Whether used as bedding plants or as indoor containerized plants, live culinary herbs are a popular containerized plant. It is important to control shoot growth to produce plants sized proportionally to containers for aesthetic appearance and to increase container density in the greenhouse and during shipping (Whipker et al., 2011). Chemical plant growth retardants (PGRs) are commonly used to control containerized floriculture crop growth (Nelson, 2012). However, no PGRs are currently labeled for use on containerized culinary herbs (Currey, 2019). Therefore, nonchemical methods of suppressing plant growth are required to control the height of containerized herbs grown for edible consumption.
There are several environmental conditions and cultural practices that can suppress plant growth. Common nonchemical approaches to controlling containerized crop growth include cultivar selection (Currey and Lopez, 2010), modifying day and night air temperature regimes (Erwin and Heins, 1995), brushing (Latimer, 1998), and restricting irrigation (Alem et al., 2015) and mineral nutrients (Whipker et al., 1999). Although more widely used for ornamental flowering plants, several of these techniques are also useful for controlling containerized herb growth. While not common for many annual herbs, there are compact sweet basil and dill cultivars, although the selection is limited (Currey and Mazur, 2018). Sweet basil (Ocimum basilicum) grown with a zero-difference between the day and night air temperatures (DIF; DIF = day temperature − night temperature) or a morning drop can inhibit basil height compared with plants grown with a positive DIF (Islam et al., 2016). Brushing can suppress containerized sweet basil, cilantro (Coriandrum sativum), and parsley (Petroselinum crispum) growth (Appling, 2012). Maintaining the substrate moisture content of containerized sweet basil, dill (Anethum graveolens), parsley, and sage (Salvia officinalis) at 40% to 50% less (by volume) than well-watered plants also suppresses growth (Currey et al., 2019). Additionally, applying 50 or 100 mg·L−1 N to water-soluble fertilizer or 0.6 to 1.5 kg·m−3 of controlled-release fertilizer can produce healthy-looking plants without excessive size (Flax and Currey, 2016). However, in addition to the total fertilizer concentration directly affecting plant growth, P affects the growth and development of herbaceous plants.
Phosphorous has a growth-promoting effect up to the species-specific maxima; therefore, restricting P can restrict growth (Frantz, 2013; Henry et al., 2017, 2018a; Justice and Faust, 2015; Nelson et al., 2012). Initial studies that have identified the effect of P on stem elongation and subsequent use of P restriction to suppress growth were focused on seedling plugs (Nelson et al., 2012). Because of the effectiveness of P restriction to restrict seedling growth, it has become a widely adopted practice for commercial plug producers (Whipker, 2014). More recently, restricting P fertilization for growth control has been extended to the finished production of containerized plants (Henry et al., 2017, 2018a; Justice and Faust, 2015). Although containerized plant P restriction research is focused on flowering ornamental species, P restriction could also be used for finishing containerized culinary herbs. However, we have found no research quantifying the effects of P on containerized culinary herb growth and development.
The objective of this experiment was to quantify the effects of P concentrations on the growth and development of four popular culinary herbs. We hypothesized that restricted P would suppress containerized herb growth and that the magnitude of the effects would vary among the different species of the study. To test our hypothesis, we formulated nutrient solutions varying only in their P concentration to provide a range of P concentrations; they ranged from no P to the maximum concentration, representing standard greenhouse practices, for containerized herbs during their greenhouse finishing or forcing period.
Appling, S.M. 2012 Colored shade cloth affects the growth of basil, parsley, and cilantro. M.S. Thesis, Virginia Polytechnic Institute and State Univ., Blacksburg
Argo, W.R. & Biernbaum, J.A. 1997 Lime, water source, and fertilizer nitrogen form affect substrate-pH and nitrogen accumulation and uptake HortScience 32 71 74
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
Currey, C.J. & Mazur, T.Z. 2018 Spinning the herb wheel. GrowerTalks 82(4):66, 68–69
Currey, C.J. 2019 Keeping your herbs under control. GrowerTalks 82(12):62, 64
Currey, C.J., Flax, N.J., Litvin, A.G. & Metz, V.C. 2019 Substrate volumetric water content controls growth and development of containerized culinary herbs Agronomy 9 11 667
Flax, N.J. & Currey, C.J. 2016 Controlled-release and water-soluble fertilizers affect growth and tissue nutrient concentrations of basil, dill, and parsley HortScience 51 S297 (abstr.)
