July 28, 2005 | By: Laura Skillman

Nursery crop producers in western Kentucky are adopting a new production technique called pot-in-pot production but are questioning if traditional fertility methods are working as well in this new system.

To help growers gain a better understanding of the best and most economical fertility method for pot-in-pot production, a two-year research project is under way by Dava Hayden, an Extension nursery crops associate with the University of Kentucky. Hayden’s position is part of the horticulture initiatives funded by the Kentucky Agricultural Development Board.

Pot-in-pot production is unique in that the pot is nested into the soil. In traditional production it sits on top of the soil on gravel or a black mat.

“Pot-in-pot production is a relatively new type of production technique for nursery containers,” she said. “It has grown in popularity, and there has been a lot of research on obstacles and opportunities for pot-in-pot production. Researchers have looked at the influence of substrate temperature, water and run-off in pot-in-pot. Those two factors may be resulting in growers not seeing the growth effects from fertilizer they would see in aboveground production systems.”

Research has been done on fertilizers in aboveground production but not in western Kentucky on pot-in-pot production, Hayden said. In pot-in-pot production there are not the extreme fluctuations in temperature compared to aboveground production and, as a result, it appears fertilizer is reacting differently, she said. 

There are a lot of advantages in using the slow-release, granular fertilizer traditionally used in nursery crop production, but it may not be the most economical for pot-in-pot production.

As an alternative to see if pot-in-pot producers should be using something else, Hayden is using three methods on Zelkova serrata “Green Village,” a deciduous tree. One uses liquid fertilizer that is injected into the irrigation system, called fertigation, another uses the slow-release granular fertilizer and a third is a combination of the two.

With the combination treatment, Hayden is using the same amount of granular, slow-release fertilizer that a producer would normally use and supplementing with liquid fertilizer during times when growers are seeing gaps in its effectiveness, such as in the spring when soils are slow to warm. Then she is using a low concentration twice a week during the growing season. If fertilizer runs out as the season progresses, liquid can be used to fill in the gap.

Slow release is generally put on only once in the spring. The research project is using an eight-month to 10-month slow-release fertilizer commonly used in the region, but she is expecting that to be depleted at the end of August. To determine that, the fertilizer granulars will have to be hand collected from the pots and examined.

Conversely, because the substrate temperatures are lower, there may be a number that have not released their fertilizer and are not allowing the plant to shut down and prepare itself for winter, which can result in damage to the tree, she said.

The research could result in a change in the slow-release fertilizer being used in terms of release time. It could also show that it is easier to use irrigation as a means to deliver the fertilizer.

To determine fertilizer being released, every two weeks the potted trees are taken out of the ground and the leachate tested. All foliage and branches that fall from the trees are being collected so they can be measured to determine growth. The trees will be taken off fertilizer Aug. 15 and the trees will be allowed to begin the dormancy process. However, before the leaves drop they will be manually removed and the dry weight will be taken of the foliage, then of the trunk and the roots.

New trees will be used in 2006.

“This project will only be replicated twice, but it should give us an answer as to what’s going on in our fertilizer program,” Hayden said.



Writer: Laura Skillman 270-365-7541 ext. 278

Contact: Dava Hayden, 270-365-7541 ext. 279