Article 4-1 Green Growth Plants Into Short Day Crop Production Plants

We use our green growth stage to grow our plants “big enough” for crop production. “Big enough” means different things to different growers (a few inches tall for one grower and several feet tall for another). But the time will come when our green plants have reached their “target size”: they are big enough to shift gears again – from active green growth to flowering and crop production plants.

Let’s look at the difference in growing conditions between these two stages:

  • 18 hours to 12 hours
  • Shortening the day length of the garden seems simple enough – just change the timer!
    Unfortunately, some plants will act up if the change is too quick. They’ll “stretch” -grow long, spindly shoots – and can wreck the size and spacing in your garden. To avoid this problem, gradually shorten day length – by two hours at a time, every few days (1 8-> 1 6-> 1 4—> i 2 hours). This allows the plants more time to adjust to their shorter day length , and should help to keep the plants compact.

Halides to Sodium Lamps

Most gardeners simply switch lamps (clear metal halides to compatible sodium lamps) or move plants to a flower room with sodium lamps in place. Usually we switch to sodium lamps when we start to shorten day length. Plants use both of these changes – shorter hours, and the change in the quality of the light, as signals to start flowering.

Green food to flower food

Changing foods mean a drop in nitrogen levels and an increase in the amount of other minerals that plants use in flowering stage. Potting soils hold a certain amount of fertilizer, so flushing (a heavy watering with plain water) will help to remove excess nitrogen from the root zone. You can feed immediately after flushing- with flower fertilizer.

Growers can use the change to flower food to help solve “stretching” problems, too. If your crop tends to stretch every time you put plants into flower, try keeping nitrogen levels low until crops start to show flowers.

For example, one flowering formula has two parts:

  • A:15-0-0 (3/4 teaspoon/gallon)
  • C: 0-26-17 (1 3/4 teaspoons /gallon)

“A” provides nitrogen supplied as calcium nitrate. “C” contains everything else your plants need, except nitrogen. Reducing the amount of “A” in your first mixture of flowering fertilizer reduces the nitrogen strength while still supplying your plants with all the other minerals they need. Try this reduced-nitrogen fertilizer mix at start of flower cycle.

  • A: 1/2 teaspoon/gallon
  • C: 1 3/4 teaspoons/gallon

Increase strength of “A” when crops shows flowers. Some growers use full strength “C” but no “A” for the first week of flowering. While this may be useful for plants growing in potting soils, especially if growers are reluctant to use a heavy flush with plain water because of concerns about lowering PH of their potting mix, it is not recommended for crop plants growing in rockwool or hydro-corn. Potting soils may hold minerals, but these other grow mediums don’t. If you decide to try a reduced-nitrogen nutrient mix when reducing day length, watch plants carefully for changes in leaf color: If your deep green leaves start to become paler, gradually increase nitrogen levels to full formula strength.

Temperature Change (30°C to 27°C)

Although this is a small change, it serves to remind us of how important temperatures are when we’re trying for good crop yield. High temperatures wreck crops. Keeping temperatures down can be hard with the high light levels and C02 generators we work with in the flower room. Sometimes more oscillating fans and a larger exhaust fan will bring down the temperature. If your garden is still too hot, replace C02 generators with tanks of bottled C02 and a flow regulator. Run a hose from the tank regulator to the back of an oscillating fan and let your fans blow the C02 through the plants toward the exhaust fan. Plants love C02 delivered this way, and they will gobble it up. Meanwhile, your oscillating fans and exhaust fan can work without interruption, keeping temperatures constantly at the right level.


CONTROLLING “STRETCHING” IN SHORT-DAY FLOWER CROPS ‘Long-day’ crop producers have it easy. Their tomato and rose plants seem to slide effortlessly into flowering and crop production. But ‘short-day’ growers have to contend with unwanted growth during the transition period between green growth stage and flower production. When compact ‘green’ plants suddenly sprout long, thin shoots at the start of flowering stage, growers say their crops ‘stretched’.

This used to be a simple problem for commercial growers to solve. A number of chemical growth regulators were available to control stretching in ornamental flowering crops (azaleas, geraniums, poinsettias, hydrangeas) fruit trees (apples, cherries, peach trees) even vine crops (grapes).

For growers today, however, the use of these chemicals is ancient history. Many are now off the market and gardeners have serious health concerns about the rest. So how do we control ‘stretching’ in our crops without chemical regulators? The answer lies in using a combination of crop management practices that work together to keep plants compact and sturdy at the beginning of flower cycle.

    Give ‘green’ plants proper spacing to avoid tall spindly plants. Well spaced gardens produce short broad ‘green’ plants with lots of growing tips to spread the energy of the plant constructively.

