Creating a Balance : Vegetative vs Generative Growth

Part 2 - It's All in Your Water

There are many factors that play a role in managing vegetative and generative growth, and it is important to consider a well-rounded approach when attempting to swing the scales. Keeping a balanced growing environment is important for a highly productive plant and changing one thing and nothing else will end up causing more harm than good.

In part 1 of this mini-series, we addressed the need for vegetative growth to have a high yielding crop. Vegetative action is required early in the crop cycle so the plants can establish themselves. By creating this strong base, the plant will be able to support a highly productive generative state later on.

The generative growth phase focuses on managing plant productivity. It is achieved through strategic stress induction in your plants. These minor stresses are going to push the plant to divert resources to reproductive organs (fruits), while ensuring that all other plant processes can be maintained. The key word here is minor – pushing the plant too far is not going to have the response you are looking for.

How Do I Manipulate the Plant?

A few of the major contributing factors to vegetative and generative growth are listed here below. We will address the impact that each factor has on crop steering.

•        Water availability
•        EC
•        Day/Night temperatures
•        Vapour Pressure Deficit (VPD)
•        Pruning
•        Fruit load

Water Availability

Watering frequency, duration and timing plays a role in pushing the plant towards a more vegetative or generative state.

In vegetative action, water is readily available for the plant when it needs it. The plant does not have to work hard to uptake water and will readily create new above- and below-ground biomass. As roots and leaves are being produced, the plant is preparing for full-blown production. Higher water content in the substrate is achieved through small, frequent irrigation events throughout the day.

Once it is time to switch to generative growth, these watering events become longer and more infrequent. As water becomes less available, less energy is put towards the production of root and shoot material, and more will be diverted to fruit production. The plant will now have to actively seek water compared to it being readily available in the vegetative stage.

Figure 1. Depicted here is the general irrigation strategy for substrate-grown greenhouse crops (ex. Tomato). Water content (WC) is depicted in green. While the timing and frequency of watering for generative and vegetative phases will vary, the general concept applies. As the day ramps up, you slowly increase the amount of water you deliver to the crop. After you achieve first run-off, you can start hitting the crop with water at regular intervals (determined, in part, by the weather that day). As the end of the day approaches, irrigation stops all together. Photo credit: Greenhouse Canada, June 2010 (https://www.greenhousecanada.com/september-2010-2418/)

While the daytime irrigation strategy is important in crop steering, you must also consider what is happening through the night. The length of the dry-down period of your growing media will help to tip the scales towards vegetative or generative tendencies. A short dry-down period (usually achieved by scheduling the last irrigation event of the day 1-2 hours before sunset) encourages vegetative growth. A longer dry-down period (which would have the last irrigation event happening earlier in the day) will encourage generative tendencies.

EC Measurement

The electrical conductivity (EC) of your fertilizer solution is important to consider when encouraging vegetative or generative action. EC is an indication of the salt content in the solution and will therefore impact water availability to the plant. A higher EC value means a higher salt content, and the harder the plant must work to take up water. As the plant works harder to take up water, less resources will be sent to vegetative growth (leaves, roots) and more will be sent to the generative tissue.

Here is a rough guideline of where your target EC should be, based on the crop stage:

Plant Stage	Target EC
Germination (vegetative)	0 - 1
Plant raising (vegetative)	2.5 – 3
Harvesting (generative)	2.75 – 3.5*
Full harvest (generative)	2.75 – 4*

*Should be watering with an EC of around 3, but you will see a higher substrate EC as the salts accumulate in the grow media

Understanding how your watering habits sway the crop in one direction or the other is a good starting point. Irrigation is something that all protected producers have control over, and it is important to see that watering plays a huge role in plant phenology and overall production capacity.

Creating a system that encourages maximum production capacity is in everyone’s best interest, and it is extremely important that all factors are addressed when trying to push for a more generative crop. Adjusting the watering and EC alone are not going to be enough to hit the target yield. All plant processes are intertwined and should be carefully considered whenever adjustments are made.

Stay tuned for our next post on vegetative vs generative growth, which looks at the role of temperature and humidity in crop steering.

Posted by: Talia Plaskett