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The Secret of Day-Night Temperature Differentials · Hydroponics Daily

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  Hello there and welcome back to
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  Hydroponics Daily, your go-to podcast for everything soilless cultivation.
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  I'm your host Dr. Russell Sharp and today's episode is all about day-night temperature
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  differentials or DIF for short and this is not a subject that I would dive straight
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  into if you're new to hydroponics.
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  If you're new to hydroponics then go to one of the earlier episodes that we recorded in January.
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  If you can't find them on Apple or Spotify, go to Podbean, where we host the podcast.
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  If you are an expert, then get ready and settled in for a deep dive into a subject
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  that can really improve your grow and also replace the need for growth regulators
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  by manipulating the environment.
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  So this all stems from day-night temperature differentials were discovered in
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  the 1980s at Michigan State University by a researcher called Dr. Royal Hines.
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  Good name that, isn't it? Dr. Royal Hines. And he found that the time of day
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  you apply heat or increase the temperature has a dramatic effect on how plants grow.
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  If it's hotter during the day, the plants will grow much taller than if the
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  temperature is kept a constant for 24 hours.
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  So if you put the heat on during the day, then plants will grow taller.
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  This is known as a diff positive heating as the difference is calculated by
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  subtracting the night temperature from the day temperature.
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  The amount of increased growth is then proportional to the increase in the diff.
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  In contrast if the nights are warmer than the days then it's classed as diff
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  negative then the plants will stay squat.
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  Again the inhibition of growth proportional to the diff.
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  Dr Hines in Michigan developed his findings into guidelines for commercial growers
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  and now diff techniques are widely used in cut flower growing especially to
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  accurately control the length of flower stalks where they do want some growth
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  but not a massive amount.
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  And so if you think a bit from my grow room
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  perspective hydroponics then if you had a negative
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  biff warmer temperatures during the night then you
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  could potentially keep your plants a lot lot squatter and
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  they wouldn't get if they're tall plants they wouldn't get
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  close to the lights and that's where we suffer from an
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  issue in hydroponics the sort of flowers get
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  burnt and then the foliage gets
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  damaged if it gets close to the to the
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  lights because they're just so much hotter and the lights density so much higher obviously
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  one of the big issues here is going to be that when the lights are on during
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  the day they are creating a lots
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  of heat if not the biggest bulk of heat that's
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  going into the the grow room so if you're going to have
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  a negative diff you're going to have to put money into heating your
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  grow room during the night and also
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  potentially cooling your grow room during the day
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  and that is not always possible it's not
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  always cost effective as well so it's something to
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  consider but i appreciate that you can't always have
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  a negative diff sometimes you can
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  get close to or just try and get close to the main
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  thing might be to prevent such a positive
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  diff created by the
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  lights and then just having no heating during the night that could be potentially.
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  Where your stretch and your legginess is coming from so differentials are used
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  commercially and they're manipulated by growers to particularly look at stretch and plant height.
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  An added complexity there is that you're going to have to have a controller,
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  an environmental controller that allows for a diff to occur.
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  And so this could be a computerized system
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  or it could be that simply your heaters come on exactly at the time that your
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  lights go off and that your cooling comes on exactly at the time that your lights
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  come on and that's that's one way around it rather than having a computerized
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  expensive computerized system.
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  Obviously, a positive diff is more natural and usually results in faster photosynthesis,
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  efficient respiration at night, and obviously that's stem elongation.
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  So a positive diff is something I would use for lettuce or leafy greens,
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  and any crop that you don't need to worry about it getting close to lights.
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  So tomatoes and peppers in their vegetative stage, cut flowers that need long,
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  strong stems, you're obviously going to have to have a positive diff and increase
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  that as you want more growth,
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  but that obviously needs to
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  be balanced by the elongation and the the cost
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  of that so a negative diff potential other
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  situations other than just in a hydroponic situation shorter.
