I too had some odd green tiny mushrooms sprout in my seed starting mix. It was probably due to the richness of the soil and the compost that was added. I would pull them out of the soil when you see them. Since my seedlings have taken over and are now uncovered to allow them to grow, the mushroom population has dropped due to a drier soil. Any mushrooms growing in seed starting soil will take away nutrients from the plants.

No, no, no. :) Leave the mushrooms. Mushrooms are decomposers, they break down organic matter into nutrients your plants can use, they don't use them themselves. Much of what happens in a compost pile is the work of fungus' including mushrooms. If you have some growing alongside your plants that means there's most likely some organic matter in the compost or potting soil that wasn't completely broken down before hand. Don't worry about the mushrooms robbing your plants of anything, they're actually doing just the opposite.

I must assume that all mushrooms do the same thing. The only thing I wonder is when I grow mushrooms from a store bought kit that has 10 inches of 'stuff' in a big cardboard box and a thin layer of peat moss on top, they said to dispose of the medium as its been spent of all nutrients. The 'stuff' looks like semi composted manure. I plan to toss it into my compost pile though, but thats after I don't see any white mushrooms sprouting anymore.

My mushroom experience is very limited, however due to some recently popping up in my yard I've been doing some reseach. From what I have read, there are hundreds of mushroom varieties, making a positive identification very complicated. From everything I've seen though, color (esp oranges and reds) in mushrooms is not good- seems a lot of the poisonous varieties are colored. Also, their common place of growth can be inconsequential (e.g. the woods), because sometimes even if you have a lawn, an old rotting piece of wood under the ground can be a starting ground for mushroom fungus that will eventually sprout to the surface. On the other hand, I've only just begun learning, so don't take my word for it-- I would just suggest that you avoid eating them and not let any pets around them either (since they sometimes lack common sense when it comes to mushrooms- hence my own sudden interest in them).

Here are some websites I found helpful:

http://www.naturallist.com/fungipoi.htm
http://www.conservation.state.mo.us/nathis/mushrooms/mushroom/

NoelleQ: Pull them if you want- but what causes damage will still be lurking below. Think of mushrooms being an apple. The tree is in your soil. and consider cleaning or getting new packs / soil. Most likely they will only help your soil but some are very aggressive and could eat plants. With delicate seedlings you might want to microwave or bake your moist soil prior to use. If you find them in your garden area, make the environment a better place and leave them.

Ksrogers: the mushrooms in your kit ate all of the nutrients they needed- like various sugars and minerals and proteins. Whats left is what plants like: NPK. Also other things (unused sugars, minerals, proteins) are in a more useable state for plants and other garden friends like worms. And here's a hint: do some research on the variety you are growing. If you put it in the right kind of compost at the right time you may get some extra crops.

"From everything I've seen though, color (esp oranges and reds) in mushrooms is not good- seems a lot of the poisonous varieties are colored"

This is really not the case. There is no way to determine the toxicity of a mushroom without knowing what it is. Some of the more toxic species I can think of are not particularly colorful.

Though I think there are a couple fairly common (in yards) species of Amanita that are attractive to dogs and toxic enough to harm them, many more pets die from pesticides, antifreeze, and even plants, than die from ingesting mushrooms.

Also, I find it curious that some folks who won't tolerate mushrooms in the yard that may be a bit toxic, have no problems with toxic plants in the garden. If one were to start randomly sampling mushrooms and plants on my property, they would surely die first from plant poisoning, what with the digitalis, castor, and datura I grow...

found this via google and it's exactly what i needed. little mushrooms started popping up in my seedling trays as well. after reading these replies, looks like it would be best to leave them in.

thanks!