According to a national gardening survey published in 2018, over 77% of U.S. households are involved in gardening activities, and 30% of those activities take place indoors (NGA, 2018). Indoor food gardening, which integrates the production of edible plants (e.g., herbs, greens, and low-profile fruiting vegetables) with indoor farming, provides an opportunity to support the gardening experience for consumers with limited access to a growing space (from now on referred to as “indoor gardeners”) (Halleck, 2018). However, compared with large-scale commercial production, indoor food gardening has received limited research attention. Most research-based information about growing plants indoors aims to maximize yield by providing optimal cultural practices and environmental conditions. In contrast, indoor gardeners tend to grow plants in a variety of environmental settings such as residential living rooms and kitchens, classrooms, or office spaces, which are conditioned for human comfort and function, and may not be conducive to optimal plant growth and development. Information is lacking about plant responses to practices and environments that differ from those recommended for commercial production, especially regarding the minimum inputs required to effectively provide a continuous supply of fresh produce for indoor gardening.
Hydroponic systems are popular among hobbyist gardeners because they offer the opportunity to reduce or eliminate weeding and watering, which are considered two of the most burdensome tasks with conventional outdoor gardening (Resh, 2015). In addition, water and fertilizer conservation is a feature of most hydroponic systems (Sharma et al., 2018), making them attractive alternatives for gardening. Hydroponics systems can be “open,” where excess or runoff nutrient solution is not reused; or “closed,” where nutrient solution is collected and reused. Indoor gardeners tend to prefer closed systems because these offer flexibility in terms of system design and nutrient solution handling and disposal (Resh, 2015). However, closed hydroponic systems require constant monitoring of pH and salt levels, which can become challenging for indoor gardeners.
Maintaining a balanced nutrient solution within hydroponic systems requires periodic water refills, fertilizer replenishment, and/or complete nutrient solution replacements (Christie, 2014; Resh, 2015). Several strategies can be implemented to manage the nutrient solution in closed hydroponic systems. One common strategy consists of replacing the entire solution after 1 (Jones, 2005; Lykas et al., 2006) or 2 weeks of use (David et al., 1996; Samarakoon et al., 2006; Spensley et al., 1978). Another strategy recommends the constant monitoring of ions, considering the different uptake rate of nutrients by plants (e.g., active, intermediate, and passive) (Bailey et al., 1988). However, factors such as system design and capacity, environmental conditions, water quality, type and quantity of fertilizer, number and target size of plants and their species, among others, can affect nutrient uptake and thus should be considered when handling the solution, particularly if it is being recirculated and recycled during the production cycle of a crop (Brooke, 2003; Bugbee, 2004).
Commercial growers tend to constantly monitor the electrical conductivity (EC) as an indication of nutrient concentrations in a solution (Jones, 2005; Mackowiak et al., 1989). However, EC largely reflects the accumulation of passive ions over time and thus can be a misleading indicator of nutrient availability, as it does not represent the quantity of nutrient ions absorbed by plants, nor does it differentiate among those being taken up by plants (Bugbee, 2004). There is a lack of consensus about the most appropriate method to manage nutrient solutions within closed hydroponic systems. Discarding the nutrient solution at regular intervals can be considered burdensome, time consuming, and wasteful when undertaken too frequently (Bugbee, 2004; Jones, 2014). In addition, the difference in environmental conditions (e.g., light, temperature, humidity, airflow, among others) between commercial hydroponic production (which typically occurs in a greenhouse) and indoor gardening is also expected to affect plant growth and development. Therefore, solution management strategies should differ when plants are grown in a greenhouse following commercial practices, or in an indoor environment used for indoor gardening.
Basil (Ocimum basilicum) plants are suitable for indoor gardening as they can successfully be grown in a variety of conditions such as temperature ranges from 10 to 27 °C, EC from 0.5 to 4.0 dS·m−1, pH from 4.3 to 8.2, and daily light integrals (DLIs) as low as 4 mol·m−2·d−1 (Moya et al., 2014; RSADA, 2012; Solis-Toapanta and Gómez, 2019; Walters and Currey, 2018; Wortman, 2015). This versatility may enable basil to outperform other edible crops that can be used for indoor gardening. For example, basil can be produced for an extended period, whereas salad greens and microgreens must be harvested and planted several times per year to supply a continuous harvest. Similarly, compared with some fruiting crops, basil does not need pollination, requires minimal training when pinched regularly, and can tolerate a wide range of EC values in the nutrient solution (Walters and Currey, 2018). In addition, indoor gardeners could start harvesting leaves as early as 6 weeks after sowing, which, if performed in moderation, should not affect further plant growth and development (RSADA, 2012). Finally, basil could be less susceptible to unintentional neglect (e.g., due to time and effort constraints by indoor gardeners) compared with other crops and thus is a good candidate for successful indoor gardening experiences.
