Can I backfill against a metal building

I have had my garage for almost 15 years and all this time there has been a trench around it where it was dug out to put the barn on a level concrete pad. The guy who put the cement in put a 4 inch cement curb - not sure what else to call it - around the entire foundation except for the front wall. The garage is inset where it is level at the front and about 3 feet down at the back. I have left the trench there but it always grows tons of weeds and small trees, thorny vines and such. What I want to know is can I backfill against the side of the garage. If I can then I could just mow right up against the building. As it is I can't mow withing 3 feet of the back wall. Any suggestions?

You can't backfill against the building. You have a couple options. One you can use either block or cast in place concrete and create a retaining wall a few feet away so you can even level out both the grass and this area. Or two build the retention wall on the existing footing and frame the building on that. Either way you should hire a contractor and for option two also hire an engineer to tell you what and how this can be done.

Just whatever you do, don't backfill against the building.

Pictures would probably be helpful...

You would need to put some type of waterproof barrier on the metal wall first and will also need to make sure that it is strong enough to support the extra weight pushing on the panels. There are several types of plastic or even tar based films that you can apply first. Any type of barrier that just butts up to the existing wall would need to be sealed to the wall or water will be trapped and rust out your wall. It also wouldn't hurt to put a drain tile at the bottom before backfilling. I have seen a bubble plastic film with a mesh over it that would help drain water from the wall area but it needs to be sealed to the wall on the back with tar. The bubbles provide a drain path for water and the mesh prevents dirt from clogging up plastic. They used this stuff in the 4' deep planters at Trump Tower in Las Vegas to keep water away from the poured concrete building walls on the 7th floor. They did not want water stains on the outside of the walls. Personally I would start with a drain tile, then a layer of gravel, then some top soil along with a waterproof wall covering if the wall will support it. A poured concrete retainer is another option but you will have the same issue with water trapped unless you address it with a similar barrier.

Pictures or not the answer is no. Wall framing is designed to hold the roof and walls up, not accept a lateral load.You would also be opening yourself up to water intrusion.
As stated above, cast or retaining wall a few feet off the wall. If you are within less than 4' of the building, i would suggest a drain tile on the back side.

I wouldn't do it either, it would seem to me to be like "an accident waiting to happen" so in my opinion it is something best not done. But a picture would certainly help a lot.

How far is it from the walls to the concrete curb?

Easy answer is ....no you can't and you shoul not.

If it was me I would dig out a larger space and install a retaining wall. Open up about a 3-4' space that you can lay gravel and weed barrier down.
This will give you easy access to that area as well as keep the earth away from the building.

Bob