Milk jugs or bricks to take up space in the bottom of your pots are actually better than peanuts or expanding foam. The reason is, they reduce the volume of soil that CAN be occupied by perched water. In doing that, they reduce the amount of perched water a container can hold. Packing peanuts and a layer of expanded foam at the container's bottom will simply cause water to perch in the soil above the layer of material, so all you've done is reduce the volume ov the container ...... and you can do that by using a smaller pot or not filling a pot as full as possible.

If you look at example D in the sketch below, you can see how an over-turned pot or other objects (bricks, empty soda bottles, ....) that take up space at the bottom of the pot reduce the volume of perched water a soil can hold
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Al

Hi Al,

I appreciate the advise. My objective is to reduce the volume of the pot as most plants need 12" or less of soil. Upturned pots still leave excess volume that waste soil.

What I am thinking is filling the container with expanding foam while running a drain tube to the bottom. This should resolve the weight and volume issue once and for all whole retaining drainage. The top of the foam can be shaped for drainage as well.

I have used pots of all sizes, pop/water bottles, ect. as you described for many years and I still find it messy in the fall as well as using unnecessary mix. My only real concern was whether the foam would have any ill effects on plants.

Just wondereing if anyone has tried this and more importantly, successfully.

Thanks again.

If you simply insert a drain tube, you're still just creating a smaller container. If you fashion a narrow funnel-shaped depression in the foam that can be filled with the same soil as the rest of the pot (a tapered soil column), you'll have essentially the same effect the over-turned pot offers. It doesn't matter how you get there, only that you apply the concept appropriately.

Al

expanded PU foam is inert. I have used it as mortar in koi ponds and aquariums. It will not hurt your plants at all. It is closed cell so water won't effect it. I don't get the stuff in the cans though. i use a 2 part system so that I can mix up however much I need and pour it quickly and easily. Plus, then you don't have to worry about not using the whole can and having the tube clog up. Also, you can get various densities with the 2 part.

I would put a trash bag in the pot first as a liber before using the foam. That will act as a release if you ever decide you need totake the foam out. otherwise, the foam will be permanent.

I've used canned foam for various project such as backgrounds for critter cages. I agree with nil13 that it is inert, but I have always waited a few days after using it before introducing critters to make sure that any gasses from the releasing of the foam are gone.
I like nil's idea of the trash bag too.

hmmmm.....inert or not, I sure wouldn't use that foam anywhere around my food.

Plants love carbon. Paper is made of mostly carbon. Suggest that you use torn up paper or cardboard to reduce the volume of the soil. Water will drain through and if the roots get that deep they will enter the paper. I usually break up a few twigs and mix them with the torn up black and white newspaper and card board. The wieght of the pot is much less than if you used soil.

Plants get the carbon they need from the air, in the form of CO2. In the soil, carbon serves only as a part of the bond in hydrocarbon chains. Carbon from the soil isn't used, unless the plant just happens to absorb some of the CO2 molecules that gas off as soil particles' hydrocarbon chains are cleaved by microorganisms.

Al

if PU foam submerged in acidic water doesn't effect the fish living in that water, I am pretty confident that it wouldn't effect me after growing some food plants near it and then consuming that food.

This chemophobia thing is getting out of hand.