Suggestions For 'Drying Out' Miracle-Gro Potting Mix in a SWC?

[rnewste]

Even though I have reduced the size of the wicking basket in the EarthTainer II, I am still finding the moisture level is running in the "Very Moist" range. After reading Container growing posts, I am considering trialing a mix of 2 parts Miracle-Gro Potting Mix, 1 part Floor-Dry (or Turface), and 1 part bark fines (or Lowes Soil Conditioner).

As many folks who build EarthTainers do not have the desire to mix their own 5:1:1 type of custom mixes, I need to recommend something built on a base of commercially available potting mixes, then supplement this with other additives to lessen the moisture content of the EarthTainer growing medium.

I am ready to plant out my Fall crop in several 'Tainers in the next month, and would like to experiment with a moisture-reduced formulation. Any ideas / suggestions are very welcome. I would like to include this in the next Revision of the EarthTainer Construction Guide, so many will benefit from the knowledge shared here.

thanks,

Ray

[dice]

You could try half MG, half perlite (and 3/4 MG, 1/4 perlite, for
good measure). Perlite is commonly available in big bags,
and 3rd worlders will quickly figure out that it is basically
lightweight volcanic sand.

A pricier alternative would be to substitute pumice for
the perlite. (Not usually a big box store item.)

[rnewste]

dice,

Thanks for the reply.

So here is a "visual" on my situation:



Two separate issues. One, my potting mix is running too moist, even though I had reduced the size and height of the wicking basket this season. Two, I added Dolomite Lime PLUS Epsom Salts this season, and I am getting a reading of about 5.7 on the pH Meter. Last season, I was getting a reading of 6.4. So, I need a suggestion on how to reduce the acidity of the mix to the proper range.

The more serious issue is how to get a "blend" of the Miracle-Gro potting mix with another commercially available amendment to have a better drained composite mix. I found this mix at Lowes today, and I am thinking about blending 1 cubic foot with about 2.5 cubic feet of the original Miracle-Gro potting mix.



Here is a close-up of the ingredients:



I am a bit concerned about the "sand" content in a SWC type of eco-system, but I am willing to experiment with any additive to reduce the moisture retention of my blend. What do you think?

Overall, the tomato plants are doing fine, but I would like to have less leggy, more robust, healthy foliage top to bottom:



Ray

[dice]

I did think of cactus mix, but I did not know if it would be
available in large enough quantities or what it would cost
(SunGro has a cactus mix that only comes in 4 qt bags,
for example). Anything that takes up space and allows
good drainage without absorbing water should lower
your moisture levels, hence the perlite suggestion.
(I am thinking bark fines may soak up water pretty well.)

The pH looks like you need another cup of lime in those
31-gallon containers.

Mine are running in the wet range this year, but a couple
of ticks lower than pegged, and pH is 6.2-6.8, depending
on which container it is. The plants seem healthy enough.

Edit:
Some bark sheds water initially, but it may revert to a normal,
water-holding hunk of compost-like organic matter as
it decays.

[dice]

[pH]

The fastest natural fix for low pH is usually wood ashes. You
could mix up a cup or two (not very dense) with water and add
to the reservoir. You probably want to work up in stages: try a
cup, test in a week, test again a week later, decide if it needs
more, ....

(It is a little late in the season for a cup of dolomite to do much
for you, because of the 8-week breakdown time.)

I do not know where you find wood ashes in your part of
California in mid-summer (no one is using a wood stove,
even if they have one, burn bans at campgrounds, etc).
Ash from burnt newspaper would probably substitute
without problems, but unless it happens to be raining
(not likely), I do not know where you could burn a pile
of newspaper around there without potentially getting
arrested for violating a burn ban.

This stuff might break down faster than 8 weeks:

http://www.groworganic.com/item_F157...on_Grade_.html

For a really quick fix, there are also the liquid pH adjusters for
the hydroponics industry:

http://homeharvest.com/hydroponicphadjusters.htm

ProTekt seems to be popular for a variety of uses, but
I do not know how cost compares to some of the granular
products there. I seem to recall that you have a family
member experienced with hydroponic products. What would
he recommend?

[rnewste]

dice,

Did I make a MISTAKE by adding in Epsom Salts this season? I didn't add this last year, and I had a more desirable pH level of 6.4 then. I see others suggest adding in Epsom Salts to containers, but if this is lowering the pH, then it is probably something that I should not do next year.

