Fertilization
Fertilization is the key to success with any garden mum crop. Mums demand fertilizer and providing their needs early will solve many headaches that could occur later in the crop.
Fertilization rates vary depending upon the type of media and fertilizer bring used, and the frequency of application. A constant fertilization program (fertilization with every watering) using 300 to 400 ppm from a complete fertilizer N-P-K is a good basic program to use from day one for producing quality garden mums. This rate may need to be adjusted up or down depending on the media and the weather. For example:
- Bark mixes usually need to be fertilized at higher levels of 350 to 400 ppm because the bark will tie up some of the nitrogen making it less available to the plant.
- If rainy weather occurs for more than two or three consecutive days, provide booster feeds of 400+ ppm.
- If severe hot weather occurs, plants may partially or totally shut down until temperatures moderate. If your soil tests show readings in the desired level, but the plants show little growth, you may need to reduce feed or stop feeding until cooler weather occurs or plant growth resumes. Booster feedings of 350 to 400 ppm will be needed to maximize the growth resurgence once the temperatures have moderated.
When you are in a position to easily manipulate the fertilization program, start from the day the cuttings are planted with 300 to 400 ppm of 20-20-20 or a fertilizer that is at least 60% ammonical nitrogen. This fertilizer rate will continue with every irrigation for 28 to 35 days. After four to five weeks the plants should have reached their second stage of branching. This is when the laterals from the original cutting have laterals approximately one-inch long. This is the point at which the body of the plant has been built and all that is left is building plant size before flowering. From here through day 42 to 49, continue fertilizing with every irrigation but reduce feed levels to 200 to 250 ppm and switch to a Cal-Mag type feed or a fertilizer with more nitrate nitrogen to provide strength to the stems. Keep in mind that weather conditions may require adjustments as defined above. Six to seven weeks after the cuttings were planted until the flowering plants are sold, feed levels can be reduced to 150 to 200 ppm twice weekly until color, or even go bi-weekly with a Cal-Mag type feed. This will maintain foliage color without creating excess growth before flowering.
If liquid fertilization is not possible, controlled-release fertilizers may be used. Reliance on controlled-release fertilizer alone is not recommended as the initial fertilizer release will seldom be enough to maximize initial plant growth and control of the release later in the crop is not possible. When controlled-release fertilizers are used, a topdressing of a 3- to 4-month release formula such as 14-14-14 or 15-9-12 or similar types at the medium to high rate (see label) per 8 x 5-inch mum pan is often applied at planting. For soilless media, choose a formulation with micronutrients (e.g., “Plus” types). Be careful to distribute the fertilizer evenly over the soil surface. Applying this fertilizer in a single pile may cause burning of the plants. The fertilizer must be placed so it is moistened at each watering to be effective.
Controlled-release fertilizers may also be incorporated into the media prior to planting. Medium to high rates (6 to 12 pounds per cubic yard; see label) are also used. Such mixes should be used for planting within a week after mixing since prolonged contact of the fertilizer with moist media could result in excessive soluble salts that may injure plant roots. Either method, topdressing or incorporation, works if properly managed.
The rate of release of a controlled-release fertilizer is affected by its formulation (rate of release), soil temperature and frequency of irrigation. Most formulations release at temperatures of 70°F or above. This is of particular significance for outdoor plantings where the late spring/early summer temperatures are cold. This is when liquid feedings become extremely important to get the plant moving and create vegetative growth. It is doubly important if cool temperature stress kicks the plant into reproductivity. Liquid feeds of at least 60% ammonia forms of nitrogen, combined with no water stress, are a must to minimize severe premature budding! A second application of a 3- to 4-month formulation will likely be needed if it is the only source of fertilizer, since high summer temperatures and frequent irrigation accelerate the release/leaching of fertilizer from the fertilizer capsules. The second application should be applied 3 to 6 weeks after the first. I using a 3 or 4-week interval, a third application will be required to finish the crop and should be applied 3 to 4 weeks after the second application. Unseasonably high temperatures can cause problems with young plants when the rate of release is sudden and massive due to the high temperatures.
Fertilization should be continued at least until the buds are just starting to show flower color.
Use foliar and root medium analyses to monitor crop nutrition. Guidelines for foliar analysis: N: 4 – 6.5%; P: 0.25 – 1.0%; K: 3.5 – 6.5%; Ca: 0.5 – 2.0%; Mg: 0.3 – 0.6%; B: 25 – 100 ppm; Cu: 5 – 50 ppm; Fe: 50 – 300 ppm.
Guidelines for root medium analysis (saturated media extract): EC (Units note: mS/cm = millisiemens/cm = mmhos/cm): Establishing 0.8 – 1.5 mS/cm, Growing 1.7 – 3.0 mS/cm, Finishing 0.8 – 1.5 mS/cm; N: 50 – 250 ppm nitrate; 0 – 30 ppm ammonia; P: 5 – 50 ppm; K: 50 – 200 ppm; Ca: 75 – 300 ppm; Mg: 25 – 100 ppm; B: 0.05 – 0.5 ppm; Cu: 0.001 – 0.06 ppm; Fe: 0.3 – 3.0 ppm; Mn: 0.03 – 3.0 ppm; Zn: 0.3 – 3.0 ppm.