Using a single cinder block as a heat sink/planter for eggplant?

16 years ago

Hello everyone...

I garden in a small (100 ft^2) city plot in the Pacific Northwest, USDA zone 8. The temperatures in the summer generally stay in the high 70s to low 80s for most of the summer (June through early September), and night time temps range from low 50s to low 60s for much of the summer.

This year I planted some eggplants, and while most of them survived and managed to produce fruit, they did not get very big, and were not very prolific (I will still get maybe 3 or 4 tiny eggplants before the end of season- these are Asian variety eggplants). So I have been trying to come up with a way to grow them next year that will keep them warm (eggplants need night time temps of 60 F or better to do well) and healthier without much fuss.

Beyond the normal measures of putting down hoop houses and using plastic mulch to heat up the soil, I had another idea: there are a lot of discarded cinder blocks around, so I thought that maybe planting eggplants inside the blocks themselves (NOT in a raised bed, but one plant per block, inside the hollow space in the block) might help keep the roots warm.

I recently gathered two 7 1/2 x 7 1/2 15 inch blocks, with 1 +inch thick walls. What I would do is knock out the piece of concrete that divides the cinder block in two, leaving basically a hollow square of concrete. Then I would simply place this directly on the ground with the opening running vertically, fill the block about 2/3rds or 3/4th of the way with soil, and plant my eggplant transplants inside this soil when the normal planting time arrives. Since the hollow space in the block would not have a bottom, the roots would eventually be able to grow down into the ground itself. The idea is that the cinder block would absorb heat from sunlight during the day which ought to provide a better climate for the young eggplant. I though about possibly painting the block black to help it absorb more heat, though I suppose that this might be overkill. Also, slugs are a huge problem around here, and it would be easy to put barriers/traps/slugicides around the wall or rim of each block to keep them at bay.

On the one hand, I known that the block would absorb a god deal of heat, but would the setup allow it to really benefit the plant? Also, I am concerned that maybe the earth inside theblock might get too hot. Also, would the soil inside the block drain quickly of water and nutrients? Would the space inside the block be too narrow for the plant initially? Are there other issues that I am not aware of?

If anyone has any comments about this idea, let me know! I suppose if it hasn't been done before, I could give it a try and post my experience here. Your ideas are appreciated.

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Comments (5)

fishymamas
16 years ago
Well, I grow garlic, shallots and herbs in my cinder block holes, so I can tell you that in zone 9 it's not too hot. I say try it, and let us know.
murphy_zone7
16 years ago
Plantslayer, I say go for it. I can share that I planted bell peppers in the holes of cinder blocks this year. They did better and produced more than the plants in the SFG. So much so, that next year I am going to use the cinder blocks for all my peppers. I dropped a broccoli seed in two of them last week and they are already up and growing. I am in upstate SC and we have had major drought conditions all summer and those peppers are still producing.
Good luck and let us know.
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One thing you would have to deal with is the extreme drainage. Water seeps out of/is wicked away by the cinder block, or most cinder blocks anyway, the $2 masonry blocks. Thus I think that growing a plant in that narrow cinder block column would not work well unless you do something to counter-act this, and even then I think that the long narrow column would be kind of hard for the plant to get used to. I want to try growing hot peppers in the blocks, because I am hoping they will serve as a good heat sink and help keep the plants warm. In my case though it will be just a single block buried halfway in the ground.
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slashy
16 years ago
Tell me about your cinder blocks! I just used a bunch left over from a construction site across the street to actually construct my (as-yet-unfilled) raised garden beds, so my beds are literally framed by cinder blocks, with all that added extra space for planting. Also if I had a good use for them I could easily acquire more. I was only planning on putting herbs & small flowers in the cinder block spaces, but would love to hear more about what people have grown successfully in them.

Also how big are the cinderblocks you're using? I have two types- all the same length (about 40cm per block/20cm per opening) but different widths (10cm for some, 20cm for others). I would've thought that even the wider ones would be too small for something like bell peppers or eggplants but if it's been done successfully I'd love to try it!
patapscomike
16 years ago
I did this with marigolds as a border around a raised bed this summer. Even with soil on one side they dried out really, really fast- in less than a day the soil was bone dry. I was watering them twice a day when it was really hot out.

And while they will warm faster during the day than a plant in the ground, they will also cool off faster at night.
pjintheozarks
16 years ago
I accidentally had a bell pepper grow in the 8" x 8" square in one of my cinderblocks. I'm not sure how deep the roots were, this was in a very raised (24" in that case) garden wall. It was much smaller than the others, both in plant and fruit and yield -- but it grew and fruited. (It was actually really adorable. If someone only wanted a small yield and wanted to keep a plant short to prevent shading to grow other things behind it, it would be an interesting method.) I don't know about the cinderblock making the soil warmer, but I do know it's likely to make the soil in that part dryer.

Using a single cinder block as a heat sink/planter for eggplant?

Comments (5)

fishymamas

murphy_zone7

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