Answer: I guess there can be too much of a good thing, but organic matter is so helpful to the soil that you can safely spread a 4"-5" layer over the top of the soil and till it in without worrying about over-amending. After planting, add a 2"-3" layer of organic matter as a mulch. At the end of the season you can dig or till the mulch into the soil. Since compost breaks down over time, you can add a similar amount year after year to your garden.
Dahlia's grow best in warm soil. Wait until the eyes on the tubers begin to show before planting them. The amended soil will make the tubers very happy!
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