Answer: The answer to your question is going to depend on the amount of sun they receive and whether or not you can water them regularly and if there is concrete or soil beneath the blocks. Then you will still need to experiment a bit and see what does well for you before planting the entire area. You might also want to experiment with one or two larger containers such as half barrels instead of trying the blocks themselves, especially if it is sunny all day because that will be very hot for many plants. Some seeds to try would be dwarf marigolds or portulaca for sun, some annual plants to try for shade might be impatiens and coleus. Perennials to try might be sedums and low growing dianthus for sun to part shade, and ferns for deep shade.
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