Can you sprinkle rock salt on the base of asparagus to keep weeds out of it?
Asparagus has a higher tolerance for salt in the soil that many weeds do, so an old practice used to be to pour the salty water from the ice cream maker over the asparagus bed to kill weeds. However we don't recommend this now, because too much salt in the soil will eventually kill the asparagus, too! The best option is to use mulch and Preen to control the annual weeds.
Or here's another technique used by commercial growers. At the last harvest of the season cut down all the spears, so there's no foliage or anything above the ground. Rake the soil over the top of the spears. Then overspray the entire planting with glyphosate (RoundUp). Glyphosate becomes bound by the soil particles when it hits them, so will not damage the crowns below ground. This will control annuals and tough perennial weeds. The spears will then re-emerge from the soil and not be damaged by the glyphosate at all. Apply some mulch to help with the weed control, then Preen.