Ray

[oc tony]

I'm just guessing but it might be the forest products in the cactus mix. I've read that the people in Maine do not like to use sawdust in their gardens because it turns the soil acid. If you have any cactus mix left put some in a small pot & keep it watered and test it over the next week or two.

[dice]

(I do not think he actually used the Cactux Mix yet, he was just
wondering how that might work to reduce the moisture holding
capacity of the MG potting mix.)

Another thing that you could try for the moisture levels is a
container with all Cactus Mix. It usually drains a little too well
for ordinary containers where the water drains out at
the bottom (unless you are growing succulents, palms, etc),
but that might not be a problem in a wicking, self-watering
container like the Earthtainers.

Epsom salt does not lower pH. I read in passing somewhere
that epsom salt had a "slightly alkaline effect", but most
places where it is mentioned it is considered a pH neutral soil
amendment (not enough affect on pH to worry about if used
in moderation). I do not see why one would actually need
epsom salt if using dolomite, but maybe the magnesium in
the epsom salt covers the plant's need for magnesium for
the first couple of months while the dolomite is breaking down.

A note on those pH meters: I have one of the Rapitest meters
with the probe on a little cord. I just checked it in a hot tub,
and it reads pH 5.8 for the water in the hot tub, while a
Kem-Tek test strip reads pH 7.2. Looks like I need to check it
with some neutral calibrating solution and see how accurate
it is before relying on it in the garden. The worst part is that
if it is not accurate, the amount it is off by is not necessarily
linear up and down the pH scale. (It could read 6.0 when the
pH is actually 7.0, off by one full point on the pH scale, but
read 5.5 when the pH is actually 6.0, only off by half a point
at a different place along the PH scale.)

[rnewste]

dice,

I will try the all Cactus Mix in one 'Taner to see how it wicks, at one end of the spectrum, then do a 1/3 Cactus Mix with 2/3 Miracle-Gro potting mix in another 'Tainer to then compare results.

These moisture and pH meters are not good to rely on for absolute readings - -but I like to use them to gauge "relative change" as an indicator from one experiment to the next. It was interesting in the 'Tainer where I did not add Epsom Salts that the pH was reading 6.4 just now. Again, no faith in absolute numbers, but it indicated to me that the Epsom Salts in the one 'Tainer *may* be the cause as to why I am getting a lower reading on the scale in that one 'Tainer.

Ray

[Barbee]

Ray,
I use a sterile mix in my containers that is for tobacco seedlings. It is used in the tobacco float trays to start seeds. A tobacco float tray is a plug tray that floats in a water filled basin. It is very light and fluffy..lots of perlite plus ferts added in. So you might check out some soiless mixes that are used in hydroponics to mix in with your MG potting mix. I'm not sure if Lowe's/Home Depot type stores carries the stuff though?

[rnewste]

Barbee,

Thanks, I hadn't thought about going to a Hydro Shop and researching their grow media.

I am tempted (again), to reduce the size of the wicking basket to a 4 inch square one, with a 3.5" by 3.5" opening in the aeration bench, as a simplistic approach to continue use with the standard Miracle-Gro potting mix, to try to constrain the flow of moisture up into the SWC. But at some point in reducing the opening of the orifice the 'Tainer might not fully wick properly, and areas of potting mix may run dry.

I guess I would rather find a potting mix (or a blend of two) that will exhibit the desired saturation characteristics ideal for tomatoes. Darn Hobby!!!!!

BTW, The Peppers and Corn both love the current design's moisture eco-system!

Ray

[dice]

A home brewing site claims that epsom salt does acidify
a solution, so my previous information on that could be
incorrect (it may depend on what other nutrients are
present in what concentrations, too). I guess you could
test easily enough. Get a gallon of distilled water, and
test it with your pH meter. Add a tablespoon of epsom
salt, and let it sit overnight. Then test the water again
with the same pH meter.

Edit:
Note that the effect of epsom salt on soil pH is still not
a question with a simple answer, regardless of what effect
it has in distilled water.

Say you have a soil with plenty of magnesium, more than
the plants need, but the supply of sulfur in it is barely
adequate. The plants are using up magnesium at whatever
rate they find convenient, but they are scavenging every
bit of sulfur they can find, because it is part of their nitrogen
metabolism (plus it has other roles in the plant).

