Onions Grown on Colored Mulch
Robert C. Hochmuth¹

Sweet onion production is popular among dozens of small vegetable growers in north Florida.  Onions are often used as a partner crop to strawberries on farms in the region.  In addition, many farms that market at Farmer’s Markets, or by other direct-to-consumer situations, use onions as a high value crop to increase sales of other cool season vegetables. 

Onions are produced using plastic mulch systems frequently, although open soil (non-mulched) systems are also used.  Mulch systems are popular because many of the farms already use plastic mulch for many other crops they produce, such as strawberry, fall tomato, specialty greens, etc.  Producers may apply new mulch in the fall, or use existing mulch from a fall crop for a double-crop. 

Most onions on plastic mulch are produced on black plastic.  Onions produced on black plastic are generally a few days earlier than those produced on open soil culture.  Occasionally, other mulch colors are used as a matter of convenience, especially in double crop situations after a fall crop.  Fall crops in north Florida are usually grown on white or white-on-black mulch.  The use of white, white-on-black, or reflective silver mulches can be very detrimental to onion production in cold winters.  The winter of 2001-2002 was an unusually cold winter with temperatures in January through March reaching lows of 15-20^oF three or four nights throughout the region.  These cold nights resulted in damage to onions in the region, even some to those grown on black plastic mulch.  However, the most sever cold damage was to onions grown on white plastic.  The cold damage there was so severe the onion crop was effectively destroyed due to the resulting small size of the bulbs at harvest on farms in Madison County.  Onions grown on black plastic sustained less cold damage than those grown on open soil culture or white mulch.  Demonstration plots at the North Florida Research and Education Center – Suwannee Valley over the past few years have shown the same results on various mulch colors.  Therefore, growers should not use white, white-on-black, or silver-on-black mulches for onion production in north Florida.

Onions on black mulch

Onions on silver mulch

Onions on white mulch

¹ Authors

Robert C. Hochmuth, Multi-County Extension Agent, University of Florida, IFAS, North Florida Research and Education Center - Suwannee Valley, 7580 County Road 136, Live Oak, FL 32060