guideline. Copious top-watering also tends to leach nutrients along with accumulated metal salts, increasing the necessity for additional fertilizer applications. I know Bob already knows all of this, so I offer it mainly for the other readers. By reading his posts, I'm sure he's pretty well satisfied with his methods and has this well-covered.
While I'm here though, I might offer a tip on how to water a container thoroughly and efficiently:
Wet the soil thoroughly over the entire surface (I almost always try to keep foliage dry), using what you gauge to be the approximate maximum volume you can apply w/o water draining from the container bottom. Wait 10 minutes while the water also disperses laterally through the container and water again so that about 10 - 15% of the total volume used on that container drains from the bottom. This method effectively allows accumulated salts to go into solution and flushes them from the container in draining water when done on a regular basis. Of course, this is assuming your soil is well-aerated and drains well enough to allow this kind of watering.
Al
Tapla: You write: "This method effectively allows accumulated salts to go into solution and flushes them from the container in draining water when done on a regular basis." But I am lazy and just allow the plants to drain into a saucer. I assume that defeats the purpose of what you are describing -- you would want those accumulated salts to go down the drain each time, yes? Not that I will change my ways, but I guess I need to feel even more remorseful!
Lolol! Yes - you should be wracked with sobs of sorrow after you find out how right you are! ;o)
Prolly not the biggest deal we have to worry over though. Once you're aware of the possibility of problems, a little effort goes a long way. A quick empty & rinse of the drain saucer would be helpful ....
Al
This message was edited Feb 15, 2007 12:35 AM
To be honest, I'd probably rather shed a few more tears than mess with dumping the drain saucers every time I water. What a bad bad person I have grown up to be!
(this will be especially evident in the top 1/3 of the soil volume) How does the salts build up only in the top 1/3 when the wick only wets about 2/3 of the way? I like keeping the top of the soil dry by wick watering due to Gnats or fungus.
This message was edited Feb 14, 2007 2:51 PM
The entire volume of soil will draw water upward through capillary action. The greatest amount of evaporation will occur in the portion of soil with the greatest exposure to air. This will be the soil's surface & the area just below, where air circulates freely. Since the greatest evaporation occurs in the upper part of the container, the highest concentration of residual metal salts (both from fertilizers and dissolved solids in irrigation water) will occur there as well.
Please note that when media feels dry to the touch, it does not necessarily mean that it is dry. You cannot detect moisture in most media by "feel" at saturation levels less than about 35%, but this does not mean that water migration and evaporation is not occurring. Even wick-watered containers that always feel dry to the touch at the surface will eventually exhibit white deposits from metal salts build-up at the soil's surface.
Al
You are such a good teacher, Al!
Al- You are amazing :-) I want to come garden with you! I once posted a question about soil, and you explained it in the same easy to understand detail you have done here. I am going to try your mix- so far I have been pretty disappointed with most of the bagged stuff I have bought. I am going to try the wick with some of my houseplants, as here in Philly there is nothing outside right now other than my perennials and my ash bonsai, all waiting patiently for spring. And that salt deposit that you mention- I have a devil of a problem with that in my water here- I get them routinely, and have to get rid of it. I'm on a right wavelength though, as I've already been flushing the soil and occasionally rinsing my saucers and bowls that my housplants sit in- just made sense to me, although its a job since I have many, many houseplants. Watering is a chore sometimes, but those plants bring such joy to me that it makes it all worth it. Thanks for sharing your wealth of information with us again- take care!
Samantha
Ohhh gosh - you guys are soo kind. I often get chided from friends for the tendency not to acknowledge such nice compliments because I get embarrassed, so I better tell those that have gone out of their way to offer thanks or encouragement along the way, that I really appreciate your efforts. It makes any effort on my part seem like no effort at all. Thanks to all of you - and to Dave's too, for providing us a place to exchange ideas and learn together. ;o)
Al (still a little embarrassed)
Nobody does it better, Al.
This is a great thread- I've learned so much. Thanks, Al!
This should be a Sticky thread :)
I agree. I've learned so much on this thread. Thank you to all y'all with knowledge and experience to share and to everyone with thought-provoking questions to ask!
I have a question about rock wool. I recieved a free sample baggie of small cubes about 3/4 inch square (dry) and have done nothing with it. Should I try to grind it up to use in container gardening? Use as is..in the super duper potting mix described above? Or should I use it to propagate in water, which was I believe the original intent for the product?
carol
Hi, Carol. I'd bet that they are 1 x 1 seed starting cubes. Usually, you would start a seed in/on the cube & when roots appear at the bottom, move it to a larger cube that has been hollowed out and specially prepared to receive the smaller cube or plant in another appropriate medium. I suppose you could reduce the size of the pieces & add it to a soil if you feel there is a need for more water retention in that soil.
