An example of a mobile transplanting line designed to improve production efficiency by using transplant plugs into the dibbles holes. | W. Garrett Owen, OSU
In a recent e-Gro Alert, W. Garrett Owen of The Ohio State University looks at problems associated with the extended holding of rooted cuttings and plugs in liners and trays, respectively. Here’s a look at multiple ways to mitigate the risk of damage to cuttings and plugs to ensure high-quality crops in your greenhouse or growing operation.
The Risks of Holding Liners and Plugs for Too Long
There are many ways that prolonged holding in liners or plug trays and damage and “significantly impact plant quality.” One prominent example includes the stretching of plants, which happens as a result of competing for sunlight in overcrowded trays. Stretched plants are much more fragile, meaning they are “prone to damage and resulting in uneven growth in finished containers.”
Additionally, overcrowded and stretched plants “with dense foliage can create microclimates within trays.” This microclimate of high humidity and limited airflow makes the plant material more susceptible to diseases, while the general stress of their prolonged holding and subsequent health make them more susceptible to pest infestation (aphids, mites, thrips) and nutritional deficiencies.
Avoiding Problems Associated with Extended Holding
1. Proper Planning
Owens says, “Proper planning is essential to avoid issues caused by holding rooted cuttings and plugs too long.” Propagation and transplanting timelines should be optimized ahead of time to minimize the amount of time young plants spend in liners and trays and ensure transportation can occur as soon as possible after successful transplanting.
2. Prompt Transportation
As previously stated, “The most effective way to avoid problems associated with prolonged holding is to transplant rooted cuttings or plugs into their final containers as soon as possible.” Proper optimization and coordination of transportation scheduling ensures that all young transplants have the needed “space, light, and nutrients to grow uniformly.” Excess time prior to transportation can lead to extended holding of plants currently in liners and trays, as well as the delayed transplanting of other young plants waiting for more space to open up. In turn, delayed transplanting increases the risk of stretching, exacerbating plant health problems down the line.
3. Environmental Condition Management
In the event that there are delays in transportation, greenhouse environmental conditions are crucial to mitigate the risk of stretching brought on by extended holding periods.
Adequate spacing between liners and trays reduces shade and limits competition for light. Additionally, proper photoperiods should be maintained to prevent premature flowering.
However, one of the most important factors is your greenhouse’s air temperature. Owen recommends the options of DIF (temperature differential) and DROP.
As the difference between day and night temperatures affects plant growth, a negative DIF can inhibit growth, while a positive DIF can promote growth. Meanwhile, the DROP technique is a method that “involves lowering the greenhouse temperature by 5°F-10°F for two to three hours starting at sunrise,” as a means to manage plant height without resorting to plant growth regulators (PGRs).
4. Irrigation and Nutrition Optimization
Owen also recommends employing irrigation and nutrient strategies to control the growth of young transplants. “Implementing mild water stress can limit stretch,” but not so much that plants start to wilt. Additionally, growers should “avoid over-fertilizing during holding periods” as excessive nitrogen and phosphorus can lead to stretching.
For three additional risk mitigations outlined by Owen, and additional information on avoiding damage when handling plugs and liners, please read the full e-Gro (Electronic Grower Resources Online) alert “Avoid Holding Rooted Cuttings and Plugs Too Long.” Additional and current e-Gro alert pieces from Volume 14 (2025) can be found online.
