Garden mums require plentiful amounts of water and delivering adequate water during the summer is not a simple task. Irrigation frequency is affected by characteristics of the growing media, container size, stage of growth, and the environment. Because garden mums are often grown outdoors, the weather can play a large part in irrigation timing. Rain reduces the need for irrigation, while hot, dry weather can greatly increase irrigation frequency. The media should be moist, or allowed to dry only slightly between waterings. Enough water should be applied at each irrigation to completely saturate the medium plus 10 to 15 percent leachate. This leaching prevents soluble salts buildup in the substrate.
Garden mums should not be allowed to wilt. Water stress will greatly reduce plant growth and can cause yellowing of lower leaves or even death on bright summer days. In the middle of the summer, the water demand of mums may require multiple waterings per day. This makes hand watering impractical. Few garden mum growers depend entirely on manual irrigation with a hose. Manual watering cannot provide the degree of control over soil moisture required for quality mum culture and the cost in time and labor is high. Most garden mum growers have the crop on some form of automatic watering system when placed at final spacing outdoors. Overhead sprinkler-type watering systems have not proven satisfactory because they waste a lot of water, provide poor watering uniformity especially on windy days, and keep the foliage wet for extended periods.
Microtube systems are widely used for garden mums and provide the greatest uniformity with the least waste of water. It is important that installation of a microtube system be 'designed' for the area in which it will be used, preferably by those experienced in microtube system design. Uniformity and water application rate can be checked by collecting water from several tubes in different locations on the same station for a known period of time. Measuring the amount of water collected in each container can be used to determine the time required to deliver a specific amount of water to plants.
Garden mums require large quantities of fertilizer during the vegetative stage of production, especially nitrogen and potassium. It is vital that plants be supplied ample nutrition beginning the day of potting. However, as flowers begin to open, fertilization should be reduced to very low levels and may be discontinued if levels have been adequate during production. This is because much of the growth of the plant is completed by the time flowers begin to open so the plant requires less fertilizer. In addition, the keep quality of garden mums in the retail setting is improved by reducing soluble salts levels in the medium before shipping.
Most garden mum growers deliver a water soluble fertilizer to the crop using a fertilizer injector. These devices inject a small amount of concentrated liquid solution into the water line so that plants receive fertilizer every time they require water. It is important to fertilize with enough solution to completely saturate the medium plus 10 to 15 percent leachate. Damaging amounts of fertilizer can buildup if the medium is not fertilized thoroughly.
Apply 200 to 250 parts per million (ppm) nitrogen with a fertilizer injector at each watering using a complete N-P-K fertilizer such as 20-10-20 or 15-15-15. Choose a fertilizer that has between 60 and 75 percent of the total nitrogen in the nitrate form. Many growers will alternate between 20-10-20 and a fertilizer containing calcium and magnesium such as 15-5-15 Cal-Mag. The fertilizer rate can be reduced to about 125-150 ppm nitrogen when flower buds begin to show color. Although these rates are for a constant fertilization program, liquid fertilizer can be applied at weekly intervals when constant fertilization is inconvenient or labor intensive. For weekly application, use 400 to 500 ppm nitrogen.
Benefits have been observed in garden mums when liquid fertilization in combined with a controlled-release fertilizer. Osmocote 14-14-14 or 19-6-12 slowly releases fertilizer over a period of 2 1/2 to 3 months and can be either mixed with the medium before potting or added as a top dressing after potting. Experience has shown that application is often more beneficial when applied to the media surface. Keep in mind that once a controlled-release fertilizer has been added to the medium, it cannot be removed and the grower has little control over fertilizer availability. Therefore, follow the manufacturers recommendation rate for soil mixing or as a top dress. Liquid fertilization rates should be reduced when used in combination with controlled-release fertilizers.
Growers should manage the fertility program for garden mums by performing a soil test and tissue analysis at least once a month. Floral crop soil tests provide medium pH, soluble salts, and levels of macro and micro nutrients. The soluble salts for garden mums should be 1.5 to 2.0 mmhos/cm (2:1 extraction) but should not exceed 2.5. Low readings often mean not enough fertilizer is being applied, application is too infrequent, or a combination of both. High readings may mean too much fertilizer is being applied, application is too frequent, not enough water is applied to wet the medium and obtain drainage, drainage is poor, or a combination of these conditions exists. Tissue analysis provides information about what nutrients are being absorbed by the roots and transported to the foliage. Guidelines for tissue analysis values can be found in Table 4.