I only use cedar mulch to line the botton of large pots and to mulch the surface of the soil when growing my paeoniifolius'. I improve standard potting mix drainage using extra perlite and sand, and triple phosphate. Additionally, I set the bottom of the bulb on pure sand and cover the top, in a general cyclinder shape, directly above the center of the tuber, at 50% of the tuber diameter, up to the surface of the soil with straight perlite. This area seems most likely to rot. When I water them I never water in the center, only around the sides.

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