BALANCING GROWTH IN THE GARDEN
Excessive Vegetative Growth
Overly vegetative plants are usually easy to spot. They tend
to produce large, lush, lighter-green leaves. Tomatoes and
similar crops may have thick stems, often described as tree
trunks, and any flowers that develop are often small, weak
and may even drop from the plant. The plant canopy is
usually dense with many long leaves, fast growth and rapidly
increasing plant height. This sort of excessive vegetative
growth is common in young plants and is also partially
genetic—some cultivars are naturally much more vegetative
than others. Other conditions that favor vegetative growth
include substrates that retain a lot of moisture, such as
fine-grade coconut fiber; a lower EC; plenty of water from
frequent irrigation; use of vigorous rootstocks; and a mild,
stress-free environment. Low light, overcrowding, high
humidity and excessive warmth can also push a plant in a
more vegetative direction.
Overly vegetative plants are usually easy to spot. They
tend to produce large, lush, lighter-green leaves.”
What to Do About Excessive Vegetative Growth
Growers battling excessive vegetative growth should select
cultivars described as having a generative growth habit.
These exist for tomatoes, peppers, cucumbers and an
increasing range of other flower and fruiting plants.
The main tools used to steer plants in a more generative
direction are temperature, CO2, high light, reduced
moisture and increased nutrient (EC) levels. CO2
enrichment favors generative growth once flowering and
fruit set has occurred.
Generative growth (flower stem production), as shown on this lettuce plant,
must be avoided in plants grown for harvest in the vegetative stage.
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Maximum Yield USA | October 2015
Spinach is a long-day plant, meaning it tends to flower rapidly during
the warm, long days of summer.
A more advanced tool is the use of day/night temperature
differentials (DIFs), which can be used to steer a crop
back into more balanced growth. DIFs are widely used in
commercial crop production, but they work just as well in
indoor gardens where the grower has good control over
temperatures. High daytime temperatures tend to promote
plant stretching as well as an increase in leaf area. Night
temperatures do not play a role in this, but the difference
between day and night temperatures is important for flower
and fruit development. Environmental conditions also play
a role. Low light combined with warm temperatures results
in stem elongation and a tall, weak plant, so temperatures
should be matched to the light levels.
Keeping day/night temperatures similar stimulates
vegetative growth, while a greater DIF (night temperature
much lower than the day temperature) results in more
generative growth. It’s a good idea to run day/night
temperatures that are fairly close to each other early in the
plant’s life to stimulate good foliage growth, then switch to a
greater DIF with much lower night temperatures as the plant
comes close to fruit set. From then onwards, tomato and
capsicum growers may change the DIF settings to push either
vegetative or generative growth as required.
Stressing plants out slightly by using a higher EC and deficit
irrigation practices will also have a generative effect. Deficit
irrigation practices include reducing the volume of water
applied at each irrigation, allowing more time between
watering and allowing the media to dry out slightly overnight
by restricting early morning and evening irrigations. This
method must be used with caution, as moisture fluctuations
in the root zone can lead to an increase in fruit splitting and
cracking, and it is also associated with an increase in blossomend rot under certain growing conditions.