Greenhouse production of microgreens: growth media, fertilization and seed treatments
Date
2006
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Publisher
University of Delaware
Abstract
A series of experiments was conducted with the objective of lessening the greenhouse production time and cost for selected microgreen species. Initially, seeds of table beet (Beta vulgaris ‘Early Wonder Tall Top’; TB), arugula (Eruca vesicaria subsp. sativa; AR) and amaranth (Amaranthus tricolor; AM) were determined to be of high quality (high germination percentage and rate) across a 15 to 25° C range. The seeding rates recommended commercially (Johnny’s Select Seeds) for these crops resulted in the greatest shoot fresh weight/m2 (economic yield), but in the lowest fresh weight per shoot compared to lower seeding rates. ☐ Peat-lite was found to be superior to lower cost wood or paper fiber mulches as growth media for TB, AR or AM microgreens. Insufficient nutrient levels and low cation exchange capacity, as well as excessive liquid retention or inadequate aeration, probably contributed to reduced growth of the microgreens in the mulches. Increasing concentration of solution fertilization (0, 75 or 150 mg N/L daily) increased shoot growth of AR and TB in all media, but especially in peat-lite. Preplant incorporation of nitrogen fertilizers at 2000 mg N/L of peat-lite affected AR shoot fresh wt/m2 in the order Ca(NO3)2 > NH4NO3 > CO(NH2)2 > (NH4)2SO4. Adding the Ca(NO3)2 as liquid rather than as solid increased shoot fresh wt/m2 by 6%. The preplant incorporation of Ca(NO3)2 in the peat-lite, by stimulating microgreen shoot growth, would reduce production time. ☐ Germinating seeds in a medium within an incubator then sowing the germinated seed-medium mixture on the peat-lite in the greenhouse would reduce production time. Germinating AR and TB seeds in the hydrophilic polymer, Supersorb C, compared to fine, grade 5 vermiculite resulted in greater and earlier germination. Since the human toxicity of Supersorb C is unknown, only vermiculite was used in further experiments. The optimum water concentration (% of vermiculite dry weight) and incubation period at 20° C for TB was 150% for 5 days (50% germination, 6.5 mm long radicles), and for AR was 200% for 1 day (81.5% germination, 2 mm long radicles). Combining these germination treatments with preplant incorporation of Ca(NO3)2 at 1000 mg N/L of peat-lite plus daily solution fertilization with 75 mg N/L from 21-5-20, gave the greatest shoot fresh weight per m2 of AR and TB in the university greenhouse when compared to control seeds and other fertilization treatments. ☐ The final experiment compared the standard ARC Greenhouses production practices for TB microgreen production (control seed, no preplant incorporation of nitrogen fertilizer in the peat-lite, and daily solution fertilization with 100 mg N/L from 21-5-20) with selected seed and fertilization treatments that might hasten production in the greenhouse. Sowing TB seedballs germinated in vermiculite (200% water, 4.5 days at 20° C) increased shoot fresh weight/m2 by 13% at 15 days after planting. A further increase in shoot fresh weight/m2 to 52% above that achieved with standard production practices resulted from incorporating Ca(NO3)2 at 1000 mg N/L into the peat-lite before planting (along with the standard daily 100 mg N/L solution fertilization).