Download BH notes wk9-06

BASIC HORTICULTURE – NOTES
WEEK #9
THE AMBIENT ENVIRONMENT –TEMPERATURE
THE ROOT ENVIRONMENT - WATER and SOILS
HAND BACK LAB SHEETS – ASSIGNMENTS
PASS BACK EXAM and REVIEW
THE AMBIENT ENVIRONMENT - TEMPERATURE
Plants EVOLVED with the EARTH’S various TEMPERATURE
regimes
 Limited to 0 – 50 degrees C (32 – 122 degrees F)
 BEST GROWTH @ 10 - 30 degrees C (50 – 85 degrees F)
o @ 0 degrees C (32 F) - biological ACTIVITY SLOWS
or STOPS
o @ > 122 degrees F - PROTEINS destroyed, PLANT
INJURY or DEATH
As TEMPERATURE RISES every 10 degrees GROWTH can
INCREASE 1.3 – 5 X’s (2 X’s average)
 Growers use this fact to INCREASE or DECREASE
GROWTH by increasing or decreasing TEMPERATURE
THERMOPERIODICITY
 Is the FLUCTUATION of DAY and NIGHT
TEMPERATURES
 Most plant GROWTH occurs at NIGHT
o STOMATA are closed, decrease in TRANSPIRATION
o ROOTS still take in water, increase of TURGOR
pressure in cells,
o CELLS swell and ENLARGE for GROWTH
 Plants from GROW BETTER with THERMOPERIODICITY
o Important to TEMPERATE CLIMATE plants because
they have ADAPTED to FLUCTUATION
o Not so important to tropical plants
VERNALIZATION
 The INITIATION of FLOWERING in plants by exposure to
EXTENDED COLD PERIODS
o Most BIENNIALS – only FLOWER after first season
of COLD WINTER TEMPERATURES
 First year – VEGETATIVE GROWTH
 Second year – FLOWERING after a COLD
PERIOD
Example: Foxgloves, Cabbage, Dill, Onion,
Celery, Hollyhocks
 Some plants have specific CHILLING REQUIREMENTS
o ABSOLUTE – a certain number of DAYS BELOW a
certain TEMPERATURE to flower in spring
Example: beets, celery, and cabbage
o QUANTITATIVE – flower EARLIER and MORE with
exposure to COLD
 Stimulus for this VERNALIZATION is perceived in the
APICAL MERISTEM
o Not fully understood
o APPLICATION of GIBBERELINS can substitute for
LOW TEMPS
 HIGH TEMPS can REVERSE vernalization or
DEVERNALIZE plants
Example: Onion sets are stored at HIGHER TEMPS so they
will keep in a VEGETATIVE STATE otherwise at lower
temps they would go to flower too early
DORMANCY and HARDINESS
 DORMANCY is state of INACTIVE GROWTH due to
INTERNAL and EXTERNAL FACTORS
o ADAPTIVE MECHANISM that SLOWS DOWN plant
PROCESSES during winter months
o Only allows a plant to BREAK DORMANCY when
ENVIRONMENTAL CONDITIONS are
FAVORABLE for GROWTH and DEVELOPMENT
o Ensures SPECIES SURVIVAL
 BUD BREAK in deciduous plants
 SEED GERMINATION
 PLANT and BUD DORMANCY
o DORMANCY is key for SURVIVAL of PERENNIAL
plants growing in TEMPERATE or COLD
CLIMATES
o GRADUAL PROCESS that STARTS as GROWTH
TAPERS in SUMMER
 TRIGGERED by:
 SHORTENING DAYS
 LOWER TEMPS
 DROUGHT
 STEPS to PLANT DORMANCY:
 PHOTOSYNTHESIS SLOWS or STOPS
o DECIDUOUS plant STOPS
o EVERGREEN SLOWS
 GROWTH STOPS
 TRANSLOCATION of FLUIDS reduced
 Decreased ENERGY REQUIREMENTS
 PROGRESSION through plant
 AXILLARY BUDS first
o summer pruning
 TERMINAL BUDS >>> BRANCHES >>>
TRUNK >>> BARK last
 ROOTS never become truly dormant, they
CONTINUE to GROW as long as SOIL
TEMPS > 40 degrees
o ROOTS can never attain cold
HARDINESS
o Can attain some COLD TOLERANCE
but it can be LOST in 24 HRS
o MULCHING for ROOTS is important
to MODERATE EXTREME TEMPS
 HARDINESS and ACCLIMATION
o HARDINESS - The ABILITY of a DORMANT plant
to withstand COLD TEMPS without severe TISSUE
DAMAGE
 DORMANCY must be achieved FIRST before
HARDINESS
o ACCLIMATION - the ability to DEVELOP
HARDINESS
 Plants gain HARDINESS through a CONSTANT
EXPOSURE to COLDER TEMPS or
ACCLIMATION
o DEGREE of HARDINESS changes in RESPONSE to
the ENVIRONMENT, and the responsiveness of the
plant DEPENDS on the GROWTH STAGE of the plant
(Show overhead)
 BUD BREAK to LEAF MATURITY – not hardy
 Initiation of HARDINESS begins as DAY
LENGTH DROPS below a CDL
 TRIGGERS DORMANCY HORMONE in leaves
 AUXIN lessens breaks down
 ETHYLENE GAS & ABSCISSIC ACID
(ABA)
 By LEAF ABSCISSION - DORMANCY
COMPLETE
 ACCLIMATION occurs with continued COLD
TEMPS
 EARLY FALL FREEZES may be a problem
as tissues not acclimatized yet
 But NON-KILLING FROSTS actually can
INCREASE RATE of acclimation
“What doesn’t kill you - makes you strong!”
