Seed stratification

Syntropy / Seed stratification - Improving the triple performance of market gardening farms

Arboriculture Arboriculture Seed sowing Syntropy

Seed stratification is a pre-germination treatment aimed at mimicking natural winter conditions to break seed dormancy and promote germination.

It is an essential technique for many perennials, forest, aromatic, or ornamental species.

Principle

In nature, many seeds do not germinate immediately after falling: they need to pass through winter (cold, moisture, sometimes freeze/thaw cycles) before they can germinate in spring.

👉 This "waiting period" is called dormancy, and stratification consists of artificially reproducing these conditions to break this dormancy.

The two main types of stratification

Type	Conditions	Species concerned	Example
Cold stratification	Temperature from 0 to 5 °C, moist medium (sand, peat, moist vermiculite), for several weeks to months	Seeds from temperate zones	Apple, raspberry, lavender, carrot, parsley, maple
Warm stratification	Temperature from 15 to 25 °C, moist medium, before or after a cold phase	Certain tropical seeds or seeds with double dormancy	Laurel, peony, some legumes

Sometimes both are combined: warm phase (soften the seed coat) + cold phase (break physiological dormancy).

How to proceed (typical cold stratification)

1. Mix the seeds with a moist substrate (sand, fine potting soil, vermiculite).
2. Place everything in an airtight container (bag, box).
3. Put in the refrigerator (between 2 °C and 5 °C).
4. Duration: from 3 to 12 weeks depending on species.
5. Then, sow immediately under favorable conditions (warm and bright substrate).

Uses

• Break natural dormancy and homogenize germination.
• Speed up germination to save time in the nursery.
• Successfully sow difficult plants (lavender, thyme, carrot, peony, trees forest species…).
• In market gardening or horticultural production, it allows precise sowing scheduling.

Not to be confused with

• Scarification: abrasion or cracking of the hard seed coat (mechanical or chemical).
• Stratification: action of time + temperature + moisture to break internal dormancy.

👉 Both are often combined for seeds with double dormancy (e.g., black locust).

Stratification durations and conditions for main species

🌿 Species	🌾 Plant type	⚗️ Stratification type	🌡️ Temperature	⏱️ Average duration	💡 Practical notes
Cup plant (Silphium perfoliatum)	Energy / melliferous	Cold	3–5 °C	4–6 weeks	Dormant seed; stratification essential for uniform germination
Common lavender	Aromatic	Cold	4 °C	4–6 weeks	Slightly moist substrate (sand + peat)
Common thyme	Aromatic	Cold (optional)	4–5 °C	2–3 weeks	Significantly improves germination rate
Wild / cultivated carrot	Vegetable / melliferous	Cold	2–4 °C	3–4 weeks	Improves germination uniformity and reduces dormancy
Parsley	Vegetable	Cold (optional)	4–6 °C	2–3 weeks	Can be replaced by prolonged soaking (24 h at 20 °C)
Poppy (Papaver spp.)	Melliferous / ornamental	Cold	2–4 °C	2–4 weeks	Then sow on moist and bright substrate
Yarrow	Melliferous	Cold	4 °C	3–4 weeks	Light dormancy; useful for uniform germination
Phacelia	CIVE / melliferous	Cold (optional)	4 °C	1–2 weeks	Generally not essential but improves earliness
Red / crimson clover	Legume	Cold (optional)	2–5 °C	2–4 weeks	Often satisfactory germination without treatment
Alfalfa	Legume	Cold + scarification	4 °C	4–6 weeks	Hard seed coat: scarify before stratification
Apple (Malus domestica)	Fruit tree	Cold	2–5 °C	8–12 weeks	Requires high controlled moisture
Maple (Acer spp.)	Forest	Warm + cold	20 °C (3 weeks) then 3 °C (8 weeks)	Double dormancy (coat + embryo)
Oak (Quercus spp.)	Forest	Cold	3–5 °C	6–8 weeks	Be careful not to let acorns dry out
Raspberry	Shrub	Cold	3–5 °C	8–10 weeks	Long dormancy; sometimes two cycles needed

Standard cold stratification method

1. Mix seeds with a moist substrate (1 part seeds / 3 parts sand or vermiculite).
2. Put in a bag or airtight box.
3. Place in refrigerator (3–5 °C) for indicated duration.
4. Check moisture weekly.
5. Sow as soon as first seeds show signs of germination.

Practical tip

For long-cycle species (e.g., cup plant, lavender, maple), you can:

• place seeds in a closed box in the refrigerator in February,
• sow in March–April: thus mimicking a full natural winter.

