Seed Dormancy

Part of Seed Saving

Seed dormancy is a survival mechanism that prevents germination at the wrong time of year. A seed that germinates in autumn will die in the first frost. Dormancy forces seeds to wait for seasonal cues — cold, moisture, light, or passage of time — before germinating. Understanding dormancy types is essential for propagating wild species, perennial food plants, trees, and some crops that retain dormancy mechanisms.

What Dormancy Is and Why It Evolved

Dormancy is not death, disease, or poor seed quality. It is an active physiological state in which germination is suppressed even when basic requirements (water, temperature, oxygen) are present. A dormant seed may have 95% viable embryos — but none will germinate until the dormancy mechanism is satisfied.

Dormancy evolved because random germination timing is lethal. Seeds that germinate immediately after dispersal in autumn will freeze. Seeds that germinate in mid-summer drought will desiccate before establishing roots. Dormancy aligns germination with favorable seasonal windows.

For most agricultural crops, millennia of human selection have reduced or eliminated dormancy — farmers preferred seeds that germinate promptly and reliably. Wild plants and many perennial species retain strong dormancy that must be deliberately broken.

Types of Dormancy

1. Physiological Dormancy (PD)

The most common type in agricultural and wild species. The embryo is physiologically inhibited from germinating, usually by abscisic acid (ABA) — a plant hormone that suppresses growth. Cold, wet stratification causes ABA to break down and promotes accumulation of gibberellins, which stimulate germination.

Crops commonly showing PD: Many wild herbs, some grains (rye can show PD at harvest), wild relatives of vegetables, many perennial food plants (elderberry, hawthorn, rose hips).

Treatment: Cold moist stratification (see below).

2. Physical Dormancy (Coat-Imposed Dormancy)

The seed coat is impermeable to water, preventing imbibition. The embryo itself is not dormant — if you breach the seed coat, the seed will germinate readily. Common in legumes and plants of the bean family, as well as many tree species.

Crops and plants with physical dormancy:

Species	Dormancy Level
Morning glory	Strong
Moonflower	Strong
Scarlet runner bean	Mild (often grown without treatment)
Lotus	Strong
Many wild legumes	Strong
Kentucky coffee tree	Strong

Treatment: Scarification (see below).

3. Morphological Dormancy

The embryo is underdeveloped at the time of seed dispersal and must complete its development after dispersal. The seed appears viable but is not yet ready to germinate.

Common in: Carrots, parsley, celery (Apiaceae family), and many tropical plants.

Treatment: Warm stratification to allow embryo development, followed by cold stratification. This is called warm-cold stratification. Time requirements can be months.

4. Morpho-Physiological Dormancy (MPD)

Combination of underdeveloped embryo and physiological inhibition. The most complex dormancy type, requiring multi-step stratification.

Common in: Many tree fruits (apple, pear, plum), elderberries, many woodland plants.

5. Combinational (Double) Dormancy

Both physical (impermeable seed coat) and physiological dormancy are present. The seed requires scarification AND stratification.

Common in: Hawthorn, rose, viburnums, many native trees and shrubs.

Treatment: Scarification first, then cold stratification.

Breaking Dormancy: Stratification

Stratification mimics the natural conditions that break dormancy. “Cold stratification” simulates winter; “warm stratification” simulates summer or autumn.

Cold Moist Stratification

The most commonly needed treatment for temperate-zone perennials.

Method:

1. Soak seeds in water for 12–24 hours
2. Drain and mix seeds with a moist medium: sphagnum moss, peat moss, vermiculite, clean sand, or coir fiber
3. Medium should be moist but not wet — if squeezed, no water should drip out
4. Place in a sealed plastic bag or container
5. Refrigerate at 2–5°C for the required period (see table below)
6. Check every 2 weeks; remove and sow any seeds that show a radicle emerging

Species	Cold Stratification Duration
Apple, pear	60–90 days
Plum, cherry	90–120 days
Elderberry	60–90 days
Hawthorn (after scarification)	90–120 days
Many perennial herbs	30–60 days
Rye (harvest dormancy)	4–6 weeks
Wild carrot relatives	30–60 days

Do Not Freeze Stratifying Seeds

Stratification requires temperatures near freezing (2–5°C), not below. Freezing stratifying seeds in moist media damages them. Ensure your refrigerator is not too cold — use a thermometer.

Warm Stratification

Used for morphologically dormant seeds and the first stage of warm-cold stratification.

Method: Same as cold stratification but held at 20–30°C (room temperature or slightly warmer). Duration: 1–3 months depending on species.

