Effects of Fertilizer Source and Rate On Zinnia Cut Flower Production in a High Tunnel

This study evaluated the effects of pre-plant compost incorporation and fertigation with different levels of conventional and organic fertilizers during the growing season on zinnia (Benary’s Giant Mix) plant growth and number of cut flowers produced in a high tunnel. The study was arranged as a 4 × 5 factorial, with a split plot design. The main plot was one of four pre-plant compost applications: composted broiler litter, vemicompost, cotton gin compost, and control (no compost).  The compost rate used was 4 tons/acre and the compost was incorporated into the bed before laying the plastic mulch. Under each compost treatment, there were five fertigation treatments: no fertilizer, organic low (100 ppm nitrogen (N) from MultiBloom), organic high (200 ppm N from MultiBloom), conventional low (100 ppm N from Peter’s 20-10-20), and conventional high (200 ppm N from Peter’s 20-10-20). Each treatment combination included 10 zinnia plants which were planted half ft apart with two parallel rows on one bed. Each treatment combination was replicated 3 times. Plants were transplanted into the beds in early April and each plant was supplied with 200 ml of solution from each fertigation treatment once a week for one month and then twice a week from May through September. Zinnia stems were harvested as soon as the blooms were completely opened, starting from mid-May through September. The number of stems longer than 12 inches was recorded. Results indicated that the pre-plant compost had significant effect on leaf SPAD reading and plant growth index during early stage of plant growth, and plants that received composted broiler litter had significantly higher SPAD reading and plant growth index than other treatments; however, pre-plant compost had no effect on the total number of stems produced. Plants that fertigated with high rate of organic fertilizers produced similar stems as plants treated with conventional high, but more stems than lower rates of either conventional or organic fertilizers. Plants that did not receive any fertigation produced the lowest number of stems. This study shows that growers can have summer long production of zinnia cuts in a high tunnel in Mississippi. The data also shows that similar levels of N from either the conventional or organic fertilizer tested in this study can produce similar number of zinnia stems.