How to Fuel Garden Mums for Peak Performance
Ideal pH & General Fertility Approach
The foundation of a successful garden mum fertility program begins with maintaining an ideal media pH of 5.4 to 5.8. This acidic range supports optimal micronutrient uptake, especially iron. In situations where controlled-release fertilizers (CRFs) are used exclusively—particularly with irrigation water that has high alkalinity—acid injection may be necessary to maintain this low soil pH target. For reference, fall asters, often grown alongside mums, prefer a slightly higher pH range of 5.7 to 6.2, requiring different management.
Garden mum fertility can be managed using CRF, water-soluble fertilizer (WSF), or a combined approach known as “Half and Half”, as described by GGSPro. The method selected often depends on irrigation practices: CRF works well with outdoor overhead irrigation, while WSF is more effective with drip irrigation. The Half and Half approach offers both adaptability and consistent nutrition, particularly helpful in outdoor production where rain can leach nutrients.
Regardless of the program used, initial WSF feeding is essential for the first 2-3 weeks after transplant, even when CRF is incorporated. This readily available, early nutrition supports soft, vigorous growth needed for strong branching and crop establishment. Formulations used in CRF plans should be selected based on season-long nutrient release stability, assuming heat and excessive rainfall will decrease overall product longevity. Some common CRF options for mums include Osmocote Plus 15-9-12, Florikan 12-4-11, and Nutricote 13-11-11.
Figure 1: Healthy garden mum crop with adequate fertility.
Fertility Timing & Application Strategies
The first two to three weeks of production are critical for mum development. This period sets the structural foundation for heavy roots, adequate branching, and overall form. During this phase, high-phosphorus fertilizers such as 20-20-20 or 20-10-20 are ideal to stimulate early growth and vigor as well as help push soil pH down. These formulations should be applied regularly during the initial period, regardless of the long-term fertility strategy selected.
For those following a WSF-only program, constant feeding at 300 ppm nitrogen (N) from planting through week 2-3 is recommended. In Half and Half systems, a 250 ppm N constant feed during this period is appropriate. For CRF-only systems, a weekly 300 ppm N feed supports early growth before CRF becomes fully active.
As the crop matures, from week three to first color, growers on WSF or Half and Half programs should reduce nitrogen rates to 200–250 ppm N, transitioning to lower phosphorus formulations such as 21-5-20, and begin incorporating calcium nitrate-based fertilizers (e.g., 15-0-15). A 3 to 4:1 rotation of acidic (e.g., 21-5-20) to calcium containing-basic (e.g., 15-0-15) formulations balances pH management while providing sufficient calcium supply, which is crucial for stem strength in later development.
From first color through sale, WSF-only growers can taper down to 100 ppm N, while Half and Half and CRF-only programs typically shift to clear water.
Nutrient-Specific Considerations
Iron
Garden mums are heavy feeders of iron and highly sensitive to even moderate deficiencies, especially as pH drifts above 5.8. Early signs of iron deficiency include interveinal chlorosis in young leaves, with veins remaining green or the entire leaf turning bright green or yellow in more extreme situations. Symptoms often emerge in specific varieties before affecting the entire crop which should be an indicator that a correction needs to be made promptly.
The first step in correcting or preventing iron issues is to adjust the pH downward, either through sulfuric acid injection or acid-based fertilizers. If symptoms persist despite optimal pH, apply a chelated iron product such as Plantex Iron Chelate DTPA or EDDHA at a rate of 4–5 oz per 100 gallons as a one-time drench only. Avoid foliar applications due to the risk of phytotoxicity, especially under high light or heat stress. If applying overhead, always rinse foliage thoroughly with clear water before drying and avoid applying iron to drought-stressed plants.
Figure 2: Garden mum displaying iron and magnesium deficiency.
Magnesium
Mums also have moderate magnesium requirements, and deficiencies typically present as interveinal chlorosis on lower leaves. The most efficient solution is the addition of Epsom salts (magnesium sulfate). This can be supplied constantly at 2 oz per 100 gallons with non-calcium containing fertilizers or as a biweekly pulse at 8 oz per 100 gallons. An alternative is using a fertilizer that already contains elevated magnesium levels, such as 18-8-17, which is similar to 20-10-20 but blended with a higher concentration of Epsom salts.