The specific objectives of this study were to: 1) compare final growth and nutrient uptake of hydroponic basil plants grown with or without a nutrient solution replacement in a greenhouse or an indoor environment; and 2) characterize growth over time in both environments using a nutrient solution replacement every 2 weeks. We hypothesized that in both environments, plant growth would be higher with a biweekly nutrient solution replacement because nutrient concentrations would be close to ideal levels. In contrast, nutrients and other ions would accumulate or become depleted in the reservoir without a nutrient solution replacement. We further hypothesized that plants grown in a greenhouse would produce more biomass and have higher nutrient uptake compared with those grown in an indoor environment because of faster growth rates induced by close-to-optimal environmental conditions.
Bailey, B.J., Haggett, B.G.D., Hunter, A., Albery, W.J. & Svanberg, L.R. 1988 Monitoring nutrient film solutions using ion-selective electrodes J. Agr. Eng. Res. 40 129 142
Bauder, T.A., Waskom, R.M., Sutherland, P.L. & Davis, J.G. 2011 Irrigation water quality criteria. Crop series/irrigation. Colorado State Univ. Extension, Fort Collins, CO. Fact sheet no. 0.506:1–4
Beaman, A., Gladon, R. & Schrader, J. 2009 Sweet basil requires an irradiance of 500 μmol·m−2·s−1 for greatest edible biomass production HortScience 44 64 67
Brooke, L. 2003 Advanced nutrient management for hydroponic growers. General Hydroponics, Sebastopol, CA
Bryson, G.M., Mills, H.A., Sasseville, D.N., Jones, J.B. & Barker, A.V. 2014 Plant analysis handbook III: A guide to sampling, preparation, analysis, and interpretation for agronomic and horticultural crops. Micro-Macro Publishing, Inc., Athens, GA
Bugbee, B. 2016 Toward an optimal spectral quality for plant growth and development: The importance of radiation capture Acta Hort. 1134 1 12
Chang, X., Alderson, P.G. & Wright, C.J. 2005 Effect of temperature integration on the growth and volatile oil content of basil (Ocimum basilicum L.) J. Hort. Sci. Biotechnol. 80 593 598
Chartzoulakis, K. & Klapaki, G. 2000 Response of two greenhouse pepper hybrids to NaCl salinity during different growth stages Scientia Hort. 86 247 260
Christie, E. 2014 Water and nutrient reuse within closed hydroponic systems. Georgia Southern Univ., Statesboro, MS Thesis. 1096
David, P.P., Bonsi, C.K., Trotman, A.A. & Douglas, D.Z. 1996 Nutrient management effects on sweetpotato genotypes under controlled environment Acta Hort. 440 65 69
Dunn, B. & Singh, H. 2016 Electrical conductivity and pH guide for hydroponics. Oklahoma Coop. Ext. Serv. HLA–6722:1–4
Frąszczak, B., Kałużewicz, A., Krzesiński, W., Lisiecka, J. & Spiżewski, T. 2011 Effect of differential temperature and photoperiod on growth of Ocimum basilicum Žemdirbystė Agr. 98 375 382
Gao, G., Becker, R., Brown, M., Ellis, M., Prochaska, S., Welty, C. & Williams, R. 2009 Midwest home fruit production guide: Cultural practices and pest management. The Ohio State Univ., Columbus, OH. 12 June 2019
Halleck, L.F. 2018 Gardening under lights: The complete guide for indoor growers. Timber Press, Portland, OR
Heidekamp, A.J. & Lemley, A.T. 2005 Hard water. 4 July 2019. <http://waterquality.cce.cornell.edu/publications/CCEWQ-50-HardWater.pdf>
Jones, J.B. Jr 2005 Hydroponics: A practical guide for the soilless grower. 2nd ed. CRC Press, Boca Raton, FL
Jones, J.B. Jr 2014 Complete guide for growing plants hydroponically. CRC Press, Boca Raton, FL
Kang, J.G. & van Iersel, M.W. 2002 Nutrient solution concentration affects growth of subirrigated bedding plants J. Plant Nutr. 25 387 403
