decomposed granite as a top-dressing?

[kelc0370]

Hey there! Does anyone use decomposed granite for top dressing in their container plants? I'm asking because I have been, but it seems like after watering it forms a hard shell (almost dry clay like and it's around the base of the plant to the rims of the pot) and I'm worried air won't be able to escape therefore leading to root rot... any thoughts??

Thanks in advance!

[Minime8484]

I've used decomposed granite for top dressing, but I always sift out the fines first.

[MrXeric]

I use it all the time! You do want to rinse off all the fine dust though, or at least sift it out, or it'll act like cement when wet. I sift first to remove loose dust and fine sand, then I rinse the granite to remove the dust stuck to larger particles.

The hard "shell" top isn't a cause for concern, provided you have the right substrate for it (large-grained with hardly any organic or otherwise water-retentive materials) and keep the plants in the right climate (hot and dry). I use porous terracotta for planst with fine-grained top dressing for good measure too.

[kelc0370]

This makes so much sense! Thank you, just ordered a sifter!

[DaveW]

For all top dressings, if not already dust free, always remove the dust with a fine sieve. I sometimes use crushed granite in the UK sold by builders merchants as "quarter inch to dust". However as you found if you don't sieve the dust out it sets just like cement. The dust is not so bad using it as an ingredient mixed completely in with organic mixes which stop it setting, but in mineral mixes you also need to remove the dust or it will clog them and stop it draining.