Calcium
Later in the season, calcium becomes important for structural strength, bloom development, and overall plant resilience. Products like 17-4-17, 15-5-15, and 13-2-13 provide both calcium and magnesium, though calcium nitrate-based feeds should be rotated with acidifying fertilizers such as 20-10-20 to maintain an acidic growing media pH.
Salinity & Root Health
Mums are sensitive to high salts, despite their reputation as heavy feeders. The most common causes of salt injury include applying fertilizer over dry media or allowing plants to dry out before fertilizing. In both scenarios, salt concentrations around the roots become too high, causing physiological drought or direct root damage. To avoid this, always irrigate to ensure moist media prior to fertilization, and avoid fertilizer build-up by implementing occasional clear water irrigations, especially in WSF programs.
Figure 3: Unhealthy root system in garden mum.
Conversely, low fertility can stall a mum crop. In regions where mum growers receive excess rainfall during the summer months can lead to the leaching of fertilizer out of growing media. Having CRF in the media helps ensure nutrition is available to the plant regardless of heavy rain events. However, for growers solely using WSF, it is important to fertigate plants immediately after a rain event to put fertilizer back into that container rather than waiting to the next dry down.
Conclusion
A successful garden mum nutrition program balances initial vigor, media pH management, and long-term nutrient availability. Whether using WSF, CRF, or a hybrid system, the early weeks set the tone for branching, color, and marketable quality. Pay close attention to iron and magnesium nutrition, monitor media pH regularly, and prevent salt buildup by respecting the moisture status of the media. With thoughtful, season-long planning, growers can produce strong, vibrant mums that meet quality standards and customer expectations year after year. For more information or personalized guidance, feel free to reach out to GGSPro by phone or email. We’re here to support your crops every step of the way.
Water Soluble Fertilizer (WSF)
Controlled Release Fertilizer (CRF)
Misc. Supplements
Note: not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 6th Edition GGSPro Technical Reference Guide. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!
The foundation of a successful garden mum fertility program begins with maintaining an ideal media pH of 5.4 to 5.8. This acidic range supports optimal micronutrient uptake, especially iron. In situations where controlled-release fertilizers (CRFs) are used exclusively—particularly with irrigation water that has high alkalinity—acid injection may be necessary to maintain this low soil pH target. For reference, fall asters, often grown alongside mums, prefer a slightly higher pH range of 5.7 to 6.2, requiring different management.
Garden mum fertility can be managed using CRF, water-soluble fertilizer (WSF), or a combined approach known as “Half and Half”, as described by GGSPro. The method selected often depends on irrigation practices: CRF works well with outdoor overhead irrigation, while WSF is more effective with drip irrigation. The Half and Half approach offers both adaptability and consistent nutrition, particularly helpful in outdoor production where rain can leach nutrients.
Regardless of the program used, initial WSF feeding is essential for the first 2-3 weeks after transplant, even when CRF is incorporated. This readily available, early nutrition supports soft, vigorous growth needed for strong branching and crop establishment. Formulations used in CRF plans should be selected based on season-long nutrient release stability, assuming heat and excessive rainfall will decrease overall product longevity. Some common CRF options for mums include Osmocote Plus 15-9-12, Florikan 12-4-11, and Nutricote 13-11-11.
Figure 1: Healthy garden mum crop with adequate fertility.
Fertility Timing & Application Strategies
The first two to three weeks of production are critical for mum development. This period sets the structural foundation for heavy roots, adequate branching, and overall form. During this phase, high-phosphorus fertilizers such as 20-20-20 or 20-10-20 are ideal to stimulate early growth and vigor as well as help push soil pH down. These formulations should be applied regularly during the initial period, regardless of the long-term fertility strategy selected.
For those following a WSF-only program, constant feeding at 300 ppm nitrogen (N) from planting through week 2-3 is recommended. In Half and Half systems, a 250 ppm N constant feed during this period is appropriate. For CRF-only systems, a weekly 300 ppm N feed supports early growth before CRF becomes fully active.
