Controlled Environment Agriculture

Frequently Asked Questions

Hydroponics Basics


Vertical Farming


Hydroponics Basics

  • What is the definition of hydroponics?
  • Hydroponics simply means growing in a root medium that is not natural soil. This means the poinsettia you buy for the holidays is also "hydroponic" because the root medium is a mix of peat moss and something else. For the purist, hydroponics means growing with only nutrient solution.

  • Where can I get a list of all crops that can be grown hydroponically?
  • We do not know of such a list. In a general sense, almost anything can be grown hydroponically. In a practical sense, we would not grow crops such as corn and wheat in hydroponic systems. Any crop that can be grown in a field and stored for a long period of time (carrots, potatoes) would not be a good candidate for indoor hydroponic production.

  • How difficult is it to use hydroponics? I know people can do it at home but there is a big difference when it comes to large scale commercial use.
  • It is a very technical skill needed. One needs a special eye to "know" when the plants are ailing (before the average person can tell). One needs to know about horticulture, computers, environments, energy matters, mechanical systems, marketing, sales, personnel management, pest management, plant pathology, plant nutrient management, and on and on and on. Yes, people can do it at home. People could raise a 4-H calf in the garage also, but that is somewhat different from operating a 1000 head dairy farm.......

  • I’m getting mixed information on whether or not hydroponics is cost effective.  What is your opinion on this?
  • It is being used commercially, so it must be, at least in a limited sense. However, one needs a niche market or a product that is not easily obtained locally to make it profitable. is like any farming. That is, profit margins and investment returns are not as high as in some other industries. You have to "want" to do it and not be concerned with maximum return on investment.


  • I am considering starting a small business growing hydroponic produce.  Where do I begin?
  • The first book I recommend is by Howard Resh, titled "Hydroponic Food Production".  Beyond that, you should consider what might appeal to a niche market in your local community.

    Once you have chosen a crop, you must find a greenhouse that is available to rent/purchase or decide on a structure to build. Furthermore, you must consider if you want to be in production year-round. If this is the case, then you will have to evaluate the potential of the natural light that is available to you during the winter. If the natural light available during winter is not adequate, you will need to consider supplemental lighting. For lettuce, this means about 75-80 kWh/ft2 of lit area (using HPS luminaires, which are still the most efficient today), assuming sufficient light to grow the crop rapidly (17 mol/m2 of daily light integral). Yes, you can add less light, making the crop slower to grow, but then the total cost per unit of production increases. Plant growth is directly proportional to the accumulated light integral. As a comparative example, we are in Ithaca, NY, which is one of the most cloudy regions of the U.S. Even here we obtain 70% of our yearly light from the sun and energy is still a large part of production cost. A first step toward deciding how much supplemental light you want to design for would be to determine how much natural light you receive year-round.

  • Are there any crops that should not be considered when determining what to grow in a Controlled Environment facility?
  • While almost all crops that can be grown outdoors can be produced indoors, there are certain crops that should not be considered because of either the difficulties associated with the type of plant or because the crop is a commodity that cannot be produced at a competitive price due to the increased overhead associated with CEA production.  Examples of the first type of crop include corn (height) or fruit trees. Examples of commodity crop would also include corn along with iceburg lettuce, melons, and grains. Any crop that can be grown in a field and stored for a long period of time (carrots, potatoes) would not be a good candidate for indoor hydroponic production.

  • How can I recruit a head grower?  Where can I go to learn how to become a grower.
  • This is a difficult problem. There is not a facility that produces a large number of greenhouse growers on a regular basis. Often head growers are recruited away from existing greenhouse operations including those in Europe. There are a few organizations that house ‘short courses’ that address certain aspects of greenhouse production (Crop King $595/2 days, AZ $625/3 days, Ohio Short Course).

  • Why is spinach not being grown hydroponically on a large scale?
  • It eventually succumbs to a water-borne fungal disease called Pythium aphanerdamatum. The CEA group at Cornell has done extensive research on methods that may be used to control this problem. To date, a large-scale operation using CU CEA Pythium prevention techniques is not in production.

