Lawns have many good properties, but it can be some of those very same properties that make it hard to get rid of when you want put in a garden bed. Any method will take time, but some will be easier and/or longer lasting than others. I have personally tried 5 different ways to get rid of grass.
Digging up the grass by the roots is very labor intensive. If it is a very small section, a shovel might be barely okay. It takes a lot of muscle to cut through sod, either vertically to cut into it or horizontally to slice it from the ground. Part way through any such effort, I have lost all self-control about doing it neatly.
A sod cutter can be rented, which is a much faster and neater way to remove it. Assuming you have the upper body strength to keep the machine in a straight line. I didn’t. Finally, a couple men in my life took pity on me and helped get that particular garden bed done, but I knew it would be unlikely I would ever try to use that machine again.
One advantage of digging is that you will probably have less of an issue with regrowth from the roots. You will end up with a depression a few inches deep, but since you will probably want some sort of border to keep grass from growing into the garden bed, this could be useful. If you have the strength, yours or someone else’s, to dig grass out, the next steps in preparing the garden can be done without waiting. You could even plant in it the same day, assuming you haven’t run out of daylight.
Quick analysis: hard, but thorough
2. Weed Killers
Spraying or spreading something to kill the grass is relatively easy. The most important thing is to make sure it is not something that will also inhibit growth of future plants. That would be bad. There are some herbicides that are designed to linger and keep anything from growing for quite a while. There are also simple household plant killers, like salt, that will stay in the soil a long time and hinder garden growth. Read labels and research such things before using something.
It can be more challenging to kill the grass in the exact geometry desired with this method. Unless your spray is colored somehow, it can be difficult to see exactly where it ends up. I made some interesting zigzag edges in places. Regrowth from roots can be a problem, too. Grass has such a vast network of roots, that it is nearly impossible to kill unless you are killing the whole lawn.
Quick analysis: easy, but careful research required
By this, I mean just putting your new garden soil right on top of the grass. The deeper the layer, the more likely this will work. I would recommend covering with at least 6 inches of soil for any chance of this working. Even for grass sprayed with herbicides and then covered with only a couple inches of soil, I have had regrowth of the grass into my garden beds. Grass is tenacious. Lawn grasses often worse than weed grasses, at least where I live. The lawn grasses tend to be more densely and laterally networked, which leads to damaging other plants when trying to remove it.
Quick analysis: easy, but will likely leave grass growing
This involves putting something over the grass in a way that either cooks or suffocates it. Black plastic or cardboard or old rugs are the sort of coverings that might be used. After a couple of weeks, depending on the weather, any plant that was underneath will have been snuffed out. That doesn’t mean there won’t be seed from overgrown grass or weeds waiting to sprout at the first habitable conditions. This method is low labor and even faster than spraying. My main concern with it is that it could kill a lot of beneficial insect and fungal life in the soil, too.
Quick analysis: easy, but could kill good microbes and insects
This is by far my favorite way to get rid of grass. First of all, you get to watch the very happy chickens. Secondly, it is very thorough. If you leave chickens in an area for a couple weeks, they will decimate it. There are very few plants that chickens don’t bother, and they LOVE to scratch up grass. The resulting garden bed has a little extra fertilizer added to it from their droppings and it is completely free of any residual weed killers. Even though pure chicken manure has to be aged for a few months to reduce acidity before putting it in the garden, when it is mixed with dirt and they have only been there a couple weeks, it would be surprising if there was enough to be a problem. I even dig compost straight from my chicken pen to spread on my garden beds without having any aging regimen.
The biggest problem with this way of killing grass is containing and directing the chickens. I don’t let my chickens free range in my yard for the very reason that they make a mess of everything with their scratching. Dirt gets spread everywhere I don’t want it. But by using a temporary fence and chicken tunnel system (here is how we made a more permanent chicken tunnel), a garden bed could transform before your very eyes. They WILL eat every worm they find. There will also be amazing excavations that have to be leveled, but it will be worth it.
Quick analysis: thorough and fun, but requires set-up and chickens
I’m not disparaging lawns, by any means. I have come to appreciate them more over the years, as I write here about 15 Reasons Why Gardeners Should Love Their Lawns. But if you want to put in a garden bed where there is currently lawn, it will take some doing. If you understand the pros and cons of the options, you can make choices that are most likely to be satisfactory to you. After the grass is dealt with, you can move on to more fun things, like deciding what kind of raised beds to build.