As the crop matures, from week three to first color, growers on WSF or Half and Half programs should reduce nitrogen rates to 200–250 ppm N, transitioning to lower phosphorus formulations such as 21-5-20, and begin incorporating calcium nitrate-based fertilizers (e.g., 15-0-15). A 3 to 4:1 rotation of acidic (e.g., 21-5-20) to calcium containing-basic (e.g., 15-0-15) formulations balances pH management while providing sufficient calcium supply, which is crucial for stem strength in later development.
From first color through sale, WSF-only growers can taper down to 100 ppm N, while Half and Half and CRF-only programs typically shift to clear water.
Nutrient-Specific Considerations
Iron
Garden mums are heavy feeders of iron and highly sensitive to even moderate deficiencies, especially as pH drifts above 5.8. Early signs of iron deficiency include interveinal chlorosis in young leaves, with veins remaining green or the entire leaf turning bright green or yellow in more extreme situations. Symptoms often emerge in specific varieties before affecting the entire crop which should be an indicator that a correction needs to be made promptly.
The first step in correcting or preventing iron issues is to adjust the pH downward, either through sulfuric acid injection or acid-based fertilizers. If symptoms persist despite optimal pH, apply a chelated iron product such as Plantex Iron Chelate DTPA or EDDHA at a rate of 4–5 oz per 100 gallons as a one-time drench only. Avoid foliar applications due to the risk of phytotoxicity, especially under high light or heat stress. If applying overhead, always rinse foliage thoroughly with clear water before drying and avoid applying iron to drought-stressed plants.
Figure 2: Garden mum displaying iron and magnesium deficiency.
Magnesium
Mums also have moderate magnesium requirements, and deficiencies typically present as interveinal chlorosis on lower leaves. The most efficient solution is the addition of Epsom salts (magnesium sulfate). This can be supplied constantly at 2 oz per 100 gallons with non-calcium containing fertilizers or as a biweekly pulse at 8 oz per 100 gallons. An alternative is using a fertilizer that already contains elevated magnesium levels, such as 18-8-17, which is similar to 20-10-20 but blended with a higher concentration of Epsom salts.
Calcium
Later in the season, calcium becomes important for structural strength, bloom development, and overall plant resilience. Products like 17-4-17, 15-5-15, and 13-2-13 provide both calcium and magnesium, though calcium nitrate-based feeds should be rotated with acidifying fertilizers such as 20-10-20 to maintain an acidic growing media pH.
Salinity & Root Health
Mums are sensitive to high salts, despite their reputation as heavy feeders. The most common causes of salt injury include applying fertilizer over dry media or allowing plants to dry out before fertilizing. In both scenarios, salt concentrations around the roots become too high, causing physiological drought or direct root damage. To avoid this, always irrigate to ensure moist media prior to fertilization, and avoid fertilizer build-up by implementing occasional clear water irrigations, especially in WSF programs.
Figure 3: Unhealthy root system in garden mum.
Conversely, low fertility can stall a mum crop. In regions where mum growers receive excess rainfall during the summer months can lead to the leaching of fertilizer out of growing media. Having CRF in the media helps ensure nutrition is available to the plant regardless of heavy rain events. However, for growers solely using WSF, it is important to fertigate plants immediately after a rain event to put fertilizer back into that container rather than waiting to the next dry down.
Conclusion
A successful garden mum nutrition program balances initial vigor, media pH management, and long-term nutrient availability. Whether using WSF, CRF, or a hybrid system, the early weeks set the tone for branching, color, and marketable quality. Pay close attention to iron and magnesium nutrition, monitor media pH regularly, and prevent salt buildup by respecting the moisture status of the media. With thoughtful, season-long planning, growers can produce strong, vibrant mums that meet quality standards and customer expectations year after year. For more information or personalized guidance, feel free to reach out to GGSPro by phone or email. We’re here to support your crops every step of the way.
Water Soluble Fertilizer (WSF)
Controlled Release Fertilizer (CRF)
Misc. Supplements
Note: not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 6th Edition GGSPro Technical Reference Guide. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!
