Starving Weeds Through Smarter Fertilizer Placements
June 2, 2026 In a recent e-Gro Alert, Manjot Kaur Sidhu of the University of Maine and Debalina Saha of Michigan State University (MSU) cover how strategic fertilizer placements can be utilized to manage weeds in ornamental container production.
Weeds are a persistent threat in greenhouse environments due to high humidity and soil moisture. Their presence creates competition with ornamentals for a variety of resources, including:
- Nutrients
- Oxygen
- Soil/growing medium
- Space
- Water
If left untreated, this results in the reduction of plant quality and uniformity and, therefore, a reduction in market value and ROI.
Additionally, Sidhu and Saha note that “certain aggressive weeds can produce allelopathic compounds,” which can “actively inhibit the root development of the surrounding ornamental species.”
With many herbicides not cleared for greenhouses, and hand weeding a time- and labor-intensive process, the pair looked to cultural practices for weed management and how fertilizer placements can aid in the effort.
Sub-Surface Methods of Fertilizer Placement for Weed Control
Two alternative methods were singled out to influence weed control in greenhouses:
1. Dibbling
Dibbling involves “placing the CRF in a concentrated pocket directly below the root zone at a depth of a few inches” to deliver nutrients directly near a crop’s roots, and, in doing so, starving surface weeds.
2. Sub-Dressing
Sub-dressing involves “applying the CRF in a uniform layer a few inches below the soil surface during the potting process” to ensure that deep roots have “exclusive access to nutrition” while growing. In addition to suppressing weeds, this method also reduces “nutrient leaching during irrigation events” as the fertilizer is barricaded by the substrate above it.
Both methods help increase the availability of nutrients, giving plants a competitive advantage in their battle against weeds. Additionally, many weed seeds have limited energy reserves, meaning that without a strong connection to the fertilizer, they’ll fail to develop. Lastly, cultural practices, such as these, help to minimize the need for herbicides, making them an important part of an integrated pest management (IPM) program.
For additional information on alternative methods of plant fertilization to help with weed control, including a look at several studies conducted at MSU to test the sub-surface applications, please read the full e-Gro (Electronic Grower Resources Online) alert “Starving the Competition: A Smarter Way to Fertilize Your Plants.“
Additional and current e-Gro alert pieces from Volume 15 (2026) can be found online.
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