Presentation to Boulder County Master Gardeners, 5 March 2012

1. SEED GERMINATION: SUCCESS WITH SEED

2. What is a seed?
Steven E Newman, Ph.D., A.A.F.
Greenhouse Crops Extension Specialist
and Professor of Floriculture

3. "A sower went out to sow. And as he sowed, some seeds
fell along the path, and the birds came and devoured
them. Other seeds fell on rocky ground, where they had
not much soil, and immediately they sprang up, since
they had no depth of soil, but when the sun rose they
were scorched; and since they had no root they withered
away. Other seeds fell upon thorns, and the thorns grew
up and choked them. Other seeds fell on good soil and
brought forth grain, some a hundredfold, some sixty,
some thirty. He who has ears, let him hear.”
Matthew 13:1-9

5. Seed – Source of Faith
Though I do not believe that a plant will spring up where
no seed has been, I have great faith in a seed. Convince
me that you have a seed there, and I am prepared to
expect wonders.
Faith in a Seed
Henry D. Thoreau

6. What is a seed?
• A seed is a miniature plant
in an arrested state of
development – a mature
ovule
• Seeds have their own food
supply - endosperm
– Carbohydrates
– Fats True leaves
– proteins Root radicle
Cotyledon

7. Gymnosperm seed
• Single fertilization produces the diploid embryo (2n)
• Food source is the haploid megagametophyte

8. Flowering plant seed
• In angiosperms (flowering plants) there two
cotyledons
• A triploid (3n) endosperm
• Endosperm is the food source
• Diploid (2n) embryo

9. • Dicot has two
cotyledons (bean)
• Monocot has one
cotyledon, which
absorbs the endosperm
tissue during
germination (corn)

10. What is germination?

11. Germination
Definition - Physiologically, germination is the sequential
process including resumption of previously suppressed
metabolic pathways and the differentiation of oxidative and
synthetic pathways. This ultimately brings the embryonic axis
into a state of active growth, which has been suspended
during quiescence or dormancy. Morphologically,
germination is the transformation of an embryo into an
actively growing seedling.

12. Germination
STAGE EVENTS
PREGERMINATION (a) Rehydration – imbibition of water.
(b) RNA & protein synthesis stimulated.
(c) Increased metabolism – increased respiration.
(d) Hydrolysis (digestion) of food reserves by enzymes.
(e) Changes in cell ultrastructure.
(f) Induction of cell division & cell growth.
GERMINATION (a) Rupture of seed coat.
(b) Emergence of seedling, usually radicle first.
POST GERMINATION (a) Controlled growth of root and shoot axis.
(b) Controlled transport of materials from food stores to
growing axis.
(c) Senescence (aging) of food storage tissues.

13. Respiration
Mitchondria Soluble
Initially anaerobic
reconstituted Later aerobic sugars
ATP
RNA activated
Polysomes
Protein synthesis (0.5h)
Enzymes (proteins)
DNA synthesis (45h)
Mitosis (70h)

14. The control of food reserve hydrolysis
• Control by growth promoters such as
gibberellin and growth inhibitors such as
abscisic acid
• These directly affect the genes for enzyme
synthesis or the activity of the enzymes
themselves
• The growth substances are affected by
environmental factors (e.g. light, temperature,
humidity)

15. Stages of Seed Germination
• Imbibition of water
• Activation of
enzymes
• Radicle elongation
• Hypocotyl
elongation
• True leaf
development

16. When a seed starts to germinate
Fresh mass increases
it absorbs water from the soil

17. Once the plumule appears
above the soil
the young leaves appear and
carry out photosynthesis
If the rate of photosynthesis is
faster than that of respiration
the dry mass increases

18. Conditions for seed
germination
Water
Warmth
Oxygen

19. Squash seedlings

20. Lettuce seedlings

21. Basil seedlings

22. Tomato seedlings

23. What do I need?

24. Seed and Supplies

25. Interpreting the
seed packet
• Cultivar or variety
– Most seed packets list the name of
the variety and tell you if it is a
hybrid.
– Flowers also are identified as
annuals, biennials, or perennials.
– Annuals are plants that grow, bloom,
and die in one growing season.
– Biennials bloom the second year
after planting and generally die after
flowering.
– Perennials are those plants which
come up year after year.

26. Interpreting the
seed packet
• Cultivar or variety
• Date
– Buy only seed that is packed for the
current year.
– The date is generally stamped on the
back flap.
– Poor storage conditions will reduce
the viability of seeds.
– Unless you know the seed was
stored under proper conditions,
always buy fresh.

27. Interpreting the
seed packet
• Cultivar or variety
• Date
• Germination
– Percentage Germination.
– Direct sow - germination rate about 75
to 85% for vigorous seeds.
– Less vigor - expect 10-50%.
– Under ideal conditions, count on a
slightly higher germination rate.

28. Interpreting the
seed packet
• Cultivar or variety
• Date
• Germination
• Culture
– Information on how and when to plant,
– The number of days to seed
germination and days to harvest.
– Spacing requirements, height and
spread at maturity, thinning
instructions, growth habit, and special
cultural considerations.

