Answer: They may be pulling seedling weeds out of the mulch or attacking shiny plant labels, but who knows what goes through the minds of crows. They may also be eating some early season caterpillars, grubs, armyworms or other pests. Here are some typical suggestions for deterring them in vegetable/corn patches, perhaps some of these would work in this case as well.
What pests! You might try setting a protective barrier of wire mesh over the plants, you can string clear monofilament fish line 6-8" above each row, and a couple down either side of the plot to keep the crows from landing in the patch so they'll encounter the line when they try to land, and get confused by the unseen obstruction, or possibly a floating row cover would exclude them.
Continuous flagging is the most traditional way to keep birds from crops such as corn. Stakes are placed 15 to 20 feet apart all around the corn patch and a long flag of cloth is attached to the top. The flag can be tied directly or tied first to a string and the string attached to the stake (gives more play in the wind). Set up the stakes before the corn is attractive to the crows.
Another method, although more frequently used for ripening fruit trees or small fruits, is bird netting although in my experience this may not be strong enough to stop crows.
Noise makers like a radio (got any neighbors who might be bothered?), mylar or metallic flash tape and balloons (the reflection bothers the birds), strings down the row with streamers of flagging tape, all have been used with varying degrees of success. Varying your scare tactics works best, as it keeps the crows from getting used to them.
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