This photo shows uneven distribution of controlled release fertilizer prills in 72 size cells used for growing vegetable transplants for the field. One cell had 2 prills, another had 7 or more prills. Controlled release fertilizers pre-mixed in the growing media can cause uneven growth if the fertilizer prills are not uniformly distributed between the cells. Growers should work with their media suppliers to match the proper growing media with the cell size being used. Growers can count the prills in the individual cells to determine the accuracy of the distribution of prills.
There are many causes for uneven growth of transplants. Uneven growth can result from differences in air circulation and watering between cells within trays. This problem can exist when the outside cells are drier and growth is reduced compared to the plants located in the centre of trays. The problem can become exaggerated when larger plants shade the growing media while the shorter plants are exposed to more evaporation. As a result, individual flats become dome-shaped. This problem tends to occur either where flats are not placed tightly against one another, allowing for greater air flow and drying, or where the sun warms up one side of the tray disproportionately compared to the other sides such as along a walkway.
Uneven watering and fertilizing can also cause uneven growth.
Another type of uneven growth occurs when seedlings of different sizes are transplanted side by side. Stunted transplants will continue to grow poorly due to overwatering and overfertilizing.