Optimizing Bag Material and Potting Mix Components for ‘Gardening In a Bag'

Abstract. Gardening in a bag has been proven a viable method to easily create garden beds for such plants as vinca (Catharanthus roseus). However, ideal bag material and components of the potting mix inside the bags have not been determined. This experiment attempts to identify the type of bag and potting mix components that result in best growth and performance of vinca grown in bags in the landscape. Vinca ‘Pacifica XP White’ plants were planted on 3 June into plastic or paper bags filled with 3/4ths cubic foot of topsoil, potting mix, topsoil + mushroom compost, or potting mix + mushroom compost. Vinca were also planted in the ground. Each bag or ground treatment contained three plants. The research plots were covered with about 1 inch of mulch around the plants and enough mulch around and between bags to hide the bags. Data collections occurred on 20 July and 20 September. No data were taken in August because plants and the research plot were stressed by 13 inches of rain that fell in less than one week in early August. In July, vinca in the ground were smaller and had fewer flowers than plants in all other growing regimes, except for plants growing in topsoil in plastic bags. Plants growing in treatments containing potting mix, whether in plastic or paper bags, tended to be taller and wider, had more flowers, and earned a higher visual rating than plants growing in treatments containing topsoil. Bag treatment had no effect on flower size. In September, vinca growing in the ground were still smaller and less floriferous, and had the lowest visual quality among plants in all growing regimes. Vinca growing in treatments containing potting mix tended to be taller than plants in treatments containing topsoil, but plant width and flower and leaf diameter were generally not significantly different among the bag treatments. Plants growing in bags made of paper had more flowers than plants growing in plastic bags with the exception of plants growing in plastic bags containing topsoil + compost. The highest-quality plants, based on visual ratings, were those grown in topsoil in paper bags, although several other bag treatments produced plants that were statistically similar in appearance.