Jen,

Because asparagus is a perennial plant that can grow for years and even decades, it is very important that you properly prepare the soil before you plant.

Part of that soil preparation is to get all the grass out of the area. I will assume you've already done your research and know how to prepare the bed.

If you use a tiller to break up the soil and mix amendments into the soil, be sure you remove every single grass root, rhizome and stolon you see. If you have a grass like bermuda grass, even tiny pieces of stolons about 1/4" long can regrow and carpet that bed with grass.

If I was making a new asparagus bed, I would be tempted to build a raised bed with the soil double dug beneath the raised bed to remove any and all grass roots and seed. Once I had double dug the soil, I would lay down big pieces of cardboard, like from an appliance box. Basically I'd be building a lasagna bed, if you are familiar with lasagna gardening. Then I'd build that raised bed on top of the cardboard. By the time the asparagus roots need to grow way down into the doubledug soil, the grass roots that survived double-digging might be all smothered out by the cardboard.

As a bonus, the decomposing cardboard will attract earthworms and they are very beneficial to the soil.

After you plant your asparagus crowns, immediately mulch with at least 2 inches of organic matter like compost or shredded leaves or finely ground bark mulch. This will both conserve moisture in your soil and help keep the weeds down. When weeds of any sort show up, remove them while they are still small so they don't interfere with the growth of your asparagus. This is very, very important.

You have to keep grass out of your asparagus at all costs. If you ever let the grass get into that bed, you will never get rid of it all. This is especially true of bermuda grass if you have it in the area. I would use round-up to keep grass away from the edges of the asparagus bed if I had a persistent creeping or running grass nearby. You also have to watch for Johnson grass. If those nasty Johnson grass rhizomes pop up in the asparagus you have to hand dig them.

Once your spears are up and growing you can continue to add mulch to help keep the grass and weeds out. The only real solution to grass in an asparagus bed is to keep it out to begin with. If it ever gets into that bed, you'll have trouble with it forever. Oh, and you can scatter handfuls of corn gluten meal over the top of the bed after your spears emerge. Corn gluten meal is a natural, non-toxic organic pre-emergent and also will feed the asparagus plants a little as it breaks down.

Good luck,

Dawn