Propagation/Greenhouse ManagementUnit 1.3 | Part 1 – 109
Lecture 2: Managing Environmental Conditions
c) Rapid germination in chamber’s compact space can save growers significant heating or
cooling costs, depending on the season
d) Higher percent germination can reduce seed costs
e) Must be regularly monitored: Once seedlings germinate, propagation trays must
immediately be removed from the darkness of the chamber and moved to a sunny
location to facilitate normal cell development and photosynthesis
- Cold Frames: Small-scale, low-tech structures used to modify environmental conditions.
Similar to passive solar greenhouses and hoop houses that do not contain any
supplemental infrastructure.
a) Simple structures, normally placed directly on the ground, consisting of four low walls
(insulated in colder climates) and a sloping, hinged roof that allows in sunlight for
warmth and photosynthesis. Roof can be opened to facilitate cooling and air circulation.
b) Often built of recycled materials, such as wood and rigid insulation board for siding and
old windowpanes or clear acrylic panels salvaged from local resource recovery facilities
for the roof
c) Sunlight can quickly heat internal air and enclosed air mass will provide some buffer
against cold nighttime temperatures; due to small size, cold frames provide limited
buffering capacity and are prone to rapid temperature shifts as external temperatures
change
d) Cooling and air circulation are achieved through opening the roof. Relying on this
passive exchange, while effective, can be problematic if the cold frame is left closed for
too long during warm conditions.
e) Irrigation is usually done by hand and can provide a secondary form of cooling through
evaporation
f) Through greater venting or leaving a cold frame open overnight, increased air flow and
day-night temperature fluctuation can help initiate hardening off
- Outdoor Benches: In most growing environments, seedling maturation or hardening off
is completed by placing seedlings outdoors on benches, exposing plants to conditions
that closely approximate the in-ground environment they are moving toward. As detailed
above, full exposure to sunlight, wind, and temperature swings stimulates carbohydrate
reserve buildup and strengthens cell walls so that plants can withstand the vagaries of the
in-field environment. - Shade Structures: While most annual vegetable seedlings require full sun to optimize
growth, shade cloth may be needed in hotter climates to prevent soil media from drying
out so rapidly that the grower must constantly devote time and water to keep young
seedlings healthy
D. Irrigation Management and Delivery
- Greenhouse irrigation concepts and terminology are similar to those used in the garden
and field setting (see Unit 1.5, Irrigation–Principles and Practices). However, because of the
small soil volumes plants are growing in and because of the design of propagation and
nursery containers, water behavior in greenhouse containers and consequent practices can
be quite different.
a) Saturation: As with field soils, saturation in containers comes at the point when
irrigation water fills all of the pore space in the soil medium, but in high quality mixes,
this is only a very temporary state and excess moisture quickly drains from the mix
b) Container Capacity: Similar to Field Capacity, container capacity is when excess water
has drained, air has returned to part of the pore space, and maximum water is held in
the pore spaces against the forces of gravity