Your co-worker sounds like a very savvy person. Yes, indeed, you should get some compost if you are gardening!
Compost is "a mixture of decaying organic matter, as from leaves and manure, used to improve soil structure and provide nutrients." Mushroom compost is the material used by commercial mushroom growers. After the mushrooms have been harvested, the growing medium cannot be reused so the growers sell it. We gardeners buy the mushroom compost and add it to the soil in our gardens because compost enriches our soil. If you're interested in the components of mushroom compost, here's a link to check out: http://www.americanmushroom.org/compost.htm
I love mushroom compost, but I also love the compost I make in my yard at home by piling together grass clippings, shredded newspaper, manure, vegetable and fruit scraps, and chopped leaves. This can be done even in a small area and it's free.
You might want to run a forum search on compost. You'll turn up all kinds of interesting information and suggestions!
Compost is a good addition to your soil, but have you dug in and really looked at your soil? Since for an organic grower the soil is the most important part of the garden is still baffles me that people don't suggest to new growers that they should look closely at their soil. Start by contacting you local USDA Cooperative Extension Service office for a soil test to find out what your soil pH and nutrient levels are. Then dig in and do these simple tests to really get to know your soil; 1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fillting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it it for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top. Your primary concern is the OM level and yours may be pretty good.
2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.
3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.
4) Smell. What does your soil smell like. Pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.
5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
Once you know what your soil is and has then you can properly plan what you need to do to improve it.
What you will be using in containers is much different than the soil you would grow in in the ground, although many "recipes" for potting soils do include some soil. Any compost, not just mushroom compost, will work well. Mostly probably in the past you have used a "soilless mix" and unless you mixed it your self there is little likelyhood that it contained any compost. Adding compost to your soilless mix will help a lot.
