Use of sawdust and bark of Pinus radiata as substrates for Belgian Chrysanthemums grown for summer production

Abstract

In search for alternative substrates for containerized ornamentals, potted Dgndranthema grandiflora (chrysanthemum) plants were grown in Maule Region for summer flowering, using pure fresh sawdust and sawdust plus pine bark (both from Pinus radiata) in mixes as growing media, with soluble fertilizer in fertigation. Rooted cuttings of cv. 'Marina' (Belgian type) were planted individually in 17 cm (diameter) x 14 cm (height) pots filled with different media. For 75 days, plants were kept in an unheated greenhouse under artificial long days and were fertilized weekly with a soluble fertilizer. After pinching, plants were taken outside the greenhouse to full sun conditions, and artificial short days were applied for 8 weeks. In a split plot design, 8 treatments were carried out: 4 media mixes (pure sawdust and sawdust: bark in ratios 1:1, 2:1 or 3:1 by volume), and 2 frequencies of watering with soluble fertilizer; daily and every 2 days (applying a solution of 200 ppm N, based on a soluble NPK fertilizer, with 3 replica per treatment. Plants showed a reduced growth in pure sawdust (25.5 cm height) as compared with sawdust: bark (30 to 35 cm). Media mixes and fertilization frequency affected diameter; plants in pure sawdust had a smaller diameter (34 cm) than plants cultivated in sawdust: bark (40 cm). Plants fertilized every 2 days had a smaller diameter (36 cm) than those fertilized daily (41 cm). Plants grown in pure sawdust had yellowish-green leaves, while the leaves of plants grown in sawdust plus bark showed colors close to dark green. Flowers showed different color as when grown in autumn (yellow vs. orange). Plants of all treatments bloomed on the same date. The pH of all media mixes in all measurements during cultivation time was close to 6.0. It is concluded that it is possible to grow potted chrysanthemum in all the tested media mixes, but in the case of pure sawdust, to avoid problems due to its low retention of irrigation solution, it is advisable to mix it with pine bark in a 3:1 ratio.