Shoveling is the same as for a small garden, however, you might want to kill the grass with Round Up or some similar herbicide (give it 2 weeks to work and for the grass roots to start to break down) before you start. If you have no grass or just the junky weeds that grow in the Midwest, go ahead and just start shoveling. How much shoveling you do at once is up to you and your physical capabilities. Pay attention to what your body tells you!! It is very easy to get caught up in the excitement of a garden. I have found it very easy to ignore heat and thirst signals in particular. Some general tips are the same as those for any exercise program: Drink fluids at least every hour, and remember to take breaks.
If you decide to till, try to get ahold of a rear-tine tiller. They're a lot easier to handle. With ALL tillers, if you hit a hidden rock, tree root, or other item that won't till, the machine will bolt on you. But it is a lot easier to remain in control of a rear-tine tiller like a Troy-Bilt. I rented a front-tiner once and it was taking off all the time and trying to dig to China just like in the old Troy-Bilt ads!
Set the tiller for about a 6 inch depth. This will destroy a lot of weed roots, plus give whatever you plant easy sailin' for their own roots until they hit that depth, by which time they will be strong enough to continue with ease.
I always recommend hitting it once, then hitting it again in two weeks because this will kill the weeds which will sprout up after their seeds are disturbed the first time. The other weed seeds are usually wimpy and it will take a long time to get many weeds after the second tilling. But, if you have land which has already been cultivated, you may not need to do this (if you don't mind more weeds!). If you are busting sod, however, even with a Troy-Bilt Horse it will probably take 2 hits to break up the grass clumps.
The bigger the space, the harder it will be to find enough natural soil amendments. If you have clay, sand, or poor soil adding some compost or peat will help immensely. Whatever compost you have made on your property can go right in. Till or shovel it in! Compost left on top of the ground is subject to being washed away by rain. Mixing it with the ground will help to control this, since the grass, edging, or whatever you have around your garden will hold it in along with the dirt.
As with any sized garden, compost, peat, manure, or other natural material will help improve the texture of any dirt. If the dirt is already rich, you will probably not want to use manure, since it can add a lot of richness which some plants will not like!
If you do not have enough natural material of your own, consider buying a truckful (the size of the truck depends on your needs) of compost if you can get it or topsoil and mixing that in the ground. WORK ALERT!! Spreading it out is a LOT of work!!! Consider hiring a couple of local teenagers to help you.
Commercial fertilizers may come in handy on a mid/large garden if you cannot get enough natural (humus-rich) material. But, the commercial stuff tends to disappear fast, and will not do much, if anything, for the texture of the dirt.
Good luck and Happy Gardening!
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