Engels injection moulding machine.
Robot arm for removal of mouldings from injection moulding die.
Miracle-Gro tub, as manufactured at Unimark's Reedsville facility.
Coloured polypropylene granules used for the injection moulding.

Unimark Plastics has installed a new custom manufacturing and assembly line at its Reedsville facility, Pennsylvania, USA. The line has been created to meet the demand for a new injection-molded polypropylene (PP) tub for Miracle-Gro plant food, manufactured by The Scott’s Company of Ohio. The product is manufactured and assembled at Unimark’s Reedsville facility. The soluble plant food Miracle-Gro is retailed in a PP molded tub, which holds 3.75lb of the product in three measured flexible film bags.

While the majority of Scott Co’s Miracle-Gro products have been retailed in fade- and moisture-resistant cartons in sizes from 0.5lb to 15lb, the new tubs have been a major success according to the latest sales figures. This has led Scott Co to increase their orders for the new plastic container from Unimark Plastics.


Innovative Solutions, the research section of Alltrista Plastics, designed the Miracle-Gro bucket-type container in collaboration with Unimark. The design was based on the container’s aesthetic appearance, water resistance and stackability, resulting in ease of lid removal and no need for layer pads and dividers. The new container is a PP molded tub of dimensions 6.5in wide at the top (5in wide at the bottom) by 6.2in high. For improved appearance, the edges of the container are rounded.

The lid is of a snap-on design with a prominent molded Miracle-Gro logo. Unimark designed it to have a domed shape that sheds water. The lid also bears a square raised area that fits into a square molded indentation of the base of another tub. These two features allow up to six containers to be stacked one upon the other on shelves and remain stable, without the molded lid being deformed.

The tub and lid are available in various color combinations according to the type of plant food they contain: green and yellow for All Purpose Plant Food; pink and blue for Azalea, Camellia, Rhododendron Plant Food; yellow and green for Bloom Booster® Plant Food; and red and yellow for Rose Plant Food. The carry handle is made from a galvanized 0.92in wire, which rotates to both sides.

The labels appear both on the back and front of the tubs and are pressure-sensitive and brightly printed with illustrations of the plants for which the food inside is targeted. York Tape & Label converts the labels.


The manufacture and assembly of the Miracle-Gro tub takes place in the Unimark facility at Reedsville. The facility occupies two buildings providing 76,000ft² of floor space. Each building has a class 100,000 cleanroom and a ‘white’ room. There are 44 injection molding machines. The plant for the production of Miracle-Gro containers was custom-designed and built by Unimark and Progressive Automation and Manufacturing.


The injection molding is carried out by the Engel ES 1000, a 1,000t clamp force injection molder. The machine was chosen for its excellent repeatability and accuracy. The machine uses a five-point toggle clamp system, which ensures efficiency and high throughput of material.

The ES 1000 is controlled by an Engel CC100 controller, which makes use of 32-bit RISC-based system architecture for data processing and then digital signal transmission to control the assembly line.

The Engel injection molding machine molds four tubs per cycle from a PP resin. The tubs are removed by a robot arm, allowed to cool and are then placed on a belt assembly line. There, a pneumatic gripper attaches the wire handles and an in-line, dual-head applicator attaches the labels, front and back.

Finished tubs are picked up and stacked in predetermined stack sizes by vacuum grippers, and are indexed out of the assembly cell. After that, they are manually loaded onto pallets for transport to the filling plant.