After warm stratification, transfer directly to cold stratification without allowing seeds to dry out.

Breaking Dormancy: Scarification

Scarification physically breaches the impermeable seed coat, allowing water to enter.

Mechanical Scarification

Physically abrade or cut the seed coat.

Methods:

• Sandpaper: Rub seeds on sandpaper (40–60 grit) until a slight thinning of the coat is visible; do not sand through to the embryo
• File or nail file: Nick the seed coat opposite the hilum (seed attachment scar) with a file
• Knife nick: Use a sharp knife to nick the seed coat; precise but risks cutting too deep
• Shaking with sand: Place seeds and coarse sand in a jar and shake vigorously for several minutes

The goal is to create a small breach — not to remove the seed coat entirely. Even a small abrasion is sufficient for water to enter.

Chemical Scarification (Acid Scarification)

Concentrated sulfuric acid rapidly degrades hard seed coats. Used commercially; manageable at small scale with care.

Acid Scarification Hazards

Concentrated sulfuric acid is dangerous. Wear acid-resistant gloves, eye protection, and work outdoors or in a well-ventilated area. Have water and baking soda solution available to neutralize spills. Never use aluminum containers — sulfuric acid dissolves aluminum, releasing hydrogen gas.

Method (sulfuric acid scarification):

1. Place seeds in a glass container (never metal or thin plastic)
2. Cover with concentrated sulfuric acid (98%)
3. Stir gently with a glass rod for the required time:
   • Thin coats: 15–30 minutes
   • Medium coats: 30–60 minutes
   • Very hard coats: 1–2 hours
4. Pour off acid carefully into a larger container of water (never add water to acid)
5. Rinse seeds thoroughly with water 5–6 times
6. Sow immediately while seeds are wet, or dry briefly and stratify if both treatments are needed

Hot Water Scarification

Simpler than acid, effective for many legumes.

Method:

1. Bring water to 80–90°C (near boiling but not actively boiling)
2. Drop seeds into the hot water
3. Remove from heat and allow to soak for 12–24 hours as water cools
4. Sow seeds that have visibly swollen (they have imbibed water successfully)
5. Seeds that remain hard can be re-treated or discarded

This works because the temperature temporarily softens the seed coat, allowing a small amount of water entry. As water cools, the coat contracts and water is locked in.

Practical Decision Guide

Before treating seeds for dormancy, determine whether dormancy is actually present. Many seeds simply need appropriate temperature and moisture.

Observation	Likely Cause	Action
Seeds fail to germinate at any temperature	Test viability first (cut test)	If embryo looks healthy, try stratification
Seeds germinate eventually (weeks later)	Physiological dormancy	Cold stratification
Seeds don’t swell with water	Physical dormancy	Scarification
Seeds swell but don’t germinate	Physiological or morphological dormancy	Stratification
Seeds germinate under one temperature but not another	Temperature requirement mismatch	Adjust germination temperature

Cut test for viability: Cut 10 seeds in half with a sharp blade. Healthy embryo = firm, creamy-white tissue. If embryo is shrunken, discolored, or absent, seeds are not viable — dormancy is not the problem.

Dormancy in Common Crops

Most agricultural crops have minimal dormancy. Exceptions:

Crop	Dormancy Present?	Notes
Wheat, barley	Sometimes (harvest dormancy)	Disappears after 4–6 weeks storage
Rye	Occasionally	Warm dry storage for 1 month resolves
Wild relatives (wild carrot, wild mustard)	Yes, often strong	Stratification needed
Parsley	Mild	Soaking 24h in warm water helps
Celery	Mild	Light required; do not bury deeply
Perennial herbs (lavender, sage, rosemary)	Variable	Cold stratification often beneficial

Time After Harvest

Many crop seeds with harvest dormancy (freshly harvested rye, wheat) will germinate without any treatment if simply stored dry at room temperature for 4–8 weeks. Before applying stratification or scarification, allow freshly harvested seeds several weeks of dry storage to see if dormancy dissipates naturally.

Seed Dormancy Summary

Dormancy prevents seeds from germinating at the wrong time of year and must be understood and managed for propagating wild species, perennial food plants, and some crops. The main types are physiological (broken by cold stratification), physical coat-imposed (broken by scarification — mechanical, acid, or hot water), morphological (broken by warm then cold stratification), and combinations thereof. Most agricultural crops have little dormancy; wild relatives and perennial species often have strong dormancy requiring multi-week treatment. Always verify viability with a cut test before attributing germination failure to dormancy.