Page 13 - Griffin Gazette Issue 2 - 2018
P. 13

lettuce is to direct air straight down to the
            crop using large, paddle fans.
            Growing in a northern climate can help
            with temperature control, but it creates a
            need for supplemental lighting. According
            to Dr. Neil Mattson, lettuce requires a
            daily light integral (DLI) of 17 mol/m /
            day. Beaman et al  reports that optimal
            light intensity for basil production is 500
            µmol/m /s, which would equate to nearly
            29  mol/m /day  under  their  suggested
            16-hour photoperiod. Assuming a 65%
            light transmission rate, the natural light
            level outside the greenhouse would need
            to be 25 mol/m /day to hit 17 mol/m /  ensure that they will maintain their integrity   Aphids  top the list for insects  with
            day in the greenhouse. This seems fine   in the hydroponic system. Sleeved   Botrytis and powdery mildew topping
            until you study the Clemson DLI maps   products, such as Jiffy 7-O and Elle pots   the list for diseases. Sclerotinia can also
            and realize that most growers in the US   are gaining in popularity and can support   be a problem in lettuce, though it’s less
            don’t  come  anywhere  near  25  mol/m /  a more organic approach. Traditional   commonly encountered. Expect to stock
            day outside from November to January,   peat-based media can also be used with   your chemical cabinet differently to prevent
            and northern growers don’t reliably hit his   net pots.               and control these pests—chemicals must
            level until sometime in March. One option   Fertility                 be labeled for greenhouse use on the
            is to  grow the crop slower and longer.   Flower growers know a great deal about   specific crops you are growing.
            The problem with this approach is two-  fertilizers  and  managing  media  pH.  This   Basil is highly susceptible to downy
            fold: Lower quality and lower revenue.   knowledge will be put to good use when   mildew, which can be devastating to
            Grower reports indicate that crop quality   growing food, though things change a   the  crop.  Preventing  downy  mildew  in
            increases dramatically with supplemental   bit  when  it  comes  to  lettuce  and  herbs.   basil starts at sowing with preventative
            lighting in winter months. So, conversly,   Remember  that  inert  media  does  not   treatments and should continue through
            your winter crop will be of lower quality   provide the same buffering that a peat-  shipping. Fortunately, there are several
            when it is not lit (lower weight, thinner   based mix affords, so the fertility needs   very good products to help prevent the
            leaves, etc). Additionally, growing a longer   to be more tightly managed. Recirculating   disease from developing, and a couple of
            crop means that you turn fewer crops, so   systems generally include monitoring for   effective  options  that  can be  used if  the
            your revenue per square foot goes down.   both pH and EC, and many will make   disease appears.
            The impact amplifies when one considers   automatic adjustments to control both.
            that winter is a time when supply and   Speaking of EC, the fertility level needed   We all know that the ornamental market
            demand greatly favor a grower that can   for basil is similar to that used for many   is  relatively  flat.  Unlike  ornamentals,  the
            consistently produce a high quality crop.                             market for greenhouse grown vegetables is
                                               flower  crops,  at  200 ppm. However,   rapidly expanding, bringing opportunities
            Are some lights better than others for   GGSPro recommends lower fertility rates   for growers around the country to expand
            lettuce and herb production? Basil can   for lettuce, at only 150 ppm. For lettuce,   their businesses. Once you have identified
            easily be lit with either HPS or LED lights.   this is about half the rate you're used to   your path to market and demand in your
            However, there are several reasons to   using for your spreading petunias.   town, city or region, it’s just a matter of
            turn to LED lights for lettuce crops. First,   The balance of nutrients needed is a little   removing some benches and adding
            HPS lights generate a fair amount of heat.   different, too. Both lettuce and herbs   some NFT equipment and lights to bring
            Remember that lettuce is a crop that   require a relatively high amount of calcium.   a new, year-round revenue stream to
            prefers to be grown cool, so adding heat   Since the inert media commonly used for   your business.
            to the crop can be problematic. LEDs add   production has very low cation exchange
            far less heat to the production space than   capacity (CEC), it’s very important to   Would you like to learn more? Join
            HPS. Additionally, LEDs generally contain   deliver a consistent source of calcium in   GGSPro and a collection of industry
            light from the blue end of the spectrum.   the fertilizer solution. There are some very   experts at our upcoming Lettuce and
            Blue  light  increases  anthocyanin  good hydroponic formulations available   Herb Production workshops that will
            production in lettuce, which means your   that will help you do this, though it’s   be held in conjunction with the Griffin
            red leaf lettuce will have better color.                              Expos in both Worcester, Mass., (August
                                               not uncommon to supplement these   27) and in Lancaster, Penn., (September
            Media                              formulations with some calcium nitrate.   25). Our half-day workshops will help you
            While many flower growers probably   Before implementing any fertility program,   understand lettuce and herb production in
            produce some herbs in peat-based media   it’s critical to understand your water   greater detail. From there, the Griffin team
            for garden center sales, most commercial   quality. There's  less  room  to  manage   and our suppliers at the Expos will help
            greenhouse  production  of  lettuce and   the root zone pH with fertilizer alone and   you understand how you can bring it all
            herbs occurs in inert media, such as   the need for pH adjustments should be   together in your greenhouse.
            rockwool and Oasis foam. Use of these   understood before production begins.
            products keeps the system free of debris   Pests                      1 Beaman, A.R, R.J Gladon and J.A Schrader.
            while allowing good porosity around the   The most common pests that create   2009. Sweet basil requires an irradiance of
            roots. Stabilized media products can also   problems  in lettuce and leafy greens   500 umol/m /s for greatest edible biomass
            work, but they should be evaluated to                                 production. HortScience 44:64-67.
                                               crops are well known to flower growers:
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