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gojosan

Attn: Al: Amending youir mix for semi-arid/drought conditions?

gojosan
15 years ago

Hello Al!

I have really enjoyed reading your posts, they are very informative and you have a way of explaining it well. If you have a minute I'd appreciate some assistance.

I live in an area (about 36degrees N lat.) where it is semi-arid and we are under drought like conditions near the middle/end of summer. Because of this I want to limit the frequency and amount I water my plants (seasonal veggies, tomatoes, peppers, etc). I do want to limit the water usage but I don't want to inhibit good levels of air/water exchange in the rootzone. I want to amend your base mix to retain more moisture but without causing reduction in rootzone health.

I would like to limit the watering to once a week or so. I am using 15 gallon containers (about 2.25 cu ft) which will be in full sun all day except when shaded by the growing plants. Im going to have a few veggie plants in each container.

I am going to mulch the top of the soil in the containers to retain more moisture. I'm also going to pile a little wall of indigenous soil around the containers. Then I'm going to seed the indigenous soil with drought resistant native grasses. Buy piling and seeding the indigenous soil around the outside of the container I am insulating the soil and helping keeping an even, cool temp in the rootzone...not to mention the "insulation" should help retain more moisture. Finally I'm going to add a "wick tube" or two to each 15 gallon container. Please see this thread for info on a wick tube:

(what is the proper HTML code to insert a link?)

http://forums2.gardenweb.com/forums/load/contain/msg050146536217.html?1

If you were to amend your mix for semi-arid, occasional drought like conditions what would you add? I was thinking about using the following mix but I'm concerned there will not be enough air exchange due to the earthworm castings and extra peat/coir.

Amended "Al's Mix" Proportions:

5 parts pine bark fines

2 parts fresh earthworm castings

2 part coco coir or peat

1 parts perlite [large sized particle]

garden lime (or gypsum in some cases)

Amended Big Batch:

3 cu ft pine bark fines

10 gallons e.castings

10 gallons coir or peat

5 gallons perlite [large sized particle]

3-4 cups dolomitic (garden) lime (or gypsum in some cases)

On a side note:

What effect does pine bark fines have on soil ph and microorganisms? Does the pine bark enrich the soil at all or is it just for soil "body"? I use homemade ACT and AEM (aerobic and anaerobic beneficial microorganisms) to inoculate my soils and along with my watering/nutrients; will the pine effect microorganisms?

I found "mini pine bark nuggets" at Lowes, I assume they are the same as "fines"?:

http://www.lowes.com/lowes/lkn?action=productDetail&productId=97822-66882-97822&lpage=none

What do you think about coco coir to replace peat?

Peat:

I am not concerned with the peat breaking down as I'm only growing seasonal veggies like tomatoes, peppers, etc. Peat is supposed to absorb water more readily than coir in general. But as you've mentioned it's all about the 30% moisture content; I guess they both with be hydrophobic at that point (which I hope I wouldn't get to!). I do have some organic yucca extract I can use to in either case, if peat or coir is not very permeable I could use the yucca.

Coir:

I like it more as it is more environmentally friendly, has better water retention, holds more air then peat, doesn't break down as quickly or turn to "soup", provides a better home for microorganisms and especially fungi and is more ph neutral around 7ish.

P.S.

Just wanted to let you know I was going to use "ProMix" or "SunShine Mix" this summer but they are like 80% peat. After reading your posts on particle size, etc, I decided I should go for your mix. I am just concerned about the water retention issue...but besides that you've made me a believer!!! Thanks a ton :-)

Comments (9)

  • zubababy
    15 years ago
    last modified: 9 years ago
  • gojosan
    Original Author
    15 years ago
    last modified: 9 years ago

    thanks zubabab!

  • gojosan
    Original Author
    15 years ago
    last modified: 9 years ago

    :-)

    OK, I found a source for aged pine bark fines in my area. Just in case anyone was interested in the difference:

    Pine bark fines = 1/2" or less

    Pine bark mini-nuggets = 3/4"-2"

  • justaguy2
    15 years ago
    last modified: 9 years ago

    To give you my honest opinion you are probably going to do just as well buying the Pro-Mix and tossing it each year.

    Why?

    Because in your [understandable] quest to extend the watering interval you are adding such a high percentage of small particles that the benefit of the larger particles is lost. Those small particles are just going to settle in around the larger ones, filling up the air spaces.

    The other part of the reason is you are growing veggies which are short season and among the more tolerant of plants when it comes to handling the lower oxygen/higher water conditions. Don't misunderstand me to be saying it is ideal, just that veggies, for the most part, are tolerant enough to deal with it and still yield well.

    Here is the thing about your quest to maintain good aeration while extending the watering interval. It can't really be done beyond a certain point. For example you could do it to a small degree by replacing the perlite with Turface MVP. They serve the same purpose, but between the 2 the Turface will hold more water than the perlite and neither will collapse into smaller particles any time soon.

    There is another part to the equation though. How much air a mix can hold is related to the space between particles. Regardless of how many air spaces there are and their size, the air gets stale due to the roots polluting it, primarily with CO2. The only way to drive that stale air out and get fresh air in is by watering. The water pushes the stale air out and draws fresh air in. This is why we can only maintain good aeration AND extend the watering interval to a point.

    A good solution in your case might be a self watering container, perhaps even with an automatic top off valve. The addition of an auto top off valve means you don't have to worry about watering and it will only add water to the extent the plants use it making it the most water wise approach there is to container gardening. This isn't necessarily a low cost option, but it is very water efficient.

  • gojosan
    Original Author
    15 years ago
    last modified: 9 years ago

    Great info justaguy2, thank you!

