Evaluation of water and nutritional consumption of New Guinea Impatiens and poinsettia grown in two compost-based substrates

In order to reduce the use of peat in growing media for pot cultivation of ornamental plants, two compost-based substrates were evaluated in comparison to standard peat substrates. Plants of New Guinea Impatiens (Impatiens hawkeri Bull.) cv. Boogy and poinsettia (Euphorbia pulcherrima Willd.) cv. Peterstar were cultivated in media containing 50% of pine bark compost or 50% of green waste compost and compared to a primarily peat-based substrate. Three levels of nitrogen were given through subirrigation with ebb/flow system: 75., 150 and 225 ppm. Fertigation frequency was regulated using tensiometric measurements and the amounts of water and fertilizer absorbed by each substrate were recorded. Substrate containing pine bark compost was similar to peat-based substrates for physical characteristics and for water and fertilizer absorption. Plant development was also similar. Green waste compost, however, reduced water holding capacity of the substrate and the absorption of nutrient solution. Growth of the two species tested was lower than in the other substrates. Pine bark compost has the tendency to immobilize nitrogen: a significant enhance of height was observed in poinsettia by increasing N level from 75 to 150 ppm. The highest N level tested was too high for New Guinea Impatiens grown in pine bark compost substrate.