An Agricultural Research Service (ARS) scientist has developed a new method for propagating June-bearing strawberry varieties that allows the plants to fruit in the fall, continue fruiting until December, and then fruit again in the spring.

This double cropping of June-bearing strawberries is a phenomenon not normally observed in most states, where the plants traditionally flower and bear fruit only in spring.

The new method of double cropping June-bearing strawberries requires harvesting small plants (called runner tips) from mother plants in early July, rooting them and transplanting them in early September. They will flower and fruit during the same fall. Where the danger of freeze exists, the strawberries should be grown in hoophouses. The same plants will fruit again in spring, earlier inside the hoophouse than they would in the open.

With the standard method, runner tips are harvested in early August and planted in the field as four-week-old transplants. They will flower and bear fruit only during the following spring.

ARS horticulturist Fumiomi Takeda developed the new method. He is based at the ARS Appalachian Fruit Research Station in Kearneysville, W.Va.

There are clear economic benefits for growers who wish to use Takeda’s method. Not only are two crops harvested in one year, but fruit harvested in late fall or early winter commands prices four times as high as fruit harvested in the May-June period.

Dr. Takeda explains the work done in Florida on the variety ‘Carmine’ which was published in the April 2006 issue of HortScience. Daughter plants (runner tips) harvested July 6-8 were stuck in 72-cell packs and placed under intermittent mist sprinklers until some roots protruded through the drain holes in the bottom of the cell pack. After that, strawberry transplants were placed on a greenhouse bench and irrigated and fertilized as needed until Sept. 1. Then they were transplanted into a plasticulture system, with embossed black plastic and drip irrigation. 85% of the transplants flowered that fall. The fall crop did not reduce fruiting on the same plants in spring.

“We have also conducted studies with ‘Chandler’ and ‘Sweet Charlie’ with good results,” Dr. Takeda told Growing for Market. “That is, when runner tips were plugged in early July and transplants were established in the field in early September, the plants flowered as early as 1 October and we were able to begin harvesting fruit 1 November. We also planted July plugged ‘Sweet Charlie’ under a tunnel. They produced more fruit in November and December than ones plugged in August.

“In those studies we looked at the effect of tip size on fall flowering. Among ‘Chandler’ tips we plugged in July, 80 to 100% of large tips (2 to 5 g size) flowered in the fall while only 40% of small (about 1 g size) flowered in the fall. None of the August-plugged plants flowered in the fall. ‘Carmine’ was more responsive and even some of the tips we plugged in August flowered. In contrast, none of July- or August-plugged ‘Northeaster’ plants flowered in the fall. We have also tried a variety called ‘Ventana’. The earliest it flowered in the tunnel was in early January. They were really large but we could not keep the temperature under the tunnel above 32°F, so they were killed.

“We are using runner tips or unrooted daughter plants that we detach from mother plants. Large runner tips have about 0.25 to 0.30 inch diameter crowns (pencil size) with two or three leaves on 4-inch petioles. Small tips are about 1/16 to 1/8 inch diameter at the base and have two or three small leaves on 1-1.5 inch long petioles.

“An added benefit of planting July-plugged transplants is that you can get a larger crop in the spring. We have done these studies for 4 years and looked at 4 varieties so far. We have never seen July-plugged plants produce less fruit in spring than August-plugged plants. This means that the presence of fruit in the fall does not decrease spring yield.

“The potential is there to double crop short-day strawberry varieties even in areas with colder winters like Kansas and Oklahoma by using transplants that are plugged in early July. We now know that it is not necessary to condition transplants with artificial lights and chilling temperatures to accelerate flowering. We can get the same results by advancing the plugging date by one month.”

Based on the data from the studies with the variety ‘Carmine’ Takeda thinks each flowering plant will produce about 0.25 pound of fruit before Christmas. These same plants will produce nearly two pounds each during the spring cropping season.

“Remember growers can get about $4 per pound in the fall and only $1.25 in spring,” he said. “If one uses these prices, then your fall/winter crop has a gross value of about 40% of spring crop even though you are not harvesting that much.”

Propagating your own plugs is allowed only for strawberry varieties that are not patented. A plant patent covers plants that are asexually reproduced, and is in effect for 20 years from date of introduction. ‘Chandler,’ one of the most popular varieties for hoophouse production, and one of the best fall producers for the USDA researchers, was patented in 1982 so its patent has expired.

Conventional ‘Chandler’ plants and tips can be purchased from Jersey Asparagus Farms, 856-358-2548. Organically grown ‘Chandler’ plants can be purchased from Peaceful Valley Farm Supply, www.groworganic.com or 888-784-1722.