    Re-pot well before the start of the flower stage. Growers using nursery pots and ‘sunshine mix’ potting soil should re-pot to final pot size two to four weeks before start of crop production. Stop using ‘Growth Plus’ at least two weeks before starting the flower stage. Don’t use again until flowers show on the crop. Many growers find this organic product useful for fast green growth and better flower production, but it can cause ‘stretching’ if used too close to the start of flower production. Stop using ‘Growth Plus’ well before the start of flowering, and be sure flowers are showing on the plants before using it again. Giving your crops about a month’s rest from ‘Growth Plus’ allows a more compact, natural shift into the flowering growth.
    Growers in rockwool and hydro-com can easily rinse ‘green growth’ fertilizer from their roots and containers using room-temperature, pH balanced water. This removes any residue of high-nitrogen fertilizer from roots and grow mediums.

    Growers using potting soils and nursery pots can also ‘flush’ their root zones, but watch for two things:
    • Compacting (packing down) of the medium from repeated flushing.
    • pH changes: pH drops when lime is flushed from the medium.
    A heavy rinse with water can pack down the Sunshine Mix, reducing the air and water holding capacity of the medium. Rinsing potting soils can ‘leach’ (wash out) Dolomite Lime in the potting mix and create acid conditions that interfere with nutrient uptake by the plants. Add dolomite lime to Sunshine Mix after flushing and loosen compacted soil gently with an old kitchen fork. This mixes in the Dolomite Lime and restores pore spaces for air and water in the potting soil – It is a good idea to add one tablespoon of Dolomite Lime for each ‘gallon’ of pot size. (Three tablespoons for a three gallon container, for example.)
      The best way to control nitrogen levels in the early flowering stage is to use a two-part flowering fertilizer with ’15-0-0′ for the nitrogen source and all other nutrients in ‘0-27-17’. These powdered foods are easy to dissolve and use, giving you total control over nitrogen levels at the start of flowering. If your crops have ‘stretched’ in the past at this stage, try using 1/2 strength 15-0-0 (3/4 teaspoon for two gallons) with full strength (1 3/4 teaspoon for one gallon) 0-27-17. Maintain this mix until:
      • flowers begin to show on crops or
      • leaves start to lose deep green color.
      Then use complete, full strength flower formula. with full recommended nitrogen levels.
      By slowly shortening the day length of your crops, you allow your plants to gradually adjust to their new stage of growth. This helps keep crops compact while they figure out what to do next. Try reducing day-length by two hours, every second day , until you ‘ve reached your desired day length.
      Hot, crowded flower rooms will create more thin, stretched growth than crops in well-organized gardens with controlled conditions. Maintain good light levels from the start of flower cycle. Attention to spacing, air movement, and temperatures during light cycle (and during dark cycle) is important. All these conditions can influence the health and growth of your crop. Establishing great growing conditions right from the start of the flower cycle will not only keep plants compact, they’ll reward you for all your hard work down the road!

Using these grower’s tips should keep your plants well-behaved through the transition stage from green growth to crop production. Long, thin, stretched growth is weak as well as ugly, with more potential for pest and disease problems than compact, sturdy growth. And over-grown crops can crowd lamps, as they grow bigger, creating heat damage to the plant. Keep them ‘the right height’ until the flowers show, and you’re on your way to a great crop!


  • Minimum 1000 watts light for each 8 x 8 area.
  • Use sodium (yellow) lamp for flowering crops.
  • Some plants flower well with regular ‘high pressure sodium’ lamps as only light source.
  • Some plants prefer a mix of sodium and metal halide (white light) lamps.
  • Other lamps used for flower production:
  • ‘Compatible’ sodium lamps – sodium lamps which operate with metal halide ballasts.
  • ‘Phosphor coated’ metal halide lamps – the coating shifts the light spectrum towards sodium light characteristics.
  • Reduce the day length from 18 hours (green growth) to 12 hours for autumn-flowering crops.


  • Use of reflectors is decided by type of lighting:
  • Short crops (up to one meter tall) – use-reflectors for top lighting.
  • Tall crops (one meter or more) -use ‘broadside’ lighting.
  • Reflector choice is affected by shape and type of lamp:
  • sodium lamps – horizontal reflectors – no-hoods.
  • halide lamps – horizontal or vertical reflectors
  • Reflector choice is decided by size of the area to be lit:
  • ‘flat’ reflector – 8 foot x 8 foot area.
  • parabolic reflector – 6 foot x 6 foot area.
  • horizontal reflector – 5 foot x 5 foot area.


Use two oscillating fans per lamp. Stand fans are useful for tall plants, or plants on benches and stands. Blow air through plants toward exhaust fan. Oscillating fans are especially useful during flowering stage of crop production:

  • maintain correct temperature (move hot air away from plants towards exhaust fan).
  • supply fresh air and C02 to plants.
  • help move water and nutrients from roots to top growth a provide protection against plant diseases.
  • prevent pests from gaining a foothold in the garden
  • remove excess humidity from garden
  • Exhaust fans remove hot, moist air from the garden. Fan size requirements are based on the amount of heat in the garden:
  • heat from lamps.
  • heat from C02 generators.
  • heat from outside (sunlight).
  • reflected heat from plants’ leaves.
  • Minimum recommended fan sizes:
  • for a one-lamp garden – 265 CFM exhaust fan.
  • for two or three lamps – 465 or 550 CFM fan.
  • for larger gardens – consult retail store staff for advice when planning large exhaust systems.
  • Heat control is very important for achieving the best quality and quantity of your crop�especially for autumn-flowering crops, since they prefer lower daylight temperatures than during green growth stage.