Lykas, C., Katsoulas, N., Giaglaras, P. & Kittas, C. 2006 Electrical conductivity and pH prediction in a recirculated nutrient solution of a greenhouse soilless rose crop J. Plant Nutr. 29 1585 1599
Mackowiak, C.L., Owens, L.P., Hinkle, C.R. & Prince, R.P. 1989 Continuous hydroponic wheat production using a recirculating system. Natl. Aeronautics and Space Administration, John F. Kennedy Space Center, FL
Morano, G., Amalfitano, C., Sellitto, M., Cuciniello, A., Maiello, R. & Caruso, G. 2017 Effects of nutritive solution electrical conductivity and plant density on growth, yield and quality of sweet basil grown in gullies by subirrigation Adv. Hort. Sci. 31 25 30
Moya, E., Sahagún, C., Carrillo, J., Alpuche, P., Álvarez-González, C. & Martínez Yáñez, R. 2014 Herbaceous plants as part of biological filter for aquaponics system Aquacult. Res. 47 1716 1726
National Gardening Association (NGA) 2018 National gardening survey. 8 Aug. 2019. <https://www.globenewswire.com/news-release/2018/04/18/1480986/0/en/Gardening-Reaches-an-All-Time-High.html>
Nelson, P.V. 2012 Greenhouse operation and management. 7th ed. Pearson Education Inc., New York, NY
Owen, W.G., Cockson, P., Henry, J., Whipker, B.E. & Currey, C.J. 2018 Nutritional monitoring series: Basil (Ocimum basilicum). 2 Aug. 2019. <https://urbanagnews.com/wp-content/uploads/2018/05/Nutritional-Factsheet_Basil.pdf>
Republic of South Africa Department of Agriculture (RSADA) 2012 Basil production. Directorate Communication Services, Private Bag X144, Pretoria, South Africa
Resh, H.M. 2015 Hydroponics for the home grower. CRC Press, Boca Raton, FL
Samarakoon, U.C., Weerasinghe, P.A. & Weerakkody, W.A.P. 2006 Effect of electrical conductivity (EC) of the nutrient solution on nutrient uptake, growth, and yield of leaf lettuce (Lactuca sativa L.) in stationary culture Trop. Agr. Res. 18 13 21
Savvas, D., Stamati, E., Tsirogiannis, I.L., Mantzos, N., Barouchas, P.E., Katsoulas, N. & Kittas, C. 2007 Interactions between salinity and irrigation frequency in greenhouse pepper grown in closed-cycle hydroponic systems Agr. Water Mgt. 91 102 111
Sharma, N., Acharya, S., Kumar, K., Singh, N. & Chaurasia, O.P. 2018 Hydroponics as an advanced technique for vegetable production: An overview J. Soil Water Conserv. 17 364 371
Solis-Toapanta, E. & Gómez, C. 2019 Growth and photosynthetic capacity of basil grown under constant or increasing daily light integrals for indoor gardening HortTechnology 29 880 888
Somerville, C., Cohen, M., Pantanella, E., Stankus, A. & Lovatelli, A. 2014 Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fish. Aquacult. Tech. Paper 589:1–259
Spensley, K., Winsor, G.W. & Cooper, A.J. 1978 Nutrient film technique—Crop culture in flowing nutrient solution Outlook Agr. 6 299 305
Strunk, C. & Lang, U. 2019 Gardening as more than urban agriculture: Perspectives from smaller Midwestern cities on urban gardening policies and practices. Case Studies in the Environ. Univ. of Calif. Press, Berkeley
Taiz, L. & Zeiger, E. 2006 Plant physiology. 4th ed. Sinauer Press, Inc., Sunderland, MA
U.S. Department of Agriculture (USDA) 1978 Indoor gardening: Artificial lighting, terrariums, hanging baskets, and plant selection. Agr. Res. Serv., Hyattsville, MD
Walters, K.J. & Currey, C.J. 2018 Effects of nutrient solution concentration and daily light integral on growth and nutrient concentration of several basil species in hydroponic production HortScience 53 1319 1325
World Health Organization (WHO) 2011 Guidelines for drinking-water quality. 4th ed. WHO Press, Geneva, Switzerland
Wortman, S.E. 2015 Crop physiological response to nutrient solution electrical conductivity and pH in an ebb-and-flow hydroponic system Sci Hort. 194 34 42