Answer: According to John Hart, soil scientist with the Oregon State University Extension Service, Mushroom compost can supply nutrients and increase the water-holding capacity of the soil. But mushroom compost can be too much of a good thing for seeds, seedlings and young plants, says Hart. "The soluble salts and other nutrients in fresh, undiluted mushroom compost are too concentrated for germinating seeds, young plants, and other salt-sensitive plants including members of the heath family such as rhododendrons, blueberries and azaleas," said Hart. To avoid killing germinating seeds and stressing heath family members, Hart recommends mixing mushroom compost with garden soil before using it on young plants. Or, order a supply of mushroom compost in the fall and let it sit uncovered, to "cure" over the winter. Dicentra prefers acidic soil and mushroom compost tends to be alkaline so I'd amend the planting bed with peat moss before planting Dicentra and using mushroom compost.
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