  • When you say lettuce should have 17 mol/m^2 of PAR per day, what does this mean?
  • This refers to the combination of natural light that is transmitted through the glazing as well as any artificial light that is used. Our research has shown that an average of 17 mol/m2/light/day gives optimal growth while minimizing tipburn in lettuce.

  • I know that we cannot afford to set up a system such as the one you describe for producing floating hydroponic lettuce.  What advice can you give for creating a crude production system in an existing but unused greenhouse?
  • You can get into greens production at many different levels. What is being done at Finger Lakes Fresh is at the upper end, in terms of technologies. Probably the aspect that makes it most different is the use of supplemental lights, controlled to a constant daily light integral, so production can be very consistent from day to day. This means installing both supplemental lights and movable shades. If your greenhouses are not constructed to install a shade, and at least 4m (13 ft) high at the sidewalls to accommodate lighting, you should consider something more along the lines of seasonal production. Growth is always proportional to the integral of light so production will be noticeably slower from October through April.

    A second question must relate to marketing. Have you carefully explored marketing options and associated prices? As a small grower, you would be very much at the mercy of larger outlets such as supermarket chains, suggesting you might find better opportunities in restaurants, ethnic markets, niche markets, and perhaps in the "boutique" greens business where prices are higher. Along with this, you will need to be careful about what type of packaging will be required, for some types of packaging is relatively expensive. Along with marketing information, you will also need to explore transportation. If the size greenhouse you propose is not large, so a refrigerated truck of typical size will likely be too large to be efficient. However, you will still need some way to keep the product cool during summer transport.

    As another factor, you will need to explore the requirements for food safety that are imposed by the buyers. The produce industry is becoming very fussy about such matters, and not all customers may impose the same rules, making production protocols a bit of a puzzle at times.

    I suggest you think about trying to specialize at first, however, because becoming an instantaneous expert on growing a mix of crops in hydroponics is a challenge beyond the reach of most folks. Moreover, different crops require their own specific conditions for best production, making growth of many species, or even cultivars of the same crop, in a "multi-cultural" greenhouse problematic.

  • How can I calculate the cost per square foot that will be required to heat the greenhouse?
  • There are a few pieces of information that you will need to gather: Set point temperature for the greenhouse, type of glazing used, Average outside temperature during the winter (note: you do not want the absolute coldest that it could possibly get – you could end up installing way too large of a system). The general equation is: Q = U A Δ T where Q = heat loss, U = heat transfer coefficient, a property of the material heat is being lost through, A is the area in square feet of each surface of the structure and Δ T is the difference between the internal temperature of the greenhouse and average outdoor temperature during the coldest portion of the time you intend to use the facility. U ranges from 0.13 (8”concrete block plus 1” urethane) – 1.13 (single layer glass)BTU/ft 2 - °F- hr. For a worksheet to help you calculate this, see Greenhouse Engineering – NRAES 33, 1994.

    For a website to assist with the calculations:

  • Where can I find information on the average amount of light that is available from the sun in during all the seasons of the year in different parts of the country?
  • This is a question without a good answer. We have good data for the U.S.,and world-wide data is available - although probably sketchy once you leave the U.S. and Europe.

    I suggest, as a first try, go to:, enter as a new user, and see whether they may have something useful for your study. It is a bit cumbersome to use, but has a lot of data.

    A few other sites that may (or may not!) be interesting are:

    Only U.S. Data:
    Quick Overview:
    Maybe Useful?:
    You may need to convert units to evaluate the data, so an online calculator may be found at:

  • How much does hydroponic nutrient solution cost per square foot of production area?
  • We have limited data on that because the nutrient cost is quite low and not of great concern. For example, using lab-grade chemicals, we calculated the value of nutrients in one head of lettuce to be $0.002. We also calculated roughly the same number per harvested tomato. Back to the lettuce, if our system produces 85 heads per square foot, per year (as it does when changes not yet on the web site are made), that leads to a cost of nutrients of $0.17 per square foot, per year. And that is with lab grade chemicals, which are more expensive than commercial grade.