Al
Hi Al,
It is a lavasand by GreenSense. I have a picture of the bag, and a picture of the sand in my journal.
http://davesgarden.com/journal/ed/index.php?tabid=1720
I also have this thread linked to the journal. The sand is very dense, so you are right in the fact that aeration suffers, which I have learned in the school of hard knocks the past few summers. In my journal I explain where I picked up the idea of using the sand. You explained what I meant as far as the product allows a greater amount of time for the plant roots to draw nutrients, other than the fast wash of "stuff" going throgh the container. I am convinced once I get the combination correct the "lava sand" will work well. I have had some great success with it in a hit and miss way. Now that you've pointed out aeration, the light bulb clicks on and I have to go and put the latest mad scientist potting medium together!
I am very much interested in trying the calcined clay. I'm sure I'll be able to get this at my favorite garden store, but in case..is this something available at Home Depot or other common places? I have an image of kitty litter...LOL.
Re the journal, you'll have to probably interpolate some of my conjecture in what I'm trying to say.. You say it a bit better than I.
Rj
"Ohhh gosh - you guys are soo kind."
"Al (still a little embarrassed)"
Al, fantastic thread! And bigtime thanks! Also, no need to be embarrassed because you chose to share so much valuable info. I've read, re-read, and use this thread as a great "research and remind me" source for quite a while now!
Love it! I hope this becomes a Sticky at some point in time.
And now, continue on...
Happy Growing,
Shoe
I would vote for making this thread a sticky.
Me, too!
Count me in too!!!
Definitely needs to be a sticky!!!
Add my vote for a sticky, please! It's too valuable to get lost with the size of DG.
It would be great to "sticky" this thread -- lots of great information here, clearly presented!
I'm using wicks now whenever I repot... I thought that was a great idea! In the winter, most of my pots sit inside on saucers, so the wicks won't help with drainage (although they may permit me to do some bottom watering)... but in the summer, I use little pot stands under many of the pots on the deck, so the wicks would be able to dangle down. (Having the weight of the pot rest on the 3 little feet of the stand isn't very linoleum-friendly, or I'd use them in the winter also.)
Somebody mentioned kitty litter -- why not use (clean) kitty litter? It's just little granules of clay, right? I'm thinking of the cheap stuff from the dollar store, not anything with perfumes or "mystery crystals."
I've got all-day sun on my deck, so I do use polymer moisture crystals in all my pots... when it's less hot, I can skip a day of watering, and even when it's 100 degrees I only have to water once a day (without the crystals, I'd be watering twice a day and plants would still droop).
I know a great place to get bulk quantities (2 lbs, 10 lbs, or even 55 pounds which I just ordered to split with a friend) of moisture crystals: http://www.watersorb.com/index.htm. Even with shipping (included in the price), it's cheaper than buying the containers of "Soil Moist" et al. at the box store or the nursery. "Medium" crystals are the right size for containers. Don't put in more than the recommended amount -- when the crystals expand, your potting mix will heave around, or the crystals will come popping up and over the lip of the container like weird little jello cubes -- a little goes a long way.
Unfortunately, all kitty litter is not created equal. Those that are of appropriate particle size and are fired at temperatures high enough to insure stability when wet are perfectly usable in soils. Those fired at low temperatures will revert to clay and present drainage/compaction/aeration issues in soils.
Thanks for the link on the polymer crystals. I'm adding it to my FAVORITES. ;o)
Al
I noticed on the link that has the soil media porosity listings (http://www.agf.gov.bc.ca/ornamentals/floriculture/aeration.pdf#search=) that fir bark has 15% water retention and 54.7% aeration.
Would this help my ground soil in providing aeration if mixed with the soil?
Yes, both directly (physically) and indirectly (promote bio-activity), but if you are using in any quantity, even though fir bark breaks down fairly slowly, you may need to compensate for some N tie-up with extra N applications.
Al
"you may need to compensate for some N tie-up with extra N applications"
What does this mean?
Since you're asking this question about mineral (garden) soils, it is probably more a question for the Soil and Composting forum; but, unstabilized wood products can tie up nitrogen in the soil and cause nitrogen deficiency in plants. Microorganisms in the soil use nitrogen to break down the wood, making it unavailable for plant uptake. In time, nitrogen is released and again becomes available to plants. This occurs frequently with the incorporation of wood products with a high surface area to mass ratio and fresh (uncomposted) wood products (sawdust, e.g.). If you plan to incorporate wood chips (especially fine ones) you may need to apply nitrogen fertilizer at the same time to help avoid nitrogen deficiency.
Al
What about adding old horse manure, does that take care of the nitrogen?
Manure's primary shortcoming when considered for use in containers is that it breaks down very quickly, thus inhibiting drainage & aeration. Other problems include the fact that it can be too hot in containers when fresh and often contains plenty of troublesome seeds. I used to use a small amount of composted manure in containers but found it more trouble than it is worth. I abandoned its use in favor of other more reliable ways of delivering the minor elements.
Al