Germination

What is Germination?

Germination is the awakening of a seed—the moment when a dormant embryo begins to grow after potentially months or years of waiting. It's the critical first step in a tree's life, when the seed absorbs water, swells, breaks open, and sends out its first root.

The Germination Process

Stage 1: Imbibition (Water Absorption)

Rapid Water Uptake:

• Dry seed absorbs water quickly
• Seed can swell 50-200% in volume
• Rehydrates dormant embryo
• Takes 6-48 hours depending on species

Seed Coat Response:

• Hard seed coats may need scarification first
• Soft coats split naturally from pressure
• Water enters through micropyle (tiny opening)
• Triggers metabolic reactivation

Stage 2: Activation

Metabolic Awakening:

• Enzymes become active
• Stored food mobilizes (starches → sugars)
• Respiration increases dramatically
• Energy production begins
• Temperature critical at this stage

No Visible Change Yet:

• Seed looks the same externally
• Internal biochemistry ramping up
• Point of no return—seed committed to growth
• Failure here = seed death

Stage 3: Radicle Emergence

First Visible Sign:

• Embryonic root (radicle) breaks through seed coat
• OFFICIAL GERMINATION MOMENT (botanically)
• Grows downward due to gravity (gravitropism)
• Begins absorbing water and nutrients
• Usually 2-14 days after imbibition

Critical Period:

• Seedling most vulnerable now
• Must maintain moisture
• Fungal infection risk high
• Predation by insects/birds

Stage 4: Seedling Establishment

Root Development:

• Radicle develops into primary root
• Lateral roots begin forming
• Root hairs appear for absorption
• Anchors seedling in soil

Shoot Emergence:

• Cotyledons (seed leaves) push up
• OR remain below ground (hypogeal germination)
• True leaves develop
• Photosynthesis begins
• Seedling becomes self-sufficient

Types of Germination

Epigeal Germination (Above-Ground)

Process:

• Cotyledons emerge above soil
• Act as first photosynthetic organs
• Green and leaf-like
• Stay attached to seedling for weeks/months

Characteristics:

• Common in beans, squash, many tropical trees
• Provides quick energy from photosynthesis
• Vulnerable to herbivory
• Needs good light

Costa Rican Examples:

• Pochote (Pachira quinata): Large cotyledons emerge
• Frijolillo (many legumes): Classic bean-style germination
• Balsa (Ochroma pyramidale): Fast epigeal emergence

Hypogeal Germination (Below-Ground)

Process:

• Cotyledons stay underground
• Remain inside or attached to seed
• Act as food storage organs
• First true leaves emerge directly

Characteristics:

• Common in oaks, peas, many grasses
• Protected cotyledons
• Slower initial growth
• Less vulnerable to surface hazards

Costa Rican Examples:

• Roble (Quercus spp.): Acorns remain below
• Mango (Mangifera indica): Large seed stays buried
• Almendro (Dipteryx panamensis): Seed contains large energy reserve

Environmental Requirements

Water (Critical)

Moisture Needs:

• Seeds need consistent moisture for germination
• Too much water = oxygen deprivation, rotting
• Too little = desiccation, death
• Sweet spot varies by species

Costa Rican Context:

• Rainy season planting ideal (May-November)
• Dry season germination risky without irrigation
• Some species wait for rain to break dormancy
• Flash flood risk in heavy rains

Temperature

Optimal Ranges:

• Tropical lowland trees: 25-35°C (77-95°F)
• Highland species: 15-25°C (59-77°F)
• Temperate imports: May need cool stratification first

Too Hot:

• Enzyme denaturation
• Embryo death
• Increased pathogen activity

Too Cold:

• Metabolic slowdown
• Germination delayed or prevented
• Rare problem in Costa Rican lowlands

Oxygen

Respiration Requirement:

• Seeds need oxygen for cellular respiration
• Waterlogged soil = anaerobic conditions
• Well-drained soil essential
• Seed depth affects oxygen availability

Depth Considerations:

• Small seeds (Balsa, Melina): Surface or very shallow (1-5mm)
• Medium seeds (Pochote): 1-2 cm deep
• Large seeds (Almendro, Guanacaste): 3-5 cm deep
• Too deep = insufficient oxygen, weak emergence

Light

Variable Requirements:

• Light-requiring seeds (photoblastic positive): Need light to germinate
• Dark-requiring seeds (photoblastic negative): Inhibited by light
• Light-indifferent seeds: Germinate either way

Costa Rican Pioneer Species:

• Many require light gaps
• Won't germinate in deep shade
• Triggered by canopy opening
• Examples: Balsa, Guarumo, Cecropia

Seed Dormancy

Why Seeds Don't Germinate Immediately

Adaptive Strategy:

• Prevents germination at wrong time
• Avoids dry season emergence
• Allows seed dispersal period
• Ensures genetic mixing

Types of Dormancy

Physical Dormancy:

• Hard, impermeable seed coat
• Prevents water absorption
• Needs scarification (abrasion, fire, acid, weathering)
• Examples: Many legumes (Guanacaste, Cenízaro)

Physiological Dormancy:

