Creating a Balance: Vegetative vs Generative Growth

Part 1 - Setting the stage 

Most greenhouse vegetable producers will have come across vegetative versus generative growth in their vine crops (tomato, pepper, cucumber). Over the next few weeks, we will be exploring the differences between the two types of growth, what they look like, and how we can manipulate the plants to encourage one form of growth over the other. This information will be focused on tomato production, but it is important to note that the same concepts apply to other crops.

Vegetative growth is characterized by:

• Thick stems
• Lots of leaves and suckers
•  Leaves are long and can be twisted/curled
• Dense growing tip
• High density of leaves
• Small fruit
• Elongated fruit truss

The plant is putting most of its energy towards the production of plant material. While leaves are important for photosynthesis, tipping the balance towards a more vegetative state does not leave enough energy being diverted towards fruit production. The size and quality of the fruit coming off a vegetative plant will be significantly less than what you would want.

Figure 1. An image of an overly vegetative tomato plant. Notice the thickness of the stem, the high density of plant material, and the curling of the leaves. Photo credit: Government of Alberta, Tomato plant propagation in commercial greenhouse tomato production (https://www.alberta.ca/tomato-plant-propagation-in-commercial-greenhouse-tomato-production.aspx)

Generative growth is characterized by:

•       Thin stems
•       Fewer leaves, typically shorter in length
•       Good sized fruit
•       Slight purple tinge to the growing tip

These features indicate that the plant is putting most of its resources towards fruit production. While we want to see generative growth, it is possible to tip the balance too far. A plant that is overly generative, will not have the leaf resources available to power plant growth. Overly thin stems with few leaves will not be able to support a high fruit load, and the resulting fruit will not be of market quality.

 

Figure 2. A tomato plant that is growing generatively. Notice that the stem is significantly thinner here compared to Figure 1. The leaves are much less densely packed, and the leaves are not curling excessively. Photo credit: Talia Plaskett, Perennia.

Production of greenhouse crops requires both types of growth for optimum production. The act of rooting after transplant is considered vegetative. You want to encourage the plant to establish a good strong base in the growing media, so that it can support the plant through the growing season, and push for high yields. After a certain point, you want to start pushing the plants to a more generative state. This will encourage more fruit, and of a higher quality as well.

How do I know where I stand?

Designate one or more areas within the greenhouse as being your primary monitoring spot. This area should be representative of the growing conditions in that space – many growers will choose the centre of the tunnel/greenhouse, and pair this with the location where they are collecting information on drain EC/pH and slab weight. Each production space should be considered its own entity, as temperature, humidity, air circulation etc. will vary between bays despite our best efforts.

Within this monitoring block, a series of measurements should be taken weekly. Things like stem width (measured below the youngest flower cluster with an open flower), internode length, leaf length, weekly growth, and number of leaves/clusters will let you know how the crop is doing. Keeping this information on record will help you get an idea of how your interventions paid off, and generally how the crop is doing. These measurements can also be used to forecast future yields and therefore what will be available for retail.