What variety of marigolds are they. I see some white ones and they grow tall--at least 18 ". Marigolds have a large root system especially the taller ones. I predict that before the summer is out they will have filled up those holes with roots and will be root bound. Besides that they will need water every day because they can't get it from the ground. If you really want them there I'd suggest you get a few balcony planters

never fert a new transplant... they are in shock.. not hungry ...

who knows if your experiment will work ... but do keep us posted ...

ken

BTW ... the unfinished cement might wick water out of the media.. and make it hard to water ... deeply ... in the high heat of summer ...

also ... if you repeat such next year .... trade out the media.. cement may also leach into the media ... but i doubt it will have any impact inside one season ...

ken

I've seen tons of photos on google images showing people planting marigolds in cinderblock holes so I would have hardly classified this as an experiment. We will see what happens as the warmer weather sets in.

everything you do... IN YOUR GARDEN... in your blocks.. in the media YOU chose .. in your zone... etc ...

is an experiment for you ...

i am sure. for every success you see on the web.. there were two failures .. that didnt make the web ..

do keep us posted ...

ken

one thing a good rain may have done .. is wet the cinder block ...

they have thrived so far.. congrats

ken