Jun 19, 2017

High tunnel production well suited for root crops

Carrots, beets, radishes, turnips and parsnips are popular cool-season root crops for high tunnel production and marketing in West Virginia.

According to Lewis W. Jett, commercial horticulture Extension specialist at West Virginia University, beets are closely related to spinach and Swiss chard, while carrots are botanically related to celeriac, celery, dill, fennel and parsnips. Radishes and turnips are brassica vegetables. Beets are a great source of folate, while carrots are high in vitamin A.

Jett made his comments during a presentation at the most recent Mid-Atlantic Fruit & Vegetable Convention in Hershey, Pennsylvania.

“Most root crops such as beets and carrots do best in a light-textured, deep soil without stones,” Jett said. “Raised beds, which can be filled with a lighter texture/soil compost blend, are well suited for root vegetables.”

Beets, radishes, turnips, parsnips and carrots should be seeded early or late enough in the year to grow or mature under cool weather conditions that favor both yield and quality. Parsnips have a long growing season and can be overwintered within high tunnels.

Choosing a root crop

There are several types of carrots, based mainly on shape and intended market use such as fresh market, processing or storage, Jett said. Carrots vary in color from orange, yellow, red, purple and white. Shape and size of carrot roots differ as well. Nantes carrots have long, cylindrical shape and blunt tip. Impersonator carrots have long, tapered roots and grow best in deep soils. Chantenay carrots have a thicker, cone-shaped appearance and do well in heavy soils. In West Virginia, most carrots produced within high tunnels are Nantes- type carrots, Jett said.

Beet roots and turnips are actually enlarged portions of the stem called hypocotyl, with most modern varieties having a round shape. However, there are some beet, radish and turnip cultivars that have a cylindrical-shaped root. Some beets also have edible foliage and are eaten as greens.

“Root crops can be harvested as small vegetables, often referred to as baby vegetables,” Jett said.

Radishes and turnips are fast-maturing, cool-season crops that have a diversity of skin color with white or yellow flesh.

“Both radishes and turnips are excellent companion plants for such crops as tomatoes and peppers during early season production,” he said.

Planting root crops

Root vegetable crops grow best in a soil with a pH of 6.0-6.8. Beet “seeds” are actually fruits containing several seeds. Thus, when seeded, beets are typically thinned to one plant. Each seed is planted 1-2 inches apart and thinned to one plant every 2-3 inches, Jett said.

“Beets can be either direct-seeded or transplanted,” Jett said. “Transplant trays containing 128-200 cells should be appropriate. Beets should be sown beginning in February, within a high tunnel to six weeks before the last spring frost for open-field production.”

For fall beets, Jett said, seeding in August-September is suitable for high tunnels or low tunnel production. For a continuous supply of beets and carrots, a new seeding is made after the first true leaf appears on the current planting.

If the objective is to harvest beet greens for a salad mix, the beets can be broadcast-seeded over a bed. When the leaves are approximately 2 inches long, they can be harvested.

Radishes are seeded in spring and fall, when temperatures are cool with shorter day length and less pest pressure. They are not recommended for summer production, Jett said.

Radishes are direct seeded and thinned to 2-3 inches between plants. Turnips can be seeded in both spring and fall, but have better quality when exposed to progressively cooler weather. Parsnips have a long growing season and are seeded in spring in both high tunnels and open field plantings.

Carrots seeds are very small, but pelleted seeds are available that make it easier to sow and reduce thinning labor. The pellet is an inert clay material that dissolves in the soil moisture.

“Carrots within high tunnels are typically grown as fall-winter carrots that are seeded form August-October for harvest in December-March,” Jett said.

In the open field, carrots can be seeded four to six weeks before the last frost in spring, or six to eight weeks before the first frost in fall. Seeding rate is approximately 30 seeds per linear foot when using non- pelleted (raw) seed. The seed is sown approximately 0.25 inches deep, either in rows or broadcast-seeded.

“When seeding in rows, the rows are spaced 12-18 inches apart for spring and summer carrots and 6-8 inches apart when growing winter carrots,” he said.

“Even watering is critical for good germination and emergence of carrots. While drip lines can be used for growth, overhead watering (misters) will be needed to have a good germination in hot weather. After emergence, the carrots can be thinned to approximately 1-2 inches apart.”

After thinning, the carrots, radishes and beets should be evenly watered, Jett said. Drip irrigation is the preferred method of watering root crops, since this form of irrigation wets only the soil without wetting the foliage.

Approximately 60 pounds per acre (1.4 pounds/1,000 per square foot) of actual nitrogen can be applied before planting with additional 30 pounds (0.7 pounds/1,000 per square foot) applied as a side dress four to six weeks after planting.

“Do not apply nitrogen through the drip lines when growing beets or carrots,” Jett said. “Too much nitrogen can reduce quality of both beets and roots. Carrots will fork when too much nitrogen is applied to the crop. Uneven soil moisture will cause carrots to be misshapen, and beets exhibit a condition called zoning, that is, uneven internal colors.”

Both beets and carrots can be grown on either organic or plastic mulches. Since both crops do not compete well with weeds, the mulches reduce weed competition and soil moisture loss.

“However, the preferred way to manage weeds is to use a stale seedbed technique in which weeds are allowed to germinate in advance of seeding,” Jett said. “The emerged weeds are then desiccated with a contact herbicide or tilled, followed by seeding the root crop.”

— Gary Pullano, managing editor