Field Capacity & Dryback
How to measure field capacity, the P3 target math, and the veg vs generative dryback bands for coco and rockwool.
8 min read
Field capacity is your ceiling; dryback is your steering wheel
Field capacity (FC) is the maximum VWC a substrate can hold before it sheds leachate — irrigate past FC and the extra just runs out as runoff. FC is not a book number; it is a property of your batch of media, and you measure it with a saturation test: irrigate to heavy runoff, then record the VWC at the moment runoff stops. That reading is your FC.
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