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hairmetal4ever

temperature regulation of media and mulching...

hairmetal4ever
9 years ago

So I did a little experiment the past few days.

Despite using light colored and/or fabric pots, on a sunny, 87 degree day, the temperature of my 5-1-1 mix generally broke the 100 degree F mark 1" under the surface (it was moist, not that dry yet, I'd imagine drier would be even hotter), and was in the mid to upper 80s even at the center of the containers.

It actually seems that it was NOT the container sides getting hot, it was actually the sun directly on the SURFACE of the 5-1-1 mix that was making it hot - as the immediate insides, deep down but against the container wall was only 1-2 degrees F hotter than it was in the center.

So, I took some of my leftover pine bark, the stuff too big and chunky to make it in my 5-1-1 and mulched over top of the 5-1-1 about 1" deep. That seemed to keep it no hotter than 90-92 or so on a similar day and with a moist soil. It also seemed to keep the very top surface of the soil from drying out almost immediately.

Anyone else try this?

Comments (11)

  • the_yard_guy
    9 years ago

    Interesting information, thanks for sharing.

    I have never taken the soil temperature of my containers so I can't offer any additional information about this. My containers get direct morning sunlight until about 1:00PM, but by the hottest time of the day (early to late afternoon) the containers are in shade. They are typical black plastic nursery containers with a few extra holes drilled into the sides so I'm sure they do absorb heat until they pass into shade. How much heat I cannot say.

    I have not mulched my 5-1-1 soil with larger pieces of pine bark, but interesting idea for environments in hotter zones that get many hours of direct sun. Mulching your mulch I suppose.

    I'm wondering how much of a temperature difference it would make if you build a container soil using only Turface (or DE) and perlite? Since all the materials are nearly white and much lighter than bark I'm wondering if the light-colored materials would reflect away most of the solar heating that you are describing? I've never made a soil from only Turface (or DE) and perlite but I bet it could be done for experimental purposes with a couple of test plants.

    Might be worth a try just to see what happens.

    TYG

  • hairmetal4ever
    Original Author
    9 years ago

    Good idea. I wonder if mulching with the perlite could have some benefit for the same reason.

  • the_yard_guy
    9 years ago

    I would think that a top dressing of perlite would at least cut down the amount of heat absorption to some degree.

    However, remember that perlite is very light and would probably float to the top of the containers and wash out over the edge when they plants are watered. You would have to be very careful when watering or else your top layer of perlite would wash away in no time.

    Just thinking out loud here but I wonder if a very light colored granite, like the Gran-I-Grit brand, which is mostly white or light gray, would be of any help? The granite I use is a darker grayish color (Manna Pro) so that brand might not work, but the photos of Gran-I-Grit look nearly white so that might be something else to try. The weight would keep it in the container when watering.

    TYG

  • howelbama
    9 years ago

    You could also put the perlite in fine mesh bags to prevent it from washing away.

  • the_yard_guy
    9 years ago

    Yes that is also a possibility. if you used very coarse perlite then those mesh bags might help.

  • jodik_gw
    9 years ago

    The majority of my containerized plants are kept on the east side of a garage, so they get the milder sun of morning... by afternoon, they receive indirect light instead of the hotter afternoon sun. This keeps anything from overheating or requiring more waterings in a day than I can give.

    If a plant requires enough sun that it would heat the soil mass higher than was healthy for the plant, I would do one of two things... change the pot color to white or a light color... or plant the item in the ground instead of keeping it in a container.

  • greentiger87
    9 years ago

    Mulching with perlite does help, it's just a pain to work with because of the floating. Mylar covers, cut in circle with one slit to fit it around the stem, really, really well. It's just ugly as sin and annoying to water around.

    The best thing is to drench the containers at midday. Not practical for most people for obvious reasons.

  • greenman28 NorCal 7b/8a
    9 years ago

    Mulching with the leftover bark is a standard practice. It works quite well to improve moisture retention....or, rather, more *even* drying of the mix throughout the layers (so that the top inches don't go dry too much sooner than the lower inches).

    With a plant like a Citrus, I will often mulch in the Summer, then simply remove the excess bark for the Winter indoors to ensure that the mix dries out sooner.

    Josh

  • the_yard_guy
    9 years ago

    Josh,

    Just to clarify, when you say that "mulching with the leftover bark is a standard practice" are you referring to using the larger pieces of pine bark that did not fit through the 1/2" screen? Essentially, using those large pieces of pine bark as a top dressing of mulch on top of the 5-1-1 or grit mixes?

    Thanks

    TYG

  • Ohiofem 6a/5b Southwest Ohio
    9 years ago

    Most of my vegetables are in large black smart pots with 5-1-1. By mid to late June, the canopy of leaves keeps the surface and sides of the pot in shade all day, so I don't really worry about solar heating. I worry a little more about the surface drying out. A few years ago, I tried using red plastic mulch circles on tomatoes in pots that are 22 inches in diameter, but it definitely was a hassle to water. The stuff would float around and it was hard to tell if I watered well enough.

    I've been thinking of using a couple inches of straw on the tomato pots this year. My reasoning is that it could reduce evaporation, possibly lower soil temps and protect the plants from splashing potting mix on the lower leaves.

  • greenman28 NorCal 7b/8a
    9 years ago

    TYG, that's exactly right.
    I use the bigger pieces that don't pass through the screen.

    Josh