Poinsettia Growth and Development Response to Container Root Substrate with Biochar

A greenhouse study was conducted to evaluate the growth and development of poinsettia 'Prestige Red' (Euphorbia pulcherrima) grown in a commercial peat-based potting mix (Sunshine Mix #1) amended with biochar at 0%, 20%, 40%, 60%, 80%, or 100% (by volume) at four different fertigation regimes: F1: 100 to 200 mg.L-1 nitrogen (N), F2: 200 to 300 mg.L-1 N (control), F3: 300 to 400 mg.L-1 N, or F4: 400 to 500 mg.L-1 N. The experiment was a two-factor factorial design with 10 replications for each combination of biochar by fertigation. As the percentage of biochar increased, root substrate pore space and bulk density increased, while container capacity decreased. Root rot and red bract necrosis only occurred in F4 combined with 100% biochar. Plants grown in 40% biochar had a similar growth and development to those in 0% biochar. Up to 80% biochar, plants exhibited no significant change, except in terms of dry weight, which decreased at higher biochar percentages (60% and 80%). In summary, at a fertigation rate of 100 mg.L-1 N to 400 mg.L-1 N, up to 80% biochar could be used as an amendment to peat-based root substrate with acceptable growth reduction and no changes in quality.