• Internal biochemical blocks
• Requires after-ripening period
• May need cold/warm stratification
• Chemical inhibitors must break down

Morphological Dormancy:

• Embryo underdeveloped at seed fall
• Needs time to mature inside seed
• Common in some tropical species

Combinational Dormancy:

• Multiple factors combined
• Most difficult to break
• Requires specific sequence of conditions

Breaking Dormancy (For Propagation)

Scarification Methods

Mechanical:

• Sand paper rubbing
• Nicking with knife
• Filing
• Be careful not to damage embryo

Hot Water Treatment:

• Pour boiling water over seeds
• Let soak 12-24 hours as water cools
• Works for many legumes
• Simple and effective

Acid Scarification:

• Sulfuric acid treatment (concentrated)
• DANGEROUS—professional use only
• Mimics animal digestion
• Very effective for hard-coated seeds

Natural:

• Passage through animal digestive system
• Fire (some species)
• Weathering over time
• Bacterial/fungal action

Stratification

Cold Stratification:

• Refrigerate moist seeds
• Mimics winter conditions
• Needed for temperate species
• Rarely needed in Costa Rica

Warm Stratification:

• Keep seeds warm and moist
• Allows after-ripening
• Breaks physiological dormancy
• Common for tropical species

Pre-Soaking

Simple Method:

• Soak seeds in water 12-48 hours
• Softens seed coat
• Begins imbibition
• Reveals viable vs non-viable seeds (sinkers vs floaters)

Germination Success Factors

Seed Quality

Viability Indicators:

• Fresh seeds: Higher germination rates
• Proper storage: Cool, dry conditions
• No damage: Intact seed coat and embryo
• Float test: Viable seeds sink, dead ones float

Seed Maturity:

• Collected at right time
• Fully developed embryo
• Adequate food reserves
• Proper color/hardness for species

Site Selection

Microsite Quality:

• Appropriate light level
• Good drainage
• Protected from wind
• Moderate temperature
• Absence of allelopathic plants

Pest Protection

Threats:

• Insects eating seeds
• Fungi causing damping-off disease
• Rodents/agoutis digging up seeds
• Birds pecking seedlings
• Leaf-cutter ants

Protection Methods:

• Wire mesh covers
• Fungicide treatments (minimal)
• Companion planting
• Regular monitoring

Costa Rican Germination Patterns

Seasonal Timing

Rainy Season Germinators:

• Most native tree species
• Germinate May-July
• Rely on consistent moisture
• Examples: Guanacaste, Roble, Pochote

Dry Season Germinators:

• Some pioneer species
• Wind-dispersed seeds
• Germinate Dec-April
• Benefit from less competition

Fast vs Slow Germinators

Fast (1-2 weeks):

• Pioneer species: Balsa, Guarumo
• Many cultivated fruits: Guanábana, Cacao
• Small seeds with minimal dormancy

Moderate (2-8 weeks):

• Many native hardwoods
• Pochote, Cenízaro, Madero Negro
• Some dormancy but not extreme

Slow (2-12 months):

• Hard-coated species: Guanacaste (can take 2 years!)
• Large-seeded trees: Almendro
• Require specific conditions

Germination in Reforestation

Direct Seeding

Advantages:

• Natural taproot development
• Lower cost
• No transplant shock
• Mimics natural regeneration

Challenges:

• Lower success rates (20-60%)
• Seed predation high
• Competition from weeds
• Requires more seeds

Best Practices:

• Plant 3-5 seeds per spot
• Time with rains
• Light mulching
• Protection from animals

Nursery Germination

Advantages:

• Controlled conditions
• Higher success rates (70-95%)
• Protection from predators
• Can select healthiest seedlings

Challenges:

• Higher cost
• Transplant shock possible
• Facilities needed
• More labor intensive

Best Practices:

• Use deep pots for taproot species
• Well-draining germination medium
• Consistent moisture
• Shade cloth initially

Why It Matters

Understanding germination helps with:

• Tree Propagation: Know when and how to plant seeds
• Reforestation: Plan timing and methods
• Species Identification: Recognize seedlings early
• Nursery Management: Optimize germination rates
• Conservation: Collect and store seeds properly
• Troubleshooting: Diagnose why seeds aren't germinating

Common Germination Problems

Seeds Don't Germinate

Possible Causes:

• Dormancy not broken
• Old/non-viable seeds
• Too deep or shallow planting
• Wrong temperature
• Too wet or too dry
• Seed eaten by pests

Seedlings Die After Emergence

Damping-Off Disease:

• Fungal infection at soil line
• Seedling stem rots and collapses
• Caused by overwatering, poor drainage
• Prevention: Good air circulation, fungicides

Weak, Leggy Seedlings

Insufficient Light:

• Seedling stretches toward light
• Thin, pale stem
• Small, pale leaves
• Solution: Increase light gradually

Field Recognition

Germinating Seed Signs:

• Cracked or split seed coat
• Root tip emerging
• Soil surface disturbed/lifted
• Cotyledons pushing through soil
• Fresh green color

Timing to First Emergence:

• Check species-specific information
• Generally 1-8 weeks for most trees
• Be patient—some take months
• Mark planted areas to track