Both. DE dries up fairly fast outdoors. It might actually work okay if you cover the top to retain moisture as intended with SWC. I don't cover the tops /w plastic because i like the soil to be able to get air and mulch it with straw. And also i like to be able to top water to flush out excess salt build up over time. With DE added you will have to water more often. At least that has been my experience with adding DE to growing medium. No negative impacts to plants but.. soil medium dries up real fast.
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