Tuning self watering container mix wetness(perlite, vermiculite?)

14 years ago

Hi,

I've been wondering about how to "tune" the mix for an SWC to make it wetter or drier. I've only seen one thread that seems to discuss this directly: http://forums.gardenweb.com/forums/load/tomato/msg0815372312517.html, although (it may just be me) I can't seem to find a final conclusion/summary.

It seems that SWC mix needs to

1) be well aerated

2) wick well.

Below are some ideas I've picked up from googling, etc. I may be way off base, so I'd like to hear opinions/thoughts on the matter.

You can make the soil wetter by getting it to wick more, and also by adding more water retaining material to it. To make a mix wick better you can add perlite, which at the same time also aids aeration. Adding e.g. vermiculite will make the soil wetter, but would it reduce aeration?

If you want to make a "dry" mix, you could probably start with a very coarse mix (Al's Gritty?) and then add just enough perlite to make it wick.

You can also affect the wetness/dryness by changing the size of the wicking-basket opening. My suspicion is that this won't make any difference in the static case (i.e. very little or no water loss where the whole container will attain a constant wetness), but when plants/evaporation start drawing a lot a water, the larger opening will maintain wetness closer to the static case.

Now, I hope, interesting discussion will ensue :)

Regards

Neilen

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Comments (3)

sprtsguy76
14 years ago
Its the million dollar question for a lot of us swc gardeners. Raybo is trailing several combination mixes this year as well as myself. My newest combination includes 5 parts fir bark fines that are 1/4" or smalller and I would say most of it is well under 1/4", 2 parts peat and 1 part perlite. You need an ingredient that is pretty fine for wicking, some use turface. I'm using 18 gallon totes made by Rubbermaid for my swc's. I've gone from a 6 inch diameter wicking basket to a 4 inch square basket to now a 3 inch diameter wicking basket. I've tried using a more gritter mix and for me it didn't work. If you get to gritty in your mix with swc's I think you start breaking that water bond which is important in swc's. I'm now using a crf this year that is 18-6-12 at half strength. I hope to get a 'seasons' use per swc out of this crf, but just in case I dont I've got some FP in my back pocket.

damon
rnewste
14 years ago
Brick,

Finding the optimal combination of ingredients for the best self-wicking operation is a quest of numerous folks on this Site. After a couple of Seasons using "straight" Potting Mix, I have experimented with numerous combinations of ingredients (31 combinations in all), and to date, a ratio of 3:2:1 Potting Mix, Bark Fines, and Perlite has given me the best results in my SWC EarthTainers.

When I have tried Combo Mixes where the Bark Fines ratio exceeded that of the Potting Mix, I consistently ended up with stunted tomato plants vs. the 3:2:1 Mix (above).

Having said that, I am very happy that Damon, EG, and others are concurrently experimenting with their Mix ideas, and out of all the trials, we collectively should come up with the best of all trials. Going to be an interesting 2010.

Raybo
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Mark, the modified mix Al recommends is a good place to start, but are you planning on covering the container and relying upon a strip of fertilizer on the surface to feed the plants? This is critical because if you will use the cover/fert strip you really need a fast wicking potting mix and this means peat and vermiculite. What I often tell people getting started with Earthboxes where a cover and fertilizer strip will be used is that the system was designed with peat based mixes and it works very well with them so give that a try for a year. It will give you a good frame of reference for tinkering in subsequent years. Assuming you do not wish to do this then: I would encourage you to make a mix and set it outside to see if it will keep the surface moist for a couple days before committing. This is if you will use the cover and fertilizer strip. If you won't use either then Al's mix (original or modified) will work fine. Keep in mind my experience is in Wisconsin, somebody in a hotter/drier/windier climate might need to modify a bit. Even with the cover on, the wind gets under it from the holes we must cut for the plants. This wind may not seem like much, but it can quickly dry the surface. You really do need to test though, that's the best approach. Just do it outside. I say this because I made the mistake of evaluating how well various materials wicked *inside* (I was going through an endless winter and wanted a gardening 'project'). How something wicks indoors is waaaay different than how it wicks outside due to temp, wind, humidity etc. Again though, you really only need to modify Al's mix with fast wickers like vermiculite or peat if you want to use the cover and fert strip. One last tip, if you find that the very surface goes and stays dry, but an inch down it's moist you can simply bury the fertilizer strip an inch under the surface. This gives more latitude in compromising between a coarse mix that drains well and one that can wick fast enough to keep that fert strip working. Happy growing.
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sprtsguy76
14 years ago
Raybo- Check it out. So you remember I was telling you about Redi-Grow and their fir bark mulch over at Summer Winds. I dont know if you ever picked some up for trial, but it just so happens they make a much more fine fir bark mix that I think would be ideal for swc's. Its not like peat fine but fine enough to keep the water bond together yet create more air pockets then peat. Its called Turf Topper, the closest place that carries it in our area is a place over in Scotts Valley called Scarborough Gardens. Anyway I've already bought five bags and made some mix and I'm real excited about it.

Damon

Tuning self watering container mix wetness(perlite, vermiculite?)

Comments (3)

sprtsguy76

rnewste

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