Do I need to/should I till up lawn before putting raised beds on top?

Question

I have a lawn that I am considering turning into more garden space. (roughly 25' x 25')

I've done raised beds on top of an existing garden in the past, but never on top of lawn/grass without ripping up the sod/grass.

Would I run into issues just putting soil on top of the lawn and putting in beds, or should I rip up the grass? I suspect it might work ok, and want to avoid tilling (400 sq feet or so) but I am not sure. (Especially as someone else pointed out issues with root crops)

I'm curious if anyone has had experience or definite knowledge about this

EDIT - after a request for a little more detail

The goal is to have veggies and likely a greenhouse over them for parts of the year (plastic tunnel ala Eliot Coleman).

• beets
• carrots
• spinach
• peppers (sweet and habanero)
• tomatoes
• herbs (rosemary, dill, basil)
• cucumbers
• squash
• beans
• peas
• onions
• etc

I might even try artichokes

Answer 1

If you have enough soil to go on top, I recommend "sheet mulching" by putting down cardboard on top of the grass to kill it. Otherwise, it will inexorably work itself up, and you'll have a raised bed full of grass.

This is the basis of so-called "lasagna gardening," where you layer cardboard, compost, soil, and mulch to turn lawn into garden space.

If you can forego your root crops for a year, you'll find that by the time the grass has died and the cardboard decomposed, you'll be ready to open the bed with a broadfork or spading fork.

I know you don't want to till, but roots need oxygen, so you'll need to do something eventually to open it up. If you plant things with spreading roots in your lasagna garden the first year, then fork it thoroughly the next year, the beets and carrots should be happy.

Answer 2

Yes, I would till. Lawns tend to be fairly compacted, and vegetables do much better with deep, loose soil. The upside to tilling is that you'll have to import less soil for the same "working depth" in your beds. The act of tilling will introduce air to the soil and actually increase its volume. You also won't need to raise your beds as high in order to provide your plants with the same depth of usable (non-compacted) soil.

In your situation, what I would do now (June) to prepare an area for raised beds next spring (or perhaps even this fall):

1. Kill the existing sod. Lay down black plastic over the area to be converted for a few weeks. This will kill the grass. You could also do this with cardboard or other heavy, dark material. As a (more labor intensive, but faster) alternative, you could cut away the turf and either use it elsewhere or stack it for composting. (If you choose the "cut away" approach, you'll be losing some soil depth.)
2. Get your soil tested. Unless you've already got tests from your lawn, send off a soil sample while the sod is dying so that you'll have results when you're ready to start the next phase.
3. Loosen the soil. Till the area to be converted to a depth of at least 6". Remove rocks and any other obstructions you find (e.g. roots). (If you are a fan of double digging, now is the time to do it.)
4. Amend the soil. Add whatever amendments are recommended by the lab (i.e. lime or sulfur, fertilizers, organic matter).
5. Build your beds. Whatever you normally do for raised beds.
6. Plant a cover crop. If you aren't going to plant a fall crop, sow a cover crop in the new beds.