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.
BaileyB.J.HaggettB.G.D.HunterA.AlberyW.J.SvanbergL.R.1988Monitoring nutrient film solutions using ion-selective electrodesJ. Agr. Eng. Res.40129142
BauderT.A.WaskomR.M.SutherlandP.L.DavisJ.G.2011Irrigation water quality criteria. Crop series/irrigation. Colorado State Univ. Extension Fort Collins CO. Fact sheet no. 0.506:1–4
BeamanA.GladonR.SchraderJ.2009Sweet basil requires an irradiance of 500 μmol·m−2·s−1 for greatest edible biomass productionHortScience446467
BrookeL.2003Advanced nutrient management for hydroponic growers. General Hydroponics Sebastopol CA
BrysonG.M.MillsH.A.SassevilleD.N.JonesJ.B.BarkerA.V.2014Plant analysis handbook III: A guide to sampling preparation analysis and interpretation for agronomic and horticultural crops. Micro-Macro Publishing Inc. Athens GA
BugbeeB.2016Toward an optimal spectral quality for plant growth and development: The importance of radiation captureActa Hort.1134112
ChangX.AldersonP.G.WrightC.J.2005Effect of temperature integration on the growth and volatile oil content of basil (Ocimum basilicum L.)J. Hort. Sci. Biotechnol.80593598
ChartzoulakisK.KlapakiG.2000Response of two greenhouse pepper hybrids to NaCl salinity during different growth stagesScientia Hort.86247260
ChristieE.2014Water and nutrient reuse within closed hydroponic systems. Georgia Southern Univ. Statesboro MS Thesis. 1096
DavidP.P.BonsiC.K.TrotmanA.A.DouglasD.Z.1996Nutrient management effects on sweetpotato genotypes under controlled environmentActa Hort.4406569
DunnB.SinghH.2016Electrical conductivity and pH guide for hydroponics. Oklahoma Coop. Ext. Serv. HLA–6722:1–4
FrąszczakB.KałużewiczA.KrzesińskiW.LisieckaJ.SpiżewskiT.2011Effect of differential temperature and photoperiod on growth of Ocimum basilicumŽemdirbystė Agr.98375382
GaoG.BeckerR.BrownM.EllisM.ProchaskaS.WeltyC.WilliamsR.2009Midwest home fruit production guide: Cultural practices and pest management. The Ohio State Univ. Columbus OH. 12 June 2019
HalleckL.F.2018Gardening under lights: The complete guide for indoor growers. Timber Press Portland OR
HeidekampA.J.LemleyA.T.2005Hard water. 4 July 2019. <http://waterquality.cce.cornell.edu/publications/CCEWQ-50-HardWater.pdf>
JonesJ.B.Jr2005Hydroponics: A practical guide for the soilless grower. 2nd ed. CRC Press Boca Raton FL
JonesJ.B.Jr2014Complete guide for growing plants hydroponically. CRC Press Boca Raton FL
LykasC.KatsoulasN.GiaglarasP.KittasC.2006Electrical conductivity and pH prediction in a recirculated nutrient solution of a greenhouse soilless rose cropJ. Plant Nutr.2915851599
MackowiakC.L.OwensL.P.HinkleC.R.PrinceR.P.1989Continuous hydroponic wheat production using a recirculating system. Natl. Aeronautics and Space Administration John F. Kennedy Space Center FL
MoranoG.AmalfitanoC.SellittoM.CucinielloA.MaielloR.CarusoG.2017Effects of nutritive solution electrical conductivity and plant density on growth, yield and quality of sweet basil grown in gullies by subirrigationAdv. Hort. Sci.312530
MoyaE.SahagúnC.CarrilloJ.AlpucheP.Álvarez-GonzálezC.Martínez YáñezR.2014Herbaceous plants as part of biological filter for aquaponics systemAquacult. Res.4717161726
National Gardening Association (NGA)2018National gardening survey. 8 Aug. 2019. <https://www.globenewswire.com/news-release/2018/04/18/1480986/0/en/Gardening-Reaches-an-All-Time-High.html>
NelsonP.V.2012Greenhouse operation and management. 7th ed. Pearson Education Inc. New York NY
OwenW.G.CocksonP.HenryJ.WhipkerB.E.CurreyC.J.2018Nutritional 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)2012Basil production. Directorate Communication Services Private Bag X144 Pretoria South Africa
ReshH.M.2015Hydroponics for the home grower. CRC Press Boca Raton FL
SamarakoonU.C.WeerasingheP.A.WeerakkodyW.A.P.2006Effect of electrical conductivity (EC) of the nutrient solution on nutrient uptake, growth, and yield of leaf lettuce (Lactuca sativa L.) in stationary cultureTrop. Agr. Res.181321
SavvasD.StamatiE.TsirogiannisI.L.MantzosN.BarouchasP.E.KatsoulasN.KittasC.2007Interactions between salinity and irrigation frequency in greenhouse pepper grown in closed-cycle hydroponic systemsAgr. Water Mgt.91102111
SharmaN.AcharyaS.KumarK.SinghN.ChaurasiaO.P.2018Hydroponics as an advanced technique for vegetable production: An overviewJ. Soil Water Conserv.17364371
Solis-ToapantaE.GómezC.2019Growth and photosynthetic capacity of basil grown under constant or increasing daily light integrals for indoor gardeningHortTechnology29880888
SomervilleC.CohenM.PantanellaE.StankusA.LovatelliA.2014Small-scale aquaponic food production: Integrated fish and plant farming. FAO Fish. Aquacult. Tech. Paper 589:1–259
StrunkC.LangU.2019Gardening 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
TaizL.ZeigerE.2006Plant physiology. 4th ed. Sinauer Press Inc. Sunderland MA
U.S. Department of Agriculture (USDA)1978Indoor gardening: Artificial lighting terrariums hanging baskets and plant selection. Agr. Res. Serv. Hyattsville MD
WaltersK.J.CurreyC.J.2018Effects of nutrient solution concentration and daily light integral on growth and nutrient concentration of several basil species in hydroponic productionHortScience5313191325
World Health Organization (WHO)2011Guidelines for drinking-water quality. 4th ed. WHO Press Geneva Switzerland
WortmanS.E.2015Crop physiological response to nutrient solution electrical conductivity and pH in an ebb-and-flow hydroponic system SciHort.1943442