Frantz, J.M. 2013 Uptake efficiency of phosphorous in different light environments by zinnia. (Zinnia elegans) and vinca (Catharanthus roseus) HortScience 48 594 600
Gibson, J.L., Whipker, B.E. & Cloyd, R. 2000 Success with container production of 12 herb species. NC State Univ. Horticulture Informational Leaflet 509, Raleigh. 8 p
Gibson, J.L., Pitchay, D.S., Williams-Rhodes, A.L., Whipker, B.E., Nelson, P.V. & Dole, J.M. 2007 Nutrient deficiencies in bedding plants: A pictorial guide for identification and correction. Ball Publishing, Batavia, IL
Henry, J.B., McCall, I., Jackson, B. & Whipker, B.E. 2017 Growth response of herbaceous ornamentals to phosphorous fertilization HortScience 52 1362 1367
Henry, J.B., McCall, I. & Whipker, B.E. 2018a Phosphorous restriction as an alternative to plant growth retardants in angelonia and new guinea impatiens HortTechnology 28 136 142
Henry, J.B., McCall, I., Nelson, P.V. & Whipker, B.E. 2018b Source-sink interactions lead to atypical reproductive stage phosphorus deficiency symptoms on the upper foliage of Capsicum annuum and Chrysanthemum × morifolium Scientia Hort. 238 288 294
Islam, N., Torre, S., Wold, A.-B. & Gislerød, H.R. 2016 Effect of temperature DIF and drop on the growth, quality, total phenolic content and antioxidant activity of herbs. J Multidisciplinary Engineering Science Studies 2 266 271
Johnson, C.N., Fisher, P.R., Huang, J., Yaeger, T.H., Obreza, T.A., Vetanovetz, R.P., Argo, W.R. & Bishko, A.J. 2013 Effect of fertilizer potential acidity and nitrogen form on the pH response in a peat-based substrate with three floricultural species Scientia Hort. 162 135 143
Morgan, L. 2005 Fresh culinary herb production: A technical guide to the hydroponic and organic production of commercial fresh gourmet herb crops. Suntec, Tokomaru, New Zealand
Nau, J. 2011 Part 2: Crop culture, p. 199–736. In: J. Nau (ed.). Ball redbook, vol. 2: Crop production. Ball Publishing, West Chicago, IL
Nelson, P.V. 2012 Greenhouse operations and management, 7th ed. Prentice Hall, Upper Saddle River, NJ
Nelson, P.V., Songg, C.-Y., Huang, J., Niedziela, C.E. Jr & Swallow, W.H. 2012 Relative effects of fertilizer nitrogen form and phosphate level on control of bedding plant seedling growth HortScience 47 249 253
Van Vuren, D.P., Bouwman, A.F. & Beusen, A.H.W. 2010 Phosphorous demand for the 1970–2100 period: A scenario analysis of resource depletion Glob. Environ. Change 20 428 439
van Wyk, B.-E. 2014 Culinary herbs and spices of the world. Briza Publications, Pretoria, South Africa
Whipker, B.E. 2014 Remember the fundamentals of phosphorous nutrition. Greenhouse Grower 31(1):67–68, 71
Whipker, B.E., McCall, I. & Latimer, J.G. 2011 Growth regulators, p. 95–105. In: J. Nau (ed.). Ball redbook, vol. 2: Crop production. Ball Publishing, West Chicago, IL.
Whipker, B.E., Dasoju, S., Dosmann, M.S. & Iles, J.K. 1999 Effect of fertilizer concentration on growth of double impatiens HortTechnology 9 425 428
Whipker, B., Gibson, J. & Scoggins, H. 2018 Visual symptoms of nutritional and other disorders, p. 207–224. In: D.J. Merhaut, K.A. Williams, and S.S. Mangiafico (eds.). Water, root media, and nutrient management for greenhouse crops. University of Calif. Agr. Nat. Res., Davis, CA