Crop Steering Cannabis: Developing an Irrigation Plan

How to successfully steer plants with irrigation techniques.
23 July 2021
7 min read
Crop Steering Cannabis: Developing an Irrigation Plan

Contents:
  • 1. Developing a cannabis irrigation plan
  • 2. Types of substrates
  • 2. a. Different pot sizes
  • 3. Calculating substrate watering volumes
  • 4. Daily irrigation plan
  • 4. a. Phase 0: lights on to first irrigation
  • 4. b. Phase 1: first irrigation to runoff
  • 4. c. Phase 2: runoff to last irrigation
  • 4. d. Phase 3: last irrigation to lights on
  • 5. In conclusion

As mentioned in part 1, crop steering can help you achieve the desired results by controlling the growing conditions. These growing conditions not only refer to the temperature and humidity but also irrigation. An irrigation plan will allow you to get the desired plant growth by combining the right substrate with water volume and frequency of irrigation. So if you already read the first part read along to know how to improve irrigation and get perfect results.

1. Developing A Cannabis Irrigation Plan

Irrigation is a vital element of cannabis crop steering, in order to apply this technique successfully growers must manage the root zone properly, and to do it properly, it’s essential to take the following aspects into consideration:

  • Type of substrate;
  • Irrigation equipment;
  • Frequency of irrigations;
  • And Water volume.

 

Crop steering cannabis: developing an irrigation plan

Some of the elements of an automated irrigation system.
 

These are key elements that every grower should have in mind in order to develop an irrigation plan. Just have in mind that there are several ways to setup an irrigation system but there's no best way, as long as your plants are getting watered properly, anything goes!

2. Types Of Substrates

When developing a cannabis irrigation plan, you must check with the manufacturer if there are any special considerations to take into account. In general, rockwool is considered more steerable because it’s basically inert, this means that it has less influence on the pH and nutrients of the nutrient solution, so it requires less runoff than other substrates. Coco, soil, and other organic substrates have an organic matter that can compete for the nutrients and stop or pH changes, thus requiring more runoff to maintain ideal conditions. Also, the quality of this type of substrates can vary, so the water holding capacity and dry back speed may differ.

Different Pot Sizes

Apart from the type of substrate, the size and height of the pot play an important role in irrigation steering. This happens because taller pots can create larger differences in water content, in some cases having a difference higher than 30% when comparing the substrate at the bottom and top, so it’s important you take this into account.

Apart from the difference in water content, taller pots can make it harder to achieve the desired dry back and this can result in stress or nutrient lock in some parts of the medium so, ideally, you should use the smallest container you can while still having enough room for the roots to develop as they should.

3. Calculating Substrate Watering Volumes

As mentioned, the amount of water you use to irrigate your plants is an important factor in irrigation steering, because of this, you need to calculate the ideal irrigation volume for your substrate. This may seem a bit hard but it’s actually quite simple. The amount of nutrient solution you water with will depend on the amount of substrate you have per plant and whether you want to stimulate vegetative growth (1 - 3% of substrate volume) or flowering growth (4 - 8% of substrate volume). This means that if, for example, you had a substrate volume of 10 L, you have to multiply the substrate volume by the desired percentage, something like this:

Calculating Substrate Volume

For rockwool cubes, you first need to find out the volume, so you need to multiply the length x width x height:

Rockwool cube size = 46.5 cm x 46.5 cm x 46.5 cm ≈ 10000 cm3

Cubic volume ≈ 10000 cm3 ≈ 10000 ml = 10 L

 

For substrates such as soil or coco, you don’t really need to calculate the cubic volume because if you’re growing in a 10 L pot then you would already know the cubic volume of the pot.

 

Crop steering cannabis: calculate substrate volume

How to calculate substrate volume.
 

Once you have this information, it’s time to calculate the irrigation volumes which is quite simple, you just have to multiply the substrate volume by the irrigation volume percentage.

Calculating Irrigation Volume For Vegetative Growth

Substrate volume = 10 L

Desired irrigation volume for vegetative growth = 3 % of substrate volume

Vegetatve growth irrigation volume = 10 L = 10000 ml x 0.03 = 300 ml

 

In order to calculate the irrigation volume for flower growth, it's quite simple, you just need to use the irrigation volume percentage for flower growth, which ranges between 4 - 8%.

Calculating irrigation volume For Flower Growth

Substrate volume = 10 L

Desired irrigation volume for flower growth = 8 % of substrate volume

Flower growth  irrigation volume = 10 L = 10000 ml x 0.08 = 800 ml

 

As mentioned in part 1,  irrigation volume is the amount of water (or nutrient solution) that you will be feeding your plants. In order to perform this technique correctly, you will have to feed this amount between 3 - 9+ times per day when the lights are on. 

Irrigation Volumes

Desired Growth Type Volume
Vegetative 1 - 3% of substrate volume
Flower4 - 8% of substrate volume

 

Managing your irrigation plan daily is vital to successfully steer your plants into the desired growth and by measuring drain volumes, the root zone root, water content, and electrical conductivity (EC) you can adjust your irrigation plan to individual plants and steer your garden to the desired result.

