Propagation/Greenhouse Management
10 | Unit 1.3
Students’ Lecture 1 Outline
- Seedling development: Management of temperature and moisture conditions often
changes from seed to seedling. Plants are often moved to alternative structures (e.g.,
greenhouse to hoop houses) in response to their expanding range of physiological
tolerance.
a) Temperature management remains critical, especially when trying to extend seasonal
parameters. Note: Optimal temperatures for germination and subsequent growth may
differ (e.g., Brassicas) (contrast appendix 2 with appendix 5, Approximate Monthly
Temperatures for Best Growth and Quality of Vegetable Crops).
b) Maintenance of good air circulation continues to be important to prevent disease and
promote strong structural/cellular development
c) Moisture delivery during seedling development typically begins to decrease in
frequency but increase in depth to accommodate developing root system and leaf
canopy, and thus increases in transpiration rate
d) Availability of light for photosynthesis to manufacture nutrients and promote strong
cellular growth becomes of critical importance
- Seedling maturation and hardening off: The final step prior to transplanting. Over three
days (minimum) to two weeks, seedlings are gradually exposed to conditions that most
closely resemble those of the field. This process decreases the likelihood of transplant
shock and promotes the accumulation of carbohydrate nutrient reserves and continued
strengthening of cell walls via:
a) Exposure to natural day-night temperature fluctuation, promoting carbohydrate reserve
buildup
b) Little or no buffering from natural air circulation or prevailing wind patterns, thus
promoting thickening of cell walls
c) Moisture delivery continues to decrease in frequency but increase in depth/volume
relative to specific needs of species and container type to promote maximum root
development and tolerance of moisture stress
d) Exposure to light should also be equivalent to field conditions to build plant strength
and decrease likelihood of transplant shock