Answer: Mulch away, says Casey Foos, horticulturist and onion specialist at Nichols Garden Nursery in Albany, Oregon. A light mulch of 1 to 2 of straw placed between rows of onions will not have an effect on the bulbing of your onions. But don't mulch heavily near the bulbs, because they're highly susceptible to many rotting organisms that thrive in moist, wet conditions, she explains. The only possible way mulch would inhibit the bulb formation is if the onion plant was completely covered with mulch, adds Foos.
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