29. Cell Packs and Trays

30. 804
806
1203
1204

31. Container depth
• Deeper cells hold more • However, can be
oxygen and have better maintained too wet
root development

32. Container depth
– Affects drainage
– The smaller the container, the greater the effects
Sponge is 2 x 4.25 x 8.5 inches
Total sponge volume = 1,184 ml
Total pore space = 950 ml
Total porosity = 80%

33. Container size
4 inch 48
6 inch 288 648
Air 20 13 8 3 0.5
Water 67 74 79 84 86.5
Solid 13 13 13 13 13

34. Peat Pots
• Peat pots and peat pellets are popular in
many markets in that the container can be
planted
• When transplanting peat pots, make sure
that the edge of the pot does not stick
above the ground surface

37. Peat Pellets

38. Peat Pellets

40. Germination Containers

41. Germination Containers

42. Germination Containers

43. Germination Containers

45. Germination Containers

46. Germination Containers

47. Germination Containers

48. Rhizosphere Substrate
• aka - Potting soil
• Seedling mix

49. Root Substrates
Functions of substrates (media)
• Serves as a reservoir for plant nutrients
• Serves as a reservoir for water available to plants
• Must provide gas exchange between roots and the
atmosphere outside the root substrate
• Provides anchorage or support for the plant

50. Root Substrates
Limitations of materials
• Sand
– Excellent support and gas exchange
– Poor water and nutrient holding capacity
• Clay
– High nutrient and water holding capacity
– Poor gas exchange

51. Root Substrates
Limitations of materials
• Water
– Can supply water and nutrients
– Can even supply gas exchange
– Provides no support
• Field soils (in the pot)
– Excellent support
– High nutrient and water holding capacity
– Poor gas exchange

52. Root Substrates
Desirable properties of a substrate
• Stability of organic matter
– Decomposition of organic components
• Smaller particle size = finer texture
• Smaller pores = reduced gas exchange and reduced aeration
– Loss of substrate volume
– Straw and sawdust (excluding some wood waste like
redwood) are examples of materials with poor stability

53. Root Substrates
Desirable properties of a substrate
• Carbon-to-Nitrogen ratio
– Organic materials are broken down by microorganisms
– Microorganisms require nitrogen for decomposition
– C:N ratio > 30 C: 1 N and substrate contains organic
material that can be readily decomposed, the
microorganisms will use N
– C:N ratio of sawdust = 1,000 C : 1 N
– C:N ratio of pine bark = 300 C : 1 N
• Still useable, why?

54. Root Substrates
Desirable properties of a substrate
• Carbon-to-Nitrogen ratio
– C:N ratio of 30:1 desirable
– Requires free nitrogen for microorganisms

55. Root Substrates
Desirable properties of a substrate
• Wet bulk density
– Weight of weight of media at container capacity volume
– Given in lb/ft3
• Container capacity (water holding capacity)
– Water content of media after complete saturation and loss
of gravitational water
– ([volume to saturate-drainage] volume of container) x
100
– Reported as percent of total volume

56. Root Substrates
Desirable properties of a substrate
• Wet bulk density
– Too light
• Topples and is hard to ship
– Too heavy
• Shipping expenses
• Labor handling
– Desirable level
• 40-60 lb/ft3

57. Root Substrates
Desirable properties of a substrate
• Moisture retention and aeration
– Goal
• Adequate available water
• Sufficient aeration
• Acceptable wet and dry bulk densities
– Substrate at container capacity
• Solid particles
• Pores filled with
– Unavailable water and available water
– air

58. Root Substrates
Greenhouse substrate porosity
Most media are between 80
and 90% porosity Mineral soil
1 Soil : 1 Peat : 1 Sand
3 Bark : 1 Peat : 1 Sand
1 Peat : 1 Vermiculite
1 Peat : 1 Rockwool
0 20 40 60 80 100

59. Root Substrates
Desirable properties of a substrate
• Unavailable water (hygroscopic water)
– Water held by solid particles
– Unavailable to roots
– Common definition
• Water held at tensions greater than 15 bars
• In order for roots to take up water, they would have to draw more
than 15 bars to separate water from the particles

60. Root Substrates
Desirable properties of a substrate
• Available water
– Volume of water at container capacity less
volume of water remaining at 15 bars tension
– This is the water that is used or available to the
plant

61. Root Substrates
Desirable properties of a substrate
• Substrate components
– Not as important as how processed
• Milling
• Composting
• Particle size
– Largest component by volume
SPACE

62. • Lightly fill and brush Effects of
• Do not pack into compaction
containers
Compaction Air space
• Do not stack filled flats
 Light 9
or pots
 Medium 4
 Heavy 2

63. % Moisture Gal/yd3
0 0
10 2
20 5
33 10
Pots 50 20
60 30
Cells 67 40
72 50

64. Root Substrates
Desirable properties of a substrate
• Cation exchange capacity (CEC)
– Many substrate components have fixed negative electrical
charges
– Attracts and holds positive charged ions (cations)
– CEC = milliequivalents per 100 cc of dry substrate
– 6-15 meq/100 cc desirable
– Clay, peat moss, and coir have high CEC’s

65. Root Substrates
Cation Exchange Capacity
-- - - - - Ca++
- - --
- - - - - - K - - +
- Mg -
---- -
H +
- - ++
--
- - -

66. Root Substrates
Desirable properties of a substrate
• pH
– Measure of the concentration of H+ ions in a solution
– Most greenhouse crops grow best where the:
• pH = 6.2 to 6.8 (soil-based media)
– [20% or more soil]
• pH = 5.4 to 6.0 (soilless media)
– Components have pH and some affect pH
– Best to adjust pH prior to planting with dolomitic
limestone

67. Don’t forget to label your seeds

68. Remember proper sowing depth

69. Presoak your media

71. Transplanting

72. Transplanting Plug Seedlings
• Plug seedlings should be transplanted as soon as possible
after reaching finished size
• Goal is rapid root growth into the growing medium
– EC <1.0 dS/m
– High quality potting medium (not germination medium)
• Transplant medium must be moist but not wet
• Bottom heat is effective – 68 to 70°F
• Wait one week after transplant before fertilizing

82. Light