Volume 1, Issue 2

Equipment Evaluation: Fertilizer Dispenser (Part 1)

In this edition of green-O-vations, we will review an equipment evaluation of a controlled-release fertilizer dispenser.  Studies conducted by Scott Langlois, MSU Coastal Research and Extension Center Engineer, at nurseries specializing in containerized plant production showed that dispensing or top dressing with a controlled-release fertilizer represents a significant labor cost and raises various safety and quality concerns related to the dispensing process.

Also known as time-released fertilizer, controlled-release fertilizer is widely incorporated by growers in the initial potting medium when growing in containers, but is sometimes also added at various times throughout the plant’s ‘nursery life cycle’. This life cycle is represented by the entire time a plant spends on location at a nursery or greenhouse operation.  Plants with longer life cycles generally are top dressed more often, incurring added labor and product cost with each application.

The traditional dispensing method for the process of top dressing containers is commonly known as the bucket and scoop method as shown in Figure 1. Labor intensive, this method is considered low cost with respect to the equipment required: a 2 to 5 gallon bucket and various sized scoops or cups to denote different dispensing rates. Langlois has noted that in addition to added labor costs, growers share a concern about the impact to the quality of the containerized plants when using this method. Although the amount dispensed can be controlled with a prescribed scoop, operator error can influence even application. Problems such as not filling the scoop completely or uncontrolled dispensing (spilling outside the container) can ultimately impact plant quality. Ergonomically, this method presents challenges to worker safety and comfort, mainly due to the stooped-over posture required to pour fertilizer into each container.

Several products are available on the market, all designed to increase overall dispensing efficiency and applicator safety. Two of these products were recently evaluated. This is the first of a 2 part series describing these products. The first is the FertilTM Dispenser. This is a backpack-style product capable of holding about 30 pounds (approx 5 gal) of resin-coated granular style fertilizer. The unique metered stainless steel dispensing chamber is adjustable from 2 to 26 grams and was shown to be very repeatable in the dosage.  The unit is very comfortable to wear for both short and tall employees, due to the design of the molded backpack and the adjustable straps. A side advantage of the design is a molded ‘foot’ at the bottom of the backpack which stabilizes the unit during storage or filling operations.

Comparison tests showed that this unit could reduce top-dressing cycle time by at least 25% depending upon plant variety and dosing amount. When used to fertilize plants requiring more than the maximum  dosage, multiple releases or ‘shots’ were easy to apply. Single-dose production rates of over 1200 containers fertilized per hour were easily attainable.  Some usage problems were noted and were attributed to operator error. Should the end of the dosing chamber come into repeated contact with container media, clogging of the unit may occur, reducing its accuracy. Other than this misuse issue, no bridging or clogging problems were noted in the dosing chamber or the feed hose. Overall, minimal operator training is required. Safety improvement was significant as worker posture and comfort was drastically improved (Figure 2). Workers reported reduced back and arm fatigue compared to that of the traditional bucket method. Langlois noted that the only significant safety concern would be prolonged use of the trigger mechanism (Figure 3) which would most likely result in hand (thumb) fatigue.  

Overall, this product may be a viable alternative to top dressing container grown plants. It offers real cycle time savings and will significantly reduce operator fatigue. The unit cost of approx $600 is reasonable for a product that offers this level of productivity and safety improvement.   

In the next issue, we will review another promising fertilizer dispenser: a battery powered model that has an unconventional look and feel.

For more information related to this article, contact Scott Langlois at

Mention of trademark, proprietary product, or vendor does not constitute a guarantee of warranty of the product by Mississippi State University and does not imply its approval to the exclusion of other products or vendors that also may be suitable.