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Agronomic Services — News Release


Contact: Dr. Bobby Walls
(919) 733-2655

Greenhouse crops thrive as a result of agronomic sampling

WASHINGTON — Phil and Joann Black of Black Brothers Farm are picking tomatoes this week, and they’ve been picking them since December. Five years into this “experiment,” their greenhouse tomatoes are a definite success, but only, they add, because the solution and plant tissue analysis services of the N.C. Department of Agriculture and Consumer Services helped them develop an appropriate fertilizer application program.

The venture started in 1997 when Phil decided to devote one of his three greenhouses to tomatoes. Cuts in tobacco allotments meant he couldn’t justify growing three houses of tobacco transplants any more. Black visited some commercial operations, talked with growers, and soon planted his own greenhouse tomato crop.

He was still on a learning curve the second year when the tomatoes started showing symptoms of nutrient deficiency. For assistance, he called NCDA&CS regional agronomist Roger Sugg.

“Roger had given me lots of help with other crops,” Black said. “I knew I could call him, and he’d be here the next day. The first thing he told me was that I should collect nutrient solution and plant tissue samples when growing any greenhouse crop.”

For the next two years, Black sampled irrigation source water, nutrient solutions, and plant tissue intensively. These tests helped him discover quickly that his crop was not receiving enough potassium. Black changed to a 20-10-20 fertilizer grade with twice as much potassium as a 10-20-10.

Subsequent tissue tests indicated that potassium levels in the crop were still low. Sugg advised Black to try a specialty 10-5-40 fertilizer with four times as much potassium as he was originally applying. While this fertilizer supplied the crop’s need for potassium, it did not provide enough nitrogen so Sugg also advised supplemental applications of calcium nitrate.

By the third year of production, Black had worked out a suitable fertilization schedule, and the crop took off. His greenhouse holds more than 500 plants, each of which can yield up to 40 tomatoes. So far, all of these have been easily sold from the farm’s roadside stand, even during the winter.

“I’m in a good location between Washington and Belhaven off N.C. 32 near Douglas Crossroads,” Black said. “Lots of people stop by here. Still, if it hadn’t been for the Agronomic Division, we might have lost the greenhouse. It’s good to have a source of advice and information.”

As a rule, solution and plant tissue analyses are valuable tools for producers of all greenhouse crops, not just tomatoes. With the tomato market saturated in many areas, growers are turning to crops like lettuce, melons and peppers. When starting out, growers should always test their water source for pH or mineral problems that may clog injection nozzles or react with nutrient solutions. The diluted fertilizer solution should also be tested to verify nutrient content.

Plant tissue samples should be taken at least twice during the growing season to monitor nutrient uptake. For tomatoes, samples should be taken once before flowering during mid- to late vegetative growth and at least once after flowering during the set of the second to third fruit cluster. Growers of most greenhouse crops prefer to take tissue samples every two weeks during the growing season.

A typical solution analysis measures pH, total alkalinity, electrical conductivity and water hardness as well as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, boron, chloride, and sodium. It does not identify problems due to pathogens or pesticides. A staff agronomist reviews lab results and makes relevant comments on usability, hazards and management strategies.

The plant analysis report lists current concentrations of primary, secondary and minor nutrients present in the plant. Any recommendations to modify fertilizer application are specific for the crop and its stage of growth. Best recommendations are possible when growers provide detailed information on fertilization history, plant appearance, pesticide application and environmental conditions.

Samples, information forms, and processing fees ($4 per sample) can be sent to NCDA&CS Agronomic Division, Plant/Waste/Solution Section, 4300 Reedy Creek Road, Raleigh, NC 27607-6465. Growers can access their reports two to three days after samples are received at the lab by visiting the Agronomic Division’s Web site at A copy of the report is also mailed to the grower.

Growers who have never collected solution or plant tissue samples or who would like some guidance should contact a local agricultural advisor. Call (919) 733-2655, or visit the Web site,, to find out how to reach the NCDA&CS regional agronomist for your area.


Last Update July 29, 2008


NCDA&CS Agronomic Services Division, Colleen M. Hudak-Wise, Ph.D., Director
Mailing Address: 1040 Mail Service Center, Raleigh NC 27699-1040
Physical Address: 4300 Reedy Creek Road, Raleigh NC 27607-6465
Phone: (919) 733-2655; FAX: (919) 733-2837

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