Currently, only three different varieties have been selected for acceptable yield and marketability using plasticulture in North Carolina, extending the harvest season over a six-week period. In cooler springs the season may last eight weeks. In hotter years, it can be as short as four weeks. These varieties are: Sweet Charlie, Chandler and Camarosa.
Both Sweet Charlie (early variety) and Chandler (early midseason variety) are widely adapted throughout North Carolina. Camarosa (a midseason variety) is limited to the growing areas with a milder winter, such as the coastal plains of North Carolina. Camarosa is also being grown throughout the Piedmont with the provision that over-winter row covers are used from late December through early March. Sweet Charlie is used in limited numbers to start the harvest season. Chandler is the most reliable variety for the upper Piedmont, foothills and mountain regions. In addition to regional climate variations, market purpose may also determine which variety a grower chooses. Chandler is an excellent U-pick berry, but its shelf life is limited as a pre-pick berry compared to Camarosa.
While strawberry varieties are classified as June bearing, everbearing and day neutral depending on their response to photoperiod (flowering relative to daylength), the commercially grown varieties in North Carolina are all June bearers. Home gardeners may choose everbearing or day neutral berry varieties, but they are not currently considered viable options for large scale production.
Considerable research is now underway testing day neutral strawberries that are best adapted to summer and fall fruiting in high elevations (2,500 ft or more). Two California cultivars, Albion and Seascape, have proven to be high yielding with dessert quality fruit. Both varieties are worthy of trial in the summer and fall fruiting system at high elevations.
Sweet Charlie. For an early market niche, Sweet Charlie is the variety of choice. It ripens about five to seven days ahead of Chandler, and possibly two weeks ahead if a row cover is applied in mid-winter. Growers do not generally plant more than 10 percent of their acreage with Sweet Charlie, but in some years that 10 percent will account for 20 to 25 percent of the operation’s profits. The ripening season for Sweet Charlie is rather interesting; it has two weeks of very good quality early production, but then size falls off rather drastically and it does not compete well with Chandler, an early-midseason variety. In some years, growers experience a second crop of very large Sweet Charlie berries in the final week of the strawberry season. Many consumers actually show a preference for Sweet Charlie berries, which have a high sugar to acid ratio. Sweet Charlie should be planted at 12-inch in-row plant spacing (for a double-row bed on a five-foot center, 12-inch in-row spacing will require 17,500 plants per acre).
Optimum planting dates for Sweet Charlie will vary with region. But, as a general rule, this variety must be transplanted at least seven days ahead of Chandler. Plugs are usually preferred for Sweet Charlie over fresh dug, bare-root transplants. Field observations suggest that Sweet Charlie may be more susceptible to Phythophthora cactorum (crown rot) than Chandler or Camarosa. Sweet Charlie is generally recognized as being resistant to anthracnose fruit rot.
Chandler. This is the standard cultivar for the U-pick producers in North Carolina because of its high yield compared to other plasticulture varieties and because it is well liked by consumers for its good flavor, size and attractive red color. Given its widespread use for U-pick, it should be planted at 14-inch in-row plant spacing for easier customer harvest (for a double-row bed on five-foot center, 14-inch in-row spacing will require 15,000 plants per acre). Plugs and fresh dug, bare-root plants are usually comparable in yield performance for Chandler, but fresh dugs may have an advantage from the standpoint that they do not concentrate the ripening of the crop as much as plugs in some spring seasons. Optimum plug planting dates for Chandler vary with region (fresh dugs should be set three to five days earlier than plugs):
- Mountains, high elevation: first week of September
- Mountains, lower elevation: second week of September
- Foothills: third week of September
- Upper Piedmont and tidewater: fourth week of September
- Piedmont transition to coastal plain: first week of October
- Sandhills: first week of October, but the last week of September is also fine for colder locations, especially for fresh dugs
- Lower coastal plain: second of week of October or third week for warmer sites. For southeastern counties like Brunswick, it is fine to go as late as the fourth week of October.
Chandler is quite cold hardy and does not generally require winter protection (straw or row covers) for most growing areas in North Carolina. However, winter temperatures below 10 degrees Fahrenheit will cause extensive flower and crown injury in this variety. For this reason, row covers are strongly recommended for areas where there is a potential for periods of extreme cold in winter (less than 10 degrees Fahrenheit). Based on recent research with row covers in upper mountain areas (elevations higher than 2,500 feet), it has been determined that row covers (1.5 oz per sq yd) applied in late November to early December for additional winter protection and then removed in early March (before new blossoms reach the “popcorn” stage) can significantly improve Chandler yields compared to unprotected plantings. The row covers will also assist with deer protection, and they can be reapplied for cold protection of flower buds and blossoms in late winter to early spring.
Camarosa. Camarosa is primarly grown for pre-pick operations and is gaining popularity as a U-pick variety. Camarosa has superior shelf-life and handling characteristics compared to Chandler. In the warmer winter areas of North Carolina, Camarosa production now surpasses Chandler in acreage. The fruit is very large and firm and holds up well in rainy weather. To achieve the best Camarosa flavor, it is important to delay picking past the glossy bright red stage and to train pickers to harvest Camarosa when it takes on a darker color. However, when it becomes wine-red in color, it is becoming overripe. It is currently believed that the optimum planting dates for Camarosa are about the same time as Chandler, but most growers prefer to set this variety at least three days ahead of Chandler. Camarosa is typically planted at 14-inch in-row plant spacing (for a double-row bed on a five-foot center, 14-inch in-row spacing will require 15,000 plants per acre). Camarosa can really strengthen mid-to-late season sales when Chandler quantity and quality declines as the temperatures increase. This variety is receiving increased attention for its season extending potential.