How much compost do I need?

So after an extensive search I don't quite see anyone having discussed this before.

Relatively new to SFG, just got my beds set up, and have done the math on how much compost I need to get my MM set up to start. I am going with slightly less than 1/3 Peat Moss to account for the moss content in my store bought compost, but thats a separate issue, and easily calculated.

At the same time I am looking at composting options, and am trying to determine what my recurring compost needs will be.

I have a total of 72 sq ft of growing space, which will probably be expanded to 96 next spring.

I've read that you add a trowel fool (not nearly precise enough for my math brain) after each harvest, which in some cases will be once a year and in others could be 3-4. I also want to add several inches before winter in anticipation of next spring, etc. I've been unable to find anyone who has quantified that a SFGarden uses an average of XX KG/Liters (or lbs/cuft for those yet to embrace the metric system) of compost per square foot of growing space, per year.

Obviously home grown compost will be of superior quality. No debate there. So that aside, what I am looking for is to estimate what my annual compost bill would be if I was entirely dependent on store bought compost, so that I can gauge what a reasonable amount of money to invest in a home composting set up might be.

Lastly, I am trying to estimate what the yield of compost produced in this store bought compost bins could be annually. (I am limited in space for one of the bigger cage style compost factories.) I know total yield will depend on how much I feed it and how much I turn it over, but I really have no idea about that either.

So basically I'd like to hear people stories and experiences about compost usage, preferably with some real numbers attached. Ie, last year I was all store bought on compost and used XXX amount of bags for my XXX sq ft gardens, or, Last year my compost bin produced xx amount of compost with xx amount of work and it did/did not meet my needs based on xxx sized garden.

Bottom line, right now store bought compost looks inexpensive, and I forsee that my total needs will be so low that composting at home likely won't be worth it, other than to ultimately have a better product. From most peoples stories it seems like even with home composting I will still be buying lots of store bought compost anyways.

Educate me!

Thank you all kindly in advance.

I make my own compost, but I "cold compost" so it takes for-eh-vah to get compost. I still do it, because I'd rather have a place for my kitchen and garden scraps than the garbage.

As such, I've supplemented my MM every year with a truckload of compost from a local farmer. I get it at $40/yard which is an awesome price when you compare it to bagged compost.

If I had to put a number on it, I'd guess that my MM goes down by about an inch every few years, depending on how much I pull up when I uproot plants at the end of the season.

That being said, I'm going to start leaving as much of the MM intact and just cut the stems of plants off (unless I need the square to replant, which I usually don't being as I have a 90 day growing window if I'm lucky).

HTH!

I do a tremendous amount of composting, which I use heavily for not only the raised beds, but for fruit trees, berries, etc.. I have two twin compost tumblers, which allows me to produce on section of the tumbler every 30 days. I get free juicer pulp from 2 neighbors, as well as from one juice bar, so I have a lot of input to feed the compost tumblers. I used to add coffee grounds from Starbucks, but that is on hold until the stores start re-opening.

As far a quantity, I don't know there can be a one-size-fits-all answer. I add 2 or 3 inches of compost to each bed every fall, and may add another inch during the summer growing season. If you 72 sq ft of bed, and you add 3" of compost, that could be computed as to the amount of cubic feet of compost that would be needed:

72sq ft x .25 ft = 18 cu ft. = .667 cu yd.ut

But, if you only need to add 1" of compost, that would compute as the amount of compost needed as:

72sq ft x .0333 ft = 6 cu ft

So when I set up my garden boxes this spring, I had about 5 gallons of spare compost that I kept in a bucket in teh shed. As I turned over my squares I did the whole trowel full thing. Again, I am more leaning towards getting a 1 litre scoop just cause my brain can't handle measuring life by the trowel. 

IN any event I am still working on that first bucket, and never needed to go back to the store for another batch. 

I obtained to two of the typical black plastic compost buckets and have been dutifully filling one all seasons. I turn it over every 3 days or so, and it can't get full cause it keeps composting down. I know i should just fill it first, then work it, but I am curious. After having put enough material into it to fill it three times over, I've just decided to start filling the other bin and to finish this one off before the winter cold comes. I'd say at best the composter will produce half a cubic yard of finished compost. Which will most certainly meet my recurring compost needs. SO thats good. 
Looks like these back yard composters are actually going to be able to get me the compost I need on a recurring basis. 

I am still going to be going back to the store for a one time large purchase to fill the two new beds I just finished framing.

Glad you are able to make enough compost for your needs.