4. Daily Irrigation Plan

All of the things mentioned will help you steer your crop to the desired outcome but only when combined into an irrigation steering plan. You can feed your plants however you want but a multi-phase irrigation schedule has shown the best results. 

 

Crop steering cannabis: multi-phase irrigation plan

Multi-phase irrigation plan.
 

A multi-phase cannabis irrigation plant consists of four irrigation phases which take place daily throughout the entire lights-on period, and they are the following.

Phase 0: Lights On To First Irrigation

Phase 0 of this cannabis irrigation plan starts when the lights in your grow room are turned on and are actively transpiring. Before starting with the first irrigation of the day you should verify that they’re transpiring by verifying the water content in the substrate because, as the plants absorb water, the water content in the substrate will decline.

Irrigation Phases

Phase 0Lights On to First Irrigation
Phase 1First Irrigation to Runoff
Phase 2Runoff to Last Irrigation
Phase 3Last irrigation to Lights On

 

The dry back percentage before you can start the first irrigation of the day will depend on the type of growth you wish to achieve. In order to steer plant growth, the dry back should be between 1 - 4% for vegetative growth or for flower growth 4 - 6%, once the dry back is between the desired ranges you can go on and start phase 1.

Phase 1: First Irrigation To Runoff

Once your plants are transpiring, they’re ready for the first irrigation of the day, and this is when Phase 1 of this cannabis irrigation plan starts. The goal for the first irrigation of the day is to increase the substrate's water content (which will allow your plants to continue to perform transpiration properly) and get runoff 1 - 3 hours after irrigating.

 

Crop steering cannabis: phase 1

Irrigation plan phase 1: irrigation to runoff.
 

The number of irrigation needed to produce the runoff required will vary depending on water content, irrigation volume, and irrigation frequency but in all cases, getting a minimum dry back of 1% between each irrigation is vital to ensure you’re not getting runoff water too quickly. If your goal is to get flower growth and the irrigation volume is 6% or higher, you should aim for a minimum dry back of 2 - 3% between irrigations to avoid oversaturating the substrate and getting too much runoff.

Phase 2: Runoff To Last Irrigation

During phase 2 of this cannabis irrigation plant, the goal is to reduce the EC to the lowest value while the light intensity and temperature are at their peak, this usually happens during the midpoint of the day and it will make your plants work their hardest.

 

Crop steering cannabis: phase 2

Irrigation plan phase 2: runoff to last irrigation.
 

Since you’ve already provided the desired water content and drainage in phase 1, phase 2 consists of adjusting the volume and frequency of each irrigation in order to maintain a consistent water content in your substrate. You can achieve this by reducing the irrigation volume and adjusting the dry back between each irrigation; During this phase, you should aim for a minimum of 1 - 3% dry back between irrigations if you’re aiming for vegetative growth and 3 - 6% if you’re aiming for flower growth.

Phase 3: Last irrigation To Lights On

Phase 3 of this cannabis irrigation plan marks the last irrigation and it’s super important because you need to allow a certain time in order to get the proper dry back overnight; Depending on the type of growth you are aiming for, you should achieve between 2 - 6% dry back between the last irrigation and lights off.

 

Crop steering cannabis: phase 3

Irrigation plan phase 3: last irrigation to lights on.
 

Lights off marks the end of the day but the work doesn’t stop there, once the lights are turned off you need to ensure that the dry back overnight is around 10 - 15% for vegetative growth and 20 - 30% (or more) for flower growth. This will allow you to start the next day with a blank slate and be able to repeat the whole process all over without encountering any problems regarding water content in the substrate. Remember that this is just one of the several ways to irrigate your crop and it’s essential you adjust your irrigation plan according to the specific strain and growing conditions, but you can always use this multi-phase irrigation plan as a base to develop your own.

5. In Conclusion

Now, creating an irrigation plan may seem like a hard task for the average home grower but luckily, you can find equipment that will help you meet your goals. A vital component of crop steering is the management of the root zone by combining nutrient dosing, irrigation frequency and volume, and dry backs; This means that the frequency and timing of feedings are super important when following an irrigation plan, and although it can be possible to do so without proper equipment, automating your irrigation is almost essential if you want to successfully steer your crop to the desired growth, especially in commercial growing and large-scale cultivation.


If you are familiar with crop steering and have some tips, feel free to help fellow growers by leaving a comment in the comment section below!

 

External References

  1. Growers guide to crop steering - Trym
  2. Estimation of Irrigation Water Requirement of Young Pomegranate Plants under Drip Irrigation - Wubs, Jasper & van Heusden, Tom & Melchers, Pauline & Bezemer, T.m. (2019)
  3. Irrigation facilities for drip irrigation of soil in inter-rows of wood and fruit plants - Shtanko, A. & Shkura, V.. (2021)
23 July 2021
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