Garden Mums: Fertility Management Programs

Although there are a variety of fertilizer programs that work well for garden mums, I would be remiss not to mention that fertilizer is not the exclusive answer when it comes to producing quality plants. Water management, especially in the early stages, is crucial in determining the final size, shape and quality of garden mums. It would be better to say that the desired outcome results from integrating both feed and water practises.

Growing a desirable quality plant of a specific size and sturdiness requires a balance between feed and moisture conditions. Regardless of the fertilizer formulation and rate of application, stress due to dryness – particularly during the early growth period – can result in woodier stems and smaller plants of lesser quality. Keeping cuttings actively growing during the first five weeks of the crop is a prerequisite to producing a strong and sturdy chassis that will support a well branched plant. Allowing plants to wilt during the early stages of growth can restrict branching activity, especially after pinching established cuttings.

Let us now examine a simplified fertilizer program that addresses the different growing phases of garden mums.

Stage 1 (Initial Vegetative Growth)

The objective at this stage is to induce strong vegetative growth. Young mums respond well to an ammoniacal-N fertilizer such as a 20-10-20 formulation until two to three weeks after pinch. Ammonium nitrogen at moderate levels will promote larger lower leaves, enhanced lateral shoot development and thick stems to produce the strong and sturdy structure necessary to support a well branched plant.

A precautionary note for northern growers who may experience cool temperatures and/or low light conditions once the plants have been moved outdoors: the use of general-purpose 20-20-20 or other high ammonia-N fertilizers can slow down plant growth if cold media temperatures persist. Lower soil temperatures slow down the activity of the nitrifying bacteria that break down the nitrogen to a usable form. It is also important to note that the higher P content in such formulations is much more than the plant requires. High P levels can contribute to plant stretch.

Stage 2 (Moderating Growth Phase)

Once the plants are actively growing, it is important to begin a feed regime that will start to moderate growth, slowing down the rapid vegetative phase. Begin to alternate between a 20-10-20 formulation and a calcium-based fertilizer. This feed program can be continued until the flower buds are just visible. As the buds begin to develop, gradually switch over to more frequent applications of calcium-based fertilizer. A calcium-based formulation with reduced ammonia will produce a smaller upper leaf area, allowing light to penetrate through the canopy to prevent the loss of lower leaves due to lack of light. Always be prepared to alternate between fertilizer formulations to achieve the desired pattern of growth.

Stage 3 (Toning Phase)

Monitoring the height of the crop and adjusting the fertility program as buds continue to mature will prevent the plants from filling in their space too fast and stretching outside their ideal height range. As the plants approach their final stages of development, the ratio of nitrogen to potassium should be addressed. You may have to use formulations with a higher ratio of potassium to nitrogen if excessive growth due to too much nitrogen is still evident. Do not forget to supplement with magnesium when feeding calcium or higher rates of potassium; this will prevent magnesium deficiency due to antagonism by these two elements.

In summary, begin with optimal spacing between plants, do not stress the young plants during the first 4 to 5 weeks of growth, keep the plants moist, and alternate well-balanced fertilizers tailored to the stage of growth and the desired size of the plants.

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