Introduction to Crop Steering

I am happy to have Doug Jacobs, one of Grodan’s top technical advisors, writing this series on plant steering. This is a term I first heard at the ACT Summit at the 2018 MJBizCon.

When growing indoors, the environment significantly affects the quantity and quality of the harvest. It encompasses all aspects of gardening: lighting, watering cycles, EC levels, pruning, and most of all, VPD, which is, of course, the relationship between temperature and humidity. How and when to manipulate these variables is the key to getting the most out of genetics. Some of it may seem complicated, but it isn’t. There are several controllers on the market that can easily be set and provide optimal VPD. You might need some new equipment to dial it in all perfectly, but isn’t that the point of indoor gardening? To be perfect takes knowledge, work, and investment, but it is possible. Enjoy this great read.

-Eric

As indoor gardeners, we have the benefit of controlling climate and irrigation, which play significant roles in how our plants grow. From temperature and humidity settings, light intensity, irrigation volumes, and frequency to the way we defoliate our plants, every action matters.

By changing environmental conditions, growers can steer the plant growth toward vegetative or generative

It is essential to understand how all of these factors affect plants to use them to your advantage. Combine taking regular measurements of climate and rootzone conditions with tracking plant growth, and you can achieve the best crops possible in the garden.

What Is Crop Steering?

Crop steering is a method of managing plant growth by adjusting irrigation and climate to force a desired response from the plant. By changing environmental conditions, growers can steer growth toward vegetative or generative. Crop steering can be used at every stage of growth, including with mother plants, propagation, and more.

What is vegetative and generative growth? Vegetative is the growth of leaves and stems, while generative is the development of fruits and flowers.

Steering With Irrigation

Examples of irrigation steering. These are specific to particular crops and varieties. In some cases, something that creates a generative action in one type of plant might be a vegetative action for another. It’s essential to test them and measure how the plants react.

Crop steering is a method of managing plant growth by adjusting irrigation and climate to force a desired response from the plant

Crop steering can be achieved in part through irrigation. The amount, frequency, and timing of irrigation influences the plant’s response and steers growth. Adjusting the irrigation strategy specifically for the environment, genetics, and stage of development will lead to ultimate plant growth and improve final product quality. If you want your plants to grow faster, you can implement a vegetative irrigation strategy by doing the following:

• Maintaining a higher overall WC in the root zone.

• Having smaller dry backs between irrigations as well as overnight.

• Using small shot sizes at a high frequency of irrigation, lower EC at the dripper and in the root zone, and higher root zone temperatures.

These steps help the plants grow and recover faster while maintaining vigor.

If you want to slow down growth and be more generative, you need to decrease the overall WC in the root zone. Do this by:

• Increasing the dry backs between each irrigation and overnight by delaying the first irrigation of the day and stopping before night.

• Decreasing irrigation frequency while increasing the volume of each shot.

• Increasing dripper and rootzone EC with lower substrate temperatures.

It is critical to test these strategies while taking regular crop registration of plant height, node spacing, overall plant development, and health.

Adjusting the irrigation strategy specifically for the environment, genetics, and stage of development will lead to ultimate plant growth and improve final product quality.

Steering With Climate

Like irrigation, the climate has a profound impact on how plants grow and can be used as a steering tool. Again, climate steering techniques shown in the chart below should be tested to see how they affect each cultivar.

For some plants, switching the day-night cycle to 12 hours on and 12 hours off are used for inducing flower. Like the change in photoperiod, other climate factors can be changed to steer the plants’ growth toward vegetative or generative. Having overall high temperatures, for example, is more vegetative. Keeping the plant more active with lower temperatures slows the growth. It mimics the natural seasonal changes the plant would experience at the end of its lifecycle, steering it toward generative.

Changes in the difference between day and night temperatures can potentially control stretching, with significant differences increasing inter-node spacing and smaller differences decreasing it. Other factors that help steer the plant include:

• The speed of the temperature changes from day-tonight and night-to-day.

• Increasing or decreasing humidity.

• The number of air exchanges in the room.

Keeping the plant more active with lower temperatures slows the growth. It mimics the natural seasonal changes the plant would experience at the end of its lifecycle, steering it toward generative

In greenhouses, the heating temperature used (pipe temperature) also helps steer the plant.

Examples of irrigation steering. These are specific to particular crops and varieties. In some cases, something that creates a generative action in one type of plant might be a vegetative action for another. It’s essential to test them and measure how the plants react.

How And When To Steer Plant Growth

Indoor gardeners know how much they grow per light and how successful they were doing it, but knowing how they achieved the results and how to do it again is vital. Take notes on how the plants develop and react to climate and irrigation conditions. These observations will help with every subsequent grow. At every stage of growth, watch the following:

• Root development speed.

• Quality of the plant and its height.

• Stem diameter.

• Leaf/stem color and node spacing.

• The amount of time it takes flowers to develop and how they fill out.

• Rootzone WC and EC measurements in relation to climate conditions.

Remember; the more you know, the better you grow. All of these recommendations will help you determine the optimum irrigation and climate strategies for your plants in every stage of growth.

By Doug Jacobs

Doug is a Technical Advisor with Grodan. He provides expert consulting on proven Precision Growing methods to optimize crop production with Grodan Rockwool growing media and proper irrigation, producing the best quality plants using the least amount of inputs. He has experience with indoor, outdoor, and greenhouse hydroponics, vertical farms, aquaculture, and CEA system design, helping to design farms across North America. Doug showcases his passion and expertise as a feature writer in various national industry publications and as a conference speaker at US events.