You add espom salt, MgSO4, and it breaks down to magnesium,
sulfur, and oxygen. The plant immediately uses up the new source
of sulfur, because it has the capacity to take in more than the soil
has available. But the magnesium is left behind, because the soil
already had plenty, and the additional magnesium released by the
epsom salt *raises* soil pH (makes it more alkaline).

Now take the opposite situation, a soil that had more than enough
sulfur but the magnesium supply was less than the plant could use.
The added epsom salt again breaks down to magnesium, sulfur, and
oxygen, but this time the plant immediately makes use of the additional
supply of magnesium, because it was not getting enough before
adding the epsom salt, but the additional supply of sulfur is left
behind in the soil as excess, and the added sulfur *lowers* soil
pH.

So epsom salt can lower or raise the pH of your soil or container mix,
depending on the relative balance of magnesium and sulfur in the soil
before adding the epsom salt. (Other things like iron and aluminum
can play a role, too, but those are more complicated interactions.)
If you added epsom salt and your container mix pH dropped, then most
likely your supply of sulfur was already more than adequate while your
supply of magnesium was limiting.

[rnewste]

Wow dice, we've got to get you a Guest Shot on "CSI-Miami".

Excellent observation!! I would need to statistically test a few more 'Tainers "with" and "without" the Epsom Salts, but you are on to something from my single 'Tainer pair comparison.

Ray

[kevokie]

Ray,

I have definately seen the pictures of your tomato plants, and I am green with envy! As a matter of fact, I look up your pictures for inspirational purposes.

Anyways, on your fine tuning quest, have you tried any different potting mix that is out there? I've seen mention of Scott's, and I've seen in some of your pictures a bag of Sta-Green(?) I think. I've been trying to brainstorm things that could be added to the mix in order to tweak the moisture level. Other than what is already mentioned, I come up with plain ol' sand or some kind of gravel. Of course, sand was mentioned earlier but I am not sure what problems it would pose. Then, there is the whole, "does this throw the pH off much?"

How much of an effect on the moisure level do you think the mulching aspect creates? What I mean is, if you removed the plastic mulching from the top, would that help with the wetness of the mix in the 'tainer? Could it be better to just use a bark type mulch or even straw mulching and eliminate the plastic all together?

Just my thoughts.

[rnewste]

kevokie,

Wow, we are on the same wavelength today!! Just came back from Lowes with 4 bags of their Sta-Green Potting Mix. I recalled when I used it last year that it had a larger particle sized composition than the Miracle-Gro. What I am learning now is that larger particle size media will lessen the moisture content, so will give this a try in a 'Tainer later today.

I am also going to load up a 'Tainer with the Cactus Mix to evaluate wetness although, I am a bit concerned about the sand component of the Mix. Again as above, the smaller particle size of the sand will actually cradle more water (think of walking on the beach on the shoreline, and how saturated that sand is when you dig into it). The sand might be good at draining a traditional container with top down watering, but how it will impact "bottom-up" capillary watering in a SWC is to be determined.

Regarding your suggestion of removing the plastic mulch, that is EXACTLY what started me off on my quest to "tune" the moisture content of the potting mix. I planted a pair of Big Beef some time ago and left off the moisture barrier. These two plants are the healthiest in my entire 'Tainer Farm today:



Green foliage from bottom to top. No "leggy" vines, etc. Perfectly shaped tomatoes. My other Big Beef with the moisture barrier has wilted branches at the bottom, and the fruit are heavily lobbed. The only downside of leaving the moisture barrier off (two actually) is that the 'Tainer will use more water per week due to evaporation give-off, and the fertilizer strip running around the top of the 'Tainer would not make good moisture contact to disperse throughout the 'Tainer.

I can bury the strip deeper into the potting mix as an option, but again, I would rather keep the moisture barrier and instead focus on controlling the top-to-bottom moisture within the 'Tainer by blending a combo-mix to give the desired "Moist" reading on the meter, and not just have the top 3 inches being drier.

I have also just purchased a couple of 2 cubic foot bags of Perlite to also blend in with the original Miracle-Gro potting mix. Not sure of the ratio that I should use, so it will be trial and error for a couple of iterations. Fun stuff!!

Ray