Crop Steering – Using stress to boost growth
Crop Steering - Using stress to boost growth
What is crop steering?
Crop steering is a method in advanced agriculture to purposely stress plants into increasing growth rate, yield and quality.
It is done in an indoor/greenhouse setting where you can adjust environment conditions to trigger a desired response from your plants.
Plants need photosynthesis to grow and for that you need certain known environmental conditions : light, CO2, water, nutrients as well as the correct temperature and humidity. So if you increase these factors proportionally your plants will be healthy, grow fast and you will increase your yield and quality. But, that works only up to some extent.
The reason is that apart from photosynthesis, plants respond to different environmental conditions such as the day length, medium water content, light spectra, day/night temperature and many more.
Plants react to those changes in the environment with hormone signaling systems.
Knowing how and when to manipulate irrigation, climate and light intensity and spectra is essential to balancing high yields and high quality.
Different cultivars will react differently in different environments. It is important to monitor the plant’s reaction to those methods and react accordingly. It’s also advised to perform a side by side comparison when possible, conduct proper research and testing per cultivar and compare operation specifics.
You are already doing this, to a degree.
To better understand crop steering here are some examples of crop steering that are already widely used, though not often referred to as crop steering.
Temperature – Lowering the temperature at the last weeks of flowering and increasing the difference between the highest and lowest temperature mimics the natural seasonal changes the plant would experience at the end of its life cycle. That signals the plant to invest its energy at reproduction (flowering).
Topping – cutting off the top of a main stem steers from vertical to horizontal growth by distributing Auxin (a growth hormone) more evenly to all nodes.
Photoperiod (day length) – When switching to a short day (12 hours of light) although you decrease the amount of light plants get in a day (DLI) the plants will switch from vegetative growth to flowering stage.
Crop steering with irrigation.
Irrigation events and high water content signal to the plant that it is time to take advantage of currently available and plentiful resources and grow as much as possible, while increasing drought cycles will steer it toward flowering stage.
Key metrics for crop steering in irrigation is monitoring your runoff/drain volume, E.C. and pH.
Drain volume – The percentage of drain out of total irrigation water. For example if each plant got 500ml of irrigation and had 100ml drain it will be 20% drain (100/500 X 100).
Drain/Medium E.C. -While it is OK that E.C. in your medium will build up during the flowering stage it is critical to monitor it so it would not exceed desired values. Burnt leaf tips will indicate that you’re not watering enough, but when these symptoms are visible the damage is already done.
Drain/Medium pH – During vegetative stage pH levels usually rise after irrigation and during the generative stage it usually drops. Keep the medium/drain in the range of 5.6-6.2 at all stages and increase irrigation as needed to stay within that range
Stage | Irrigation volume** | Irrigation Frequency | Drain E.C. | Drain volume |
Veggetive | 10%-25% | 0.5-2 / day | 2-3ms | 20%-30% |
Flowering – Stretch | 2%-5% | 8-16+/ day * | 2.5-5ms | P1 10%-20%P2 0%-5% |
Flowering – Bulk | 2%-5% | 8-16+/ day * | 2.5-4ms | P1 10%-20%P2 0%-5% |
Flowering – Rippen | 10%-25% | 2-4 / day | 1.5-2.5ms | 20%-30% total per day |
* as many as need to achieve desired runoff
** Percentage out of total medium volume
P1, P2 and P3 – Daily phases of irrigation
P1 – The first phase of irrigation starts 1-2 hours after lights are on. Use small shots of irrigation spaced 15-30 minutes until desired drain volume is reached.
P2 – The 2nd phase is maintenance irritation without drain/ with less drain, it usually starts 1-3 hours are P1 and should be spaced out 1-3 hours apart, until 1-2 before lights out.
P3 – The 3rd phase is the dry back. It starts 1-2 hours before lights out and ends 1-2 hours after lights are on.
Crop steering with light.
Both light intensity and light spectra have a huge impact on your end result. With crop steering we adjust the spectra and intensity for each stage, this allows us to control the morphology and the stretch during the vegetative stage and during the stretch stage and bulk your flowers and increase cannabinoids and terpenes content during the bulk and rippen stage.
We recommend using full spectrum light and adding and adjusting supplement red, far-red and blue lights according to the different stages.
The importance of full spectrum – We recommend using full spectrum white 3000K-4000K as a base light, since it has an ample amount of red and blue that matches Chlorophyll A and B as well as green which is great for leaf tissue penetration.
RED/BLUE RATIO – a lower ratio (more blue) will result in shorter and more compact plants which is important for the vegetative stage and critical during the stretch stage when you want to minimize the stretch, while a higher ratio will help bulk up your flowers.
Blue light is also very important for trichome production and maturity making it important for the laters stages of flowering.
RED/FAR RED RATIO – a lower RED/FAR RED RATIO (more FAR RED) is great for photosynthesis and therefore works great at the vegetative stage.
During the transition to the flowering stage it could increase the stretch and is usually avoided. A higher RED/FAR RED RATIO is recommended .
Finding the perfect timing to increase the FAR RED and getting the perfect stretch will depend on the cultivar as well as the environmental conditions. For example, with a cultivar that stretches a lot we will wait until stretching has finished, while with a cultivar that doesn’t stretch as much we will introduce it earlier so we can increase internode space.
Another important aspect of the far-red is during the rippen stage. A lower ratio of RED/FAR RED (stronger far-red) as well as keeping the far-red light on 10-30 minutes after lights out, usually referred as “End of the Day”, can mimic fall(autumn) onset which signals the plant that winter is getting closer and will shorten the flowering cycle.
Intensity – During the veggtive stage, a high intensity will result in faster growth and shorter inter node space. On the other hand, low intensity will result in a taller plant with more internode space.
High intensity, above 600 ppfd during vegtive stage could result in stunted growth.
During the bulk stage, it is important to maximize intensity as it directly affects yields.
During the rippen stage, gradually decreasing intensity will signal the plant that the season is ending and should put all its effort in reproduction (flowering).
Stage | RED/BLUE RATIO | RED/FAR RED RATIO | Intensity | CO2 |
Veggtive | lower | lower | 300-600 PPFD | 400-800 PPM |
Flowering – Stretch | lower | higher | 600-1000 PPFD | 800-1200 PPM |
Flowering – Bulk | higher | lower | 800-1500 PPFD | 1200-1500 PPM |
Flowering – Rippen | lower | lower | 600-1200 PPFD | 800-1200 PPM |
Conclusion
A key factor for crop steering is perfect synergy between all of the relevant parameters. This requires proper research and testing before applying any new technique on a large commercial scale. This will vary from one operation to another as each one is unique. A grower will need to research crop needs, goals of the operation, and goals for the end result.
Key elements should be closely monitored and logged when developing a crop steering plan:
– Drain volume
– pH
– E.C.
Same is true for parameters which indicate plant development:
– Ratio between the height and nodes
– Stem diameter