Seed stratification of tree species

Species	Tree type	Dormancy type	Stratification type	🌡️ Temperature	⏱️ Average duration	Practical notes
Pedunculate oak (Quercus robur)	Deciduous	Low	Cold	3–5 °C	6–8 weeks	Do not let acorns dry; rapid germination after stratification
Sessile oak (Q. petraea)	Deciduous	Low	Cold	3–5 °C	6–8 weeks	Same as pedunculate; moist storage essential
Beech (Fagus sylvatica)	Deciduous	Medium	Cold	3–5 °C	8–10 weeks	Seeds sensitive to drying
Common ash (Fraxinus excelsior)	Deciduous	Double (physiological + mechanical)	Warm + cold	20 °C (8 weeks) → 3 °C (16 weeks)	6 months total	Long dormancy, germination sometimes after 2 cycles
Sycamore maple (Acer pseudoplatanus)	Deciduous	Double	Warm + cold	20 °C (4 weeks) → 3 °C (8–12 weeks)	3–4 months	Can also germinate naturally the following spring
Norway maple (Acer platanoides)	Deciduous	Medium	Cold	3–5 °C	12–16 weeks	Slow germination, avoid drying
Field maple (Acer campestre)	Deciduous	Double	Warm + cold	20 °C (4 weeks) → 3 °C (12 weeks)	4 months	Careful moisture control of substrate
Wild cherry (Prunus avium)	Deciduous	Double	Warm + cold	20 °C (4 weeks) → 3 °C (12 weeks)	3–4 months	Very hard stones: scarification before stratification useful
Wild apple (Malus sylvestris)	Deciduous	Medium	Cold	2–5 °C	8–12 weeks	Very good germination after 2–3 months of moist cold
Wild pear (Pyrus communis)	Deciduous	Medium	Cold	2–5 °C	10–12 weeks	Sow as soon as seeds start to germinate
Walnut (Juglans regia)	Deciduous	Low	Cold	3–5 °C	8–10 weeks	Prefer stratification in moist sand (avoid mold)
Hazel (Corylus avellana)	Deciduous	Double	Warm + cold	20 °C (6 weeks) → 3 °C (12 weeks)	4–5 months	Deep dormancy; patience required
Hornbeam (Carpinus betulus)	Deciduous	Double	Warm + cold	20 °C (6 weeks) → 3 °C (12 weeks)	4–5 months	Slow germination, often the following spring
Rowan (Sorbus aucuparia)	Deciduous	Double	Warm + cold	20 °C (4 weeks) → 3 °C (12 weeks)	3–4 months	Pulp must be removed before stratification
Linden (Tilia cordata / platyphyllos)	Deciduous	Double	Warm + cold	20 °C (8 weeks) → 3 °C (12 weeks)	4–5 months	Hard coat: mechanical scarification possible
Black alder (Alnus glutinosa)	Deciduous	Light	Cold (optional)	3–4 °C	4–6 weeks	Often good germination without treatment
Silver birch (Betula pendula)	Deciduous	Light	Cold (optional)	3–4 °C	2–4 weeks	Small seeds: light or no stratification needed
Scots pine (Pinus sylvestris)	Coniferous	Low	Cold (optional)	2–4 °C	2–4 weeks	Non-dormant seeds: direct sowing possible
Norway spruce (Picea abies)	Coniferous	Light	Cold	3–5 °C	3–6 weeks	Improves germination uniformity
Douglas fir (Pseudotsuga menziesii)	Coniferous	Medium	Cold	2–4 °C	4–6 weeks	Uniform germination after 1 month cold
Atlas cedar (Cedrus atlantica)	Coniferous	Medium	Cold	3–5 °C	4–6 weeks	Can also germinate without stratification if freshly harvested

Practical standard method (for deciduous trees)

1. Mix seeds with a substrate (moist sand, vermiculite).
2. Place in a bag or perforated box.
3. Maintain at indicated temperature (refrigerator or temperate room).
4. Check weekly: substrate must remain moist, not waterlogged.
5. As soon as sprouts appear → sow immediately.

Pro tips

• For double dormancy species: strictly respect the warm → cold sequence.
• Always lightly disinfect the substrate (e.g., hot water or mild natural fungicide) to avoid mold.
• Never let seeds dry out for so-called recalcitrant species (oak, beech, walnut).

Sources

• Technical guide “Collection and cultivation of wild and local trees and shrubs” https://reseauhaies.fr/ressources-vegetal-local/