Nursery discovers value of "pour-through" testing

Economic return and environmental stewardship are key objectives for plant nurseries everywhere.

One approach to meeting these goals involves the routine collection of “pour-through” samples of water drained from container stock. The North Carolina Department of Agriculture and Consumer Services can analyze these samples and tell growers whether additional fertilizer application is necessary, thus enabling them to make decisions that can save money and safeguard water resources.

Tom Vissman, plant culture supervisor at Greenleaf Nursery in Tarboro, N.C., has been using pour-through testing for several years now and has come to rely on it. Greenleaf is one of the country’s largest producers of container-grown woody ornamentals.

“I use pour-through constantly,” Vissman said. “Solution analysis of pour-through leachate gives an accurate picture of secondary and minor elements. Test results tell us which nutrient issues need to be addressed. Perhaps more importantly, they tell us when not to fertilize, and that’s a definite environmental benefit.”

Before Vissman discovered pour-through, Greenleaf used to do its own in-house testing. “We purchased simple kits that measured some elements as well as pH and conductivity. The tests were quick and fairly inexpensive. They would have been worthwhile had the results been straightforward and accurate, but, as it was, their subjectivity and margin of error didn’t justify the cost.”

By 2006, Greenleaf’s source for testing supplies had gone out of business, and no similar replacement product was available. The nursery considered purchasing equipment to set up its own lab, but the cost was prohibitive. Then Vissman heard Ted Bilderback of North Carolina State University talk about pour-through analysis. For a fee of $5 per sample, he could get accurate test results in 48 hours backed up by free agronomic consultation.

Vissman followed up immediately with a call to Charles Mitchell, a member of the NCDA&CS Agronomic Division’s field services team. Mitchell advises growers regarding the use of all types of agronomic tests, including solution analysis for pour-through samples. He came out to Greenleaf to demonstrate sampling technique and discuss sampling strategy. When the first samples were processed, he took the time to explain the significance of the numbers on the report.

“Pour-through involves pouring water through the saturated growth substrate of container stock, collecting the liquid that drains from the bottom of the pot, and sending it to a laboratory for measurement of nutrient levels, pH and electrical conductivity,” Mitchell said. “It’s an effective way to monitor fertilizer release. Pour-through is more appropriate for this purpose than soil testing because most growth substrates are actually soilless media, such as compost, peat moss, perlite, pine bark, sand and vermiculite.”

Vissman uses pour-through to test the long-term effectiveness of fertilizer products. When companies advertise that products release nutrients over a 12- to 14-month period, they often base their estimate on a constant soil temperature of 70 °F, which is not realistic. Using pour-through, Vissman can determine the actual release period. If the fertilizer is gone in only six to eight months, then he knows it.

“Pour-through gives me a look at element use and the effect of particle coating on release of fertilizer nutrients,” Vissman said. “Some products release nitrogen quickly, but potash may still be fine. The test helps confirm whether fertilizers are really as available as claimed on the bag. Having this knowledge is useful when it comes to evaluating brands and suppliers.”

Greenleaf has about 100 acres of plants at its Tarboro location. Vissman and his staff collect pour-through samples year round. During the busy season from February through October, they often send as many as 20 samples a week to the NCDA&CS laboratory.

Over the last few years, Vissman has seen a noticeable change in the amount of fertilizer being applied. “Greenleaf uses less fertilizer per acre than anywhere else I’ve worked before. It’s taken some adjusting on my part, but costs and the environment are better because of it.”

In addition to NCDA&CS agronomic lab tests, Vissman has also come to rely on Mitchell’s expertise. The two have collaborated in testing the quality of various composts for use as potting media. This work promises to be beneficial because, as a rule, composts don’t require lime or micronutrients and have better conductivity and water-holding capacity.

North Carolina growers have access to one of the most comprehensive agronomic testing and advisory services in the nation. Soil testing and agronomic consulting through NCDA&CS are provided free of charge for North Carolina residents. Other agronomic tests — nematode assay and plant, waste or solution analyses—are available to residents for minimal fees and to nonresidents for slightly higher fees. Information on other tests are available online at

The NCDA&CS Field Services Section has helped North Carolina growers manage fertilization and other nutrient-related issues for nearly 30 years. The division’s 13 regional agronomists make site visits; evaluate suspected nutrient and nematode problems; and give advice on sampling, liming and fertilization. For contact information, visit

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