By Lori Wright

In response to high demand for year-round local produce, University of New Hampshire Extension researchers have successfully grown bulb onions planted during fall for a spring harvest. The onions survived and slowly grew with the aid of inexpensive low tunnels.

The research, funded by the NH Ag Experiment Station and Northeast Sustainable Ag Research and Education branch of USDA, opens the gate to new marketing opportunities for growers in cold climates.

SWEET OFF-SEASON RETURNS: These T420 onions were one of the cultivars that didn't bolt and did make it to a marketable product. Photo by Becky Sideman

"Direct-market sales are the primary outlet for growers in our region. These off-season onions would likely be sold individually at sizes determined by local market preferences," says Becky Siderman, UNH Extension horticulturist focusing on sustainable production.

Sideman and colleagues at University of Massachusetts-Amherst presented findings of their two years of work in December's issue of HortTechnology. Click on "Production of Bulbing Onion Overwintered in New Hampshire with Protection by Low Tunnels" to view their report.

Key findings
Survival, bolting and bulbing of several fall-planted onion cultivars were evaluated over two growing seasons at two New Hampshire sites. Plants were seeded in August and September, then transplanted in September and October into raised beds covered with black plastic mulch.

Low tunnels were installed in late fall. Onions were harvested from mid-April to early June 2012 and late May to early July 2013.

* Between 65% and 100% of all cultivars survived.

* Cultivars planted later exhibited lower percentages of bolting and slightly smaller bulbs at harvest.

* All plants that survived winter and didn't bolt produced a marketable bulb.

* Between 85% to 100% of Bridger, T420, Top-Keeper, and Keepsake yellow cultivars met their marketable criteria. That's a yield potential of about 37,000 to 43,500 bulbs per acre.

That's considerably lower than expected yields for major onion production regions, notes Sideman. But these yields still may be commercially viable in a high-value, direct-market situation.