  • Work with same grow mediums and same type of hydroponic systems used for green growth stage.
  • Don’t transplant crops at beginning of flower stage – it will encourage long, spindly shoot growth.
  • Final transplants to larger containers should be made at least two weeks before starting the flower cycle.


  • Use in the garden by mounting small thermometer on bamboo stake and placing in the garden, with the thermometer level with top of plants.
  • Ideal temperature for flowering and crop production: about 27°C or 80°F.
  • Move the thermometer and stake to a new location in the garden every few days to check for even temperature conditions through the garden.
  • Use small aquarium thermometer to check temperature of root zone (21°C, best) and nutrient reservoir (21° C).


  • Choose the right flowering nutrients for your grow medium. Some fertilizers work well in potting soil, but not in rockwool or hydro-corn.
  • Ask store staff for advice on the latest flowering foods for your grow medium.


  • Most growers continue with same type of irrigation system used in the green growth stage.
  • Plants may require more frequent watering as they grow larger.


  • Used to mix and hold water and nutrient solutions.
  • The size of the reservoir is determined by the number and size of plants, and type of grow medium used in the garden.
  • Larger reservoirs maintain stable food strength and stable pH level longer than small reservoirs.


  • Used to oxygenate meter and nutrient solutions in reservoir.
  • Well-aerated nutrients give plants fewer fungus problems.
  • disease can spread rapidly from plant to plant in gardens using circulating irrigation systems.
  • oxygen in water kills fungus in reservoir, stopping spread of disease through irrigation system.
  • Aerating (bubbling) nutrient solutions helps plants to take up food easier and faster�very important when using full-strength flowering fertilizers.


  • Used to check temperature of the nutrient solution.
  • Best temperature for nutrients – 21°C or 70°F.
  • Cold nutrients can shock plants and slow down growth.
  • Overheated nutrients can ‘burn’ roots and create disease problems in the garden.


  • Used to check and correct pH of nutrient solution.
  • pH affects availability of nutrients to plants.
  • Especially important when using rockwool or hydro-corn which offer little or no pH buffering protection to the roots.


  • Used to check strength of the nutrient solution in the reservoir.


  • Do not use hormone treatments until plants show flowers. Early use of hormones can cause long spindly stem growth (stretching).

When plant is established in flower stage:

  • high light levels.
  • full strength flowering fertilizer.
  • flowers showing on plant.

The time is right for using ‘Growth Plus’ hormone treatment:

  • Mix one capful of ‘Growth Plus’ with one liter of room temperature water.
  • Use this mixture as a foliar spray on flowering plants just before ‘light’s out’. Use a very light mist: a one liter mixture can treat up to 100 two-foot tall plants.
  • Stop using ‘Growth Plus’ about two weeks before crop finishes.
  • If you prefer to use ‘Growth Plus’ as a root zone supplement, use two capfuls for every five liters of water.
  • Use either foliar spray treatment or root treatment – not both!
  • Stop using ‘Growth Plus’ if plants develop disease or pest problems.


  • Early detection and control of pests is essential for plants in flowering stage.
  • Pests can spread quickly through the garden:
  • larger plants than green growth stage – more ‘hiding spots’.
  • longer dark periods.
  • higher humidity levels.
  • Pests can severely reduce crop yield.


Use yellow ‘sticky cards’ to identify flying pests in the garden. These cards work as an ‘early warning system’. Their value is in making you aware which pests have invaded your garden. You can then handle the pest problem:

  • Before bugs get a foothold in the garden.
  • Before bugs damage the crop.
  • This early detection of pests is especially important during the flowering stage, because we have a limited choice of pesticides for our use against bugs when plants are flowering: pesticides that worked well during green growth stage might damage flowers now.
  • Retail staff have studied pest problems and solutions. They have to complete a government exam to qualify as licensed sellers of pesticide products. They’ll be glad to recommend effective ways of handling bug problems without damaging your crop. Just ask!


Use ‘Benomyl’ or other recommended fungicide at first sign of disease problems. Follow instructions on label for mixing and application.

If problems persist, alternate benomyl applications with applications of a different fungicide. Consult store staff for advice on alternate fungicides.

Use hydrogen peroxide in your irrigation water to kill diseases in the reservoir and irrigation lines.

Mix peroxide into water in reservoir before adding nutrients to reservoir.

Agral 90′ helps kill fungus spores in circulating irrigation systems.