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  Ornamental plant crops without the use of
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  growth regulators so if i was growing things like rhododendrons in
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  a greenhouse or a polytunnel i then
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  you would want to look at more
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  having a negative diff if possible and prevent bolting in
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  leafy crops that would also be another situation where
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  we want a negative growth if you had a crop that was really really
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  sensitive to bolting then i would have an i would
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  have a net zero diff so just
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  constant the same temperature so i
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  would probably use a negative diff in petunias geranium
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  and chrysanthemums if one's a kitten squat too strong
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  and over negative diff can reduce photosynthesis during the
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  day as well so that's something else to consider so maybe not do this one in
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  vegetative and it could delay flowering as well
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  and it can increase susceptibility to
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  humidity related issues like gray mold if
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  you've got your humidity could go out of
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  whack by by using a diff flowering can
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  also be regulated by temperature in a number of crops
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  as well as we always think of it as being photoperiod regulated
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  but temperature can also have a very important effect so chrysanthemums and
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  lilies grow faster under specific diff conditions tomatoes and peppers which
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  are usually non-photoperiodic so it doesn't matter if you give them long days
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  short days long day nights short nights they will just flower.
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  Immaterial tomatoes and peppers may form better trusses under
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  slightly positive diff just because they've got more natural
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  higher photosynthesis rates so they can
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  get to that stage that maturity faster and orchids often require a dropping
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  temperature at night to trigger bloom initiation so not so much the high temperatures
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  during the day but that lower temperature at night really important for orchids
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  to initiate flowering and that might be why orchids in your in your house don't.
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  Flower as often as you would hope because you might
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  have a very warm house during the night and
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  diff can affect flower quality as well so the
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  intensity of petal colors stem strength and bud
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  size so it's not just about yield
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  but aesthetics and structural quality too so hydroponics
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  especially in greenhouses and vertical farms manipulating the
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  diff requires automated temperature control systems even
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  if that is just mechanical plug you
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  know those things that tick tick tick tick and then suddenly when
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  the town comes around the uh the plug
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  clicks on so for humidity for heaters cooling
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  lighting dehumidifiers things
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  like this all those controllers or a fully automated computer control
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  system that has the ability to control diff so thoughtful
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  energy management and humidity management don't forget the humidity in
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  this and then at the very least monitoring
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  and logging to understand how understand how those changes affected
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  growth in your crop if you're growing something unusual then
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  you might want to experiment with different diffs different
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  day night temperature differentials if you're growing something completely new
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  or hasn't been growing hydroponically before so things like peonies we talked
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  about marsh samphire once we talked about grapevines hydroponically could a
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  diff a i would have think a positive diff for grapevines would be good.
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  Cool but not too cold a night so things
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  like that and in vertical farms it may be easier to maintain
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  a constant temperature without risking leggy growth
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  risk humidity changing going completely out
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  of the whack things like that so there's not one size fits all
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  diff depends on your crop if you're
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  growing leafy greens you can have something way up to 10 degrees celsius
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  diff so a positive 10 degrees uplift during
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  the day temperatures tomatoes and cucumbers six
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  to eight degrees and then ornamentals that
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  we talked about a zero diff or even a minus
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  two to five diff so test test
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  it adapt it and let me know if you've used a diff
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  in the past and how it affected plant growth in
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  winter if you're growing in a domestic situation then your
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  differential can be really really high and it's something you really need
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  to look at because you could have a very very low night
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  temperatures and very high daytime temperatures if
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  you're in a grow room or in say a greenhouse
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  or a conservatory things like this so always
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  something to really look at could you have too much of a.
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  Positive diff that's causing your stretch so remember
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  temperature isn't just a background setting it's a
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  signal a positive signal to the plants plants feel
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  the difference between day and night and respond in profound
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  ways and it's not just amount
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  of growth it's the way they grow as well so in hydroponics where
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  precision is everything managing diff gives you a
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  lever to sculpt your plant growth reduce chemical
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  inputs such as growth regulators and boost quality so
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  this is somewhere where if you've heard of the term crop steering
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  then differentials temperature day
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  night temperature differentials play into that so thanks
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  very much for tuning into hydroponics daily for today as i say i'm
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  dr russell sharp you've got any temperature questions or comments on temperature
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  strategies in your grow room or your greenhouse then let me know you can always
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  get in touch with me by going onto the utrema websites as i say on the last
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  few episodes utrema is latin for wasabi so it's e-u-t-r-e-m-a,
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  and why did i call my company utrema because i like wasabi and because i thought it sounded.
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  Borderline scientific the sort of thing that many sort
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  of specialist crop input companies might be cord so that's why we're called
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  utreema and we make a number of products like gold leaf in the us and liquid
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  gold in the uk but many others as well until tomorrow where i have no idea what
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  i'm going to talk about uh thank you very much for listening goodbye.