Every kit out there tells you that it will last for 4-5 fruitings, and then you have to buy another kit. A FEW companies will own up that you can toss the spent kit into a compost or sawdust pile and continue to harvest mushrooms seasonally outside. What they don't want you to know though, is that you CAN keep them going indefinitely.

Actually, I think most companies that sell mushroom kits DON'T EVEN KNOW THIS.

There is really only one reason why mushroom kits run out and stop fruiting.

Lack of Nutrients.

The mycellium grows through the media - the sawdust, log, or compost (you WEREN'T using toilet paper, or coffee grounds, or industrial waste, were you?). It consumes nutrients as it goes. It fruits abundantly as long as the food is abundant. When it starts to run out, the mushroom will desperately fruit another time or two - a few last gasps at reproducing itself before it dies. If you don't offer it more food, it will die.

So... how do you offer it more food? How do you get MORE mushrooms from that bitty kit in the first place, and how do you get it to KEEP bearing even after the original kit is finally used up?

There are two strategies that you can use. One keeps it bearing longer, the other converts it into a new mushroom kit.

Let's cover getting MORE out of that kit to begin with. This trick works BEST with compost mushrooms, but will ALSO work with log or sawdust mushrooms.

1. Make a gallon of manure and compost tea. You need composted manure, and you need finished compost (DO NOT BUY MUSHROOM COMPOST! This is just compost that mushrooms have already used up, that isn't usable for this purpose.). Mix about 1 cup of manure with about 9 cups of compost. Stir it around with a wooden stick or a trowel until they are blended. Put ONE CUP of that into ONE GALLON of water. Stir it well. Let it sit overnight. The solids will settle to the bottom and you'll have some grungy looking water. THAT is manure and compost tea.
2. After your mushrooms fruit for the first time, when the last of them have been picked and the mycellium is resting, water well with the manure tea. For compost, soak it TWICE - once as soon as you know the fruiting is done, and then again about three days later. For logs or sawdust, water as much as STAYS ON OR IN IT. Do that DAILY for about a week, right after you know that the fruiting is finished.
3. Do this after every flush of mushrooms. This will extend the life of the kit quite a bit - the extent to which it does so is dependent on a lot of factors. But you'll get larger flushes after the first one than you would otherwise, and you'll get more of them.

Ok, so we've increased your mushroom production, and we've extended the life of your kit. That alone is pretty valuable, and all for the price of a bag of manure and a couple of bags of compost (even cheaper if you grow your own!).

Eventually, the kit will start to produce smaller flushes, and you'll know it is reaching the end of life in spite of regular feeding. At this point, you are going to expand it into something else, so it gets a whole new life.

For Compost mushrooms, you need Half-Finished Compost. That means it is rotted, but you can still see what it used to be (you can still see mangled grass, leaves, wood fibers, etc). You want the compost to have between 5 and 20% manure, depending on the type of mushroom and the type of manure. Horse manure seems to be the preferred manure in the industry (in part because it has a high amount of undigested vegetation), but a blending of about 1/3 chicken and 2/3 rabbit or goat will also work, as will a mixture of about 1/10 chicken and 9/10 cow manure. If you are using a blend, use half what you would of horse manure. Compost the manure and vegetation for about 2 weeks, turning about every other day.

For log mushrooms, you need sawdust. Most grow on hardwoods. A few grow on conifers. Make sure you know what they grow on before you proceed - your sawdust type should be right for the type of mushrooms you are growing. You need a good sized pile if doing it outdoors, or a large bin FULL if doing it indoors (it will compact down). If you use a bin, it helps to have TWO - one with small holes drilled in it for drainage, the other to set it in to catch the drainage.

Break up your kit (sawdust or compost), and mix it into the compost or sawdust. If you have a log kit, you CAN cut it up, but you can also just BURY the log into the sawdust. Wet it all down, and keep it moist over the next few weeks. You should see it start to grow if you dig around in it.

Now, that compost will fruit just like your original kit. When it starts to wear out, repeat the expansion into a new bin - or expand it into two or three bins.

The sawdust will fruit just like your original kit, BUT, you can also add a log or two, and then replace those logs periodically, to keep it going indefinitely. You can take sawdust out and start another bin or pile with more new sawdust. You can add logs, then move them once they are full of mycellium. If you add more sawdust once a year, the pile will keep going, and you can keep the whole thing going and producing for years. If you need to reduce the pile, then you can create a new one and put one of your mushroom LOGS back into the new pile to propagate more mycellium into the new pile.

As long as you keep feeding it, it will continue to grow. Compost and manure tea makes it so you don't have to change things out as often, and changing out your substrate (growing media) keeps it going permanently.

Now, you probably WILL get rogue mushrooms in there. But it won't displace your good edibles. Just ignore the rogues. You WILL get mold. It won't hurt anything. Ignore it, unless you get a nasty parasitical mold or fungus that overtakes your mushrooms before they can be picked (then you need to start over). Most of the "contaminants" are not harmful and won't interfere with good harvests and keeping it going.

Do NOT use sterilized compost or sawdust. You WILL get some grasses and weeds growing in them. Don't worry about it, they actually help the mushrooms thrive as long as they don't overtake the bin or pile - keep them low enough so you can see the mushrooms easily.

As long as you do NOT use sterilized materials, this method will work and you don't generally have to worry about the other things that come up.

Have some fun with it, and enjoy the mushrooms!