Sphagnum peat is a finite resource that is often used in the horticultural industry as a component in many substrates specifically in greenhouse production for transplants (Abad et al., 2001). Peat is mined from its natural wetland habitat, and excessive use has depleted much of these resources. Because of the depletion, less of the product is available, resulting in increase in price and decreased quality (Robertson, 1993). Peat also has disadvantages of which include difficulty to wet, providing no nutrients as media, and is acidic. As a result, much research has focused on alternative resources for peat in the greenhouse industry (Abad et al., 2001; Ostos et al., 2008; Raviv et al., 1998). Composts have also proved to suppress soil-borne pathogens found common in peatmoss such as plant fungi [Fusarium oxysporum and Sclerotinia minor among others (Veeken et al., 2005)].
Composts are an attractive option for peat substitutes in transplant production (Bustamante et al., 2008). Composts produced from cow and poultry manures maintained suitable physical properties for production of transplants (Bustamante et al., 2008). Research has (and is) being conducted incorporating composts to grow basil, coriander (Coriandrum sativum), peppermint (Mentha ×piperita), and thyme (Thymus vulgaris), among others (Bustamante et al., 2008; DeKalb et al., 2014; Herrera et al., 1997; O’Brien and Barker, 1996; Zheljazkov and Warman, 2004). O’Brien and Barker (1996) reported that shoot dry weight of peppermint transplants was larger when grown in composts derived from mixed municipal solids, mature biosolid-wood chips, agricultural wastes, and leaves. However, these authors reported limited growth with the composts containing both immature biosolids and yard wastes as a result of high salinity and ammonium (as in the case of the immature biosolid) or insufficient nutrient supply (as with the yard waste).
Raviv (2005) states that compost’s usability as a safe and environmentally responsible substrate makes it an appropriate low-cost peat substitute. Since the late 1970s, the price of high-quality peat has been increasing, especially in countries that lack a native peatmoss source (Abad et al., 2001). However, a lack of knowledge and education of growers is apparent as they continue to look for “cheap products and tend to ignore the unavoidable connection between quality and cost” (Raviv, 2005). Because of the versatility among the chemical properties and nutrient content, composts can be used as a low-cost addition to soilless substrate productions. Organic residues generated by agriculture, livestock farming, forestry, and industries and cities are being successfully used for container media for ornamental production and are considered useful value-added products (Abad et al., 2001).
Swine lagoon compost resulted in a substrate with zinc (Zn), copper (Cu), pH, and EC levels that were appropriate for germinating seedlings (Herring et al., 2018). A bioassay study found that germination of radish (Raphanus sativus ‘Cherriette’), tomato (Solanum lycopersicum ‘Moneymaker’), and marigold (Tagetes patula ‘Janie Deep Orange’) was better in the control substrate (Pro Line C/P; Jolly Gardener, Portland, ME) than in the SLC. However, numerically, germination of all the species was similar between the two substrates except for zinnia (Zinnia elegans ‘Dreamland Red’), a salt-sensitive species, because of a high EC. Growth of seedlings of each species 28 d after sowing was the same for each substrate. The finished composts averaged 1.8% nitrogen (N), 1.5% phosphorus (P), and 0.2% potassium (K). The findings of Herring et al. (2018) indicate that SLC may be a suitable substrate for herb transplant production.
Herb production is a growing market and is becoming more popular in the vegetable industry. Vegetable producers are beginning to recognize the consumer demand of fresh herbs and are incorporating herb production into their established operations; however, little information is published about how to produce herbs commercially (Davis, 1994; Morgan, 2001). Because of the consumer demand for the product, and the lack of published information about its production, the objective of this study was to compare the growth of three herb species in SLC and two commercially available substrates.
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