The main danger of using mushroom compost is that it may contain a high level of various salts. All members of the ericacea, including rhododendrons and azaleas are very sensitive to the presence of salts. pH is another issue - some mushroom composts are too akaline for azaleas.

If what you used is a bagged, commericially available product you may be able to contact the provider and find out about salt content and pH. If they are within acceptable limits, you won't have to do anything. If they are a problem, you'll probably need to remove the azaleas and replant into something more suitable.

Hi, thanks for the info. Unfortunately, what I got was not bagged. I didn't plant them in it, I used it for mulch around them. So I guess I should pull the mulch away from the plants to be safe. Do you have any idea how far I would need to pull the mushroom compost away from the azaleas? They are planted around the edges of a large bed under 2 trees in my yard, and I've already mulched almost all of it (probably about 4 yards of mulch). I'd like to just pull it back from the azaleas and keep it for the rest of the bed. I guess here is my main question:

How far back from the plant do you think I need to pull the mushroom manure to be reasonably safe for the azaleas?

Thanks very much. I just can't imagine taking it all off the bed. I'm usually so much more careful about this stuff but my neighbor uses mushroom compost and she has azaleas, so I didn't think about it. But hers are very old and probably more hearty.

Vanessa

Pennsylvania has a rather large mushroom industry. Penn State University has invested a fair amount of time studying uses for spent mushroom substrate (mushroom soil).

NUTRIENTS: Mushroom compost contains an average of 1.12 percent nitrogen in a mostly organic form that slowly is available to plants. Also, mushroom compost contains an average of 0.67 percent phosphate (phosphorous) and 1.24 percent potash (potassium), as well as other plant nutrients such as calcium (2.29 percent) magnesium (0.35 percent) and iron (1.07 percent). If sold as a fertilizer it would be a 1.2-.7-2.3 (NPK) fertilizer. The average pH of mushroom compost is 6.6 (6.0 to 7.0 is an ideal range for most plants). Rhododendrons and azaleas like 5.0 to 6.0.

SALTS: Because of the pH and salts, it is recommended to use the spent mushroom soil as a soil ammendment for turfgrasses. When incorporating spent mushroom soil as a soil ammendment, the recommendation is a layer of 1 to 3 inches mixed into the soil. Since some plants and garden vegetables are sensitive to high salt content in soils, avoid using fresh spent substrate around those plants.

WEEDS: Prior to removing the compost from a mushroom production house, the inside of the house is steam-treated (i.e., pasteurized) to eliminate any pests, pathogens or weed seeds. In the past, lawn and garden centers often advertised "mushroom soil," which essentially had been sitting outside in a pile for one or two years and had accumulated air-borne weed seeds (such as lambsquaters and velvetleaf). Then, when this compost was tilled into a garden, those weed seeds would emerge with a vengeance. Insist on a uniform and quality mushroom compost that has been pasteurized, processed, and properly stored to ensure no contamination from weed seeds.

MULCH: Research at Penn State has shown that blending used mushroom compost with a shredded wood landscape mulch at about 40 % will greatly suppress artillery fungus sporulation. Mushroom compost is very "green" and environmentally friendly.

We have a fairly large mushroom industry here too, OSU is somewhat conservative in their recommendations for the byproduct - the compost.

Here is a link that might be useful: OSU Mushroom compost