  • Do the current or future New York State Energy laws - Energy Conservation Construction Code of New York State (2010 ECCCNYS) apply to greenhouses?
  • No, as the ECCCNYS permits the use of reference standard ASHRAE 90.1-2004 and the version to be in effect next year (90.1-2007) states in section 2.3 (c) that all provisions of that standard do not apply to certain buildings and portions of building systems that use energy primarily to provide for industrial, manufacturing, or commercial processes. The Department of State Codes Division opinion considers all buildings used primarily for agricultural purposes as deployed for commercial processes and hence, per the national ASHRAE 90.1 standard, these buildings or additions are exempt from all of the code requirements.

  • Is root rot a problem in hydroponically grown lettuce?
  • No. The secret, perhaps, is not to let the solution get too warm - we want it to be in the mid 70s F (low 20's C) all year, and never more than about 78 F (25.5 C). The ponds, with the plants on Styrofoam floats, do not gain heat very rapidly so a modest amount of cooling is needed (and are heated in our winter).

    This is an advantage for the float method described in the Lettuce Handbook - with an alternate system - nutrient film technology (NFT) we measured the solution/root temperature in the channels to track air temperature, staying about 2 degrees C (4 F) below air temperature. This was frequently too high in mid-summer, even in our more moderate climate and with evaporative cooling of the greenhouse.

  • What is the initial cost of a nutrient film technique (NFT) system compared to the floating system you describe in the Lettuce Handbook?
  • I doubt there is much difference but have not made a careful study of this. The ponds can be built yourself to save money. Of course, the float system does require a totally concreted floor, which NFT does not.

  • Is there more time spent cleaning Styrofoam rafts that you use in your floating system than gutters in an NFT system?
  • Less time for the floats. The floats are dipped in a sodium hypochlorite (e.g., Chlorox®) solution, then air dried, then re-used. There is no scrubbing time required.

Vertical Farming

  • What are some of the problems associated with vertical farming?
  • The first problem is light. Plants do not "perceive" light in the same way as do humans. To begin, the human eye responds logarithmically so a low light level still looks bright. Plants respond linearly. In a vertical farm, floors above shade the floors below. This is inevitable. In Ithaca we receive 70% of the needed light to grow lettuce from the Sun, over the year. Even with this, we still need to provide approximately 50 kWh/ft2 of supplemental light in the growing area of our greenhouse to achieve the high plant productivity that we do. This means, in a vertical greenhouse, it would be necessary to provide perhaps another 100 kWh/ft2 in a year, which would be very costly and require a lot of energy! Some would say the electricity could be gotten from renewables. But the scale does not work there. If one looks at photovoltaic and assumes (optimistically) the panels will be 15% efficient over the year, and conversion of electricity to light in the most efficient light sources is 20%, this means a 3% efficiency of converting solar energy to supplemental light. This suggests a photovoltaic panel system nearly 33 times as great in area would be needed to grow plants in a vertical greenhouse.

    Second problem. Construction costs of commercial buildings with multiple stories is approximately an order of magnitude greater than construction costs of a modern greenhouse, per square foot of production area. This makes little economic sense unless food is a lot more expensive. The embodied energy within the storied building would compensate for a great deal of transportation from greenhouses located just outside cities where land is cheaper but an efficient transport system could bring the produce into the city for distribution.

    Plants suffer from air pollution, perhaps more than humans. Pollutants such as ozone along a busy highway can reduce plant growth by a third or more. City centers are usually the places with the lowest air quality.

    Hauling everything up and down and up and down is energy inefficient, difficult to do, and requires additional infrastructure in the vertical farm.

    and so on....... Yes, much information on the web it positive about vertical farms. Notice, however, that the enthusiasts are not very involved in either commercial plant growing or agriculture in any way.......