    I am truly impressed with the depth of knowledge and the willingness to share on this forum.

    I like the idea of an auto-watering system, I was reading up on jmalt31's thread "New improved homemade self watering container / Earthbox". Very interesting concept and it doesn't look like it's too expensive.

    One thing I forgot to mention is the soil where I live is actually about 2" of forest/pine humus on top of 100% red clay. So thats why I'm container gardening. That said, I am fortunate because the water level is VERY high, to about 1' of the soil surface.

    The problem is the water is full of clay, does anyone have info/experience with high clay ground water? I am going to dig a hole beneath each container and bury a few nylon ropes (loosed and un-twisted) about 2' deep. then I'm going to bury the other end of the nylon ropes within the soil in my container. This should wick up the ground water and act as an auto-watering system. As a side benifit the wicking action of the nylon will filter all the clay particulate out of the water so it's free from clay particualte when it reaches the plant ;-) . However, I'm still a bit concerned there may be other aspects of the ground water which may be harmful, any opinions?

    Thank you

  • justaguy2
    15 years ago
    last modified: 9 years ago

    Ah, I wish I would have known these would be buried (in a sense) containers, it makes a world of difference.

    Your wicking idea to draw up ground water sounds ingenious and I would love it if you would post back later in the year and let me/us know how that works out for you.

    Given that you will be joining your container to the earth, my above comments are not as relevant so don't worry about it. The only thing I am somewhat uncertain of is joining the container to the earth only via a nylon wick. I have no experience with this so really can't comment.

    From playing around with the concept of capillary action my only concern is that the wick may not be able to move water upward fast enough to replace what the container uses. I really can't comment on that though as I lack the direct experience. I don't have such a high water table, nor do I deal with arid conditions. Still, it sounds like you have thought this through pretty well and all that remains is some experimentation.

    Good luck and happy growing.

  • gojosan
    Original Author
    15 years ago
    last modified: 9 years ago

    Hi again JAG2!

    Your wicking idea to draw up ground water sounds ingenious

    Thank you. The idea was actually from a friend of mine but I thought it was a great idea too :-)

    One thought I had is that the wick system draws water up. I wonder what effect this will have on Co2 in the rootzone? If I only water the top of the containers (eg. "soil drench") a few times a month will I be promoting Co2 toxicity in the rootzone?


    ...and I would love it if you would post back later in the year and let me/us know how that works out for you.

    I will definitely do this for you!


    Given that you will be joining your container to the earth, my above comments are not as relevant so don't worry about it.

    In what regard? Do you still suggest I use ProMix? Or are you referring to the auto-watering system?


    The only thing I am somewhat uncertain of is joining the container to the earth only via a nylon wick.
    [snip]
    From playing around with the concept of capillary action my only concern is that the wick may not be able to move water upward fast enough to replace what the container uses.

    Me too! ;-) So that's why I'm going to add at least two "wick tubes" to each of my containers. Another thing I'm going to do is "rain scape"[1] my containers. If all else fails I can hand water them from above (if I have to do it the old fashioned way ;-) )

    I will be feeding with nutrients via. hand watering by soil drench about twice a month. I hope the soil drench once every few weeks will expel enough Co2 from the air pockets. How long does it take for the rootzone to become Co2 toxic (for lack of a better term)?


    Still, it sounds like you have thought this through pretty well and all that remains is some experimentation.

    Thank you. And thank you for your assistance, your further thoughts and opinions are very welcome!


    [1] "Rain scaping" (my own term, I don't know real title) is big in Ethopia where they simply make two "mounds" of soil about 5-20 feet uphill (does not need to be steep) jetting outward at opposite 45 degree angles from the container/plant. All this does is funnel the rain water towards the container/plant. In Ethiopia they make a little moat around the container/plant by encircling it with the dirt mount thus allow the water to gather and slowly be absorbed.

    Heck, it may be a good idea to put piece of "capillary mat" under my containers with about 2-3" extra on all sides. I can encircle the "moat" around the capillary mat which should help the plant absorb the rain water more effectively with less run off and wasted rain water...Yah, natural passive hydroponic outdoor container gardening! :-)

  • gojosan
    Original Author
    15 years ago
    last modified: 9 years ago

    ...actually that should be natural passive watering of outdoor container gardens! :-)

    :-P

  • justaguy2
    15 years ago
    last modified: 9 years ago

    One thought I had is that the wick system draws water up. I wonder what effect this will have on Co2 in the rootzone? If I only water the top of the containers (eg. "soil drench") a few times a month will I be promoting Co2 toxicity in the rootzone?

    I really don't know. This is what happens in a self watering container and while I am certain there are physical laws governing what happens, I do not understand them as well as I need to right now. I understand what the downward and outward movement of water does in regard to drawing air in, but when the water is moving in from the bottom I don't really understand what brings the fresh air in. If you find a credible answer, please let me know. In what regard? Do you still suggest I use ProMix? Or are you referring to the auto-watering system?

    Again, I really do not know. If your container was open bottomed and in contact with the earth I wouldn't really care what you used for a growing medium within reason because the earth would handle the movement of water and air, but given that it is just a couple of wicks joining the container to the earth and you have a high water table with an arid atmosphere I really don't even want to guess what will happen.

    Like I said, it appears you have given this a good deal of thought and I can't spot any obvious problem with your plans. If it were me I would be in the same place you are. Trying to gain a better understanding of the relevant factors while at the same time putting my present understanding into action and observing how things work out.

    As a result I hope you do post back how things go. Your experiment is something I can't do myself as our conditions are too different.