 WINTER reaches MAXIMUM HARDINESS
(November - December)
 Plants can be DEACCLIMATIZED by WARM
PERIODS
 If followed by LATE SPRING FROSTS
(January – February – March) we can have
TISSUE DAMAGE
 “INDIAN SPRINGS are far more
DANGEROUS to plants than “INDIAN
SUMMERS” as plants can QUICKLY
DEACCLIMATIZE
o MAXIMUM DEGREE of COLD HARDINESS
DEPENDS on:
 GENETICS of the plant and the HABITAT and
CLIMATE it originally ADAPTED to
Example: TROPICAL plants, such as Freesias,
can never reach cold hardiness to survive our
CLIMATE. But plants that are nearby such as
Oleander (California plant) can be BRED for cold
hardiness
 GROWTH STAGE (already covered)
 FOOD STORED in the plant
 LOW RESERVES in the plant will LOWER
COLD HARDINESS
o Poor nutrition
o Heavy foliage, flower, fruit production
o Shortened growing period
o Excessive forced growth from high N
fertilization
 PHYSIOLOGY of ACCLIMATION
o The FORMATION of ICE CRYSTALS in CELLS is
what PHYSICALLY INJURES them
 Expansion of ICE bursts CYTOPLASMIC
MEMBRANE and CELL DIES
o Plant have a variety of WAYS to KEEP SAP from
FREEZING
 CONVERSION of STARCH to SUGARS in
CELL
 As temps cool INSOLUBLE STARCH is
CONVERTED into SOLUBLE SUGARS
 ACTS like ANTIFREEZE – lets the sap get
colder than freezing without freezing
 VISCOSITY or THICKNESS of SOLUTION in
CELLS increases and LOWERS FREEZING
POINT
 ICE CRYSTALS form in the
INTERCELLULAR SPACES
 DEHYDRATES CELL - draws more water
out of cell due to osmosis
 Makes content of cell MORE VISCOUS
 “SUPERCOOLING” sap
 Some plants have the ability to
“SUPERCOOL” fluids below the freezing
point without freezing their tissues
 Not known how this is done
Example: one rhododendron was capable of
maintaining a LIQUID CELL SOLUTION
of - 40 degrees C
WINTER INJURIES (cold stress)
 DESICCATION – DRYING out of TISSUES
o TRANSPIRATION is less but EXCEEDS SOIL
MOISTURE and dries out plant
o PREVENTION:
 WATER when ground thawed
 MULCHING to retain moisture
 WINDBREAKS to decrease transpiration
 ANTI – DESICCANTS sprays reduce
transpiration for a few days, good for
transplanting
 FREEZE INJURY
o SUDDEN DROP in TEMP or EXTREME TEMP
CHANGE
o PREVENTION:
 MULCH WHOLE plant
 SPRAYING ORCHARDS with WATER
 As water freezes HEAT is released,
continually freezing water protects tissues
 @ 32 degrees F
 ROOT INJURY
o FROST HEAVING
 FREEZING HEAVES plants out of ground
 DAMAGE to shallow ROOTED or CROWNED
plants
 PREVENTION:
 MULCHING
 Better DRAINAGE
 ONCE HAPPENS - PRESS plants DOWN into
ground
o FREEZING of CONTAINER PLANTS
 PREVENTION:
 GROUP together
 HEAL into MULCH
 ICE DAMAGE
o FREEZING RAIN in Gorge and E. Multnomah Co.
o PREVENTION:
 STAKE or PROP small trees and shrubs
 Proper PRUNING and THINNING
 SLOW GROWING TREES
 BARK SPLITTING or FROST SPLITTING
o SUDDEN FREEZE before the tree attains
HARDINESS causes the BARK to SPLIT along the
CAMBIUM LAYER
o PREVENTION:
 NONE
o ONCE HAPPENS – WRAP TRUNK or TACK BARK
BACK to protect as much cambium and phloem tissue
from drying out
 WINTER INJURY or WINTER SUNSCALD
o TRUNK absorbs HEAT on a clear sunny day during the
WINTER, which DEACCLIMATIZES BARK
o Followed by a rapid DROP in nighttime TEMPS
o Causes BARK to DIE BACK on S or SW side (also
called S or SW injury)
o PREVENTION:
 Protect by WRAPPING with burlap, tree guards,
white paint
 Plant more RESISTANT, THICKER BARK
SPECIES
SUMMER INJURIES – Heat Stress
 SUMMER SUNSCALD
o Too much HEAT and TRANSPIRATION LOSS for the
plant to cool itself
o LEAVES, FRUIT and BARK can be BURNED
o PREVENTION:
 Adequate WATER in SOIL
 SPRAYING WATER on plant
 THICKER BARKED TREES
THE ROOT ENVIRONMENT - WATER and SOILS
SOILS
 Provides plants with PHYSICAL SUPPORT, WATER,
NUTRIENTS and O2
 SOIL PROFILE (show overhead / handout)
o
o
o
o
o
O Horizon – litter layer
A Horizon – Topsoil – darker, higher OM
B Horizon – Subsoil – lighter, lower OM
C Horizon – Parent material
R Horizon - Bedrock
 SOIL COMPOSITION – Ideal
o SOIL TEXTURE – Mineral portion (Show overhead)
 PROPORTION or % of SAND, SILT, and CLAY
in the SOIL
 SOIL TEXTURE difficult to CHANGE
o ORGANIC MATTER (OM) – HUMUS
 Decaying plant and animal matter
 Break down of OM provides CO2, H2O, and
NUTRIENTS for plant use
 Improves WATER holding capacity and
NUTRIENT holding capacity
 You can always IMPROVE soils by adding OM
o PORE SPACE – Ideally 50% of SOIL
 25% WATER, 25% AIR
 SIZE of PORE SPACE and how they CONNECT
determines how well WATER and AIR MOVES
in soils and how ROOTS grow in it
CONTRAST SANDY and CLAY soils
 SOIL ORGANISMS
o Whole ECOSYSTEM full of SOIL ORGANISMS
o MICRO – bacteria, fungi, algae, actinomycetes,
protozoans
o MACRO – nematodes, earthworms, arthropods, rodents
o IMPORTANT for:
 Breakdown of OM
 NITROGEN CYCLE
 MYCORRHIZAL Associations
 MIXING, AERATING and DRAINAGE
 SOIL STRUCTURE
o Few are harmful, MOST are BENEFICIAL
 SOIL STRUCTURE
o ARRANGEMENT or grouping of soil particles into
AGGREGATES or “CLUMPS”
o PORE SPACE and SOIL STRUCTURE determine
DRAINAGE, AERATION, and ROOT
PENETRATION
o SOIL STRUCTURE is CHANGEABLE
 MICROBES, HUMUS, and CLAY can cement
soil particles together to make AGGREGATES
 Poor CULTURAL PRACTICES can DESTROY
soil structure
Example: tilling in wet soil
 PLANT NUTRITION (Show overhead)
o 17 ESSENTIAL NUTRIENTS - used by ALL plants
 MAIN elements – from water and air
 C, H, O
 MACRO NUTRIENTS – used most by plants,
nutrients in poor supply in the soil
 PRIMARY – N, P, K
 SECONDARY – Ca, Mg, S
 MICRO NUTRIENTS – Trace elements
 Used in small amounts
 B, Cu, Cl, Fe, Mn, Mo, Ni, Zn
 BENEFICIAL NUTRIENTS
 Used by only SOME plants
 Na, Si, Co
o IN TERMS of SOILS:
 The PRESENCE of an NUTRIENT in the SOIL
does not guarantee UPTAKE by ROOTS
 Ions ADSORB differently to SOIL
 Ions DISSOLVED differently in the SOIL
SOLUTION
 ROOTS take in IONS SELECTIVELY
 CORRECTING a NUTRIENT DEFICIENCY in a
PLANT is not always a matter of ADDING it to
the SOIL
 This is why we LEARN about SOILS and
TESTING SOILS
o